SURFACE WATER AND GEOMORPHOLOGY                TECHNICAL REPORTPioneer Aggregates Mining Expansion      and North Sequalit...
Note:Some pages in this document have been purposefully skipped or blank pages inserted so that thisdocument will copy cor...
SURFACE WATER AND GEOMORPHOLOGY                TECHNICAL REPORTPioneer Aggregates Mining Expansion      and North Sequalit...
Contents1.0 Introduction.....................................................................................................
Impacts of the Project Alternative ..........................................................................................
TablesTable 1.    Discharge summaries (monthly means) for Sequalitchew Creek and Fort            Lewis Diversion Canal fro...
FiguresFigure 1.       Proposed Glacier Mine expansion area, surface water features, and surface                water moni...
Surface Water and Geomorphology Technical Report                                                                    1.0 In...
Surface Water and Geomorphology Technical Report                                                            2.0 Affected E...
Surface Water and Geomorphology Technical Reportrailroad grade that parallels the north creek bank intercepts these spring...
Surface Water and Geomorphology Technical Reportconstructing a golf course to provide a cap/containment facility for the f...
Surface Water and Geomorphology Technical ReportThe most recent Sequalitchew Creek discharge data were collected by Aspect...
Surface Water and Geomorphology Technical ReportSequalitchew Creek water quality was described in the original mine EIS, w...
Surface Water and Geomorphology Technical Reportbecame established. This post glacial reduction in sediment production, se...
Surface Water and Geomorphology Technical Reportcommon. Large trees would also be expected to moderate erosion along adjac...
Surface Water and Geomorphology Technical Report5-40 feet and 0.3-3 feet, respectively. Local surface raveling and exposed...
Surface Water and Geomorphology Technical Reportreaching the brackish marsh, then deposits of wood debris would be found a...
Surface Water and Geomorphology Technical Report(erosion) and deposition along various reaches of the lower stream reach (...
Surface Water and Geomorphology Technical Reportas an auxiliary outlet (Figure 1). Hydraulic structures (i.e., weirs) cont...
Surface Water and Geomorphology Technical ReportSeptember 2000 (Table 4). Samples were analyzed monthly for dissolved oxyg...
Surface Water and Geomorphology Technical Reportconcentrations of sodium and chloride in addition to high specific conduct...
Surface Water and Geomorphology Technical ReportCenter Drive and Strickland Lake (Figure 1). Although Pond Lake has no sur...
Surface Water and Geomorphology Technical Reportbox culvert (Anchor 2004c). When the tide rises to 9 feet above MLLW, salt...
Surface Water and Geomorphology Technical Reportdetermined by a complex mixture of forces, including tides, freshwater inp...
Surface Water and Geomorphology Technical Report                        3.0 Significant Impacts of the Proposed ActionCons...
Surface Water and Geomorphology Technical ReportSite Clearing and GradingMine expansion area clearing and grading would be...
Surface Water and Geomorphology Technical ReportDuring stream construction, an impoundment berm would be constructed at th...
Surface Water and Geomorphology Technical Reportintercepted by a series of dewatering wells and pumped to Sequalitchew Cre...
Surface Water and Geomorphology Technical Reportthe mine would be cool, it would not adversely impact Sequalitchew Creek w...
Surface Water and Geomorphology Technical Reportestimated to range from 40 to 120 cfs prior to construction of the diversi...
Surface Water and Geomorphology Technical ReportThe increase in the amount freshwater entering the stream could alter the ...
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Surface water and geomorphology herrera report-oct 2005

  1. 1. SURFACE WATER AND GEOMORPHOLOGY TECHNICAL REPORTPioneer Aggregates Mining Expansion and North Sequalitchew Project Prepared for Huckell/Weinman & Associates October 2005
  2. 2. Note:Some pages in this document have been purposefully skipped or blank pages inserted so that thisdocument will copy correctly when duplexed.
  3. 3. 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
  4. 4. 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
  5. 5. 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
  6. 6. 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
  7. 7. 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
  8. 8. 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
  9. 9. 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
  10. 10. 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
  11. 11. 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
  12. 12. 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
  13. 13. 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
  14. 14. 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
  15. 15. 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
  16. 16. 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
  17. 17. 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
  18. 18. 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
  19. 19. 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
  20. 20. 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
  21. 21. 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
  22. 22. 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
  23. 23. 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
  24. 24. 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
  25. 25. 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
  26. 26. 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
  27. 27. 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
  28. 28. 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
  29. 29. 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
  30. 30. 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
  31. 31. 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

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