FEIS H-Revised Stormwater Management Plan

Appendix H
Revised Stormwater Management Plan

Stormwater Management Plan
MAHAMUDRA BUDDHIST HERMITAGE

TOWN OF WAWARSING
ULSTER COUNTY

Prepared for:

Dharamakaya, Inc.
155 Buff Road
Cochecton, NY 12726

Prepared by:

Susan K. Fasnacht, P.E., Project Manager
Chas. H. Sells, Inc.
555 Pleasantville Road
Briarcliff Manor, NY 10510
914-747-1120

June 2006
Rev. June 2007

STORMWATER MANAGEMENT PLAN
MAHAMMUDRA BUDDHIST HERMITAGE
TOWN OF WAWARSING, NY

Table of Contents
BACKGROUND INFORMATION ............................................................................................... 1
INTRODUCTION ...................................................................................................................... 1
EXISTING CONDITIONS......................................................................................................... 1
HYDROLOGICAL ANALYSIS .................................................................................................... 4
METHODOLOGY ..................................................................................................................... 4
PRE-DEVELOPMENT STORMWATER RUNOFF................................................................. 4
POST-DEVELOPMENT STORMWATER RUNOFF .............................................................. 5
STORMWATER MANAGEMENT............................................................................................... 8
STORMWATER QUANTITY................................................................................................... 8
STORMWATER QUALITY.................................................................................................... 11
EROSION AND SEDIMENT CONTROL .................................................................................. 14
TEMPORARY EROSION AND SEDIMENT CONTROL FACILITIES .............................. 14
Structural Measures .............................................................................................................. 14
Vegetative Measures............................................................................................................. 15
Maintenance and Inspection of Temporary Control Measures............................................. 16
PERMANENT EROSION AND SEDIMENT CONTROL FACILITIES............................... 17

Appendices
APPENDIX SMP-1 – PRE-DEVELOPMENT DRAINAGE ANALYSIS
APPENDIX SMP-2 – POST-DEVELOPMENT DRAINAGE ANALYSIS
APPENDIX SMP-3 – SOIL TEST RESULTS
APPENDIX SMP-4 – WATER QUALITY COMPUTATIONS

List of Figures
Figure 1: Pre-Development Subbasins........................................................................................... 6
Figure 2: Post-Development Subbasins ......................................................................................... 7
Figure 3: Proposed Drainage Facilities........................................................................................ 10

List of Tables
Table 1: Design Storm Precipitation Amounts .............................................................................. 4
Table 2: Existing (Pre-Development) Drainage Conditions........................................................... 5
Table 3: Post-Development Drainage Conditions (without Mitigation)......................................... 5
Table 4: Pre- Versus Post-Development Peak Discharges (with Mitigation)................................. 8
Table 5: Drainage Area, Curve Number and Time of Concentration............................................. 9
Table 6: Drainage Calculation Results ........................................................................................... 9
Table 7: Water Quality Swales. Required Volumes and Dimensions .......................................... 12
Table 8: Water Quality Swales. Discharges and Depths .............................................................. 12
Table 9: Roof Buildings Water Quality Requirements................................................................. 13

TOWN OF WAWARSING, NY

BACKGROUND INFORMATION

INTRODUCTION
This Stormwater Management Plan is being prepared in conjunction with construction of the
proposed Mahamudra Hermitage. The purpose of this plan is to outline design and operational
measures of drainage facilities that will meet the requirements of the New York State
Department of Environmental Protection (NYSDEC) Phase II Stormwater Regulations to
mitigate stormwater runoff quality and quantity impacts, as well as impacts from erosion and
sedimentation during site construction.

EXISTING CONDITIONS
The applicant, Mahamudra, Inc., proposes to develop a 91 acre property as a Buddhist house of
worship and related hermitage facilities. The site is located in the Hamlet of Cragsmoor in the
Town of Wawarsing. It is situated west of Cragsmoor Road, which connects the Hamlet to NYS
Route 52, south of the Village of Ellenville. The proposed construction includes construction of
17 buildings and infrastructure improvements such as access driveways, subsurface sewage
treatment systems, a central water supply from drilled wells, and landscaping in addition to the
stormwater management facilities. In total the project could ultimately disturb approximately
31.5 acres or 34.8% of the property.

Stormwater runoff within the project site is generally in a south to southeast direction towards
tributaries of the Platte Kill, which connects to the Wallkill River, a tributary to the Hudson
River. The project site is situated in a watershed of approximately 152 acres. Within the overall
watershed, 36.7 acres drain in a general southeast direction and under Cragsmoor Road to an
unnamed tributary of the Platte Kill, a portion of which traverses the northeast corner of the
property. The other 115.5 acres drain south, off the property in small, semi-defined channels and
ultimately to the Platte Kill. None of the site is within the New York City reservoir watershed.

Construction activities are expected to commence in 2007 with construction of buildings to be
done in phases that would continue until at least 2014. The initial phase of the work would be
the construction of the Milarepa Center, which would necessitate the construction of a portion of
the internal driveway, the proposed well house and water lines, electric and communications
lines, and the septic system for the Milarepa Center.

Soil disturbing activities associated with construction will include: clearing and grubbing;
installing a stabilized construction entrance; installing erosion and sediment controls; excavating
for and placing water, septic systems, electric and communications lines, stormwater
management facilities, and building foundations; constructing internal roads, parking areas, and
retaining walls; grading; preparing for final planting and seeding.

Drainage facilities and the erosion and sedimentation control measures will be designed and
implemented, in accordance with New York State Stormwater Management Design Manual
(NYSDEC, Aug. 2003) and the New York State Standards and Specifications for Erosion and
Sediment Control (NYSDEC Aug. 2005), as well as the requirements for a SPDES General
Permit GP-02-01 for Stormwater Discharges From Construction Activities.

According to the “Soil Survey of Ulster County” by the U.S. Department of Agriculture, Soil
Conservation Service, on-site soils include Bath gravelly silt loam (BgC), Bath and Mardin very
stony soil (BRC), Volusia very stony soil (VSB). Outside of the project site, yet still within the
drainage basin, three other soil types are present; Mardin gravelly silt loam (MdB), Alluvial land
(AA), and Nassau-Bath-Rock outcrop (NBF). Soil characteristics are as follows:

Bath gravelly silt loam (BgC): This unit consists of deep, well drained, sloping soil
formed in glacial till. It is near the crests of hills or on convex side slopes where water
does not accumulate. Most areas are long and narrow in shape and are found on slopes
ranging from 8% to 15%. The main engineering limitations of the soil include slow
permeability and an erosion hazard during construction if proper vegetative cover is not
maintained. This unit covers approximately 13.3% of the site, primarily at the
northwestern flatter portion of the site.
Bath and Mardin very stony soil (BRC): This unit consists mostly of well drained Bath
soils and moderately drained Mardin soils that are mainly on the convex hilltops an
hillsides and on foot slopes. These are deep, very stony soils formed in glacial till. Areas
are oblong or irregular in shape and found on slopes ranging from 8% to 15%. The main
engineering limitations of the soil include slow permeability and slight seasonal wetness.
The hazard of erosion during construction may be severe in some areas, if not protected
by proper soil and erosion control measures. This unit covers approximately 75.9% of
the site, through the center of the parcel.
Volusia very stony soil (VSB): This unit consists of deep, very stony, somewhat poorly
drained soils formed in glacial till. They are found that on foot slopes and on undulating
hilltops and plains. The soil is found on concave and uniform slopes that range from 3%
to 8%. The main engineering limitations of the soil include slow permeability in the
fragipan, seasonal wetness, and stoniness. This unit covers approximately 10.6% of the
site, primarily along the stream at the northeast end of the parcel and in an area on the
eastern side close to Cragsmoor Road.
Mardin gravelly silt loam (MdB): This unit consists of deep, gently sloping, moderately
well drained soil formed in glacial till that is mainly on the convex hilltops an hillsides
and slightly concave foot slopes. Areas are oblong or irregular in shape and found on
slopes ranging from 3% to 8%. The main engineering limitations of the soil include slow
permeability in the fragipan and substratum, and a seasonal high water table. This unit
covers a very small portion of the site of less than 1,700 square feet, at the northern end
of the parcel adjacent to Old Inn Road.
Alluvial land (AA): This unit consists of deep, unconsolidated alluvium soil that is
commonly shifted or redeposited by stream overflow. Its texture varies widely within a
short distance and the soil has little or no profile development. The frequent flooding and
the variability of its texture and drainage within short distances severely affect most uses.

Page 2 of 17

This unit covers approximately 0.2% of the site, along the stream bed just before it passes
under Cragsmoor Road and off-site on the east side of Cragsmoor Road.
Nassau-Bath-Rock outcrop (NBF): This unit consists of shallow, somewhat excessively
drained Nassau soils; deep, well drained Bath soils; and Rock outcrop, or bedrock
exposures that are intermingled mainly with the Nassau soils. These soils are formed in
glacial till with the Nassau soil generally on the upper one-half to two-third of the slope,
and the Bath soils on the lower part. Rock outcrops are found on hillsides, valleysides,
and mountains. Slopes range from 35% to 65%. The main engineering limitations of the
soil result from the very steep slopes and rock outcrop, which make construction difficult.
This unit is located just west of the parcel and is not present within the site itself.

Extensive soils tests were conducted for the design of the subsurface sewage disposal systems
(SSDS). The tests consisted of percolation tests to determine the permeability of the soils and the
digging of deep test holes to observe soil types and look for evidence of soil mottling. The
results of these soil tests are found in Appendix SMP-3.

There are four broad vegetative cover types within the Hermitage property. These include
wetlands/water courses, mature forest communities, young woods, and upland meadows. The
wetlands/water courses are present in two locations along Cragsmoor Road, one location along
the western property line, and at a vernal pool near the center of the property. None of these
areas are being disturbed by the proposed development. The mature forest occupies about 50
acres of the parcel, along the south and western areas. The young woods with approximately 32
acres are situated in the northwest and eastern corners of the parcel. The upland meadow, which
covers about 8 acres in the north central part of the property, had previously been a fairway for a
golf course (pre mid-1960’s).

The site lies on a shoulder of Bear Hill just east of the Shawangunk Mountain ridge line. This
creates a topography that slopes down hill from the north portion of the property to the south.
The highest part of the parcel is found where it fronts on Old Inn Road, where the elevation is
1,831 feet. The is also is a small “knoll” located east and slightly south of the Old Inn Road
frontage at elevation 1,794 feet. From each of these high areas, the land slopes downward to the
south and east with varying grades.

The lowest elevation on the property, 1,535 feet, is found at the southwest corner. At the
southeast corner adjacent to Cragsmoor Road the elevation is 1,562 feet. Elevations vary
approximately 296 feet across the property.

A few shallow watercourses originate north of the site and drain south into Platte Kill. The three
culverts located at the eastern side of the property collect runoff from sections of the site and
discharge on the other side of Cragsmoor Road.

Page 3 of 17

HYDROLOGICAL ANALYSIS

METHODOLOGY
Computations of existing runoff amounts were completed for the Type II, 1-, 10-, and 100-year,
24-hour design storms using the Soil Conservation Service, Technical Release – 55 (TR-55)
methodology. The TR-55 method of stormwater modeling is accepted by both the USDA Soil
Conservation Service and the U.S. Army Corps of Engineers, and meets the SEQRA scoping
goals for this project, as well as the requirements of NYSDEC. PondPack®, Version 10.0 by
Haestad System, which uses a hybrid of the strengths of HEC-1 (U.S. Army Corps of Engineers)
and TR-20 (SCS) was used for completing the stormwater analyses for the project.

The software forecasts the rate of surface water runoff and watercourse flow rates based on
several factors. The input data includes information on land use, soil types, vegetation, watershed
areas, time of concentration, rainfall data, storage volumes, and hydraulic capacities of the
hydraulic structures. The computer model predicts the amount of runoff as a function of time,
including the attenuation effect due to dams, lakes, large wetlands, and floodplains. Runoff rates
during specific rainstorms may vary due to different assumptions concerning soil moisture, water
levels in ponds, snowmelt, and rainfall patterns. The input data for rainfalls with statistical
recurrence frequencies of 1-, 10- and 100-years were obtained from the U.S. Weather Bureau
Technical Papers. The National Weather Service developed four synthetic storms to simulate
rainfall patterns around the country. For analysis in Ulster County, the Type II rainfall pattern
with a 24-hour duration is valid.

The design storms analyzed correlate to the requirements of the NYSDEC for the Phase II
Stormwater Regulations in which stormwater management practices must mitigate the CPv
(Channel Protection Volume – 1 Year Storm Event), the QP (Overbank Flood Control – 10 Year
Storm Event) and QF (Extreme Flood Control – 100 Year Storm Event) storm events.
Precipitation for the required storms is contained in Table 1.

Table 1: Design Storm Precipitation Amounts

Design Storm Precipitation Amount
(Inches)
1-Year (CPv) 3.5
10-Year (QP) 6.0
100-Year (QF) 8.0

PRE-DEVELOPMENT STORMWATER RUNOFF
In order to determine the pre-development conditions for the site that will ultimately be used to
determine the stormwater detention needs for the proposed development, five analysis points (A,
B, C, D, and E) with the corresponding watersheds were chosen in relationship with the possible
impact downstream of the developed areas (See Figure-1, Pre-Development Subbasins). An
analysis of the drainage basins was run to compute the peak runoff rates during each of the
design storms. A printout of the complete results is contained in Appendix SMP-1. The input

Page 4 of 17

parameters for drainage area, time of concentration (TC) and composite curve number (CN), as
well as the analysis results for pre-development are summarized in Table 2.

Table 2: Existing (Pre-Development) Drainage Conditions
Travel Peak Runoff Rate
Drainage Drainage Curve Time (cfs)
Basin Area No. (TC) 1-Year 10-Year 100-Year
(Acres) (CN) (hr) (CPv) (QP) (QF)
A 14.65 71 0.19 19.5 56.0 88.5
B 11.53 70 0.30 12.1 35.6 57.2
C 12.30 71 0.29 14.0 40.0 63.5
D 38.70 70 0.21 47.4 139.1 221.1
E 75.05 73 0.59 63.4 174.8 273.4

POST-DEVELOPMENT STORMWATER RUNOFF
For the post-development condition similar watersheds were used, however one (Subbasin D)
was further subdivided and modified to reflect the changes of the site to analyze the hydrology
under proposed conditions (See Figure-2, Post-Development Subbasins). Input parameters were
modified to reflect changes in the drainage basin boundaries, plus changes to the times of
concentration and curve number that result because of the development of the site. The complete
analysis for the post-development condition is contained in Appendix SMP-2. The input
parameters for drainage area, TC and CN, as well as the analysis results for pre-development are
summarized in Table 3. These values reflect the peak runoff rate prior to the design of any
stormwater peak discharge mitigation measures.

Table 3: Post-Development Drainage Conditions (without Mitigation)
Curve Travel Peak Runoff Rate
Drainage Drainage No. Time (cfs)
Basin Area (CN) (TC) 1-Year 10-Year 100-Year
(Acres) (hr) (CPv) (QP) (QF)
A 11.29 71 0.19 15.0 43.2 68.2
B 17.36 73 0.23 24.9 66.6 102.7
C 6.04 72 0.28 7.4 20.8 32.6
D1 18.14 76 0.21 31.0 77.8 118.1
D2 13.85 70 0.17 18.0 52.8 83.8
D3 10.60 72 0.14 16.4 44.5 70.0
E 74.95 73 0.59 63.3 174.6 273.0

Page 5 of 17


STORMWATER MANAGEMENT

STORMWATER QUANTITY
To evaluate the change from pre- and post-development conditions, the peak flows for several of
the subbasins were hydrologically added to compute peak runoff rates at common downstream
points, in addition to being compared individually. In the case of subbasins A, B and C, the
common point would be where subbasin C joins the stream along the east side of Cragsmoor
Road. These basins are also compared individually, pre- and post-development, to ensure there is
no increase in peak runoff to the culverts under Cragsmoor Road. For subbasin D, the post-
development area would have a common discharge point where the pre-development subbasin D
exits the property. Subbasin E has the same discharge point, pre- and post-development. Using
these common discharge points a comparison was made for pre- and post-development peak
runoff rates for the site and is shown Table 4.

Table 4: Pre- Versus Post-Development Peak Discharges (with Mitigation)
Pre-Development Post-Development
Peak Runoff Rate Peak Runoff Rate
Drainage (cfs) (cfs)
Basin 1-Year 10-Year 100-Year 1-Year 10-Year 100-Year
(CPv) (QP) (QF) (CPv) (QP) (QF)
A, B,
C 44.8 129.5 204.4 30.7 79.8 131.2
D 47.4 139.1 221.1 34.4 97.7 163.4
A 19.5 56.0 88.5 15.0 43.2 68.2
B 12.1 35.6 57.2 11.1 26.1 53.2
C 14.0 40.0 63.5 7.4 20.8 32.6
E 63.4 174.8 273.4 63.3 174.6 273.0

As can be seen in the above tabulation, without detention there would be small increases in the
peak runoff rates. To mitigate any increases, several detention basins have been proposed. The
first basin is located north of the Welcome Center and detains runoff from subbasin B. The basin
has approximately 2.55 acre-feet (111,000 cubic feet) of storage and will mitigate any increase in
peak runoff for the 1-, 10-, and 100-year design storms at the common discharge point C. In
general, this includes runoff from the Milarepa Center and portions of Road B.

The second area of detention, located south of the main parking lot, consists of two ponds, one
with a volume of 2.0 acre-feet (87,000 cubic feet) and the second a volume of 2.28 acre-feet
(99,300 cubic feet). These ponds will mitigate any increase in the peak discharge for the 1-, 10-,
and 100-year design storms for flows emanating mainly from the Bodhisattva Center, portions of
Road B, the Common House and the main parking lot – subbasins A, B, and C. Figure-3 shows
the location of the proposed detention basins. The computations for the sizing of the detention
basins are contained in Appendix SMP-2.

Peak stormwater runoff rates for Subbasins D and E will be handled through the use of cisterns
and dry wells. The cisterns will be incorporated into the building construction and site

Page 8 of 17

development of all buildings and be sized to collect stormwater runoff that has been pretreated in
accordance with the “Alternative Stormwater Management Practices” section of the New York
State Stormwater Management Design Manual. Water collected in the cisterns will be used for
watering of landscaping and other non-potable water uses.

The stormwater design software StormCAD version 5.6 was used to analyze the hydrology and
hydraulics for the proposed drainage system. The times of concentration were estimated using a
combination of overland flow and gutter or grassed waterway flow times. Runoff coefficients
were estimated based solely on land use types. “n” value of 0.9 for impervious areas and 0.25
value for grass areas were used. Drainage data and calculations are shown in Table 5 and Table
6. The proposed drainage system is capable to convey a 100-year frequency storm to the
detention basins.

Table 5: Drainage Area, Curve Number and Time of Concentration
Drainage
Location Area C Tc
(Ac) (min)
CB1 5.20 0.27 23
CB2 Negligible
CB3 1.82 0.40 19
CB4 1.84 0.38 26
CB5 4.20 0.36 26

Table 6: Drainage Calculation Results
Size
Section (in) Discharge (ft3/s) Velocity (ft/s)
25-yr 100-yr 25-yr 100-yr
CB1- 15”
CB2 hdpe 3.4 3.8 13.6 14.0
CB2- 15”
CB3 hdpe 3.4 3.9 11.3 11.7
CB3- 15”
Outl. hdpe 6.6 7.8 5.4 6.4
CB5- 15”
MH2 hdpe 6.2 7.7 15.8 16.8
MH2- 18”
MH1 hdpe 6.2 7.7 5.0 4.4
MH1- 18”
Outl. hdpe 6.0 7.5 3.4 4.2

Page 9 of 17


STORMWATER QUALITY
Several Stormwater Management Practices (SMPs) are incorporated into the stormwater
management system design to maintain water quality. The methodology used for the design of
the SMPs will follow the guidelines contained in New York State Stormwater Design Manual to
meet the Phase II Stormwater Regulations.

Where appropriate, low-impact design principles were incorporated into the design of the
stormwater management system. For the most part, road curbing has been eliminated to promote
sheet flow of stormwater from paved surfaces into lawn areas, grassed swales, and vegetated
filter strips. This allows for natural infiltration and filtering of runoff through vegetated areas.
Additionally, pervious paving materials will be used wherever practical on-site for
roads/driveways and walkways, which allows for natural infiltration of runoff.

Several SMPs were used to mitigate water quality. These include wet ponds/micropools, dry
swales, plunge pools, vegetated filter strips, and dry wells/infiltrator chambers (See Figure 3).

Wet Ponds/Micropools: A large wet pond is proposed at the southern end of the entrance
circle to the Bodhisattva Center. This pond will treat runoff from the area of the
Bodhisattva Center, as well as portions of Road B and the main parking lot. Micropools
and extended detention areas will be incorporated into the three main detention basins to
provide additional water quality treatment.

Dry swales will be constructed in several locations through out the Hermitage site. The
swales will be used to provide water quality treatment for areas such as the Naropa
Center, Teacher’s House, Guest Teacher’s House and the main parking area where grades
preclude connection to wet ponds or micropools. At the upstream end of the dry swales,
plunge pools will be constructed to pretreat 25% of the water quality volume. Water
quality swales reduce the velocity, temporarily store stormwater runoff and promote
infiltration. Pollutant removal mechanisms in water quality swales include sedimentation,
adsorption, biological treatment and microbial breakdown. Two types of swales were
provided; Type A with 3.0 feet bottom and Type B with a 6.0 feet bottom. Both are
trapezoidal with a 3:1 slope and were designed for a minimum od 10 minutes detention
time. Table 7 and Table 8 show the quality swale design data.

Page 11 of 17

Table 7: Water Quality Swales. Required Volumes and Dimensions
Water
Water Drainage Quality Required Provided
Quality Area Volume- Type Length (ft) Length
Swale (Ac) WQV (ft)
(ft3)
WQS1 0.16 272 A 36 100
WQS2 0.96 886 B 36 150
WQS3 2.3 2570 B 108 220
WQS4 5.7 4370 B 126 270
WQS5 0.29 256 A 48 125
WQS6 4.6 3005 B 102 240
WQS7 0.84 1171 B 84 120

Table 8: Water Quality Swales. Discharges and Depths
Water Exist. Condition Prop. Condition Proposed Condition
Quality Discharges (ft3/s) Discharges Water Depth
Swale (ft3/s) (ft)
CPv QP QF CPv QP QF QWQ CPv QP QF QWQ
WQS1 0.2 0.7 1.1 0.3 0.8 1.2 0.01 0.4 0.6 0.7 0.2
WQS2 1.4 4.1 6.5 2.1 5.1 7.6 0.03 0.7 1.2 1.5 0.1
WQS3 3.4 9.9 15.8 5.3 12.6 18.8 0.3 1.2 1.8 2.2 0.1
WQS4 8.1 23.6 37.5 11.8 29.7 44.9 0.4 1.8 2.8 3.4 0.3
WQS5 0.4 1.2 2.0 0.6 1.5 2.2 0.02 0.5 0.8 1.0 0.7
WQS6 6.6 19.3 30.9 8.3 21.9 33.7 0.2 1.5 2.4 2.9 0.2
WQS7 1.2 3.6 5.8 1.9 4.6 6.7 0.1 0.9 1.4 1.6 0.2

The vegetated filter strips are grassed or close-growing native plants areas located just
downstream of the pollutant source. The vegetated filter strips typically treat sheet flow
directly from adjacent impervious surfaces. The vegetative strips, in general, will
encompass disturbed areas adjacent to roads and buildings to provide a level of
pretreatment and runoff reduction.

First flush runoff volumes from roof areas will be collected in drywells with pretreatment
chambers as required to provide the volume of water quality treatment prescribed by
NYSDEC guidelines. Overflow from the drywells will be connected to cisterns for use in

Page 12 of 17

irrigation and other non-potable water uses . The required roof runoff quality volumes are
shown in Table 9.

Table 9: Roof Buildings Water Quality Requirements
Area WQV WQV
Location (Ac) I Rv (ft3) (gal)
A. Milarepa Center
Building 1 0.18 100 0.95 728 5,460
Building 2 0.11 100 0.95 455 3,413
Building 3 0.03 100 0.95 120 900
Building 4 0.04 100 0.95 153 1,148
B. Bodhisattva 0.19 100 0.95 786 5,895

The use of drywells and/or infiltrator chambers (Recharger 280 or Recharger 330 per Cultec,
with a volume of 6.079 ft3/ft and 7.459 ft3/ft, respectively) was recommended.

Page 13 of 17


EROSION AND SEDIMENT CONTROL

TEMPORARY EROSION AND SEDIMENT CONTROL FACILITIES
Land disturbance at the proposed site will be carefully sequenced so that grading operations can
begin and end as quickly as possible, thus minimizing the exposed areas subject to erosion. Site
clearing, land grading, and installation of underground utilities (water, electric, telephone, etc.),
will commence initially. All material from excavation will be stockpiled in-situ to concentrate
the area of loose soil exposed to runoff. At the stock pile, silt fences will be installed and
temporary dikes/swales will be placed if necessary during construction.

During this stage, soil in areas previously covered will be exposed to runoff. Erosion of these
areas will be controlled by establishing temporary seeding and mulch, and by placing straw bale
dikes and silt fences. The purpose of the temporary seeding and mulch is to reduce sediment
carried by the runoff from the exposed areas and to control dust. Temporary seeding and mulch
will be placed as soon as the removal activity is completed. During development, areas where
construction has temporarily or permanently ceased will be stabilized within 14 days unless
construction will resume within 21 days.

Construction of the buildings and their associated site improvements will commence once site
work has been substantially completed and stabilized. Prior to starting these activities, silt fences
will be placed along the perimeter of the cleared areas and temporary seeding will be done as
necessary to install the silt fences.

Structural Measures
1. Straw Bale Dike

Straw bale barriers will be provided downgradient of all construction activities. The purpose of a
bale barrier is to trap sediment from sheet erosion before it travels overland to downgradient
properties. The straw bale dikes will be placed as construction progresses on the site.

2. Silt Fence

Silt fence sediment barriers will be installed downslope of disturbed areas with minimal slope to
filter sediment runoff from sheet flow. Silt fences will also be provided around stockpile areas
and between construction areas and property lines to reduce sediment laden runoff from traveling
off-site. Additional silt fences will be installed as required during construction activities.

3. Anti-tracking Apron at Site Entrance

A temporary stabilized construction entrance of gravel will be installed where the access area
intersects with Cragsmoor Road. During muddy conditions, drivers of construction vehicles will
be required to wash their wheels before exiting the site.

Page 14 of 17

4. Storm Drain Inlet Protection

All storm catchbasin inlets will be protected to prevent sediment laden runoff from clogging the
drain pipes during construction. Filter fabric inlet protection should be used on each inlet until
upland areas are stabilized.

5. Diversion Dike/Swale

Diversion dikes/swales will be included in the erosion and sedimentation plan to control and
reduce the amount of sediments leaving the site. These diversion dikes/swales will be placed
downgrade of disturbed areas, whenever these areas become larger than the areas allowed to be
controlled by only a straw bale or silt fence. The diversion dikes/swales will be placed following
the existing topography and will be temporarily seeded with a fast-germinating grass, and riprap
protected at any discharge points.

6. Check Dams

Check dams will be added to diversion swales/channels, as well as any temporary drainage
swales to reduce the flow velocity in the channels. This will help to reduce erosion of those
temporary drainage facilities.

7. Water Bars

Water bars will be provided across the proposed roads, particularly in areas where the grades are
in excess of 5%. The water bars will limit the accumulation of erosive velocities of stormwater
runoff by diverting the surface water to diversion or temporary drainage swales/channels.

8. Temporary Sediment Basins

Temporary sediment basins will be constructed at the permanent detention basin locations to
intercept sediment ladened runoff and to trap and retain the sediment. The size of the basin will
be in accordance with the New York State Standards and Specifications for Erosion and
Sediment Control for the area contributing to the basin during a particular construction phase.

Vegetative Measures
9. Temporary Seeding

All cleared areas which will not reach final grading for a period of more than 30 days will be
seeded temporarily with fast germinating temporary grasses to reduce erosion potential,
immediately following grading. Selection of the seed mixture will depend on the time of year it
is applied, as recommended in Section 3 of the New York State Standards and Specifications for
Erosion and Sediment Control.

Page 15 of 17

10. Erosion Control Blankets or Mulch

North American Green biodegradable erosion control blankets will be installed to provide
immediate erosion protection and vegetation establishment on excavated or fill slopes or low
flow channels which have been brought to final grade and have been seeded to protect the slopes
from rill and gully erosion and to allow the seeds to germinate properly. The erosion control
blankets will be double netting with degradable thread. This practice shall be applied especially
at areas where slopes exceed 5 percent. Mulch (straw or fiber) will be used to control dust
resulting from construction activity.

Maintenance and Inspection of Temporary Control Measures
In general, all erosion and sediment control measures will be checked weekly and after each
significant rainfall of 0.5 inches or greater, unless otherwise specified. The following items will
be checked in particular:

1. Existing riprap protection outlets will be inspected to determine if high flows have
caused scouring beneath the riprap or filter fabric. If repairs are needed, they should
be done immediately.
2. Temporary dikes/swales shall be inspected for proper functioning or signs of erosion
and shall be repaired as necessary. Sediment accumulated to an elevation one foot
below the crest of the earth barrier shall be removed and placed in the stockpile.
3. Silt fence barriers shall be inspected for damage resulting from deterioration or
undercutting and shall be repaired or replaced as necessary. Sediment shall be
removed when the level of sediment deposition reaches halfway to the top of the
barrier.
4. Catchbasins and drainage outlets will be checked for accumulation of sediment.
5. Straw bale dikes shall be inspected immediately after each rainfall. All damaged
bales, end runs and undercutting beneath bales shall be replaced or repaired.
Sediment deposits shall be removed after each rainfall or when the level of deposition
reaches half the height of the barrier.
6. Sediment shall be removed from temporary sediment basins whenever their capacity
has been reduced by fifty percent from the design capacity.
7. Construction entrance shall be inspected for evidence of off-site sediment tracking.
The paved street adjacent to the site entrance will be swept daily to remove any
excess mud, dirt or rock tracked from the site. Repair road and/or add stone as
necessary. Dump trucks hauling material from the construction site will be covered
with a tarp.
8. The paved street adjacent to the site entrance will be swept daily to remove any
excess mud, dirt or rock tracked from the site.
9. Areas that have received final stabilization shall be inspected at least once per month
until the entire site has been stabilized.
10. Disturbed areas and exposed areas used for storage/stockpiling that have not received
final stabilization shall be inspected for their potential sediment contribution to
stormwater.

Page 16 of 17

11. The seeded areas shall be inspected regularly to ensure that a good stand is
maintained. Areas where vegetation is missing or damaged shall be fertilized and
reseeded as needed.
12. Inspection schedule will be completed and maintained on-site and will contain the
following information: date, name of person conduction inspection, areas inspected,
problems/conditions encountered, actions taken to correct problem.
13. Employees will be trained to recognize any pollution source and report such
immediately. Training will be provided before the construction activity begins.
14. A maintenance schedule will be kept on-site to record and describe any discharge
incidents occurring during construction activity, including actions taken to correct the
problem, date, name of person conducting the maintenance.

PERMANENT EROSION AND SEDIMENT CONTROL FACILITIES
Land grading of the existing surface will be required in and around the proposed buildings and
roadway areas. Runoff from rooftops will be conveyed to drywells overflowing to cisterns for
reuse and as a means to reduce the quantity of runoff and an initial treatment for stormwater
quality. Surface runoff from roads, paths, and landscaped areas will be directed to drainage
swales and channels, and where appropriate catchbasins for ultimate connection to the
stormwater quality basins and detention basins. Drainage swale and channels will be
permanently stabilized with vegetative material or rip-rap to prevent erosion and control runoff
velocities.

The preformed scour holes at the detention inlets and the culvert apron at the STA 24+00 were
designed according to the Federal Highway Administration (FHWA) –RD-75-508. A riprap with
a minimum median diameter (D50) of 0.42 feet is recommended to protect all the outlets against
scour.
In order to disperse or “spread” the concentrated flow from the detention basins outlets thinly
over the existing undisturbed vegetated ground, Level Spreaders were provided. Its purpose is to
spread the concentrated outflow over a wide area so that the erosion does not occur. The level
spreader will also remove other pollutants from runoff by filtration, infiltration, adsorption and
decomposition.

Page 17 of 17

APPENDIX SMP-1
PRE-DEVELOPMENT DRAINAGE ANALYSIS

APPENDIX SMP-2
POST-DEVELOPMENT DRAINAGE ANALYSIS

APPENDIX SMP-3
SOIL TEST RESULTS

Results of Percolation Tests

Percolation
Test Hole
Test Hole Rate
Depth Soil Profile
No. (min./inch)
(inches)
Reddish brown, sandy silt loam, with traces
ML-1A 18 11
of clay/shale
ML-1B 18 Reddish brown, sandy silt loam 8
ML-1C 18 11
of clay/shale
ML-2A 18 Reddish brown, sandy silt loam 10
ML-2B 20 Reddish brown, sandy silt loam 8
ML-2C 18 Reddish brown, sandy silt loam 10
NR-1A 18 8
of clay/shale
NR-1B 18 Reddish brown, sandy silt loam 12
NR-1C 18 Reddish brown silty loam 15
NR-2A 18 Reddish brown silty loam 15
NR-2B 18 Reddish brown, sandy silt loam 15
SR-1A 18 Reddish brown, sandy silt loam 20
SR-1B 18 10
of clay/shale
SR-1C 18 Reddish brown, sandy silt loam 9
SR-2A 18 Reddish brown, sandy silt loam 22
SR-2B 18 Reddish brown, sandy silt loam 11
BH-1A 18 Reddish brown, sandy silt loam 22
BH-1B 18 Reddish brown, sandy silt loam 10
BH-1C 18 Reddish brown, sandy silt loam 8
TH-1A 18 Sandy silty loam 12
TH-1B 18 Reddish brown, sandy silt loam 9
TH-1C 18 Reddish brown, sandy silt loam 15
TH-1D 21 Reddish brown, sandy silt loam 15

1

Results of Deep Test Pits

AREA/
DEPTH
TEST HOLE SOIL DESCRIPTION DEPTH TO:
(IN.)
NO.
GR-1 0" - 8" Top Soil Mottling @ 17"
#1 8" - 17" Yellowish Brown Sandy Silt Loam Hardpan @ 50"
17" - 50" Mottling Water @ 68"
Dark Brown Silty Loam w/ Traces of
50" - 84"
Clay (~20% shale)
Water Seepage @
#2 8" - 20" Yellowish Brown Sandy Silt Loam
42"
20" - 54" Mottling Hardpan @ 54"
54" - 84"
Clay (~20% shale)
18" - 54" Mottling No Water
54" - 84"
Clay (~20% shale)
54" - 72"
Clay (~20% shale)
54" - 84"
Clay (~20% shale)
ML-1 0" - 8" Top Soil Mottling @ 20"
42" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)

1

Water Seepage @
38"
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
46" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)

2

30" - 84"
Clay (~20% shale)
48" - 84"
Clay (~20% shale)
50" - 70"
Clay (~20% shale)
50" - 70"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
SR-1 0" - 8" Top Soil Mottling @ 22"
50" - 84"
Clay (~20% shale)
#2 8" - 28" Yellowish Brown Sandy Silt Loam No Hardpan

3



48" - 84"
Clay (~20% shale)
48" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)

4

48" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
NR-1 0" - 8" Top Soil Mottling @ 16"
50" - 60"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
42" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)

5

50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
NR-2 0" - 8" Top Soil
#5 8" - 16" Yellowish Brown Sandy Silt Loam Mottling @ 16"
48" - 84" No Water
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
BH-1 0" - 8" Top Soil Mottling @ 20"

50" - 84"
Clay (~20% shale)

6

50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)

7

BH-2 0" - 8" Top Soil
#5 8" - 19" Yellowish Brown Sandy Silt Loam Mottling @ 19"
50" - 84" Water @ 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)
50" - 84"
Clay (~20% shale)

8


APPENDIX SMP-4
WATER QUALITITY COMPUTATIONS

FEIS H-Revised Stormwater Management Plan

FEIS H-Revised Stormwater Management Plan

Recommended

Recommended

More Related Content

What's hot

What's hot (16)

Viewers also liked

Viewers also liked (19)

Similar to FEIS H-Revised Stormwater Management Plan

Similar to FEIS H-Revised Stormwater Management Plan (20)

FEIS H-Revised Stormwater Management Plan