Surface water and geomorphology herrera report-oct 2005Document Transcript
SURFACE WATER AND GEOMORPHOLOGY TECHNICAL REPORTPioneer Aggregates Mining Expansion and North Sequalitchew Project Prepared for Huckell/Weinman & Associates October 2005
Note:Some pages in this document have been purposefully skipped or blank pages inserted so that thisdocument will copy correctly when duplexed.
SURFACE WATER AND GEOMORPHOLOGY TECHNICAL REPORTPioneer Aggregates Mining Expansion and North Sequalitchew Project Prepared for Huckell/Weinman & Associates 270 Third Avenue, Suite 200 Kirkland, Washington 98033 Prepared by Herrera Environmental Consultants, Inc. 2200 Sixth Avenue, Suite 1100 Seattle, Washington 98121 Telephone: 206/441-9080 October 28, 2005
Contents1.0 Introduction...............................................................................................................................12.0 Affected Environment...............................................................................................................3 Sequalitchew Creek ..................................................................................................................3 Stream Discharge ............................................................................................................5 Water Quality ..................................................................................................................6 Geomorphology ..............................................................................................................7 Hydraulic Modeling of Existing Conditions .................................................................11 Fort Lewis Diversion Canal....................................................................................................12 Canal Discharge ............................................................................................................13 Water Quality ................................................................................................................13 Sequalitchew Creek Springs ...................................................................................................14 Near-Shore Springs.................................................................................................................14 Kettle Wetland ........................................................................................................................15 Old Fort Lake..........................................................................................................................15 Pond Lake ...............................................................................................................................15 Brackish Marsh.......................................................................................................................16 Historical Geomorphic Conditions .........................................................................................16 Existing Geomorphic Conditions ...........................................................................................16 Nisqually Reach (Puget Sound) ....................................................................................173.0 Significant Impacts of the Proposed Action ...........................................................................19 Construction............................................................................................................................19 Stormwater Management ..............................................................................................19 Site Clearing and Grading.............................................................................................20 North Sequalitchew Creek Construction.......................................................................20 Access Road and Pedestrian Bridge Construction ........................................................26 Conveyer System Construction.....................................................................................27 Operation ................................................................................................................................27 Mining and Processing ...........................................................................................................27 North Sequalitchew Creek ............................................................................................27 Sequalitchew Creek.......................................................................................................32 Kettle Wetland ..............................................................................................................34 Fort Lewis Diversion Canal/Sequalitchew Lake...........................................................34 Old Fort Lake ................................................................................................................35 Pond Lake .....................................................................................................................35 Brackish Marsh .............................................................................................................35 Post-Reclamation Stormwater Management.................................................................36 Near-shore Springs........................................................................................................37 Shipping Activities........................................................................................................37 i
Impacts of the Project Alternative ..........................................................................................37 Water Resources............................................................................................................37 Geomorphology ............................................................................................................37 Impacts of the No Action Alternative.....................................................................................38 Monitoring and Mitigation Measures .....................................................................................38 Water Quality ................................................................................................................38 Geomorphology ............................................................................................................39 Significant Unavoidable Adverse Impacts .............................................................................40 Proposed Action............................................................................................................40 Project Alternative ........................................................................................................424.0 References...............................................................................................................................43 ii
TablesTable 1. Discharge summaries (monthly means) for Sequalitchew Creek and Fort Lewis Diversion Canal from 1977 through October 2004. ........................................49Table 2. Water quality standards (freshwater) and designated uses (Chapter 173- 201A-200 WAC) (Ecology 2003) applicable to surface waters of the project site including Sequalitchew Creek and the Fort Lewis Diversion Canal. ..................50Table 3. Water quality data for Sequalitchew Creek collected in the ravine bordering the southern boundary of the Glacier site from September 1999 to September 2000. ...........................................................................................................................51Table 4. Water quality data for the Fort Lewis Diversion Canal collected near the eastern boundary of the Glacier site from September 1999 to September 2000. ...........................................................................................................................53Table 5. Brackish Marsh salinity measurements (ppt) collected during low, ebb, high, and flood tides on April 14 and April 19, 2004..........................................................55Table 6. Water quality standards (marine waters) and designated uses (Chapter 173- 201A-210 WAC) (Ecology 2003) applicable to the Nisqually Reach of Puget Sound (Extraordinary Quality). ..................................................................................56Table 7. Marine water quality data collected from Ecology’s long-term ambient water quality monitoring station GOR001 in the Nisqually Reach of Southern Puget Sound from October 1996 to September 2002. ..........................................................57Table 8. Table of estimated ground water quality concentrations and North Sequalitchew Creek Concentrations within the mine expansion area compared to background concentrations in Sequalitchew Creek and Washington State surface water quality standards (Chapter 173-201A-200 WAC) (from Pacific Groundwater Group [PPG 2005]).............................................58Table 9. Best estimate of predicted annual average flows in Sequalitchew Creek with the additional flows from North Sequalitchew Creek upstream and downstream of the proposed confluence at RM 0.8 (Anchor 2004d).........................60Table 10. Best estimate of peak storm flows in Sequalitchew Creek under existing and future conditions (Anchor 2004d). .............................................................................61Table 11. Estimated peak storm flows in the proposed North Sequalitchew Creek used by Aspect to assess reclamation stormwater conditions within the mine expansion area (Aspect 2004b)...................................................................................62 iii
FiguresFigure 1. Proposed Glacier Mine expansion area, surface water features, and surface water monitoring stations, DuPont, Washington........................................................63Figure 2a. Sequalitchew Creek reach boundaries and landslides mapped by GeoEngineers..............................................................................................................65Figure 2b. Sequalitchew Creek reach boundaries and landslides mapped by GeoEngineers (continued). .........................................................................................67Figure 3. Landslide and debris fans in the lower Sequalitchew Creek ravine as interpreted from shaded relief lidar digital elevation model. .....................................69Figure 4a. Sequalitchew Creek selected erosional and depositional areas for current conditions based on hydraulic modeling results.........................................................71Figure 4b. Sequalitchew Creek selected erosional and depositional areas for current conditions based on hydraulic modeling results (continued). ....................................73Figure 5. Potential depositional and erosional reaches predicted by hydraulic modeling of existing conditions in Sequalitchew Creek (GeoEngineers 2004b). ......................75Figure 6. Sequalitchew Creek outlet and Diversion Canal surface water flow directions, DuPont, Washington...................................................................................................76Figure 7. Kettle wetland water levels at the existing Glacier Mine site from July 1999 to October 2002 (CH2M Hill 2003a)..........................................................................77Figure 8. Brackish Marsh salinity sample locations near the existing Glacier Mine, DuPont, Washington...................................................................................................79Figure 9. Historical maps of Lower Sequalitchew Creek. .........................................................81Figure 10. Current conditions within the Brackish Marsh during low tide. ................................83Figure 11. Potential depositional and erosional reaches predicted by hydraulic modeling of proposed conditions in Sequalitchew Creek (GeoEngineers 2004b). ....................85Figure 12a. Sequalitchew Creek erosional and depositional areas for proposed conditions based on hydraulic modeling results by GeoEngineers..............................................87Figure 12b. Sequalitchew Creek erosional and depositional areas for proposed conditions based on hydraulic modeling results by GeoEngineers (continued). .........................89Figure 13a. Sequalitchew Creek areas of potential adverse change based on hydraulic modeling results by GeoEngineers. ............................................................................91Figure 13b. Sequalitchew Creek areas of potential adverse change based on hydraulic modeling results by GeoEngineers (continued)..........................................................93Figure 14. Model predicted change in ground water level near Sequalitchew Creek..................95 iv
Surface Water and Geomorphology Technical Report 1.0 IntroductionThis report provides surface water and geomorphology technical detail and support to theSupplemental Environmental Impact Statement (SEIS) for the expansion of Glacier Northwest’smining operations in DuPont, Washington. Glacier Northwest proposes to expand its currentmining operations by approximately 200 acres by mining adjacent land located mostly to the eastof the current mine area. Under the proposed action, Glacier proposes to capture ground waterentering the mine expansion area from the east and convey it south to Sequalitchew Creek viaNorth Sequalitchew Creek, a newly constructed stream channel. The following technical reportdescribes surface water and geomorphic existing conditions (affected environment), as well asanalyzes potential impacts to surface water resources and geomorphology from the proposed200-acre expansion. In addition, proposed monitoring and mitigation measures for the proposedproject are presented.wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 1 Herrera Environmental Consultants
Surface Water and Geomorphology Technical Report 2.0 Affected EnvironmentMajor surface water resources within the vicinity of the existing mine and proposed mineexpansion area include: Sequalitchew Creek and its associated wetlands and springs, Fort LewisDiversion Canal, Sequalitchew Lake, Old Fort Lake, and the Nisqually Reach of southern PugetSound. In addition, numerous small kettle lakes and wetlands located in the vicinity of theproject are described below.The proposed mine expansion area is located in the Chambers-Clover basin (Water ResourceInventory Area [WRIA] 12), which has a drainage area of 171 square miles. This basin islocated within the Puget lowlands ecoregion and has an average annual precipitation ofapproximately 40 to 44 inches/year (Anchor 2004c). Sequalitchew Creek (Segment No.12-0019), located entirely within the Chambers-Clover Creek Watershed, drains a watershedcovering 38.4 square miles and discharges into the Nisqually Reach of Puget Sound (WDF1975). The headwaters of the Sequalitchew Creek drainage basin are located in Kinsey Marshon the east side of Interstate 5 (I-5). Runoff from the Kinsey Marsh flows 3.8 miles in MurrayCreek into American Lake on the west side of I-5. The water level in American Lake (1,162surface acres) occasionally overflows the outlet weir and discharges into Sequalitchew Lake(81 surface acres) (Figure 1).Sequalitchew CreekSequalitchew Creek is formed at the outlet of Sequalitchew Lake. The Sequalitchew Creekchannel downstream of Sequalitchew Lake extends for approximately 1.5 miles through EdmondMarsh. The lower 1.5 miles of Sequalitchew Creek, between Edmonds Marsh and the PugetSound shoreline, descends through a steep-walled ravine that parallels the southern boundary ofthe proposed mine expansion area and existing mine. The channel drops approximately 220 feetin elevation in 7,750 feet (average slope of 2.8 percent) between Center Drive below the uplandplateau and the brackish marsh located directly upstream of the BNSF Railroad embankment.The floor of the ravine gradually widens in the downstream direction from a minimum of 40 feetat the ravine head to a maximum width of roughly 400 feet near the railroad embankment at thebrackish marsh.Ravine slopes on either side of the stream channel over much of its length range from 30 to 80percent for an average of 60 percent. Near the mouth, Sequalitchew Creek passes through a240-foot long box culvert (5 feet wide and 5 feet high) under the Burlington Northern-Santa FeRailroad (BNSF) railroad tracks before discharging into Puget Sound. The lower 300 feet ofSequalitchew Creek above the BNSF railroad tracks is tidally influenced as evidenced by tidalchannels and a Class 1 estuarine wetland (per the City of DuPont rating system and identified asthe Brackish Marsh throughout this section).Several springs, which provide flow to Sequalitchew Creek, are located on the north and southbanks from approximately 0.6 to 1.1 miles upstream of the mouth. An abandoned small-gaugewp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 3 Herrera Environmental Consultants
Surface Water and Geomorphology Technical Reportrailroad grade that parallels the north creek bank intercepts these springs and collects the runoffin drainage ditches that are culverted under the rail bed and drain into Sequalitchew Creek. Thesprings daylight along the side slopes of the ravine at the contacts between layers of differentpermeobilites and provide most of the flow into Sequalitchew Creek along this reach (CH2MHill 2003b).Natural conditions at the mouth of the creek were substantially altered by construction of theBNSF RR along Puget Sound in 1912 (Andrews and Swint 1994). The railroad embankmentisolated the delta from shoreline processes along Puget Sound and transformed the delta into aone-half-acre brackish marsh. Since construction of the embankment, the exchange offreshwater and saltwater has occurred through the long box culvert beneath the railroad.Historically, Sequalitchew Creek has been subjected to chronic and extensive sediment inputsthroughout the project area as a result of pre-project land use (i.e., deforestation of ravine slopesand construction of the railroad grade). The dominant mechanisms delivering sediment to thecreek channel include erosion of poorly consolidated hillslopes, soil creep, shallow landslides,slumping, and ground water seeps. The Sequalitchew Creek valley has the potential tocontribute sediment due to the underlying geology of relatively unconsolidated sediments andhigh ground water table. Extensive forest clearing in the early 1900s likely increased the rate ofsediment input to the creek. Given that flows in Sequalitchew Creek were naturally moderatedby ground water and upstream wetlands, it is likely the sediment inputs resulting from forestclearing overwhelmed the creek’s sediment transport capacity. When the quantity of sedimentinput to a reach exceeds the output, sedimentation decreases the depth and increases the width offlow, further diminishing the sediment transport capacity. Bar formation and increased flowwidths would have further aggravated erosion of adjacent hillslopes. Local bank erosion isobserved where the channel is wide under existing conditions. The Fort Lewis diversion canal(an upstream system of weirs that diverts flow away from Sequalitchew Creek) built in the1950s, further diminished the creek’s sediment transport capacity by reducing stream flows.Historically, two potential pollutant sources existed near the DuPont mine site. Fort Lewis ArmyReservation Landfill No. 5 located 0.5 mile east-northeast of the mine site was used for thedisposal of reservation wastes from 1967 to 1990. The landfill was designated as a Superfundsite pursuant to the Comprehensive Environmental Response Compensation and Liability Act(CERCLA), when in 1987, sampling indicated that the landfill had contaminated the groundwater with elevated levels of heavy metals and organic compounds (U.S. EPA 2003). Closure ofthe landfill was begun in 1987. Additional sampling after the closure of the landfill foundcontaminant concentrations in ground water samples below state and federal cleanup standards,and on May 22, 1995, the site was deleted from the National Priorities List (U.S. EPA 2003).The old DuPont Works Plant, located south of the existing mine site, manufactured forty gradesof dynamite including water gel, nitroglycerine, ammonia explosives, and black powder from1909 to 1977. Several remedial actions have been taken to remove contaminated material fromthe site after the Weyerhaeuser and DuPont companies signed a Consent Decree with theWashington Department of Ecology in pursuant to the Model Toxics Control Act in 1991(URS 2000). The final environmental impact statement (FEIS) proposed action involves wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 4 October 28, 2005
Surface Water and Geomorphology Technical Reportconstructing a golf course to provide a cap/containment facility for the former explosives plant(URS 2000).Stream DischargeThe hydrology of Sequalitchew Creek is characterized by three reaches: an upper, losing reach;the ravine, a middle gaining reach; and a lower, losing reach (CH2M Hill 2003b). The upperreach extends from the outlet of Sequalitchew Lake through Edmond Marsh to a point west ofCenter Drive. This upper reach infiltrates to recharge the Vashon Aquifer (CH2M Hill 2003b).As the stream approaches the western end of Edmond Marsh, flows infiltrate the highlypermeable Vashon outwash materials. Surface flows do not extend downstream past EdmondMarsh, except during high flow conditions.During the winter, flows are regulated by a series of outlet weirs designed to manage the level ofSequalitchew Lake by diverting excess discharge into the Fort Lewis diversion canal. Severalbeaver dams on the stream cause the level of the stream to rise and back up, forcing dischargeinto the diversion canal (Aspect 2004a). The Army removed some of the beaver dams nearSequalitchew Lake in the summer of 2004, as they have reportedly done historically. Thebeavers typically rebuild the dams. Because of the very low stream gradient along this reach, thebeaver dams can cause the water to reverse its flow direction with a water level rise of 1 to 2feet. Effect of the beaver dams results in water levels in upper Sequalitchew Creek and EdmondMarsh that are higher than water levels at either end. Thus, Sequalitchew Creek discharges bothdown its historical channel to the west and through the Diversion Canal to the northwest (Aspect2004a) (Figure 1). In addition, one stormwater outlet from Fort Lewis flows into Hamer Marshand one flows into Bell Marsh, adding additional surface flow to the stream. See the DiversionCanal discussion below for a more detailed description of surface water flow pathways.The middle reach extends from west of Center Drive downstream through the ravine to the“Kitsap Cutoff,” the northern edge of the Olympia beds (CH2M Hill 2003b). This reach istypically dry between the west end of Edmond Marsh and the ravine springs (Aspect 2004a).This higher gradient portion of the creek receives discharge from several small springs from boththe north and south sides of the steep-walled ravine (CH2M Hill 2001). These springs provide aperennial water source for the creek (CH2M Hill 2001, 2003b).The stream channel within the lower reach, which extends west of the Kitsap Cutoff to PugetSound, consists of the highly permeable sands and gravels of the DuPont Delta formation. Thispermeable layer causes water within the creek to infiltrate and recharge the ground water of theDuPont Aquifer, measurably decreasing the discharge of the creek compared to the middle reach(CH2M Hill 2003b).Sequalitchew Creek discharge has been monitored periodically for several decades. Two studiesconducted during the 1970s and 1980s measured discharge in lower Sequalitchew Creek. Astudy by Thut et al. (1978) from 1977 to 1978 measured monthly discharges in SequalitchewCreek ranging from 0.1 to 12.8 cfs. Similar results were found by Firth (1991) from 1984 to1987 in lower Sequalitchew Creek, where monthly discharge averaged between 1.0 and 9.4 cfs.wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 5 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportThe most recent Sequalitchew Creek discharge data were collected by Aspect Consulting(Aspect) (2004a) and CH2M Hill (2001, 2003a) (Table 1). CH2M Hill monitored SequalitchewCreek discharge from October 1999 through September 2002 at a monitoring station locatedapproximately 700 feet upstream of the mouth. Stream flow monitoring activities at this lowermonitoring station were subsequently assumed by Aspect, which has published discharge datathrough October 2004 (Aspect 2004b). From November 1999 to October 2004, the meanmonthly discharge at the lower monitoring station ranged from 0.2 to 2.9 cubic feet per second(cfs). In addition, Aspect began operating a second upper flow monitoring station locatedupstream of the proposed confluence with North Sequalitchew Creek (Aspect 2004a). FromNovember 2003 to October 2004, the mean monthly discharge at the upper station has rangedfrom 0.4 to 2.5 cfs. At both stations, the highest discharges were measured during the wetseason (November through June) and the lowest discharges were recorded at the end of the dryseason (October/November).Discharge measured in the lower reach indicates the creek does not respond quickly to rainfallevents, with minimum flows often lagging 1 to 2 days after a major rainfall event (i.e., >0.50inches in 24 hours) (CH2M Hill 2001). The presence of Sequalitchew Lake, several largewetlands in the headwaters of the creek, and several beaver dams in the Sequalitchew Creekheadwaters help detain and retard stormwater runoff. Because the flows in the lower reach ofSequalitchew Creek are supported by ground water discharge, there is a time lag in the stream’sresponse to storm events. Water flow through the subsurface (downstream of Center Drive)moderates the discharge rates creating the lag in stream flow response. In addition, very little, ifany, surface water from the mine site enters Sequalitchew Creek (CH2M Hill 2001). Themajority of the precipitation infiltrates the highly permeable gravel deposits of the DuPont Deltaand Vashon Drift units underlying the site (CH2M Hill 2001).Water QualitySurface water quality standards for the State of Washington are established by Ecology inChapter 173-201A WAC for the protection of public health and enjoyment, and designatedbeneficial uses (Ecology 2003). Sequalitchew Creek is designated as a salmon core rearing andmigration stream (formerly as a Class AA [extraordinary] waterbody under the previous WACdesignation and described in the original EIS [City of DuPont 1993]) by Ecology). Changes tothe state’s water quality standards were adopted by Ecology on July 1, 2003 and were effectiveAugust 1, 2003. Water quality sampling results are compared to applicable state water qualitystandards in Table 2.Section 303(d) of the CWA (and later revisions) requires all states to prepare lists of surfacewater that are not expected to meet applicable water quality standards after implementation ofwater quality based controls. This list, identified as the 303(d) list, is prepared by Ecology andsubmitted to the U.S. EPA. The most current listing is the 2004 303(d) list. To-date,Sequalitchew Creek has not been identified on Ecology’s 303(d) list as a threatened or impairedwaterbody and is therefore not part of any existing or proposed TMDL. However, on the current303(d) list, Sequalitchew Creek is listed as a “waters of concern” (Category 2) due to dissolvedoxygen and temperature excursions beyond the applicable criteria (Ecology 2005a). wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 6 October 28, 2005
Surface Water and Geomorphology Technical ReportSequalitchew Creek water quality was described in the original mine EIS, which characterizedthe stream as having good water quality and generally meeting Class AA water quality standards(City of DuPont 1993). As part of the North Sequalitchew Creek Project, water quality sampleswere collected monthly in Sequalitchew Creek from September 1999 through September 2000(CH2M Hill 2001), with three additional dissolved oxygen measurements collected during thesummer of 2002 (Table 3). In addition, a continuous temperature recorder was installed inSequalitchew Creek in July 2000 to record daily temperature through December 2002. Waterquality samples were collected approximately 700 feet upstream of the mouth of lowerSequalitchew Creek at the lower Sequalitchew Creek discharge gauge (Figure 1).The sampling results (September 1999 through September 2000) indicate the waters ofSequalitchew Creek are generally cool, well oxygenated, with low concentrations of fecalcoliform bacteria. During monthly sampling, measurements of pH, temperature, dissolvedoxygen and fecal coliform bacteria met the applicable state criteria. Nitrate-nitrogen wasdetected at levels ranging from 0.28 to 0.82 mg/L, within the range presented in the originalmine EIS (City of DuPont 1993). Total phosphorus concentrations were low to moderate, andranged from 0.015 to 0.034 mg/L, with an average of 0.021 mg/L. TSS concentrations were low,with an average of 4 mg/L measured during sampling (CH2M Hill 2001). Because samples werenot analyzed for turbidity, compliance with this standard cannot be determined. However,because of the well documented link between turbidity and TSS (Packman et al. 1999), theturbidity may also have been low during sampling.During sampling, dissolved cadmium and lead concentrations were detected at concentrationsexceeding state water quality chronic criteria for each metal (based on an average hardness of44 mg/L) (CH2M Hill 2001). A dissolved cadmium sample collected in October 1999 measured0.0009 mg/L, which exceeded the chronic criterion of 0.0006 mg/L. Two dissolved lead samplescollected in May and July of 2000, both measuring 0.002 mg/L, exceeded the chronic criterion of0.0010 mg/L.CH2M Hill collected additional water temperature and dissolved oxygen data in SequalitchewCreek as part of continued project monitoring. The continuous temperature gauge recorded twoexceedances of the state temperature criterion (16°C) during August 2001 (CH2M Hill 2003c).In addition, three dissolved oxygen measurements were made during the summer of 2002 withone measurement in July (9.2 mg/L) and one measurement in August (9.3 mg/L) that failed tomeet the state minimum criterion of 9.5 mg/L (CH2M Hill 2003c).GeomorphologyHistorical Geomorphic ConditionsSequalitchew Creek has responded to a series of changes in flow and sediment regimesthroughout both geologic and more recent historical times. The ravine of lower SequalitchewCreek was initially formed by a series of meltwater floods during glacial retreat (GeoEngineers2004b). Peak flows within the channel likely declined rapidly following retreat of the glacierand cessation of meltwater floods. Erosion would have been further reduced as forest vegetationwp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 7 Herrera Environmental Consultants
Surface Water and Geomorphology Technical Reportbecame established. This post glacial reduction in sediment production, sediment-transportingflows, and increased hydraulic roughness within Sequalitchew Creek resulting from theaccumulation of wood debris would have resulted in relatively little sediment export to PugetSound. Thus as sea level rose, the creek mouth was probably characterized by a shallowembayment of open water such as depicted in historical maps of the creek and not a prominentdelta (see Brackish Marsh discussion below). Prior to European colonization, the creek wouldhave provided outstanding salmon habitat because of the perennial source of cold water,excellent substrate, abundant cover and shade, and high pool frequency created by in-streamlarge woody debris.Historical accounts of resource use by indigenous cultures and early settlers in lowerSequalitchew Creek provide qualitative evidence of significant perennial flow prior to settlementof the region. Records from Euro-American explorers arriving in the 1780s suggest perennialflow and habitat conditions within Sequalitchew Creek were sufficient to sustain a productivesalmon run that sustained the local tribal population. Discharge at the mouth of SequalitchewCreek was also used to support a trading post established in 1821 and a water-powered sawmillthat operated between 1859 and 1870. Later on, the E.I. DuPont de Nemours Companyconstructed a small dam and hydroelectric plant in the ravine in the early 1900s and maintainedthe dam until at least 1940 (Aspect 2004a). Drainage of Edmond Marsh for farming by the1850s, and the development of Fort Lewis between 1908 and 1917, impacted flows toSequalitchew Creek by reducing the storage capacity in the watershed. By the 1950s, floodingcaused by increased runoff from impervious areas of Fort Lewis prompted construction of thecurrent network of weirs and the diversion canal at the outlet of Sequalitchew Lake (Aspect2004a) (Figure 1).Construction of the diversion canal in the 1950s substantially reduced flows in SequalitchewCreek. Prior to construction of the diversion canal, the peak discharge in Sequalitchew Creek forthe 2-year storm event was estimated to range from 40 to 120 cfs, with an average value of 70 cfs(Aspect 2004a). Based on recent stream gauging and hydrologic modeling, the current estimateof the 2-year peak discharge is 10 cfs (Aspect 2004a). This major reduction in flow followed aperiod in which deforestation and development would have dramatically increased the sedimentsupply to the creek. The combination of an increase in sediment supply and reduction insediment transport capacity is consistent with field evidence of sedimentation within the ravine.This material is currently held in storage within the ravine and available for transport todownstream depositional reaches in the event of increased flow. The principal sediment trap hashistorically been the tidal area currently occupied by the brackish marsh immediately upstreamof the railroad grade, an area where sedimentation is likely to accelerate if stream flow isincreased without compensating measures to reduce sediment delivery and improve transportcapacity through the area of tidal influence (see Brackish Marsh discussion).Field observations and the natural history of the region suggest sediment transport and storagewithin the creek would have been significantly influenced by large trees and in-stream woodydebris. Large tree stumps observed on the slopes of the ravine indicate that wood recruitment tothe creek would have included logs far larger than the creek would have been able to move, andthus logs and woody debris capable of influencing the creek morphology would have been wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 8 October 28, 2005
Surface Water and Geomorphology Technical Reportcommon. Large trees would also be expected to moderate erosion along adjacent hillslopes byreinforcing creek banks and promoting a relatively narrow and deep channel. Deforestation ofthe basin in the early 1900s is likely to have exposed the highly erodible glacial sediments toerosion and severely accelerated sediment input to the creek and sedimentation within thebrackish marsh.Existing Geomorphic ConditionsThe existing geomorphic conditions of lower Sequalitchew Creek have been investigated for theproposed mine expansion project through field reconnaissance and modeling efforts. Fieldreconnaissance was completed in January 2004 by participants from GeoEngineers, CH2M Hill,and Glacier Northwest (GeoEngineers 2004b). Existing conditions in the brackish marsh wereinvestigated by Anchor (2004c) during rising and falling tides in April 2004. Additional fieldreconnaissance of Sequalitchew Creek was performed by Aspect (2004a) in April 2004 and byHerrera in September 2003 and February 2005. Landslides were mapped in the field andinterpreted from high-resolution topography of the project site.The ravine below Center Drive has been divided into four reaches based on geology (location ofKitsap cutoff), extent of tidal influence, and channel morphology (GeoEngineers 2004b). Reachnumbering (1 through 4) is upstream to downstream. Stream stationing, extending from Station00+00 at the mouth, approximately 50 feet downstream of the 5-foot box culvert: to Station70+00 (7000 feet) at the upstream end of the ravine, was established for purposes of hydraulicmodeling and provides an additional reference for discussion (Figures 2a and 2b). Theuppermost reach of the ravine is typically dry from the west end of Edmond Marsh to the firstidentified springs about 300 feet west of Center Drive. Flow at this location is intermittent.Remnants of the old dam and power works are located here as well.Reach 1 begins at Station 70+00 in the ravine, approximately 750 feet downstream from CenterDrive (Figure 2a). At this location, the ravine is roughly 60 feet wide and 40 feet deep. Reach 1is located above the Kitsap Cutoff and is characterized by relatively low channel gradient andnumerous ground water seeps emerging along the Olympia-Vashon contact. The averagechannel gradient varies from 1 to 2 percent, with the local maxima as great as 3.5 percent. Thebankfull channel depth varies from 0.3 to 3 feet. Channel width varies from 5-7 feet upstreamand increases to 15-40 feet near Station 35+00. Sediment comprising the channel bed isdominated by small gravel and cobbles and interstitial coarse sand and fine gravel. Streammorphology varies between a shallow, wide, braided channel spanning nearly the entire width ofthe ravine, to a relatively narrow channel confined against the ravine wall and causing localerosion. Deposition of sand within the active channel reflects the relatively low transportcapacity within Reach 1. Consistent with sedimentation, the channel has relatively few pools,and the ones observed occur downstream of the wood debris obstructing flow.Reach 2 extends from Station 30+00 to 18+00 and is located below the Kitsap Cutoff inunconsolidated outwash sand and gravel (Figure 2b). Channel gradient increases to 2-3 percentin Reach 2, with a local maximum of 4.5 percent. The width of the ravine bottom also increasesdownstream from 30 to 50 feet. Channel widths and depths in Reach 2 vary dramatically fromwp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 9 Herrera Environmental Consultants
Surface Water and Geomorphology Technical Report5-40 feet and 0.3-3 feet, respectively. Local surface raveling and exposed sediment at the toe ofravine slopes suggest active erosion by the stream in Reach 2. Where the channel widens, low-relief gravel bars provide additional evidence of recent scour and deposition, despite historicallylow flows. These observations clearly indicate that local sediment delivery from adjacenthillslopes still occurs and is likely to increase if flows are increased, unless mitigating actions aretaken to keep erosive flows from abutting the hillslopes (such as placement of large woodydebris). Elsewhere, the stream bed is locally armored with cobbles up to 6 inches in diameter.The downstream segment of Reach 2 between Stations 23+00 and 18+00 is similar to Reach 1and consists of a poorly defined braided channel with little or no floodplain.The width of the ravine increases in Reach 3 to about 250 ft at the downstream end of the reach(Station 5+00) (Figure 2b). Similar to the transition from Reach 1 to 2, the transition fromReach 2 to Reach 3 is marked by a change in channel morphology from a wide, shallow channelto a narrow channel incised into alluvium. Downstream of Station 16+80, channel morphologyvaries from a narrow channel confined against the toe of the ravine to a wide undefined channelwith intermittent mid-channel gravel bars. A berm constructed between Stations 9+00 and11+50 deflects the stream channel to the south side of the ravine and separates the creek from a10-foot deep pit excavated along the north side of the ravine. At Station 10+00, the creek flowswithin a relatively narrow channel in the middle of the widening valley bottom and away fromthe toe of the ravine.Reach 4 consists of a straight, plane-bed channel extending through the brackish marsh to theentrance of the box culvert at the foot of the railroad embankment (Figure 2b). The channelflows situated along the north side of the valley with its bed located below the brackish marsh,which forms the creek’s floodplain through Reach 4. The channel is armored with a layer ofcoarse gravel and is 9-10 feet wide and 1.0-1.5 feet deep. The channel does have some vegetatedbars along its right bank indicating it has undergone periods of historic sedimentation. Inaddition, there are several distinctive gravel splays or finger-like deposits of gravel on top of theadjacent tidal marsh at the upstream end of the reach (Station 5+50). Channel gradient decreasesfrom 2 percent to approximately 1.5 percent at the transition from Reach 3 to the brackish marshat Reach 4. The gradient of the box culvert beneath the railroad embankment is 1.2 percent. Thehydraulic gradient through Reach 4 is largely governed by the inlet elevation of the box culvert(-1.02 feet) and high tides, which can exceed 10 feet.Woody debris within the creek has been recruited from adjacent hill slopes because there arerelatively few trees within the ravine bottom. The majority of pools in the creek are formeddownstream of logs and in places where the banks are stabilized by tree roots. Most of the wooddebris consists of small trees, branches, and shrubs. Woody debris is not present in the tidallyinfluenced segment of Sequalitchew Creek through the brackish marsh (Reach 4), reflecting lowwood recruitment rates, insufficient transport capacity in the upstream reaches, and a low supplyof bedload in Reach 4. The lack of wood within the brackish marsh also indicates that littlewood debris is moving down the stream (coincident with a low sediment transport capacity) andwhat is moving downstream is trapped prior to reaching the brackish marsh. Some small wooddebris may be flushed to Puget Sound during low tides. But if any significant quantities were wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 10 October 28, 2005
Surface Water and Geomorphology Technical Reportreaching the brackish marsh, then deposits of wood debris would be found along the high watermargins of the marsh.Ravine slopes throughout the reaches are vegetated by ground cover and a mixed deciduous-coniferous forest. The gradient of side slopes within the ravine ranges from 30 to 80 percent.Several landslide features were mapped during a field reconnaissance of the ravine above station9+00 in January 2004 (GeoEngineers 2004b) (Figures 2a and 2b). Evidence of ancientlandsliding was noted at Stations 9+00 and 12+00 in Reach 3. These landslides are at least acentury old based on the presence of old-growth tree stumps in growth position on the surface ofboth features. A more recent landslide deposit was mapped on the ravine floor in Reach 2 atStation 23+50. This feature, a probable debris flow deposit, is about 40 years old based on thesize of the largest tree growing on the deposit (GeoEngineers 2004b). High-resolution LiDARtopography of the project area became available after completion of field mapping. Thelandslide features identified in the 2004 field reconnaissance are delineated on a map showingthe 2003 LiDAR of the project area (Figure 3). Material derived from historical or olderlandslides and chronic soil creep forms a nearly continuous sediment wedge along the toe ofravine slopes and serves as a readily available sediment supply when eroded by the creek. Localerosion of the sediment wedge occurs at sites where the creek flows along the valley edge. Atthese sites the sediment wedge has eroded and the hillslope is undercut and steepened(GeoEngineers 2004b). Unvegetated banks and ravine slopes with exposed sediment indicateongoing input of sediment to the creek.Based on observations of existing geomorphic conditions in the ravine, sediment production anddelivery processes appear to be dominated by the erosion of existing landslide deposits,gravitational creep, surface weathering, and sediment mobilized by flow from seeps and springs.Sediment derived from hillslopes is typically delivered to margins of the valley bottom where itremains in storage until eroded or entrained by the creek.Hydraulic Modeling of Existing ConditionsExisting hydraulic conditions in Sequalitchew Creek were evaluated by GeoEngineers (2004b)using the HEC-RAS model. HEC-RAS is a one-dimensional hydraulic model developed by theU.S. Army Corps of Engineers to estimate water-surface elevations for rivers and streams.HEC-RAS is typically used to evaluate stage and velocity relationships in a river given thechannel geometry, roughness, and flow rate. The channel geometry used in the model was basedon cross sections surveyed from the outlet of the box culvert at Puget Sound to the upstream endof Reach 1. Existing hydraulic conditions were simulated for the 2-, 5-, 10-, 25-, 50-, and100-year recurrence storm flow events. Hydraulic conditions in Reach 4 were evaluated underconditions of both high and low tide. Simulated flows were developed using recent gauge datafrom lower Sequalitchew Creek and correlation with recent stream gauge data from adjacentstream systems. Simulation outcomes were compared with existing bankfull elevations inferredin the field in order to calibrate the simulated channel roughness.Shear stress (i.e., force exerted on the bed by the stream) calculated by the HEC-RAS modelprovided the necessary hydraulic parameters to evaluate the potential for sediment transportwp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 11 Herrera Environmental Consultants
Surface Water and Geomorphology Technical Report(erosion) and deposition along various reaches of the lower stream reach (GeoEngineers 2004).The total boundary shear stress is the stress exerted by flowing water on the streambed andchanges with discharge, flow depth, and channel gradient. Critical shear stress for the bed is thestress required to initiate the movement of a particle and is an intrinsic property of the particlemass, shape, and size range of other particles on the bed. Because Sequalitchew Creek isarmored with the coarsest particles, the critical shear stress for initial entrainment of thestreambed was scaled to twice the critical shear stress for the 70th percentile grain size(GeoEngineers 2004b). Sediment deposition occurs when shear stress drops below the criticalparticle shear stress.The modeling results of the shear stress analysis by GeoEngineers (2004b) indicated potentialerosion in Reach 1 near Station 33+00 for storm events larger than the 2-year event (Figure 4a).However, the majority of potential erosion sites are located in Reach 2, where streambedgradients increase through the Kitsap Cutoff (Figure 4b). The results for Reach 3 indicatepotential erosion for the 2-year storm near Station 10+80, downstream of the berm and 10-foot-deep depression. Two additional sites in Reach 3, at Stations 5+58 and 5+40, indicate potentialbed erosion at the 25- and 50-year storm events just upstream of the brackish marsh.Results also identify sites where declining shear stress would cause deposition of sediment. Theshear stress analysis suggests a downstream pattern in the deposition of progressively finersediment sizes through Reach 3. For instance, all grains in transport and larger than 8.2 mmwould be deposited near Station 17+10 during 10-year flows, whereas grains larger than 6 mmwould be deposited at Station 10+05 during 25-year flows (Figure 4b). Likewise, during100-year flows, the maximum grain size transported through these reaches declines in thedownstream direction from 12 mm at Station 17+10 to 10 mm at Station 10+05. Declining shearstress through the brackish marsh indicates Reach 4 is aggrading under existing flow conditions.Relative trends in bed erosion and sediment deposition within Reaches 1 through 4 have beensummarized by comparing the ratio between the simulated shear stress and critical shear stressduring the 100-year event along a longitudinal profile of the creek (Figure 5). A ratio greaterthan 1 indicates conditions are favorable for sediment transport and bed erosion. When shearstress falls below the critical particle shear stress, sediment currently in transport would bedeposited. Results of the shear stress analysis indicate Reaches 1, 3, and 4 act as sediment trapswhile most of Reach 2 is subject to erosion and exporting sediment under existing conditions(Figure 5). The simulated decline in shear stress to just a fraction of the critical shear stress isconsistent with current observations of sedimentation in Reaches 3 and 4 and historical filling ofthe brackish marsh.Fort Lewis Diversion CanalThe Fort Lewis Diversion Canal (Diversion Canal), which borders the western boundary of theFort Lewis Military Reservation, was constructed in the 1950s to convey stormwater runoff fromFort Lewis to Puget Sound and to help control the water level in Sequalitchew Lake by serving wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 12 October 28, 2005
Surface Water and Geomorphology Technical Reportas an auxiliary outlet (Figure 1). Hydraulic structures (i.e., weirs) control the lake water level toprevent inundation of Sequalitchew Springs located near the eastern end of the lake, whichserves as a major water source for Fort Lewis (CH2M Hill 2003b). The Diversion Canal is twomiles long with trapezoidal-shaped channel, which is approximately 15 to 20 feet deep with abase width of 20 feet and 1H:1V side slopes (Aspect 2004a).Sequalitchew Lake is located entirely on the Fort Lewis Military Reservation. The lake isapproximately 81 acres in size and is shallow, approximately 17 feet deep. An 18-foot-wideconcrete structure with wooden stop logs that can be raised or lowered to adjust the elevation ofthe lake acts as the outlet diversion weir for the Diversion Canal (Aspect 2004a). The weir iscurrently set at an elevation of 211.15 feet (by the army).Stormwater runoff from the developed areas of Fort Lewis flows into the Diversion Canal,downstream of the lake outlet. The stormwater runoff is conveyed under Sequalitchew Creek viaa culvert near the lake outlet (CH2M Hill 2003b). The Diversion Canal then routes water alongthe western boundary of the Fort Lewis Landfill No. 5, ultimately discharging into the PugetSound near the Solo Point Sewage Treatment Plant (Woodward-Clyde 1990).A series of weirs controls lake level and flows to the Diversion Canal and Sequalitchew Creek(Figure 6). At low lake levels, an adjustable height weir directs flows from the lake toSequalitchew Creek, and at higher lake levels, lake outflow enters the Diversion Canal (CH2MHill 2003c). To maintain flows in Sequalitchew Creek, a second weir structure preventsSequalitchew Creek waters from flowing into the Diversion Canal. Beaver dams locateddownstream of the lake outlet can cause Sequalitchew Creek waters to back up, causing morewater to flow into the diversion canal and reducing the flows to the creek (CH2M Hill 2003c).Canal DischargeDischarge data measured by CH2M Hill (2003c) and Aspect (2004a) indicate that much higherdischarge flows through the Diversion Canal in comparison to the Sequalitchew Creek discharge.The average monthly discharge ranged from 2.0 to 21.9 cfs from December 1999 to November2002 at Wharf Road (CH2M Hill 2003c) and from 1.5 to 11.3 cfs from May 2003 to October2004 at the Diversion Weir (Aspect 2004a) (Table 1). In addition, daily winter storm dischargewas measured as high as 40 to 50 cfs (CH2M Hill 2001). Aspect (2004a) also measured thedischarge at three locations in the Diversion Canal to determine whether it was gaining or losingdischarge. Aspect (2004a) determined that the first reach between the diversion weir andDuPont-Steilacoom Road gains discharge while the next two reaches lose flow at relativelyconstant rates.Water QualityA discussion of Diversion Canal water quality was not included in the original mine EIS (City ofDuPont 1993). However, as a part of the baseline monitoring for the project, water qualitysamples were collected on a monthly basis in the Diversion Canal from September 1999 throughwp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 13 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportSeptember 2000 (Table 4). Samples were analyzed monthly for dissolved oxygen and watertemperature, and quarterly for conventional parameters and metals (Table 4). The analyticalresults indicate that the waters of the diversion canal generally have good quality, with theexception of elevated water temperatures during the late spring through early fall. During themonitoring period, state criteria were met for dissolved oxygen, fecal coliform bacteria, pH, andturbidity. A continuous temperature gauge was installed in July 2000, which recorded dailywater temperatures through August 2002. Water temperatures exceeding the state criterion weremeasured during July, August, and September of 2000.Additional temperature and dissolved oxygen data were collected in the Diversion Canal as partof continued project monitoring (CH2M Hill 2003c). The continuous recording temperaturegauge recorded numerous exceedances of the state temperature criterion (16°C) during Maythrough September 2001 and from late April through August 2002 when the continuous gaugewas removed (CH2M Hill 2003c). In addition, three dissolved oxygen measurements wererecorded during the summer of 2002 which did not meet the state minimum criterion of 9.5 mg/L(CH2M Hill 2003c).Sequalitchew Creek SpringsSeveral springs discharging from the Vashon aquifer are located along the north and south banksof the Sequalitchew Creek ravine, south of the existing mine and proposed mine expansion area.One major spring located on the north bank and two smaller seeps located along the south bankwere sampled as part of the original mine EIS studies (City of DuPont 1993). The results of thismonitoring indicate that the spring waters are of good quality (City of DuPont 1993). No newspring water quality or discharge data have been collected since completion of the original mineEIS. Similar to Sequalitchew Creek, elevated nitrate-nitrogen concentrations have beenmeasured in these springs (City of DuPont 1993).Near-Shore SpringsSeveral near-shore springs are located along the Nisqually Reach of Puget Sound, adjacent to thewestern boundary of the existing mine site. Spring discharges originate from the DuPont Deltaaquifer (CH2M Hill 2001). The largest spring (Large Beach Spring) is located in the intertidalzone approximately 1,600 feet north of the mouth of Sequalitchew Creek (Figure 1). This largespring enters Puget Sound at approximately 4 feet above mean lower low water (MLLW).Discharge data in the original mine EIS characterized the discharge from this spring as rangingfrom 11 to 18 cfs, depending on tide height (City of DuPont 1993). More recent data (CH2MHill 2001) measured discharges of 9.1 and 14.9 cfs during September 1999 and August 2000,respectively. Several smaller near-shore springs, located about 600 feet north of the large spring,had discharge that ranged between 0.05 and 0.24 cfs (CH2M Hill 2001).Based on the water quality data results presented in the previous mine EIS, waters of the largenear-shore spring generally exhibit good quality (City of DuPont 1993). Significantly high wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 14 October 28, 2005
Surface Water and Geomorphology Technical Reportconcentrations of sodium and chloride in addition to high specific conductivity measurementsreported in the original mine EIS were attributed to saltwater intrusion into the spring (City ofDuPont 1993). Salinity data were collected once in 1999 as part of the North SequalitchewCreek project in the large beach spring and two smaller springs (CH2M Hill 2001). Salinity inthe large beach spring was 5.3 parts per thousand (ppt), and was 7.7 ppt and 15.3 ppt in each ofthe smaller springs.Kettle WetlandThe Kettle Wetland, located in a large closed depression (a geologic feature called a kettle) nearthe center of the existing mine site, is approximately 2.5 to 3 acres in size (CH2M Hill 2001)(Figure 1). This wetland is located within the Sequalitchew Creek drainage basin and is inhydrologic continuity with the Vashon aquifer, where the surface water level is an expression ofthe ground water table at that location (CH2M Hill 2003b). Based on the water quality datapresented in the previous mine EIS, the Kettle Wetland has fair to good water quality (City ofDuPont 1993).Water levels in the kettle fluctuate seasonally, from 1-2 feet during the summer to 4-6 feet duringthe winter. The open water component width also varies seasonally from 50 feet during thesummer to several hundred feet during the winter. Water levels in the wetland were monitoredintermittently by CH2M Hill at a staff gauge installed in the wetland in 1999 (CH2M Hill2003a). Monthly water level data from July 1999 to October 2002 are presented in Figure 7.During monitoring, water levels reached peak levels during the wet season (November throughJune) and tended to drop with decreasing precipitation, especially during late summer and earlyfall. At the staff gauge location, water levels over the monitoring period ranged from a high of6.22 feet in December 1999 to the soil surface (0.63 feet) in October 1999.Old Fort LakeOld Fort Lake is a small kettle lake located south of Sequalitchew Creek and the proposed mineexpansion area (Figure 1). The lake is located on the former DuPont Works Site now owned bythe Weyerhaeuser Company. The lake is located in a kettle, and is supported hydrologically bythe shallow Vashon aquifer. Thus, lake water levels fluctuate seasonally and are a reflection ofthe ground water table at this location. Old Fort Lake water quality data were not summarized aspart of the original mine EIS and water quality data were not collected in Old Fort Lake as a partof the North Sequalitchew Creek Project.Pond LakePond Lake is a surface water, isolated, kettle depression wetland that is approximately 1.8 acresin size located south of the Sequalitchew Creek (WSA 2005). Pond Lake is located betweenwp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 15 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportCenter Drive and Strickland Lake (Figure 1). Although Pond Lake has no surface waterconnections to other surface waters, it is apparently connected with ground water and its surfacefluctuates throughout the year based on the local ground water elevation (WSA 2005). PondLake water levels fluctuate greatly; and lake periodically dries out for extended periods of time,such as, in 2001 and 2004 (WSA 2005). Pond Lake dries out completely at a ground watersurface elevation of approximately 201 feet above sea level. Pond Lake water quality data werenot summarized as part of the original mine EIS and water quality data were not collected inPond Lake as a part of the North Sequalitchew Creek Project.Brackish MarshThe brackish marsh is a one-half acre wetland located in the estuary of Sequalitchew Creek(Figure 8). The brackish marsh is situated on the southwest side of the main Sequalitchew Creekchannel on the landward (upstream) side of the BNSF railroad berm (Figure 8). Historicalrecords indicate that the Sequalitchew Creek estuary was once an open embayment along PugetSound which would have had a tidal wetland fringe. Historical land use beginning withconstruction of the railroad embankment and upland development, led to gradual infilling of theSequalitchew estuary, allowing emergent vegetation to become established. Infilling has furthertransformed emergent wetlands to upland vegetation.Historical Geomorphic ConditionsEarly survey maps from the late 1880s and 1908 show Sequalitchew Creek draining into a smallembayment along the coast of Puget Sound at the present location of the brackish marsh(Figure 9). Although construction of the railroad berm in 1912 isolated the mouth ofSequalitchew Creek from Puget Sound (Andrews and Swint 1994), sedimentation fromdeforestation of the basin likely initiated filling of the estuary, which probably consisted of ashallow embayment with intertidal mudflats and wetlands partially separated from Puget Sound.Topographic maps prepared after construction of the railroad embankment indicate the remnantsof the embayment still existed in 1939 and 1947 as an open-water lagoon behind the railroadembankment (Figure 9). Aerial photography from 1990 and recent field reconnaissance indicatethat considerable filling of the former embayment during the late 1900s transformed thesaltwater lagoon into the current brackish marsh.Existing Geomorphic ConditionsThe brackish marsh drains through a dendritic network of tidal channels that flow away fromSequalitchew Creek and merge into a main tidal channel, which then runs north along therailroad embankment and joins the creek at the box culvert entrance (see Figure 8). Thehydrology and water level of the brackish marsh are tidally influenced by Puget Sound (Anchor2004c). When the tide is 8 feet above mean lower low water (MLLW) or lower, flow inSequalitchew Creek remains within its channel and bypasses the brackish marsh directly to the wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 16 October 28, 2005
Surface Water and Geomorphology Technical Reportbox culvert (Anchor 2004c). When the tide rises to 9 feet above MLLW, salt water inundates themain tidal channel and fresh water from Sequalitchew Creek flows into the main dendriticchannel of the marsh (Anchor 2004c). When the tide reaches 10 feet above MLLW or higher,the brackish marsh is completely inundated (Anchor 2004c).Because the elevation of the culvert is within the intertidal zone, fresh water and sediment fromSequalitchew Creek are temporarily impounded behind the railroad embankment during hightide (Anchor 2004c). The impoundment creates conditions for the settling of fine-grainedsediment throughout the brackish marsh within the area of inundation, as well as deposition ofcoarse bedload sediment where the creek enters the impounded area at the upper end of Reach 4.Significant quantities of sediment have historically been deposited and retained in the brackishmarsh. During low tide, there is generally sufficient shear stress within the creek channel tomove sediments deposited during high tide out to Puget Sound. Deposition within the brackishmarsh is most likely to occur during high creek flow and high tides. These periods of depositioncontribute to the ongoing aggradation of the brackish marsh. Field reconnaissance conducted byHerrera in February 2005 observed gravel splay deposits emanating from the main-stem channeland covering portions of the marsh surface (Figure 10). The combination of historical surveyrecords and recent observations of coarse-grained alluvium several feet above sea level (in thearea of the former salt water embayment) indicate historical sedimentation and filling of thewetland within the brackish marsh.The current valley morphology and channelization of the creek into alluvial fan deposits isconsistent with the sedimentation predicted by the declining shear stress simulated within thelower ravine and brackish marsh. HEC-RAS modeling conducted by Herrera of the mean highwater (MHW) (approximately 9.5 feet North American Vertical Datum [NAVD], 13.5 feet abovemean lower low water, see above), indicates that aggradation below Station 8+00 is tidallyinfluenced, particularly when high tide coincides with significant sediment transporting events.Mean higher high water elevation to the 1988 NAVD is 10.5 feet and the highest observed waterwas 13.9 feet (at Olympia).During April 2004, salinity in the brackish marsh and the lower Sequalitchew Creek reach wasmonitored on two separate occasions (Anchor 2004c). The salinity was measured at severalstations during low and high tides, including an ebb tide during the second monitoring event(Table 5). The mid-depth salinity in the Sequalitchew Creek channel (SQ-1 through SQ-7)ranged from 0.1 to 27.6 ppt while the main dendritic channel (SQ-12, SQ-16, and SQ-17)mid-depth salinity ranged from 1.9 to 27.3 ppt. In general, salinity in the Sequalitchew Creekchannel remained low (0.1 ppt) unless it became inundated with saltwater. The main dendriticchannel tended to exhibit much higher salinity concentrations, especially during low tide periodswhen the marsh was not inundated with saltwater (Anchor 2004c).Nisqually Reach (Puget Sound)The Nisqually Reach of Puget Sound separates Anderson Island from the Nisqually Delta andborders the western shoreline of the project site. Water circulation in the Nisqually Reach iswp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 17 Herrera Environmental Consultants
Surface Water and Geomorphology Technical Reportdetermined by a complex mixture of forces, including tides, freshwater inputs, and winds (Cityof DuPont 1993). The Nisqually Reach hydrologic characteristics and water quality weredescribed in the original mine EIS (City of DuPont 1993).The Nisqually Reach is designated as an extraordinary marine water by Washington StateDepartment of Ecology (Ecology 173-201A-085) (Table 6). Ecology has established severalambient water quality monitoring stations in the Nisqually Reach. The station used tocharacterize Nisqually Reach marine waters in the original mine EIS (Station Id: NSQ001) hasnot been monitored since July 1996. More recent water quality data are available from a nearbystation in the reach (Station Id: GOR001) and are used to update the following water qualitycharacterization (Ecology 2005). This station is located in Pierce County, just north of Andersonand Ketron Islands (Figure 1). The water quality data collected at this station from 1996 through2002 are summarized in Table 7. Data collected in 2001 and 2002 are provisional and have notbeen finalized (Ecology 2005). Data were gathered at 0.5, 10, and 30 meters from October 1996to January 2000 and thereafter, were collected from depths of approximately 1, 10, and 30 meters(Ecology 2005b).Monitoring data indicate that marine waters of the Nisqually Reach have fair to good quality.During sampling, reach waters met state extraordinary criteria for pH and fecal coliform bacteria.However, the state extraordinary water temperature criterion (13°C) was exceeded 29 timesduring the late summer and fall (July through October). In addition, 45 dissolved oxygenmeasurements during the monitoring period did not meet the state minimum criterion of 7.0mg/L. Because turbidity was not monitored, compliance with this standard is undetermined.The Nisqually Reach/Drayton Passage area is on Ecology’s final 2004 303(d) list of threatenedand impaired waterbodies for violations of the state standards for fecal coliform bacteria,dissolved oxygen, pH, ammonia-nitrogen, and temperature (Ecology 2005a). The NisquallyReach/Drayton Passage area was also listed for fecal coliform bacteria on the 1996 list, but wasnot placed on the 1998 list (Ecology 2005a).Ecology has initiated a South Puget Sound Model Nutrient Study (SPASM), which addressesconcerns of eutrophication in South Puget Sound. However, to-date a TMDL (and proposedclean-up action) has not been established for the Nisqually Reach addressing the fecal coliformbacteria listing (McKee 2005). Ecology completed a quality assurance project plan for theHenderson and Nisqually TMDL Study that summarizes the existing Nisqually Reach data andpresents a TMDL evaluation project design (Sargeant et al. 2003). That report will serve as abackground study for establishing the Nisqually Reach TMDL. Several excursions beyond thecriterion for dissolved oxygen at station NSQ001 were identified on Ecology’s 1998 303(d) list;however, these excursions were found to be a result of natural causes and no formal listing wasmade (Ecology 1998). wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 18 October 28, 2005
Surface Water and Geomorphology Technical Report 3.0 Significant Impacts of the Proposed ActionConstructionConstruction activities associated with the proposed mine expansion would include site clearingand grading, excavation of soils for the construction of North Sequalitchew Creek, pedestrianbridge construction (over North Sequalitchew Creek), access road construction (culvertplacement), and conveyer system construction. All mining operation and processing facilitieswere constructed as part of the original mine facility and are not located within the proposed200-acre mine expansion area. Impacts from the construction of these facilities are described inthe original draft and final EIS for the mine (City of Dupont 1992, 1993). No additionalfacilities would be constructed in either the new mine expansion area or in the processing areathat is already in operation with the existing permitted mine.Glacier Northwest proposes dewatering to accommodate excavation and sand gravel extractionbelow the existing ground water table. The proposed dewatering plan would require theinstallation of a series of dewatering wells to pump and drawdown the Vashon aquifer so thatexcavation could occur under mostly dry conditions. Ground water would be discharged intoSequalitchew Creek at the approximate location of the proposed confluence with NorthSequalitchew Creek (RM 0.8). During construction, the mining operations would remove theVashon drift unit, located within the proposed mine expansion area. (See the ground watertechnical report for the discussion of impacts to ground water quality and quantity (PGG 2005).Stormwater ManagementA sediment pond and an infiltration pond would be used during construction (and operation) forthe discharge of on-site stormwater (CH2M Hill 2003c). The sediment pond would be sized totreat up to the 10-year storm event and to treat ground water base flow (i.e., approximately10 cfs) not captured by the dewatering wells (CH2M Hill 2003c). The infiltration pond would besized to store and infiltrate the 100-year, 24-hour storm, including the 10 cfs of possible groundwater baseflow (CH2M Hill 2003c).During mine excavation, stormwater runoff and some ground water baseflow would accumulatein the bottom of the active excavation pit. This pit would be graded to allow for the capturedwater to collect at a low point, which would serve as a temporary sedimentation pond. Ifnecessary, the collected water would be pumped to an on-site infiltration pond for discharge toground water.Current mining activities are covered under a Surface Mining and Associated Activities GeneralPermit (WAG-50-1178) as part of the Ecology NPDES permit program. This permit covers thedischarge for process water and stormwater associated with sand and gravel operations.Coverage under this permit allows for discharges to waters of the State of Washington subject topermit conditions under both the construction and operational phases of mining.wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 19 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportSite Clearing and GradingMine expansion area clearing and grading would be phased with mining and constructionactivities to minimize the area cleared at any one time. Site clearing and grading would consistof the removal of the topsoil and stockpiling this material on-site for re-use during sitereclamation after mining operations have ceased.An Erosion and Sedimentation Control (ESC) Plan would be prepared as part of the StormwaterPollution Prevention Plan (SWPPP) completed for the proposed mine expansion as a requirementof the mine NPDES permit. With the employment of proper and usual ESC measures, impacts toreceiving waters during clearing and grading are expected to be negligible. ESC measuresoutlined in this plan would minimize or eliminate impacts by providing adequate treatmentthrough the use of best management practices during site clearing and grading. Sediment anderosion ESC measures proposed for the mine expansion area include: Wetting roadways as necessary with water for dust control Truck wheel washing prior to off-site travel On-site infiltration of stormwater.Within the mine expansion area, construction would remove vegetative cover and expose soilsleaving this area prone to erosion during runoff events. The rate of surface water runoff fromthese areas could increase due to compaction of soils and lack of vegetative cover. If sedimententers any water resources, increases in turbidity, suspended solids, and settleable solids couldoccur. However, all storm water runoff on-site would be infiltrated to the shallow ground wateraquifer, and not reach Sequalitchew Creek (via surface flow). Therefore, impacts to surfacewater resources are not expected.Oil, grease, and total petroleum hydrocarbons (TPH) could leak or spill from constructionequipment or petroleum product storage facilities. If an uncontrolled spill occurred, there wouldbe the possibility that petroleum products could reach ground water under the construction area.These products could pose a risk to water quality at high concentrations. Release of petroleumhydrocarbons from heavy mining equipment and haul trucks is a significant concern to groundwaters, but can be prevented by mitigation measures such as strict prohibition of oil/fuelingdumping and contractual specification’s for accidental spill response and notificationrequirements, and catchment control of parking/staging areas for construction equipment. Themining SWPPP would include an Emergency Spill Cleanup Plan that outlines specific bestmanagement practices (BMPs) as they relate to accidental spills of fuel and oil and clean upprovisions for any contaminated soils and construction waste.North Sequalitchew Creek ConstructionConstruction of North Sequalitchew Creek would begin in the northern section of the proposedmine, then proceed to the south along the eastern property boundary of the proposed mineexpansion area. Early phases of mining (approximately the first five years) would include theconstruction of 4,000 feet of North Sequalitchew Creek. wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 20 October 28, 2005
Surface Water and Geomorphology Technical ReportDuring stream construction, an impoundment berm would be constructed at the southern mostend of the new stream channel, near its proposed confluence with Sequalitchew Creek, to collectrunoff and ground water seeping from the materials during excavation and mining. Thisimpoundment berm would remain in place during channel excavation to prevent turbid water andsediment from entering Sequalitchew Creek.As mining operations remove sand and gravel, the stream channel and riparian buffer area forNorth Sequalitchew Creek would be excavated. The slope above the new stream would bestabilized and planted. After the stream channel is constructed and the vegetation along the slopeand within the riparian corridors is established, pumping of the dewatering wells would bereduced. As the pumping is reduced, seeps would develop along the eastern riparian slope faceand flow down to the channel. Measures to prevent erosion along this face may include pipingthis seepage down the face to the stream (CH2M Hill 2003b). The Vashon Drift consists of twoaquifers, an upper and a lower aquifer, which are separated by a thin layer of till, and stratifiedsilty ice-contact deposits which act as a confining layer (i.e., aquitard) between the two aquifers.Most of the flow to the new stream would come from the upper aquifer, which consists of top the30 feet of the seepage face (CH2M Hill 2003b). The lower 40 feet of the seepage face wouldconsist of the lower aquifer, which would have much lower yields (CH2M Hill 2003b). Inaddition, ground water would daylight within the newly established North Sequalitchew Creekchannel along the impermeable Olympia Beds.As the pumping of the dewatering wells is decreased, the expected flow in North SequalitchewCreek would increase. As stream flows are established, flow would be monitored for totalsuspended solids, turbidity, dissolved oxygen, and temperature (CH2M Hill 2003c). Due to thelack of vegetative cover, sediment and fines would likely occur in runoff entering the stream.During this period, the project proposes to route this water to sediment pond(s) for treatment(CH2M Hill 2003c). North Sequalitchew Creek will be constructed with a variety of BMPs inplace that are intended to protect water quality and meet applicable water quality standards.These BMPs would help reduce fines and suspended sediment that could potentially betransported from North Sequalitchew Creek to the mainstem creek when the two systems areconnected.After the flow into the stream has stabilized, the temporary impoundment berm would beremoved, allowing flows from North Sequalitchew Creek to join Sequalitchew Creek. Turbiditylevels may be elevated in both streams during the initial flow period when the streams areconnected after berm removal. The estimated average monthly discharge of North SequalitchewCreek in its lowest reach prior to entering the mainstem of Sequalitchew Creek is estimated torange between 6.4 (October) and 8.7 (March) cfs (Anchor 2004d). Water quality for the newstream is discussed below under Operational Impacts.Sequalitchew CreekDuring construction, surface water runoff from the mine expansion area would not dischargedirectly to Sequalitchew Creek because all storm water runoff would be infiltrated on-site.However, during construction, ground water (Vashon aquifer) in the mining area would bewp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 21 Herrera Environmental Consultants
Surface Water and Geomorphology Technical Reportintercepted by a series of dewatering wells and pumped to Sequalitchew Creek for discharge.The dewatering wells would be used for dewatering the mine expansion area until NorthSequalitchew Creek is functioning and intercepts ground water flow. Pumped ground waterwould be piped from the mine expansion area to the south, down the steep ravine where it woulddischarge to Sequalitchew Creek via a rock pad and flow dissipater designed to prevent erosionof the ravine hill slope and stream channel. The flow dissipater would be located atapproximately RM 0.8, near the proposed confluence of the two streams. The estimateddewatering rates would range from 7 cfs to 15 cfs with an average of 10 cfs (CH2M Hill 2003c).These volumes exceed the current flow in Sequalitchew Creek, where monthly average flowsrange from 0.2 cfs (September) to 2.9 cfs (March) (Anchor 2004b). However, these dewateringrates are well below the historic peak flows within the stream that occurred prior to theconstruction of the Fort Lewis diversion canal.Water QualityDuring construction, dewatering water (ground water) would be pumped via pipe(s) toSequalitchew Creek for discharge. Because mine expansion area ground water quality data werenot available, ground water quality data ranges were extrapolated by Pacific Groundwater Group(PGG) from water quality data collected as part of (1) the Landfill No. 5 Remedial Investigation(Woodward Clyde 1990), and (2) the 2002 quarterly ground water monitoring results reportedfor Landfill No. 5 by Anteon (2002) (PGG 2005). The range of predicted dewatering groundwater quality for select parameters are compared to Sequalitchew Creek background waterquality data and state surface water quality standards in Table 8. The estimated quality of theexisting ground water is generally good (PGG 2005).Temperature, turbidity, and dissolved oxygen were not estimated by PGG because backgrounddata for these parameters did not exist either as part of the Fort Lewis Remedial Investigation(Woodward Clyde 1990) or part of the 2002 and 2005 quarterly ground water sampling at FortLewis No. 5 landfill (Anteon 2002; PGG 2005). Further, they are not regulated parameters instate ground water quality standards (Chapter 173-200-040 WAC) (Ecology 1990).Fecal coliform bacteria are regulated by state ground water standards, but were not sampled aspart of the quarterly monitoring of Landfill No. 5 as reported by Anteon (2002). Because thisdata did not exist, PGG (2005) did not establish a background fecal coliform bacteriaconcentration for ground water in the vicinity of the site. However, the fecal coliformconcentrations in the ground water would likely be low. Near the mine expansion area, there isnot a significant subsurface fecal coliform bacteria source (i.e., septic systems, etc.). The City ofDuPont (including Northwest Landing) is a sewered community. Further, fecal coliform bacteriado not survive in the subsurface environment for an extended period of time. Fecal coliformbacteria are not expected to exceed the state surface water criterion of 50 CFU/100 ml inSequalitchew Creek.During dewatering, the pumped ground water would be cool. In the project test wells, groundwater temperatures ranged between 8°C to 12°C (CH2M Hill 2003c), meeting the state surfacewater standard of 16°C (Chapter 173-201A WAC). Because the dewatering water pumped from wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 22 October 28, 2005
Surface Water and Geomorphology Technical Reportthe mine would be cool, it would not adversely impact Sequalitchew Creek water temperatures.Similar to temperature, turbidity is generally not a concern with ground water. The pumpedground water would not be allowed to discharge to Sequalitchew Creek until the wells have beenproperly purged and developed, and are free of sediment which may have been introduced duringwell drilling and installation.The dissolved oxygen concentrations of the dewatering water may be lower than the stateminimum criterion of 9.5 mg/L; however, the project proposes to utilize a rock pad anddissipater device that would aerate and increase the dissolved oxygen concentration in the waterwithin in the discharge to meet this state standard (CH2M Hill 2003c).Based on ground water quality data presented by PGG (2005), both ammonia and nitrateconcentrations in the dewatering water would be within background range of the SequalitchewCreek concentrations measured by CH2M Hill during baseline project sampling (Table 8). Thepredicted ammonia concentration in the ground water would be low (<0.1 mg/L) and would meetstate water quality standards. The estimated nitrate-nitrogen concentration in the ground waterwould be low, and is expected to range between 0.0005 and 0.02 mg/L, which is lower than thestream background which ranged between 0.28 and 0.82 mg/L (Table 8) (PGG 2005). Nitrate-nitrogen is not a regulated parameter in the state surface water standards, but is a regulatedparameter in state ground water standards and state drinking water standards. Both standards setthe limit at 10 mg/L (Chapters 173-200-040 WAC and Chapter 246-290-310 WAC, respectively)based on human health concerns.Monitoring of the dewatering water is a required element of the State’s sand and gravel generalNational Pollutant Discharge Elimination System (NPDES) permit. The permit requiresdewatering discharges to surface water be monitored for turbidity, TSS, pH, temperature, and oilsheen.During the last phase of construction, the berm between the active mine area and SequalitchewCreek would be removed to connect North Sequalitchew Creek and Sequalitchew Creek, so thatNorth Sequalitchew Creek discharge can flow into Sequalitchew Creek. During confluenceconstruction, the Sequalitchew Creek channel would be disturbed, likely causing some sedimentand fines to enter Sequalitchew Creek waters. Construction measures would employ BMPs tohelp minimize turbidity and sediment impacts from berm removal and confluence construction.In addition, when flows from North Sequalitchew Creek are introduced to Sequalitchew Creek,sediment from the disturbed channel areas would have the potential to be washed downstreamcausing temporary increases in turbidity.DischargeBased on preliminary work by CH2M Hill (2003c), the estimated dewatering rates would rangefrom 7 cfs to 15 cfs with an average of 10 cfs. Dewatering volumes would exceed the averageannual discharge in the stream of 1.4 cfs (from 1999 through 2004) below the proposedconfluence of North Sequalitchew Creek (Anchor 2004b). These discharge rates are well belowthe historic range estimated for Sequalitchew Creek, where the 2-year storm flows werewp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 23 Herrera Environmental Consultants
Surface Water and Geomorphology Technical Reportestimated to range from 40 to 120 cfs prior to construction of the diversion canal by Fort Lewis(Aspect 2004a).GeomorphologyIncreased flows from mine dewatering would affect existing sediment transport processes inlower Sequalitchew Creek. Increased discharge from dewatering of the mine expansion couldentrain greater amounts of sediment stored in the ravine bottom. Localized sections of thestream, particularly in Reach 2, already experience bed and bank erosion under the existing flowregime. Likewise, most of Reaches 3 and 4 show evidence of recent sedimentation reflectinginsufficient transport capacity and inputs from Reach 2 and local bank erosion within Reach 3.This situation is likely to remain constant in most of these segments even after flows areincreased – particularly in Reaches 3 and 4 which would be receiving more sediment fromReach 2. Based on the downstream trend in declining shear stress (i.e., the force exerted on thestreambed by the water) reported by GeoEngineers (2004), sediment eroded from Reach 2 wouldlikely be deposited in the upper portion of Reach 3. The resulting sedimentation within Reach 3would increase the potential for channel migration into unconsolidated and easily erodedsediment along the toe of valley slopes during moderate to large flood events. This in-turn couldtrigger localized erosion of the hillslopes which could further overwhelm the stream withsediment beyond what the increased discharge would have the capacity to move.Brackish MarshWater QualityThe brackish marsh located near the mouth of Sequalitchew Creek would experience increasedflows and water levels as ground water is pumped to the mainstem of Sequalitchew Creek(upstream of the brackish marsh) during mine dewatering during construction. Flow increases inthe brackish marsh would be similar to those described above for Sequalitchew Creek, whereflows in the stream channel could increase by 7 to 15 cfs (average of 10 cfs) during constructiondewatering.This initial increase in flow to Sequalitchew Creek would likely mobilize sediment and finesdownstream as the wetted-width of the channel is increased, and as fine sediments and organicsare washed downstream (Anchor 2004c). The project proposes to incrementally increase flowsto Sequalitchew Creek to limit the amount of erosion upstream in Sequalitchew Creek anddownstream deposition within the brackish marsh.Sediment and fines entering the stream during dewatering activities could have the potential toincrease turbidity downstream within the brackish marsh. Turbidity is a regulated parameter inthe state surface water quality standards (Chapter 173-201a WAC). During constructiondewatering, the project would have to maintain turbidity that is within 5 NTU over thebackground condition (in Sequalitchew Creek), as identified in the State’s surface water qualitystandards, unless otherwise specified in construction or mining permits issued for the project. wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 24 October 28, 2005
Surface Water and Geomorphology Technical ReportThe increase in the amount freshwater entering the stream could alter the salinity of the water inthe brackish marsh (Anchor 2004d). However, salinity is not a regulated parameter in statesurface water quality standards for either freshwater or marine waters. Significant changes insalinity could, however, affect the plant and animal communities existing within the marsh.These are discussed in the Plants and Animals section of the SEIS, 3.4.GeomorphologyIncreased flows in Sequalitchew Creek during construction have the potential to impact thegeomorphology and ecology of the estuary (Reach 4). The Sequalitchew Creek estuary consistsof two distinctive geomorphic process domains: (1) a fluvial corridor along the north side of theravine occupied by the stream channel, within which freshwater and sediment are not input to theestuary; and (2) a tidal marsh system occupied by a dendritic tidal slough network and salt marshvegetation, within which salt water from Puget Sound is exchanged twice daily (i.e., a diurnaltide cycle). The confluence of these two geomorphic processes is located immediately upstreamof the box culvert inlet. This domain configuration is characteristic of pocket estuariesthroughout Puget Sound where fluvial corridors become confined along the perimeter ofembayments by natural levees (created by deposition of coarse overbank sediments along marginof stream channels). These natural levees effectively increase the depth of the stream which in-turn increase sediment transport capacity and reduce the probability that tidal marshes are filledand converted to upland by stream sedimentation. The boundary between these two processdomains in the Sequalitchew Creek estuary is not well defined. Most notably absent is a distinctlevee. Because of this, Sequalitchew Creek has periodically delivered sediment to the brackishmarsh with the resulting sedimentation filling portions of the salt marsh wetland.The confluence of the tidal slough network and stream channel near the outlet to Puget Soundalso contributes to sustaining the tidal marsh domain. During low tides, the outflow dischargefrom the tidal slough network effectively increases the stream discharge and sediment transportcapacity in a locale particularly susceptible to sedimentation. The volume of water that entersand leaves between mean lower low water (MLLW) and mean higher high water (MHHW) isreferred to as a tidal prism. The greater the tidal prism, the greater the ability of the system tosustain an outlet channel to Puget Sound.Pocket estuaries in Puget Sound have been able to sustain salt marsh ecosystems for thousands ofyears through the natural segregation of the freshwater dominated fluvial domain and thesaltwater dominated tidal marsh domain. This natural segregation inhibits sedimentation fromfilling tidal salt marshes and converting them to freshwater floodplains. The process is reflectedin the fact that many pocket estuary tidal marshes are underlain by thick deposits of organic peat(created by tidal marsh vegetation) and little or no inorganic sediment representative of streamdeposition. While the Sequalitchew Creek Estuary exhibits some of general attributes of anundisturbed pocket estuary, it has undergone rapid, historic infilling uncharacteristic of anundisturbed pocket estuary. Infilling of the Sequalitchew Creek estuary has resulted fromhistoric land disturbance within the watershed and ravine. This historic trend has continueddespite the reduced flow regime in the stream and is likely to accelerate if the stream discharge isincreased, unless mitigating actions are taken. Implementing changes to the stream that emulatewp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 25 Herrera Environmental Consultants
Surface Water and Geomorphology Technical Reporta natural system (i.e., in-stream wood to trap sediment upstream of the estuary, construction of alow levee between the stream and tidal marsh, and excavation of historic infilling of the estuaryto increase the tidal prism and re-establish tidal wetlands) would offset negative impacts.Together with the proposed increase in flow, such measures would result in a net environmentalimprovement to Lower Sequalitchew Creek and estuary.The increased discharge from dewatering of the mine expansion could result in more frequententrainment of sediment stored in the ravine bottom, both through an increase in basal shearstress on the stream bed and primarily through erosion along the margins of the stream where itabuts the sediment wedge along the toe of the ravine slopes. Based on the downstream trend indeclining shear stress reported by GeoEngineers (2004b), sediment transported from the upperreaches would likely deposit in Reaches 3 and 4, aggrading the channel bed and the brackishmarsh. Sedimentation within the brackish marsh could cause raised ground elevations, lowersalinity, and a reduction in tidal flushing. Sedimentation within the marsh would be a significantimpact because it would be analogous to filling a wetland and causing a major ecologicaltransformation (i.e., conversion of salt marsh to freshwater floodplain and reduction in the tidalslough network). Ecological impacts to the marsh from increased flows are discussed in thePlant and Animal section of the SEIS.Morphological adjustments in the ravine caused by increased flow could deliver more sedimentto Reach 4 in the short-term. An increase in the bed elevation relative to the top of the existingstream bank would increase the frequency of sediment delivery to the brackish marsh andincrease the probability of the stream channel being re-directed through the marsh (similar to thechannel change on an alluvial fan or river delta). These changes would contribute to infilling ofthe brackish marsh. Additional fine sediment delivered by increased flow and held in suspensionbehind the railroad embankment during high tide, would cause additional aggradation within thebrackish marsh. Aggradation would likely be greatest at the upstream end of the brackish marsh,and, with sustained sediment supply, continue on toward the railroad embankment through time.Sedimentation and accumulation of LWD within or directly upstream of the box culvert wouldeventually diminish conveyance between the brackish marsh and Puget Sound, further reducingthe tidal prism. A reduction in tidal prism would decrease sediment transport capacity throughthe culvert despite added instream flows from North Sequalitchew Creek. This could furtheraccelerate marsh infilling and associated impacts in Reaches 3 and 4. Monitoring ofsedimentation rates within the stream channel and brackish marsh (Reaches 3 and 4) arerecommended as part of project mitigation (see Mitigation Measures).Access Road and Pedestrian Bridge ConstructionConstruction of access roads and the pedestrian bridge (over North Sequalitchew Creek) withinthe proposed gravel mining area would have no impacts on surface water resources in thevicinity of the project. The access roads and pedestrian bridge would be constructed prior to theoperation of North Sequalitchew Creek when there is no flow within the stream channel. Inaddition, the berm separating the North Sequalitchew Creek construction activities andSequalitchew Creek would be in place during construction of these features. The two access wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 26 October 28, 2005
Surface Water and Geomorphology Technical Reportroad crossings of North Sequalitchew Creek would consist of bottomless box culverts. Thepedestrian bridge would be constructed near the mouth of North Sequalitchew Creek, but prior toits connection with the mainstem of Sequalitchew Creek, thereby not impacting SequalitchewCreek.Conveyer System ConstructionConstruction of the conveyer system would not impact surface water resources. The conveyersystem would not be constructed near any on-site or off-site water resources. Similar to otherareas of the mine, stormwater runoff would be routed to a sedimentation pond and then to aninfiltration pond, for discharge.OperationOperation activities associated with the mine expansion area would include mining, processingand shipping. Operation impacts associated with the processing plant, concrete facilities, bargeloading facility and shipping were discussed in the original EIS (City of DuPont 1993) andsubsequent SEIS (City of DuPont 1995). With the addition of the new mine expansion area, thetypes of impacts from operating these facilities would not differ from what was previouslydescribed in the original EIS (City of DuPont 1993) and the subsequent SEIS (City of Dupont1995). However, the life of the mine would be extended by approximately 8-12 years while theexpansion area is mined.Mining and ProcessingGlacier proposes to capture ground water entering the mine expansion area from the east andconvey it off-site to Sequalitchew Creek via North Sequalitchew Creek, the newly constructedstream channel. Construction of this stream is described above in the Construction Impactssection. This new stream would be designed to create new fish habitat and increase flows in thelower mainstem of Sequalitchew Creek, thereby improving the existing aquatic habitat.North Sequalitchew CreekDuring the operational phase of mining, North Sequalitchew Creek would intercept ground waterand allow mining excavation to occur under generally dry conditions. This newly constructedstream channel would replace the ground water intercept function provided by the dewateringwells during construction. The new stream channel would have a low gradient (0.5 percent) anda channel length of approximately 4,000 feet (Anchor 2004a). A detailed description of NorthSequalitchew Creek is provided in the Fisheries Technical Report (Herrera 2005b).wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 27 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportWater QualityWater quality data for North Sequalitchew Creek were predicted using data collected as part ofthe Landfill No. 5 Remedial Investigation (Woodward Clyde 1990) and as part of the 2002 and2005 quarterly monitoring results of the landfill reported by Anteon (as cited in PGG 2005) andare listed in Table 8. The estimated quality of North Sequalitchew Creek would be good. Thedata presented in Table 8 indicate the stream would likely meet applicable state standards formetals, pH, and fecal coliform bacteria. However, dissolved oxygen, temperature and turbidityinitially may not meet state water quality standards in the newly constructed stream because ofthe lack of mature riparian vegetation and the physical design of the stream channel. However,the project proposes corrective actions that would be taken to assure the newly constructedstream meets applicable water quality standards and such measures are described below (CH2MHill 2003c).Unlike the dewatering discharge to Sequalitchew Creek during construction, (which proposes toutilize a rock pad and dissipater to promote aeration), discharge from the seeps and springs to thenew stream would occur as sheet flow or shallow channel flow, which initially may not introduceenough oxygen to the water to meet the state minimum criterion of 9.5 mg/L (Chapter 173-201aWAC). The proposed design of North Sequalitchew Creek would include elements, whichwould help aerate the water, to meet the state surface water quality standard. If dissolved oxygenis not meeting the standard, structural measures would be taken to introduce oxygen to thestream waters, such as constructed log weir drops in the stream channel to promote aeration(CH2M Hill 2003c).Because the source of flow in North Sequalitchew Creek would be ground water seeps, watertemperatures would be cool. However, during the initial operation, stream temperature could bea concern because the vegetation in the riparian corridor would not be fully established toprovide adequate shading of the stream channel, especially during the dry season. Therefore,warming could occur. The stream design flow rate would be 1 foot per second (fps) (CH2M Hill2003c) and at this flow rate the residence time in the stream would be approximately 3 hourswhich would allow for an increase in water temperature to occur. The planting design wouldinitially include the installation of willows along the riparian corridor which would growrelatively quickly to provide shade. As with dissolved oxygen, water temperature in the newstream would be measured for compliance to the state standard prior to final stream constructionand when flows are initially allowed to enter Sequalitchew Creek. Based on the preliminarydesign of this stream, water temperatures of 10°C to 14°C would be achievable in the new stream(CH2M Hill 2003c).Even after bank and channel stabilization, sediment and fines may still enter the new stream.Because North Sequalitchew Creek originates from ground water, this source would generally befree of silt and sediment. However, as the ground water daylights onto the steep slopes abovethe channel and travels via overland flow to the stream below, flows would likely transportsediment and fines and deposit this material into the stream. The sediment could either settle tothe bottom or be carried downstream. However, because the gradient of the new stream isrelatively flat and the proposed velocities are low, the opportunity for flushing these fines and wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 28 October 28, 2005
Surface Water and Geomorphology Technical Reportsediments from the stream are low. As a result sediment build-up could occur and adverselyimpact salmon spawning areas in the new channel.Because the stream would function as a dewatering channel during mining operations, it wouldbe monitored per the requirements of the sand and gravel NPDES permit issued for the miningoperation. Currently, the State general permit requires that dewatering water (NorthSequalitchew Creek) that discharges to a surface water (i.e., Sequalitchew Creek) must bemonitored for turbidity, TSS, pH, oil sheen, temperature, and flow.HydrologyPredicted flows in North Sequalitchew Creek were determined using the ground water modelingcompleted as part of the project (Aspect 2004a, 2004b; CH2M Hill 2003c). Based on the bestestimate for average annual conditions, the predicted flow of North Sequalitchew Creek justabove its confluence with Sequalitchew Creek would be 7.6 cfs Anchor 2004d) (see Table 9).Taking into account the sensitivity analysis of the ground water model, the best estimate forpredicted average annual instream flows could range from 6.4 to 9.8 cfs at the confluence withSequalitchew Creek (Anchor 2004d). The predicted low flow within the channel is 4 cfs(Ellingson 2005).Hydraulic ModelingCH2M Hill conducted hydraulic modeling of the proposed design for North Sequalitchew Creekusing the U.S. Army Corps of Engineers HEC-RAS model which simulates the hydraulics ofstreams and open channel systems. The model was used to determine how different streamdischarges would alter the stages and velocities within the channel and, in turn, what their affectwould have on the riffle and pool depths of the proposed design. The sensitivity analysisinvolved running the model for 2, 4, 6 and 8 cfs. This range of flows includes both the low flowand average flow conditions and was conducted to analyze the proposed stream design stagesand velocities at these different flow rates. For each flow rate in the modeled range, specificcross sections along the stream channel were selected for analysis. Based on the model results,modifications were then made to the channel geometry until the desired water depths andvelocities were achieved within the channel for optimal fish habitat (CH2M Hill 2003c).For the selected flow range 2, 4, 6, and 8 cfs, water depths in the riffle sections would range from0.8 to 1.4 feet, with discharge ranging from 0.9 to 1.9 cfs (CH2M Hill 2003c). However, themodel results for 2 cfs calculated a riffle depth of 0.3 feet, which would not meet the criteria forspawning habitat (CH2M Hill 2003c). Modeling results for the pool sections show that the waterdepths would range from 2.4 feet to 3.3 feet with a discharge ranging from 0.1 to 0.3 cfs (CH2MHill 2003c). In addition, the stream predesign report completed in 2003 by CH2MHill (2003c), adepth of 1.5 feet for the central portion of the stream channel is sufficient to convey the 2-yearflow and the floodplain would be able to accommodate the 100-year flow of 30 cfs (flowsanalyzed were based on the previous ground water modeling results).wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 29 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportBased on the most recent stormflow analyses for the 2-year, 5-year, 10-year, 25-year, 50-yearand 100-year events, flows modeled within the channel ranged from 11.3 (2-year event) and25.8 cfs (100-year event) (Anchor 2004d). The channel geometry modeled was similar to thatused previously by CH2M Hill in their HEC RAS model analysis (Anchor 2004d). Anchor’smodeling results indicate that the highest water velocity value is found in the lower 1,000 feet ofproposed stream channel (Station Id. 535.6). Model results show that the water velocities spikefor sections modeled as rock vortex drops, such as Station Id. 535.6 (Anchor 2004d). Modelingresults show that with the 2-year event, the predicted average velocity at this station (3.01feet/second) would be sufficient to sort gravel (Anchor 2004d). This average velocity would noterode the channel banks or the thalweg (Anchor 2004d). The average velocity for the 100-yearevent would also occur at this same location and would be 4.53 feet/second (Anchor 2004d).Modeling results indicate major structural features in the channel would be stable at the 100-yearevent.GeomorphologyNorth Sequalitchew Creek is the new stream channel that would be created as part of theproposed gravel mine expansion. The purpose of the new stream is to manage ground waterentering the mine site while creating new riverine habitat. In order to reduce infiltration ofsurface water, the stream bed would be installed in the low-permeability Olympia Beds. Adescription of the proposed new stream channel is provided in three reports (Anchor 2004a,2004d; Herrera 2005b) completed for the project and is summarized in the paragraphs below.North Sequalitchew Creek would be approximately 4,000 feet long and would dropapproximately 39 vertical feet in elevation between the headwaters and the confluence withSequalitchew Creek. This configuration would provide an overall channel gradient of 1 percent,although the actual gradient would vary along the new channel alignment based on the elevationof the Olympia Beds beneath the proposed channel. Based on boring logs in the area, the newstream channel would be divided into three distinct reaches characterized by different channelgradients and habitat features.The lower reach of North Sequalitchew Creek will be 900 feet long and would be constructedwith a 2.0 percent gradient to make this the steepest reach of the new channel. Large bouldersand coarse sediment would be used to construct grade control structures and to create a step-poolchannel profile. The grade control structures would also be designed to stabilize the bed andprevent head-cut erosion. Large woody debris would be placed in the channel to promote gravelsorting and habitat diversity.The middle reach would be 1,100 feet in length with a gradient of 1 percent. The elevation dropthrough the middle reach would occur over riffle segments constructed from coarse sediment.Each riffle segment would be located between channel bends and pools to create a meanderingpool-riffle channel. Large woody debris and boulders would be used to provide gravel sorting,energy dissipation, and habitat function. Habitat features in the middle reach would be designedto enhance fish rearing functions. wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 30 October 28, 2005
Surface Water and Geomorphology Technical ReportThe upper reach would be constructed at a relatively low gradient of 0.5 percent and extends2,000 feet above the middle reach. The upper reach would include side channels designed toprovide rearing and over-wintering habitat for salmon (cutthroat and coho). Side channels wouldbe constructed at locations that optimize perennial flow from seeps and interconnections with themain channel.The width of the new stream channel would vary between 10 and 20 feet and be constructed in a40- to 50-foot wide floodplain corridor. Coarse, rounded sediment would be placed along theedges of the stream corridor. The coarse sediment would extend vertically from the top of theOlympia Beds to above the anticipated maximum flood stage and would control the width of themeander belt. The bed of the new channel would be seeded with sand and gravel appropriatelysized to emulate natural sediment transport processes and the formation of habitat features. Poolformation and meander development would be encouraged by the placement of large woodydebris and engineered log jams.Grading required for the construction of North Sequalitchew Creek would result in a 75-foot-high slope on the east side of the stream. Slopes would range from 3H:1V (18 degrees) to2H:1V (27 degrees) along the lower and upper reaches, with locally steeper slopes as steep as1H:1V (45 degrees). The proposed slope angles are comparable to the naturally formed slopesabove the Olympia Beds in the ravine of the mainstem Sequalitchew Creek. Slopes within theexisting ravine range from 4H:1V to 2H:1V, with local areas as steep as 1.2H:1V. In addition,the natural variability in slope angles exhibited by the existing ravine suggests the morphology ofthe lower Sequalitchew Creek is controlled by the spatial variability in local material properties.It is expected that slope adjustments would occur along North Sequalitchew Creek and theseadjustments would likewise have an impact on stream morphology and turbidity. While theseimpacts can be minimized with aggressive reforestation, they are unavoidable and the newstream channel would be regularly monitored for potential impacts resulting from hillslopeerosion.Based on the slope conditions within the existing Sequalitchew Creek ravine, the proposedslopes above the new stream will likely undergo a period of erosional adjustment for anunknown period of time, particularly before vegetation is established on new ravine slopes.Several measures would be implemented to address soil erosion from slopes prior to theestablishment of vegetation (see the discussion of mitigation measures further along in thisreport). Hillslope runoff and runon to unstable areas would be diverted by horizontal benchesand lined ditches installed on steep slopes. Unstable surfaces would be protected with a coir-mator comparable erosion control blanket. The blanket would be staked to the ground surface toprevent the formation of gullies beneath the blanket. At a minimum, sloughing of surfacematerial and shallow slope failures are expected to accumulate sediment at the toe of thehillslope (i.e., colluvial wedge), as has been observed in the existing ravine. Sediment stored inthe stream floodplain would supply sediment (both fine-grained and essential, coarse-grainedspawning gravels) to the stream system at a rate dependent on the supply from hillslopes and themigration rate of the active channel into sediment stored at the toe of the slope.wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 31 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportSequalitchew CreekWater QualityBecause North Sequalitchew Creek flows into Sequalitchew Creek, the quality of SequalitchewCreek waters would be influenced by the waters from this new tributary stream. Similar to theanalysis presented above for the dewatering well impacts during construction (see SequalitchewCreek discussion under construction impacts), the expected quality of the ground water source ofNorth Sequalitchew Creek is generally expected to be good.During the late summer and early fall when low flow conditions occur within the stream,elevated water temperatures and low dissolved oxygen concentrations may occur. Duringbackground studies for this project, elevated water temperature and low dissolved oxygenconcentrations were measured during the summer which violated state surface water qualitystandards. With the addition of North Sequalitchew Creek flows, these conditions would stilllikely occur. However, the increased flows would help to elevate the dissolved oxygenconcentrations in the stream by increasing velocities within the channel, which would promoteaeration. In addition, instream water temperatures will be maintained by the low temperatureground water flowing into Sequalitchew Creek.The potential for sediment movement within the channel because of the increase in flow isdiscussed below under Hydraulic Modeling.HydrologyThe existing hydrology of Sequalitchew Creek would change because of the reduction of groundwater input to the stream and addition of North Sequalitchew Creek flows. The NorthSequalitchew Creek channel would intercept ground water which, under the existing conditions,partially flows into the mainstem of Sequalitchew Creek. Based on the ground water modelingand actual flow data collected in Sequalitchew Creek (Anchor 2004d), stream discharge wouldbe reduced by about 0.5 cfs (from 1.0 cfs to 0.5 cfs) in the reach upstream of the proposedconfluence of North Sequalitchew Creek. However, downstream of the confluence of NorthSequalitchew Creek, the average annual stream discharge in the mainstem would increase by 6.7cfs (Table 9).The ground water model predicts that the average annual flow of North Sequalitchew Creek at itsconfluence with the main stem Sequalitchew Creek would be 7.6 cfs. The 7.6 cfs wouldcombine with the 0.5 cfs in the mainstem resulting in an average annual flow of 8.1 cfs in themainstem below the confluence (Anchor 2004b). This average annual flow represents anincrease over the existing condition of approximately 6.7 cfs. The 2-year storm flow event inSequalitchew Creek would result in flow of approximately 20.2 cfs including 10 cfs from NorthSequalitchew Creek during the 2-year event (Table 10).Hydraulic ModelingA shear stress analysis was performed (GeoEngineers 2004b) to evaluate changes in sedimenttransport and depositional processes within the lower stream under the proposed flow conditions. wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 32 October 28, 2005
Surface Water and Geomorphology Technical ReportThe shear stress analysis followed the same methodology described for existing conditions. Thecritical shear stress for initial entrainment of the streambed was scaled using the median particlesize of the bed. Additional transport of fine sediment can occur from an armored bed or fine-grained patches before the armor layer is fully disturbed. The shear stress analysis alsosimulated conditions for sediment deposition of different particle sizes when the modeled shearstress dropped below the critical shear stress. Sediment deposition in a particular reach assumesthat sediment is already in transport in the upstream reach.Hydraulic modeling indicates the higher flow rates would result in correspondingly higher flowdepths, channel velocities, and boundary shear stresses than for existing conditions. The averagewater surface elevations are expected to increase from 2.2 to 4.0 inches throughout the ravine,with the local maximum depth reaching 6 inches in Reach 2.Relative trends in sediment transport and deposition in Sequalitchew Creek have been evaluatedfor the proposed conditions by comparing the ratio between shear stress and the critical shearstress required for bed entrainment. A comparison of existing conditions and proposedconditions are shown for the 100-year storm event (Figure 1). Results of the shear stress analysisindicate the upstream portion of Reach 1 would remain relatively stable under proposedconditions. Bed erosion is likely to continue in Reach 2, where shear stress under proposedconditions would be greater than the critical shear stress. Despite increases in flow, resultsindicate sediment deposition would continue in the upstream portion of Reach 3. The decline ofshear stress through Reaches 3 and 4 to below the critical shear stress would allow continuedfilling of the brackish marsh under the proposed conditions. In general, increases in shear stresscould shift the stream bed erosion thresholds to flow conditions having a lower recurrenceinterval, which could in turn increase the frequency of sediment transporting events within theravine and delivery of sediment to the brackish marsh (Reach 4).GeomorphologyThe increase in flow under the proposed conditions has the potential to impact the morphologyof Sequalitchew Creek. A comparison of model results between existing and proposedconditions indicate increases in bed erosion would occur at the downstream end of Reach 1(Figure 12a). The greatest potential for mobilization of the channel bed from increased flows islikely to occur in Reach 2, where shear stress is projected to increase by 40 percent relative toexisting conditions. This increase in shear stress is at least in part due to segments of the reachwhere the channel has been constricted by debris flow and alluvial fan deposits (Figure 12b).Localized increases in shear stress are expected to result in bed incision and/or bank erosion.Results of the hydraulic modeling suggest mobilization of the bed is likely to occur during a2-year flow event. Depending on the supply and availability of coarse sediment, the increasedshear stress is also likely to increase the degree of bed-surface armoring, which would conditionthe bed and increase the critical shear stress required for future bed mobilization.Areas of potential adverse change and increase in-stream bed erosion within the ravine wereidentified (GeoEngineers 2004). The abrupt increase in stream flow and shear stress at theconfluence of North Sequalitchew Creek and the main stem (Reach 1, Station 40+50) has thewp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 33 Herrera Environmental Consultants
Surface Water and Geomorphology Technical Reportpotential to induce bank erosion and stream bed scour (Figure 13a). The shear stress analysisalso identified two erosional and two depositional reaches within Reach 3 (Figure 13b). Thecoarsest fraction of sediment mobilized from Reach 2 is expected to be deposited near Station17+00 in response to declining shear stress. Results of the shear stress analysis indicate bedmobilization at the downstream end of Reach 3 would occur during flow events with a greaterrecurrence interval. The analysis also identified a location near Station 10+30, where theincrease in shear stress is approximately 25 percent greater than that for existing conditions.This station is located just downstream of the berm and 10-foot depression, and just upstream ofa depositional reach where a reduction in shear stress occurs. The proximity of erosional anddepositional reaches indicates the stream channel will respond relatively quickly to an increase inflow. Grade adjustment of the stream will be accompanied by localized channel widening andmigration both of which entail bank erosion that will further increase the sediment supply to thestream. At locations such as Station 17+00, bank erosion could lead to a major change in thestream channel if flows gained access to this 10-foot depression along north side of the ravine. Ifthe stream were to flow into this depression, it would significantly change the stream grade andinitiate a headcut that would proceed upstream and further destabilize adjacent hillslopes.Sediment produced in the process would rapidly fill the depression. Until the stream readjusted astable gradient, fish passage and water quality would likely be impacted.Declining shear stress through Reaches 3 and 4 under the proposed conditions (GeoEngineers2004b) indicates that the progressive deposition of sediment in the brackish marsh will continueunder the proposed conditions. The additional sediment transported to Reach 4 by the increasedflows is likely to contribute to the ongoing aggradation of the brackish marsh. Althoughsediment deposited within the main stem in Reaches 3 and 4 during high tide would likely beentrained during low tide and transported to Puget Sound, fine-grained sediment and graveldeposited within the brackish marsh and dendritic tidal slough network will remain andcontribute to gradual infilling of the tidal marsh area.Kettle WetlandThe Kettle wetland located within the existing permitted mine area would be removed as part ofexpansion area mining operations. Proposed mitigation for removal of the Kettle wetland isdiscussed in Plants and Animals section of the SEIS, Section 3.4.Fort Lewis Diversion Canal/Sequalitchew LakeChanges in diversion canal water levels were not analyzed as part of the ground water modelinganalysis for the project (CH2M Hill 2003b). However, subsequent modeling efforts incorporatedthe effect of the diversion canal into the ground water model (Aspect 2004a, 2004b). It wasdetermined that most of the Diversion Canal recharges the Vashon Aquifer in the vicinity of theproposed project (Aspect 2004a, 2004b). However, one small reach near the diversion canalweir is a “gaining reach” and is recharged by ground water. Therefore, the proposed project maycause less water to be recharged to the diversion canal along this reach because of the drop in wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 34 October 28, 2005
Surface Water and Geomorphology Technical Reportarea ground water levels. The ground water model did not analyze this decrease in baseflow(ground water discharge) to the Diversion Canal under future conditions (Aspect 2004a, 2004b).Based on a ground water modeling analysis completed in 2004 (Aspect 2004b), SequalitchewLake is located outside of the outer boundary of any observable ground water drawdown effectfrom the project (Figure 14). Based on this analysis, there would be no observable effect on thelake water level or lake water quality from the proposed project.Old Fort LakeBecause Old Fort Lake is hydrologically supported by the Vashon aquifer, lake water levelsfluctuate similar to the changes in the ground water table in the vicinity of the lake. Based on theground water modeling results, ground water levels could drop by approximately 0.25 feet in thevicinity of Old Fort Lake because of the project (Aspect 2004b).Based on a ground water modeling analysis completed in 2004 (Aspect 2004b), Old Fort Lake islocated outside of the outer boundary of any observable ground water draw down effect from theproject (Figure 14). Based on this analysis, there would be no observable effect on the lakewater levels or lake water quality from the proposed project.Pond LakeBased on the ground water modeling results in 2004, ground water levels could drop byapproximately 0.5 feet in the vicinity of Pond Lake (Aspect 2004b) (Figure 14). Based on ananalysis of the drawdown effects, in wetlands such as Pond Lake where seasonal saturation andinundation are controlled by the underlying ground water table, surface waters would dissipatetwo or three weeks earlier in the spring (Aspect 2004a, 2004b; PGG 2005; WSA 2004b). Withthe regional lowering of the ground water table, Pond Lake is predicted to dry out for longerperiods (i.e., when the ground water elevation is less than 201 feet above sea level), and have alower surface water elevation throughout the year (Aspect 2004b). Impacts to plant communitiesare discussed in the Plant and Animals section of the SEIS, Section 3.4.Brackish MarshWater QualityThe proposed project would increase the amount of flow into the mainstem of SequalitchewCreek by the 6.7 cfs addition from North Sequalitchew Creek (Anchor 2004d). These flowswould also alter the flow regime downstream in the Brackish Marsh which could affect salinityboth in the water column and in the underlying soil.Because the water quality in the newly constructed creek would be within the background rangeof existing Sequalitchew Creek, no measurable impacts to Brackish Marsh water quality areexpected.wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 35 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportAs part of background investigations for the proposed project, existing salinity conditions withinthe marsh (soil and water) were evaluated Anchor (2004c, 2004d). Salinity data were collectedas part of background investigations for the proposed project in April 2004 (Anchor 2004c).Salinity data indicate that a freshwater lens exists within the brackish marsh and that highlysaline conditions are present in the marsh during flood tide events. Salinity is not a regulatedparameter in state water quality standards for either freshwater or marine waters (Chapter173-201a WAC). Impacts to Brackish Marsh vegetation are discussed in the Plants and AnimalSection of the SEIS, Section 3.4.GeomorphologyIncreased flows in Sequalitchew Creek from the new North Sequalitchew Creek have thepotential to impact the existing sediment dynamics of the main stream channel (within thebrackish marsh) and the dendritic channel network within the brackish marsh, much the same asthe conditions described for construction. The increase in stream flows in Sequalitchew Creekupstream of the brackish marsh (contributed by North Sequalitchew Creek) would increase thepotential for streambed erosion (GeoEngineers 2004b). Average annual flows in SequalitchewCreek are expected to increase by 6.7 cfs (Anchor 2004d). Sediment eroded from the upperreaches of the ravine would likely be deposited in Reaches 3 and 4 in response to declining shearstress.Aggradation in the main channel would increase the possibility of an avulsion and deposition ofcoarse sediment in the dendritic channel network of the marsh. Avulsion of the channel awayfrom the current alignment could deposit considerable amounts of sediment within the maindendritic channel that runs along the toe of the railroad embankment. A shift in the main stemalignment away from the culvert inlet could accelerate filling of the dendrite channel networkand reduction in the tidal prism.Post-Reclamation Stormwater ManagementAfter mining is complete, the site would be reclaimed and re-vegetated with ground cover thatwould provide permanent erosion control (CH2M Hill 2003c). A post reclamation stormwatermodeling analysis was completed in 2004 (Aspect 2004a). For purposes of this analysis, theexpansion area was subdivided into four subbasins (Aspect 2004a), identified as subbasin E1(13 acres), E2 (34 acres), E3 (68.9 acres), and E4 (24.2 acres) (Aspect 2004a). Afterreclamation, most stormwater runoff generated within these subbasins would either infiltrate intothe ground or flow as overland flow to North Sequalitchew Creek. Subbasin E1 (northern-mostbasin) would collect stormwater via the subsurface collection system that would daylight at thehead of North Sequalitchew Creek. Stormwater runoff from subbasins E2, E3, and E4 wouldeither infiltrate into the ground or flow via overland flow to North Sequalitchew Creek (Aspect2004a). The total amount of stormwater (excluding ground water) entering North SequalitchewCreek would range from 3 cfs during the 2-year event to 17 cfs during the 100-year event(Table 11). wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 36 October 28, 2005
Surface Water and Geomorphology Technical ReportNear-shore SpringsThe capture of ground water in North Sequalitchew Creek would reduce the amount of dischargein the tidal springs located north of the confluence of Sequalitchew Creek. Based on the groundwater modeling results, the ground water component of spring discharge would be reduced by 19to 25 percent (Aspect 2004d) (Also see the ground water impact discussion for more detail).Shipping ActivitiesOperation impacts to marine waters were discussed in the original EIS for dock loadingoperations and maritime traffic. With the addition of the new mine expansion area, the types ofimpacts arising from use of the loading dock and transporting gravel off-site via Puget Soundwould not differ from what was described in the original mine EIS (City of Dupont 1993).However, because the life of the mine would be extended by approximately 8 to 12 years, thelength of shipping activities and associated impacts would be extended over this period of time.Impacts of the Project AlternativeThe proposed Project Alternative will replace the proposed North Sequalitchew creek designwith a gravel-filled interceptor ditch and a buried conveyance pipeline 5,000 feet long. Thepipeline would be microtunneled approximately 500 feet through the berm between theexcavated mine site and Sequalitchew Creek. The discharge point to Sequalitchew Creek wouldcoincide with the proposed confluence of North Sequalitchew Creek (RM 0.8).Water ResourcesThe proposed impacts to Sequalitchew Creek with the project alternative would be similar to theproposed action. The water quality of the proposed water discharged to Sequalitchew Creek viathe pipeline discharge would have similar water quality as the proposed North SequalitchewCreek (Table 8). However, water temperatures in the pipeline discharge would likely be lowerthan with proposed action, because the water will not have been subject to solar heating. Inaddition, dissolved oxygen concentration of the pipeline water may be lower than if the flowsinteracted directly with the atmosphere on the surface. With this project alternative, aconstruction access road would be built from the existing abandoned railroad bed (to the outfallarea) to transport microtunneling equipment to the site. Stormwater BMPs would be employedduring access road construction and use.GeomorphologyThe Project Alternative is anticipated to have similar effects on flow rates within SequalitchewCreek as the Proposed Action. The excavated slopes above the interceptor ditch for the ProjectAlternative will be nearly identical to the excavation plan above the creek in the Proposedwp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 37 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportAction. It is possible that fine sediment entering the proposed pipeline would be conveyed morerapidly to Sequalitchew Creek relative to sediment transport within North Sequalitchew Creekunder the Proposed Action. Hydraulic roughness provided by pools, riffles, vegetation, and in-stream wood in North Sequalitchew Creek would moderate the supply of fine sediment toSequalitchew Creek and provide more sediment storage capacity than the Project Alternative.Under the proposed interceptor trench design, sediment delivery to the drainage network fromexcavated slopes may be less than under the Proposed Action. Assuming the flow dispersionstructure at the pipe outfall in Sequalitchew Creek is effective at dissipating energy, impacts tosediment transport and habitat forming processes within the existing creek resulting from theProject Alternative should be similar to the impacts described for the Proposed Action.Impacts of the No Action AlternativeUnder the no action alternative, the proposed mine expansion project would not occur andmining of the existing Glacier site would continue as currently permitted. Potential impacts tosurface water resources, water quality, and hydrology would not differ from the impacts thatwere discussed in the original mine EIS (City of DuPont 1993). Continued diversion ofdischarge out of Sequalitchew Creek by the Diversion Canal would continue to limit streamhydrology and sediment transport. Erosion within the ravine would continue to supply sedimentthat cannot be transported out of the system by the limited stream discharge. Reaches withinSequalitchew Creek would continue to aggrade within the ravine, thereby compromisingsalmonid passage and habitat.Monitoring and Mitigation MeasuresThe project proposes to monitor Sequalitchew Creek and the Brackish Marsh for possibleimpacts from the project prior to implementing possible mitigation measures outlined below.Possible monitoring and mitigation measures, including specific timeframes formonitoring/mitigation efforts, would be refined during the permitting process. Actualmonitoring and mitigation measures would be determined by permit conditions and negotiationswith the regulatory agencies.Water QualityProposed MonitoringDuring construction of North Sequalitchew Creek, the project proposes to conduct the followingwater resource monitoring: Prior to the surface water connection with Sequalitchew Creek, monitor North Sequalitchew Creek water quality until the stream stabilizes. Stream waters would be monitored for temperature, turbidity, total suspended solids and dissolved oxygen. wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 38 October 28, 2005
Surface Water and Geomorphology Technical Report Monitor the mainstem of Sequalitchew Creek for possible erosion and turbidity during dewatering activities scheduled for the wet season.Proposed MitigationDuring construction and operation (unless otherwise noted), the following mitigation measures toprotect area water resources are proposed: Provide truck wash basins to minimize the introduction of sediments onto on-site or off- site roadways. Infiltrate of all stormwater runoff on-site. Employ stormwater BMPs as outlined in the SWPPP for mining operations. Construct access road, bridges (bottomless box culverts), and a pedestrian bridge prior to connection (construction only).GeomorphologyProposed MonitoringMonitoring for changes in channel geomorphology would consist of an annual streamreconnaissance of Sequalitchew Creek (below the proposed confluence) focusing on areas ofpotential erosion and deposition (as identified by GeoEngineers [2004b] and Anchor [2004d]).Monitoring would include the following: Document physical changes on the ravine slopes (i.e., slumps and landslides). Monitoring would note size, area and location of these landslides and slumps. Photo documentation of bank erosion, toe of slope erosion, etc. Survey longitudinal profiles and/or channel cross-sections where deposition and erosion is likely or evident, or where the consequences of erosion/deposition could be significant. Document changes in stream bed composition. At a minimum, this would include doing pebble counts at set points throughout the reach at the select cross-sections.Data would be interpreted to: 1) identify the cause and/or source of the change; 2) determinewhether the change is local or systemic in nature; and 3) determine whether mitigation measuresshould be implemented (Anchor 2004d). If, based on the monitoring results, it is determined thatreaches are scouring or aggrading (including the brackish marsh), localized restoration measurescould be put in place to ameliorate impacts. Measures such as placement of large woody debriswould be an option.wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 39 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportIn order to determine if reaches are aggrading or eroding as a result of the proposed project, abaseline monitoring program would be established in Sequalitchew Creek and the brackishmarsh prior to project construction. Three years of baseline data in addition to the data collectedthus far would be collected at selected transects throughout the four stream reaches (1 through 4).This information would be used to establish baseline rates for comparison during projectconstruction and operation. In addition, prior to project commencement, depositional anderosion thresholds would be established prior to construction based on regulatory guidance (e.g.,no net fill in jurisdictional wetlands) and best available science.Proposed MitigationPrior to project construction, the topographic depressions (e.g., 10 foot depression at Station11+00) within the ravine bottom of Reach 3 would be filled with suitable material. This wouldbe done to prevent adverse impacts that would result from the stream channel moving into thedepressions (i.e., to prevent impacts, such as head-cutting and incision upstream of where creekenters the depressions). If these depressions are filled, adverse impacts can be avoided,otherwise significant impacts could occur.Possible MitigationThe following mitigation measures could address potential geomorphic impacts of the project toSequalitchew Creek if determined due to the monitoring. Place large woody debris (LWD) in the ravine bottom to: curb erosion of adjacent hillslopes and toe-of-slope sediment wedges, control stream grade and limit head-cutting, trap sediment, increase pool frequency and channel complexity, and accelerate development of forested floodplains within the ravine bottom. LWD installations would be prioritized for those areas where flows currently abut sediment wedges or for hillslopes along the flanks of the ravine and channel segments most susceptible to bed erosion (Reach 2). LWD placement would be done during low flow conditions to ease potential impacts from disturbance in the channel, and to prevent potential adverse project impacts. Measures to prevent bank and streambed erosion at the confluence of North Sequalitchew Creek should be employed. Measures could include armoring the streambed and banks, and placement of log structures to dissipate flow energy.Significant Unavoidable Adverse ImpactsProposed ActionWater ResourcesConstruction of North Sequalitchew Creek and operation of the mine would impact waterresources located in the vicinity of the proposed mine expansion area. Because the ground water wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 40 October 28, 2005
Surface Water and Geomorphology Technical Reporttable would be lowered in the vicinity of the project, base flows within Sequalitchew Creekwould be reduced upstream of the proposed confluence with North Sequalitchew Creek atRM 0.8; however much of this portion of the creek is currently dry (Anchor 2004b; CH2M Hill2003b). However, discharge in Sequalitchew Creek downstream of the confluence with NorthSequalitchew Creek would increase, starting with the construction phase from the addition ofground water pumped to the stream during construction dewatering, and would continue with themining operations (and thereafter) from the additional flows contributed by North SequalitchewCreek.In addition, the project would lower the ground water table underneath the upgradient wetlandsby up to 1.5 feet (Anchor 2004b) (Figure 14). South of the project site, the ground water tablewould be lowered by up to 0.5 feet at Pond Lake (Anchor 2004b) (Figure 14). No measures areproposed that would mitigate for the lowering of the ground water table in the vicinity of theproject.At the end of North Sequalitchew Creek construction, the berm between North SequalitchewCreek and Sequalitchew Creek would be removed thereby allowing flows from the newlyconstructed stream to enter Sequalitchew Creek. During berm removal, even with theemployment of BMPs to protect water quality, sediment and fines would likely enterSequalitchew Creek.Tidal springs discharge would be reduced because of up-gradient ground water capture indewatering wells during construction, and as a result of ground water captured in NorthSequalitchew Creek during mining operation. This capture is estimated to reduce the tidal springdischarge by 19 to 25 percent (Anchor 2004d).GeomorphologyConstruction of North Sequalitchew Creek would impact the geomorphology of the mainstem ofSequalitchew Creek by the increase in flows to the stream that would occur during mineconstruction and operation. Based on hydraulic modeling results conducted for this project(GeoEngineers 2004b), this increase in flow would increase erosion and sediment transport atvarious locations throughout the stream channel and are identified by reach on Figures 12a and12b. The increase in sediment transport from these reaches would similarly increasesedimentation within those downstream segments having lower transport capacities.Areas of potential adverse impact were identified as part of downstream geomorphic analysis(GeoEngineers 2004b) of the proposed confluence with North Sequalitchew Creek (Figures 13aand 13b). If recommended mitigation measures are not employed prior to project construction,unavoidable adverse impacts would likely result from the project. Mitigation measures toprevent bank and streambed erosion at the confluence of North Sequalitchew Creek should beemployed. Even with LWD placement, some channel adjustment in the form of local erosionand sedimentation will be unavoidable.wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 41 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportLocal erosion of the excavated hillslope east of North Sequalitchew Creek would occur with theproposed excavation plan due to local variations in geologic materials and ground water seepage.Outflow from the Vashon aquifer located high on the hillslope, would likely result in surficialerosion down the steep hillslope. Hillslope adjustment would likely impact North SequalitchewCreek in the form of sediment input from slumps, slides, or surface erosion below seeps.Project AlternativeWater ResourcesSignificant unavoidable adverse impacts to Sequalitchew Creek and other surface waterresources within the affected environment would be similar to those described for the proposedaction. Pipeline discharge to Sequalitchew Creek would increase flows to Sequalitchew similarto the flow increases predicted with the proposed action. In addition, the ground water leveldrawdown in the area within the affected environment would be similar to the levels predictedwith the proposed action resulting in the upstream segment above where the pipeline dischargewould be located would go dry from the regional drawdown of the ground water table.Similar to the proposed action the discharge in the tidal spring would be reduced byapproximately 19 to 25 percent (Anchor 2004d).GeomorphologySignificant unavoidable adverse impacts to sediment transport and habitat forming processesresulting from the Project Alternative would not differ from the impacts described for theProposed Action, except that sediment delivery from excavated slopes to the pipeline may beless than supply to the daylighted creek in the Proposed Action. Even with the energydissipation structure, increased flows downstream of the outfall may initiate short-term channeladjustments that are unavoidable and similar to the Proposed Action. wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 42 October 28, 2005
Surface Water and Geomorphology Technical Report 4.0 ReferencesAnchor. 2004a. North Sequalichew Creek, Flow, Vegetation, and Slope Stability Evaluation.Pioneer Aggregates North Sequalitchew Creek Project. June 2004. Seattle, Washington.Anchor. 2004b. Fish Habitat Benefit Evaluation for Sequalitchew Creek, Pioneer AggregatesNorth Sequalitchew Creek Project. July 2004. Seattle, Washington.Anchor. 2004c. Brackish Marsh Water Quality Evaluation for Sequalitchew Creek. PioneerAggregates North Sequalitchew Creek Project. Prepared for Glacier Northwest. July 2004.Anchor. 2004d. Supplemental Report: North Sequalitchew Creek Project. Pioneer AggregatesNorth Sequalitchew Creek Project. December 2004. Seattle, Washington.Anteon. 2002. Third Quarter 2002 Groundwater Monitoring Report. Prepared for Fort LewisPublic Works by Anteon Corporation.Aspect. 2004a. Surface Water and Groundwater System with Predictions on Effects to WetlandHydrology Upstream of Proposed North Sequalitchew Creek. Technical Memorandum. Seattle,Washington. Prepared for Glacier Northwest by Aspect Consulting, LLC, Seattle, Washington.July 2004.Aspect. 2004b. Surface Water and Groundwater System, North Sequalitchew Creek Project.Supplemental Report. Seattle, Washington. Prepared for Glacier Northwest by Aspect Consulting,LLC, Seattle, Washington. December 2004.CH2M Hill. 2001. North Sequalitchew Creek Project, Dupont, WA. Surface Water InvestigationReport. Bellevue, Washington. Prepared for Glacier Northwest. April 2001.CH2M Hill. 2003a. North Sequalitchew Creek Project, Dupont, WA. Surface Water InvestigationReport. Bellevue, Washington. Prepared for Glacier Northwest. April 2003.CH2M Hill. 2003b. Draft Final Groundwater Modeling and Analysis Report. North SequalitchewCreek Project. Bellevue, Washington. Prepared for Glacier Northwest. May 2003.CH2M Hill. 2003c. Final Draft Stream Predesign Report North Sequalitchew Creek Project.Bellevue, Washington. Prepared for Glacier Northwest. June 2003.DuPont. 1993. Final Environmental Impact Statement. City of DuPont, Washington.DuPont. 1995. Pioneer Aggregates Barge Loading Facility and DuPont Shoreline Master ProgramAmendment SEIS. City of DuPont.wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 43 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportEcology. 1990. Water quality standards for ground waters of the State of Washington. Chapter173-200 Washington Administrative Code (WAC). Washington State Department of Ecology,Olympia, Washington.Ecology. 1995. Washington State Water Quality Assessment. Water Division, Water QualityProgram. Ecology publication # WQ-95-65b. Washington State Department of Ecology, Olympia,Washington.Ecology. 1998. Final 303(d) water quality limited list for Washington State. Washington StateDepartment of Ecology, Olympia, Washington.Ecology. 2002. Sediment quality in Puget Sound, Year 3 – Southern Puget Sound, July 2002.Information taken from the Washington Department of Ecology web site on March 30, 2005:<http://www.ecy.wa.gov/pubs/0203033.pdf>. Washington Department of Ecology, Olympia,Washington.Ecology. 2003. Water Quality Standards for Surface Waters of the State of Washington. Chapter173-201A WAC, amended July 1, 2003. Washington Department of Ecology, Olympia,Washington.Ecology. 2005a. Washington State’s Water Quality Assessment [303(d) and 305(b) Report].Washington Department of Ecology, Olympia, Washington. Information taken from theWashington Department of Ecology web site on October 28, 2005:<http://www.ecy.wa.gov/programs/wq/303d/2002/2004_documents/wq_assessment_cats2004.html>.Ecology. 2005b. Long-term marine quality data. Taken from the Washington Department ofEcology web site on January 10, 2005:<http://www.ecy.wa.gov/apps/eap/marinewq/mwdataset.asp?ec=no&scrolly=12&htmlcsvpref=csv&estuarycode=1&theyear=1996&themonth=1&staID=55>.Ellingson, Charles. 2005. Personal communication (e-mail to Jennifer Goldsmith, HerreraEnvironmental Consultants, Inc., Seattle, Washington). Pacific Groundwater Group, Seattle,Washington.Firth, Barry K. 1991. Sequalitchew Creek Regulation Under the Shoreline Management Act.Weyerhaeuser. DuPont, Washington. June 3, 1991. In: Aspect Consulting, LLC, 2004,Supplemental Report, Surface Water and Groundwater System, North Sequalitchew Creek Project.Seattle, Washington.GeoEngineers. 2004a. Geomorphic Evaluation Pioneer Aggregates North Sequalitchew CreekProject, DuPont, Washington. July 23, 2004.GeoEngineers. 2004b. Revised Report Geomorphic Evaluation Pioneer Aggregates NorthSequalitchew Creek Project, DuPont, Washington. November 1 2004. wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 44 October 28, 2005
Surface Water and Geomorphology Technical ReportGeoEngineers. 2005. Landslide identification at Sequalitchew Creek. Technical MemorandumFile No. 4747-017-01, dated August 25, 2005. Bellevue, Washington.Herrera. 2005a. Pioneer Aggregates Mining Expansion and North Sequalitchew Project Plants andAnimals Technical Report. Herrera Environmental Consultants, Inc., Seattle, Washington.Herrera. 2005b. Pioneer Aggregates Mining Expansion and North Sequalitchew Project FisheriesTechnical Report. Herrera Environmental Consultants, Inc., Seattle, Washington.McKee, Kim. 2005. Personal communication (e-mail with Alex Svendsen, Herrera EnvironmentalConsultants, Inc., Seattle, Washington). Water Clean-Up Unit, Washington State Department ofEcology, Olympia, Washington.Packman, James J., Karen J. Comings and Derek B. Booth. 1999. Using turbidity to determinetotals suspended solids in urbanizing streams in the Puget Lowlands. Canadian Water ResourcesAssociation Annual Meeting, Vancouver, B.C., 27-29 October 1999, p. 158-165.PGG. 2005. Groundwater Impact Analysis. Expansion of Glacier Northwest’s Pioneer AggregateMine DuPont, Washington. Pacific Groundwater Group, Seattle, Washington.Sargeant, Debby, Mindy Roberts, and Barb Carey. 2003. Quality Assurance Project PlanHenderson and Nisqually TMDL Study. Washington State Department of Ecology, Olympia,Washington.Thut, R.N. B.K. Firth, S.W. Vincent, D.J. McGreer, and T.S. Friberg. 1978. Water Quality Studies,Part 1: Freshwater. In: Supplemental Report, Surface Water and Groundwater System, NorthSequalitchew Creek Project. 2004. Aspect Consulting, LLC, Seattle, Washington.U.S. EPA. 2003. Fort Lewis (Landfill No. 5). Washington, EPA ID#WA9214053465. UnitedStates Environmental Protection Agency Region 10, Pierce County, Fort Lewis.<http://yosemite.epa.gov/r10/nplpad.nsf/88d393e4946e3c478825631200672c95/6dc93b881191135385256594005c0f16?OpenDocument>.URS. 2000. Former DuPont Works Site Final Environmental Impact Statement. July 28, 2000.Information taken from the World Wide Web on April 15, 2003:<http://www.ecy.wa.gov/programs/tcp/sites/weyer/Weyer_TOC.htm>.Washington State Department of Health. 2004. Drinking water standards for the public drinkingwater systems. Chapter 246-290 WAC. Olympia, Washington.WDF. 1975. A catalog of Washington streams and salmon utilization. Volume 1: Puget SoundRegion. Washington Department of Fisheries, Olympia, Washington.Wetland Science Applications (WSA). 2005. Supplemental Analysis of Sequalitchew Creek AreaWetlands.wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 45 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportWoodward Clyde. 1990. Fort Lewis Landfill No. 5 Remedial Investigation/Feasibility StudyHydrology and Water Quality Technical Memorandum. Prepared for U.S. Army Corps ofEngineers Seattle District by Woodward-Clyde Consultants, Seattle, Washington. wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 46 October 28, 2005
TABLES AND FIGURES
Surface Water and Geomorphology Technical ReportTable 1. Discharge summaries (monthly means) for Sequalitchew Creek and Fort Lewis Diversion Canal from 1977 through October 2004. Diversion Canal Upper Lower Sequalitchew Creek Sequalitchew Diversion Wier Wharf Road Creek 1977 to 1984 to 11/99 to Month (5/03 to 10/04) a (12/99 to11/02) b 12/03 to 10/04 c 1978 d 1987 e 10/04 fJanuary 11.3 12.8 2.5 9.7 5.9 2.6February – 14.3 1.4 12.8 8.5 2.7March – 21.9 0.9 12.2 8.7 2.9April 9.9 16.0 0.7 0.7 9.4 1.8May 7.0 7.7 0.6 1.6 7.8 1.0June 2.4 6.6 – 1.5 3.7 1.0July 1.5 2.9 0.4 0.2 1.3 1.0August 1.8 2.0 0.4 0.1 1.0 0.5September 2.5 2.0 0.4 0.1 1.0 0.2October – 5.5 0.4 0.1 1.4 0.3November 6.4 9.9 – 2.4 3.7 0.7December 8.9 14.7 2.0 10.5 5.1 2.7Mean 5.7 9.7 1.0 4.3 4.8 1.4a Mean monthly discharge gauged continuously by Aspect (2004b).b Mean monthly discharge gauged continuously by CH2M Hill (2003) presented in Aspect (2004a).c Mean monthly discharge gauged continuously above the proposed confluence of North Sequalitchew Creek (Aspect 2004b).d Data collected by Thut et al. (1978) presented in Aspect (2004b).e Data collected by Firth (1991) presented in Aspect (2004b).f Mean monthly discharge gauged continuously by CH2M Hill (2003a) from November 1999 to September 2002, subsequent data gauged continuously by Aspect (2004b).wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 49 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportTable 2. Water quality standards (freshwater) and designated uses (Chapter 173-201A- 200 WAC) (Ecology 2003) applicable to surface waters of the project site including Sequalitchew Creek and the Fort Lewis Diversion Canal. Salmon and Trout Spawning, Core Rearing, and Migration;Water Quality Parameter and Extraordinary Primary Contact RecreationFecal coliform bacteria Shall not exceed a geometric mean value of 50 colonies/100 mL, with not more than 10 percent of all samples exceeding 100 colonies/100 mL.Dissolved oxygen Lowest 1-day minimum is 9.5 mg/L. For lakes and streams, human actions considered cumulatively may not decrease the dissolved oxygen concentration more than 0.2 mg/L below natural conditions.Temperature Highest 7-DADMax a is 16°C. When natural conditions exceed this limit, then human actions considered cumulatively may not cause the 7-DADMax temperature of that water body to increase no more than 0.3°C. Incremental temperature increases from non-point source activities shall not exceed 2.8°C. For lakes, human actions considered cumulatively may not increase the 7-DADMax more than 0.3°C above natural conditions.pH Shall be within the 6.5 to 8.5 with a human-caused variation within a range of less than 0.2 units.Turbidity Turbidity shall not exceed 5 NTU over background turbidity when the background turbidity is 50 NTU or less, or have more than a 10 percent increase in turbidity when the background turbidity is more than 50 NTU.Toxic, radioactive, or Shall be below concentrations that have the potential either singularly ordeleterious material cumulatively to adversely affect characteristic water uses, cause acute or chronicconcentrations conditions to the most sensitive biota dependent on those waters, or adversely affect public health, as determined by Ecology.Aesthetic values Shall not be impaired by the presence of materials or their effects, excluding those of natural origin, which offend the senses of sight, smell, touch, or taste.Designated uses Shall include the following: salmon and trout spawning, core rearing, and migration; extraordinary primary contact recreation; domestic, industrial, and agricultural water supply; stock watering; wildlife habitat; harvesting; commerce and navigation; boating; and aesthetic values.Source: Chapter 173-201A-200 WAC (Ecology 2003a).a 7-DADMax or the 7-day average of the daily maximum temperatures is the arithmetic average of seven consecutive measures of daily maximum temperatures. wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 50 October 28, 2005
Surface Water and Geomorphology Technical ReportTable 3. Water quality data for Sequalitchew Creek collected in the ravine bordering the southern boundary of the Glacier site from September 1999 to September 2000. a State Water Quality Standards c Number of Observed Parameter Number of Exceedances of (units) Mean b Minimum Maximum Samples Acute Chronic State Standard cAlkalinity (mg/L) 39 15 55 12 na na na fAmmonia – Nitrogen (mg/L) 0.010 0.005 0.037 12 8.086 1.555 0BOD (mg/L) 10 10 10 5 na na naConductivity (µmhos/L) 116 89 150 12 na na naDissolved Oxygen (mg/L) 11.9 10.6 13.6 8 > 9.5 mg/L 0Fecal Coliform Bacteria (CFU/100 mL) 1.2 1.0 3.0 11 < 50 colonies/100 mL 0Hardness (mg/L) 44 33 55 12 na na naNitrate + Nitrite – Nitrogen (mg/L) 0.58 0.28 0.82 12 na na naTKN (mg/L) 0.25 0.25 0.28 12 na na naOrthophosphate (mg/L) 0.01 0.01 0.02 12 na na naTotal Phosphorous (mg/L) 0.021 0.015 0.034 12 na na NapH (standard units) 7.3 6.6 7.8 12 Between 6.5 and 8.5 0 o oTemperature ( C) 7.5 4.5 12.5 9 < 16 C 0TSS (mg/L) 4 1 10 7 na na na d,eArsenic (mg/L) 0.01 <0.01 <0.01 12 0.3600 0.1900 0 d,eCadmium (mg/L) 0.0006 <0.0005 0.0009 12 0.0015 0.0006 1 d,eChromium (mg/L) 0.001 <0.001 0.002 12 0.2749 0.0892 0 d,eCopper (mg/L) 0.001 <0.001 0.004 12 0.0077 0.0055 0 eIron (mg/L) 0.02 <0.01 0.07 12 na na na d,eLead (mg/L) 0.001 <0.001 0.002 12 0.0255 0.0010 2 eMercury (mg/L) 0.0002 <0.0002 <0.010 12 0.0018 na * d,eNickel (mg/L) 0.005 <0.005 <0.005 12 0.6931 0.0770 0wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 51 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportTable 3 (continued). Water quality data for Sequalitchew Creek collected in the ravine bordering the southern boundary of the Glacier site from September 1999 to September 2000. State Water Quality Standards c Number of Observed Parameter Number of Exceedances of (units) Mean b Minimum Maximum Samples Acute Chronic State Standard cSelenium (mg/L) d,e 0.01 <0.01 <0.01 12 0.0200 0.0050 * d,eSilver (mg/L) 0.01 <0.01 <0.01 12 0.0008 na * d,eZinc (mg/L) 0.003 <0.001 0.008 12 0.0560 0.0511 0a CH2M Hill (2001).b Values that were less than the laboratory detection/reporting limit are included in the calculation of the mean using the reporting limit for that constituent.c Chapter 173-201A-200 WAC (Ecology 2003).d Water quality criteria calculated based on an average hardness of 44 mg/L.e Dissolved fraction of the concentration is presented in the data.f Water quality criteria based on the maximum pH and temperature values observed at the monitoring station.g The mean for fecal coliform bacteria is the geometric mean.na – Not applicable, no standard exists.* Detection limit above acute and/or chronic criteria.CFU/100 mL – Colony forming units per 100 milliliters.BOD – Biochemical oxygen demand.TKN – Total Kjeldahl nitrogen.TSS – Total suspended solids. wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 52 October 28, 2005
Surface Water and Geomorphology Technical ReportTable 4. Water quality data for the Fort Lewis Diversion Canal collected near the eastern boundary of the Glacier site from September 1999 to September 2000. a Parameter Number of State Water Quality Standards c State Standards b (units) Mean Minimum Maximum Samples Acute Chronic Violations cAlkalinity (mg/L) 48 42 52 4 na na na fAmmonia – Nitrogen (mg/L) 0.040 0.031 0.053 4 13.585 1.352 0BOD (mg/L) 10 10 10 2 na na naConductivity (µmhos/L) 110 100 120 1 na na naDissolved Oxygen (mg/L) 10.5 8.6 12.7 9 > 9.5 mg/L 3Fecal Coliform Bacteria (CFU/100 mL) 9.7 2.0 31 4 < 50 colonies/100 mL 0Hardness (mg/L) 43 41 46 4 na na naNitrate + Nitrite – Nitrogen (mg/L) 0.060 0.020 0.098 4 na na naTKN – Nitrogen (mg/L) 0.29 0.25 0.36 4 na na naOrthophosphate (mg/L) 0.010 0.005 0.006 4 na na naTotal Phosphorous (mg/L) 0.020 0.014 0.030 4 na na napH (standard units) 7.1 6.8 7.4 4 Between 6.5 and 8.5 0 oTemperature (°C) 8.7 3.0 18.7 12 < 16 C 4TSS (mg/L) 4 2 6 2 na na na d,eArsenic (mg/L) 0.01 <0.01 <0.01 4 0.3600 0.1900 0 d,eCadmium (mg/L) 0.0005 <0.0005 <0.0005 4 0.0015 0.0006 0 d,eChromium (mg/L) 0.001 <0.001 <0.001 4 0.2749 0.0892 0 d,eCopper (mg/L) 0.001 <0.001 0.002 4 0.0077 0.0055 0 eIron (mg/L) 0.23 0.12 0.42 4 na na na d,eLead (mg/L) 0.001 <0.001 <0.001 4 0.0255 0.0010 * eMercury (mg/L) 0.0002 <0.0002 <0.0002 4 0.0018 na * d,eNickel (mg/L) 0.005 <0.005 <0.005 4 0.6931 0.0770 0 d,eSelenium (mg/L) 0.01 <0.01 <0.01 4 0.0200 0.0050 *wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 53 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportTable 4 (continued). Water quality data for the Fort Lewis Diversion Canal collected near the eastern boundary of the Glacier site from September 1999 to September 2000. Parameter Number of State Water Quality Standards c State Standards b (units) Mean Minimum Maximum Samples Acute Chronic Violations cSilver (mg/L) d,e 0.01 <0.01 <0.01 4 0.0008 na * d,eZinc (mg/L) 0.002 <0.001 0.002 4 0.0560 0.0511 0a CH2M Hill (2001).b Values that were less than the laboratory detection/reporting limit are included in the calculation of the mean using the reporting limit for that constituent.c Chapter 173-201A-200 WAC (Ecology 2003).d Water quality criteria calculate based on an average hardness of 43 mg/L.e Dissolved fraction of the substance is presented in the data.f Water quality criteria based on the maximum pH and temperature values observed during monitoring.na – Not applicable, no standard exists.* Detection limit above acute and/or chronic criteria.CFU/100 mL – Colony forming units per 100 milliliters.BOD – Biochemical oxygen demand.TKN – Total Kjeldahl nitrogen.TSS – Total suspended solids. wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 54 October 28, 2005
Surface Water and Geomorphology Technical ReportTable 6. Water quality standards (marine waters) and designated uses (Chapter 173- 201A-210 WAC) (Ecology 2003) applicable to the Nisqually Reach of Puget Sound (Extraordinary Quality).Water Quality Parameter Criteria Applicable to Marine Waters of Extraordinary QualityFecal coliform bacteria Shall not exceed a geometric mean value of 14 colonies/100 mL, and not have more than 10 percent of all samples (or any single sample when less than 10 sample points exist) obtained for calculating the geometric mean value exceeding 43 colonies/ 100mL.Dissolved oxygen Lowest 1-day minimum is 7.0 mg/L. When a water body’s dissolved oxygen declines below this limit due to natural conditions, then human actions considered cumulatively may not cause the dissolved oxygen of that water body to decrease more than 0.2 mg/L.Temperature Highest 1-DMax shall not exceed 13°C. When natural conditions exceed this limit, then human actions considered cumulatively may not cause the 7-DADMax temperature of that water body to increase no more than 0.3°C. Incremental temperature increases from non-point source activities shall not exceed 2.8°C.pH Shall be within the 7.0 to 8.5 with a human-caused variation within a range of less than 0.2 units.Turbidity Turbidity shall not exceed 5 NTU over background turbidity when the background turbidity is 50 NTU or less, or have more than a 10 percent increase in turbidity when the background turbidity is more than 50 NTU.Toxic, radioactive, or Shall be below concentrations that have the potential either singularly or cumulativelydeleterious material to adversely affect characteristic water uses, cause acute or chronic conditions to theconcentrations most sensitive biota dependent on those waters, or adversely affect public health.Aesthetic values Shall not be impaired by the presence of materials or their effects, excluding those of natural origin, which offend the senses of sight, smell, touch, or taste.Designated uses Aquatic Life Uses: salmon and other fish migration, rearing and spawning; clam, oyster, and mussel rearing and spawning; crustaceans and other shellfish (crabs, shrimp, crayfish, scallops, etc) rearing and spawning. Shellfish: shellfish harvesting. Recreational Uses: primary contact recreation. Miscellaneous Uses: wildlife habitat, commerce and navigation, boating, and aesthetics.Source: Chapter 173-201A-210 WAC (Ecology 2003). wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 56 October 28, 2005
Surface Water and Geomorphology Technical ReportTable 7. Marine water quality data collected from Ecology’s long-term ambient water quality monitoring station GOR001 in the Nisqually Reach of Southern Puget Sound from October 1996 to September 2002. a State Number of Standard Parameter (units) Mean Minimum Maximum Samples Violations bAmmonia - Nitrogen (mg/L) 0.014 0.010 0.045 57 naChlorophyll a (µg/L) 3.92 0.19 17.82 89 naConductivity (µmhos/L) Nm Nm nm nm naDissolved Oxygen (mg/L) 8.0 5.5 13.5 153 45Fecal Coliform Bacteria (CFU/100 mL) 1.3 1.0 5.0 52 0Nitrite + Nitrate - Nitrogen (mg/L) 0.273 0.082 0.488 57 naOrthophosphate (mg/L) 0.110 0.052 0.272 57 napH (standard units) 7.9 7.1 8.7 78 0Phosphorous, Total (mg/L) Nm Nm nm nm naSalinity (parts per thousand) 28.9 25.6 30.3 165 naTemperature (°C) 11.0 7.4 15.0 165 29Transparency, Secchi Disk (meters) 7.8 1.4 14.5 57 naa Data were gathered at 0.5, 10, and 30 meters in depth from October 1996 to January 2000 and thereafter, were collected from depths of approximately 1, 10, and 30 meters (Ecology 2005).b Chapter 173-201A-210 WAC (Ecology 2003).c Turbidity standard exists, however, no turbidity data or background data were collected, thus, Class AA violations cannot be determined.na – Not applicable, no standard exists.nm – Not measured.CFU/100 mL – Colony forming units per 100 milliliters.wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 57 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportTable 8. Table of estimated ground water quality concentrations and North Sequalitchew Creek Concentrations within the mine expansion area compared to background concentrations in Sequalitchew Creek and Washington State surface water quality standards (Chapter 173-201A-200 WAC) (from Pacific Groundwater Group [PPG 2005]). Estimated Sequalitchew Creek Water Quality Surface Water Quality Below or Within Meets Surface Estimated of North Baseline Range Range of Surface Water Quality Water Quality Ground Water Sequalitchew (1999 to 2000) Sequalitchew Standard Standard Quality Range Creek (CH2Mhill 2000a and Creek Background (Chapter 173-201a (Chapter 173- Parameter (PGG, 2005) a (PGG 2005) b 2003b) Water Quality? WAC) c 201A WAC)?Alkalinity (mg/L) 45 to 47 46 15 to 55 Yes No Standard Not ApplicableAmmonia (mg/L) < 0.1 to 0.017 <0.017 0.005 to 0.037 Yes 8.0 (acute standard) YesDissolved Arsenic (mg/L) <0.001to 0.001 <0.001 <0.01 to 0.01 Yes 0.360 (acute standard) Yes 0.1900 (chronic standard)Benzene (mg/L) <0.001 <0.001 Not Sampled Undetermined No Standard Not ApplicableDissolved Cadmium (mg/L) <0.0002 <0.0002 <0.0005 to 0.0009 Yes 0.0014 (acute standard) Yes 0.0006 (chronic standard)Chloride (mg/L) 3 3 Not Sampled Undetermined No Standard Not ApplicableDissolved Chromium (mg/L) 0.001 0.001 <0.001 to 0.002 Yes 0.2697 (acute standard) Yes 0.0892 (chronic standard)Total Copper (mg/L) 0.001 0.001 <0.001 to 0.004 Yes 0.0077 (acute standard) Yes (dissolved) 0.0055 (chronic standard)Total Iron (mg/L) 0.005 to <0.5 0.005 < 0.01 to 0.07 Yes No Standard Not Applicable (dissolved)Fecal coliform bacteria Not Modeled Not Modeled 1 to 3 Undetermined 50 CFU/100mls Undetermined,(org/100mls) but likelyTotal Lead (mg/L) <0.0004 to <0.001 < 0.001 to 0.002 Yes 0.0255 (acute standard) Acute – Yes <0.001 (dissolved) (ground water 0.001 (chronic standard) Chronic – Yes predicted total lead not dissolved)Dissolved Nickel (ug/L) 0.0005 to 0.001 0.001 < 0.005 Yes 0.6931 (acute standard) Yes 0.0770 (chronic standard) wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 58 October 28, 2005
Surface Water and Geomorphology Technical ReportTable 8 (continued). Table of estimated ground water quality concentrations and North Sequalitchew Creek Concentrations within the mine expansion area compared to background concentrations in Sequalitchew Creek and Washington State surface water quality standards (Chapter 173-201A-200 WAC) (from Pacific Groundwater Group [PPG 2005]). Estimated Sequalitchew Creek Water Quality Surface Water Quality Below or Within Meets Surface Estimated of North Baseline Range Range of Surface Water Quality Water Quality Ground Water Sequalitchew (1999 to 2000) Sequalitchew Standard Standard Quality Range Creek (CH2Mhill 2000a and Creek Background (Chapter 173-201a (Chapter 173- Parameter (PGG, 2005) a (PGG 2005) b 2003b) Water Quality? WAC) c 201A WAC)?Nitrate-nitrogen (mg/L) 0.0005 to 0.02 0.3 0.28 to 0.82 Yes No Standard Not ApplicableDissolved Oxygen (mg/L) ND Not Modeled 10.6 to 13.6(2) Undetermined 9.5 mg/L UndeterminedpH (SU) 6.7 to 7.0 6.7 6.6 to 7.8 Yes 6.5 to 8.5 YesPhosphate (mg/L) Not Modeled Not Modeled 0.01 to 0.034 Undetermined No Standard Not ApplicableSulfate (mg/L) 5to 6 5.4 Not Sampled Undetermined No Standard Not ApplicableTotal Dissolved Solids 90 to 240 156 Not Sampled Undetermined No Standard Not Applicable(mg/L)Temperature (°C) Not Modeled Not Modeled 4.5 to 12.5 Undetermined 16°C UndeterminedTurbidity (NTU) Not Modeled Not Modeled Not Sampled Undetermined 5 NTU over background UndeterminedDissolved Zinc (mg/L) 0.0016 to 0.010 0.005 < 0.001 to 0.008 Yes 0.0560 (acute standard) Yes 0.0511 (chronic standard)a Distal and ambient data were extrapolated by Pacific Groundwater Group (2005), (Table 2). See the ground water section of the DSEIS for a discussion of how data were extrapolated.b The estimated concentration of in North Sequalitchew Creek at the confluence, Table 6 (PGG 2005).c Standards were evaluated using a hardness of 44 mg/L of CaCO3 (average hardness measured in Sequalitchew Creek during baseline sampling) (CH2M Hill 2001).wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 59 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportTable 9. Best estimate of predicted annual average flows in Sequalitchew Creek with the additional flows from North Sequalitchew Creek upstream and downstream of the proposed confluence at RM 0.8 (Anchor 2004d). North Sequalitchew Creek Sequalitchew Creek Sequalitchew Creek (at confluence) (above confluence [RM 0.8]) (below confluence [RM 0.8]) Future Current Future Change Current Future ChangeObserved Average Flow NA 1.0 1.4Flows (cfs)Best Average Flow 7.6 1.0 0.5 0.5 1.4 8.1 6.7Estimate (cfs) Sensitivity 6.4 to 9.8 1.0 0.5 0.5 1.4 6.9 to 10.3 5.5 to 8.9 Analysis (cfs) wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 60 October 28, 2005
Surface Water and Geomorphology Technical ReportTable 10. Best estimate of peak storm flows in Sequalitchew Creek under existing and future conditions (Anchor 2004d). Existing Peak Flows (cfs) Location 2-Year 5-year 10-Year 25-Year 50-Year 100-YearBased Lower Gauge Observations 10 14 17 22 26 31 Future Peak Flow Conditions (cfs)Best Estimate 20.2 27.3 32.3 40.6 46.8 53.7wp4 /02-02403-000 surface water and geomorphology tech report.docOctober 28, 2005 61 Herrera Environmental Consultants
Surface Water and Geomorphology Technical ReportTable 11. Estimated peak storm flows in the proposed North Sequalitchew Creek used by Aspect to assess reclamation stormwater conditions within the mine expansion area (Aspect 2004b). 2-Year 5-Year 10-Year 25-Year 50-Year 100-Year Event Event Event Event Event EventStormwater (cfs) 3 5 7 10 13 17Groundwater (cfs) 7 7 7 7 7 7Total 10 12 14 17 20 24 wp4 /02-02403-000 surface water and geomorphology tech report.docHerrera Environmental Consultants 62 October 28, 2005
05-16-05/rtb/HEC-O-pjt/02-02403-000-057-001/SEIS Source: GeoEngineers 2004b Figure 2a. Sequaltichew Creek reach boundaries and landslides mapped by GeoEngineers.
05-16-05/rtb/HEC-O-pjt/02-02403-000-057-001/SEIS Source: GeoEngineers 2004b Figure 2b. Sequaltichew Creek reach boundaries and landslides mapped by GeoEngineers (continued).
K:Projects02-02403-000ProjectGPS points and lidar.mxd (9/20/2005) GW nd ou tS ge Existing Pu Gravel Mine 0+00 5+00 10+00 15+00 Sequalitchew Cr 20+00 ee k embankment 25+00 30+00 Railroad 35+00 40+00 Legend Landslides mapped during January 2004 field reconnaissance 45+00 (GeoEngineers, 2004b) Centerline and approximate stationing 2004 topography provided by Puget 50+00 55+00 Sound Lidar Consortium. 0 250 500 1,000 Feet 1 inch = 500 feet Figure 3. Shaded relief map developed from lidar topography and overlay of landslide and debris fans mapped during field reconnaissance (GeoEngineers 2004b, 2005).
05-16-05/rtb/HEC-O-pjt/02-02403-000-057-001/SEIS Source: GeoEngineers 2004b Figure 4a. Sequalitchew Creek selected erosional and depositional areas for current conditions based on hydraulic modeling results.
05-16-05/rtb/HEC-O-pjt/02-02403-000-057-001/SEIS Source: GeoEngineers 2004b Figure 4b. Sequaltichew Creek selected erosional and depositional areas for current conditions based on hydraulic modeling results (continued).
A 100 100 100-year flow event, Sequalitchew Creek Sediment Transport critical bed shear stress Ratio of shear stress to 10 Existing conditions 10 Bed Entrainment 1 1 0.1 0.1 0.01 0.01 Reach 4 Reach 3 Reach 2 Reach 1 0.001 0.001 0 500 1000 1500 2000 2500 3000 3500 4000 Distance from creek mouth (ft) B 1000 1000 100-year flow event, Sequalitchew Creek Sediment critical particle shear stress Ratio of shear stress to 100 Existing conditions Deposition 100 10 10 1 1 0.1 Deposition Deposition 0.1 Reach 4 Reach 3 Reach 2 Reach 1 0.01 0.01 0 500 1000 1500 2000 2500 3000 3500 4000 Distance from creek mouth (ft)Figure 5. Areas of potential sediment transport (A) and deposition (B) predicted from results of the HEC-RAS modeling for existing conditions in Sequalitchew Creek.
Figure 7 Kettle wetland water levels at the existing Glacier Mine site from July 1999 to October 2002 (CH2M Hill 2003a). 7 Staff Gage Water Level (ft) 6 5 4 3 2 1 0 7/1/1999 9/1/1999 11/1/1999 1/1/2000 3/1/2000 5/1/2000 7/1/2000 9/1/2000 11/1/2000 1/1/2001 3/1/2001 5/1/2001 7/1/2001 9/1/2001 11/1/2001 1/1/2002 3/1/2002 5/1/2002 7/1/2002 9/1/2002 11/1/2002Figure 7. Kettle wetland water levels at the existing Glacier Mine site from July 1999 to October 2002 (CH2M Hill 2003a).
(a) (b) (c) (d) 1870 1908 1939 1947 (e) 1990Figure 9. Historical maps of lower Sequalitchew Creek. (a) 1870 GLO Map, (b) 1908 Camp Lewis Map, (c) 1940 USGS topographic map (topography compiled in 1939), (d) 1994 USGS photorevised topographic map (topography compiled in 1947), and (e) 1990 aerial photograph showing sediment fill in brackish marsh.
Railroad Embankment Brackish Marsh Creek Bar Gravel Splay Deposits (a) Tidal Sloughs Creek (b)Figure 10. Current conditions within the brackish marsh during low tide. (a) Panoramic view looking west from the eastern brackish marsh boundary. (b) View looking south from the old (abandoned) narrow gauge railroad grade.
A 100 100 100-year flow event, Sequalitchew Creek Sediment Transport critical bed shear stress Ratio of shear stress to Existing conditions 10 10 Proposed conditions Bed Entrainment 1 1 0.1 0.1 0.01 0.01 Reach 4 Reach 3 Reach 2 Reach 1 0.001 0.001 0 500 1000 1500 2000 2500 3000 3500 4000 Distance from creek mouth (ft) B 1000 1000 100-year flow event, Sequalitchew Creek Sediment critical particle shear stress Existing conditions Ratio of shear stress to 100 Deposition 100 Proposed conditions 10 10 1 1 0.1 Deposition Deposition 0.1 Reach 4 Reach 3 Reach 2 Reach 1 0.01 0.01 0 500 1000 1500 2000 2500 3000 3500 4000 Distance from creek mouth (ft)Figure 11. Areas of potential sediment transport (A) and deposition (B) predicted from results of the HEC-RAS modeling for existing and proposed conditions in Sequalitchew Creek.
05-18-05/rtb/HEC-O-pjt/02-02403-000-057-001/SEIS Source: GeoEngineers 2004b Figure 12a. Sequaltichew Creek erosional and depositional areas for proposed conditions based on hydraulic modeling results by GeoEngineers.
05-16-05/rtb/HEC-O-pjt/02-02403-000-057-001/SEIS Source: GeoEngineers 2004b Figure 12b. Sequaltichew Creek erosional and depositional areas for proposed conditions based on hydraulic modeling results by GeoEngineers (continued).
05-16-05/rtb/HEC-O-pjt/02-02403-000-057-001/SEIS Source: GeoEngineers 2004a Figure 13a. Sequaltichew Creek areas of potential adverse change based on hydraulic modeling results by GeoEngineers.
05-16-05/rtb/HEC-O-pjt/02-02403-000-057-001/SEIS Source: GeoEngineers 2004b Figure 13b. Sequaltichew Creek areas of potential adverse change based on hydraulic modeling results by GeoEngineers (continued).