HomeMy WebLinkAboutBLD2006-00680 Stormwater Management PlanI
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Memo '_ o
E N G I N m I N G
2020 ENGINEERING, Inc.
''"---' 700 Dupont Street-Post Office Box 1621
Bellingham, WA 98227 USA
(360)671-2020 Fax: (360)671-0322
APPROVEDww4v.2020engineerinq.com
To: Public Works Departmgnt STORMWA FER PLAN D-1 e: September 14, 2006
Jefferson County
CC: James Westall Jikid 3 C • S.
, BU I
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From: Mark Buehrer, PE III, �1 r "
Jenifer Ramsey, EIT JEFFER 0 ),
2020 ENGINEERING KEPT.of c . • T v ME w
SIGNATURE: � 25353
Re: Westall Property —Grading Permit J ass oNA -����
• Stormwater Management Technical Memorandum q.
EXPIRES FEBRUARY 16, 2007
The purpose of this memo is to provide a summary of the stormwater management provided for the
Westall property site for building a house and its associated parking. The proposed scope of work is
to build a house consisting of five separate buildings, and two small parking areas to serve 8 cars.
The total area for the buildings and parking areas is approximately 15,000 square feet. Based on this
scope of work, the project is determined to be "large" in size, and is required to conform with
Minimum Requirements #1 through #10. The following is a summary of the project, scope of work,
and how the minimum requirements will be met.
Project Summary
The site is located near Port Discovery off of Highway 20, as shown on Figure 1. The total area for
the property is approximately 6 acres, with slopes onsite varying from approximately 10 to 70% (35
degrees). The total area proposed for new grading work is approximately 1.4 ac., as shown on the
site plan in Figure 2. In general, the overall slope of the property is approximately 23% (13 degrees).
The total elevation change is approximately 200 feet from Highway 20 down to the shoreline of Port
Discovery.
The soil survey for the site describes the soils as gravelly sandy loam. As seen form the attached
soil map, the area has Type "C' soils mapped. See attachment for soil maps and data.
Rainfall rates for the area are 1.5"for the 2-year 24-hour storm event, 2.25" for the 10-year, 24-hour
storm event, and 3.4" for the 100-year, 24-hour storm event, as seen in Figure 3 from the NOAA
isopluvial maps.
There are no lakes or ponds on the site. There is a natural Type 4 stream on the property, which
requires a 100-ft setback. The property also includes part of the shoreline for Port Discovery.
Westall Property—GradinIrmit •
Stormwater Management Technical Memorandum
Page 2 of 4
Scope of Grading Work ' T'''r' . j
The scope of work is to grade areas of the property for building pads for each of the five buildings,
and the associated walkways and parking areas. The building site is already served by an existing
driveway to Highway 20. As much native vegetation as possible will be maintained in order to limit
stormwater runoff and infiltrate any runoff that is produced. Figure 2 shows the general site plan.
Landscaped areas will use amended soil to increase the infiltration and retention of water in the
existing soils. Amended soils are existing soils with 4 inches of Grade A composted tilled into them
to a depth of 8 to 12 inches. In areas where topsoil has been removed during earthwork activities, a
compost soil blend consisting of 2/3 sand and 1/3 compost shall be applied on the ground surface at
a depth of 12 inches to provide topsoil for lawn and landscape areas.
Compost amended soils have an increased moisture holding capacity. They are able to delay and
often reduce the peak stormwater run-off flow rates. These soils hold more moisture in winter, when
precipitation in the Northwest is most abundant. Studies by University of Washington (Hielema,
1996) and the City of Richmond, WA (Harrison and Grey, 1997) have found that amended soil plots
retain 50 to 70 percent of the runoff volume produced by unamended plots under unsaturated
conditions. This essentially turns the amended soil area into"pre-existing forested conditions."
Based on StormShed1 runoff volumes for a 0.2623 ac area, the pre-existing forested 100 yr. runoff
volume for Type C soils is approximately 901 cf, whereas for a typical landscaping area, it is
approximately 1912 cf. This is a volume ratio of approximately 47%. Since amended soils have
shown they are able to retain 50 to 70 percent of the runoff form unamended plots, ameneded soils
essentially allow the existing soil conditions to approach"pre-existing forested" conditions.
Minimum Requirements
Based on the size and scope of work for the grading project, the project is considered to be "large" in
size, and is required to comply with Minimum Requirements#1 through#10.
Minimum Requirement #1: Preparation of Stormwater Site Plans. Stormwater site plans have
been prepared by 2020 Engineering, Inc. showing the grading areas and erosion control details.
Minimum Requirement #2: Construction Stormwater Pollution Prevention. Construction
stormwater quality problems are not anticipated since the area will be as minimally disturbed as
possible. Newly graded areas will drain into the existing native vegetation following existing drainage
patterns onsite. Stormwater pollution prevention measures shall be put in place by the
owner/contractor during any site clearing, grading or construction of site improvements. BMPs and
methodologies during construction shall follow the guidelines of the SWPPP attached. As
appropriate, the SWPPP measures will be located and identified on the civil plans and/or
specifications prepared by 2020 Engineering, Inc. The owner/contractor will be required to monitor
and maintain the facilities throughout the duration of these site improvements, and will maintain
buffers of existing vegetation where possible. Figures 4 and 5 show the TESC site plan and details.
Note that for this small of an area,WWHM2 could not be used as it returned an error message"too many
zeros"for the flow rates onsite.
Westall Property-GradingOrmit
Stormwater Management Technical Memorandum + -
Page 3 of 4
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Minimum Requirement #3: Source Control of Pollution. As a residential area, minimal source
controls are expected to be necessary. The following recommendations shall be implemented to
minimize the likelihood of discharging pollutants into offsite drainage systems.
• Fertilizers, Herbicides and Pesticides. Owner and contractors shall be encouraged to store
these items indoors or under roofs, to apply them only during dry (non-precipitation) periods
and at doses not exceeding the manufacturer's recommendations, and to dispose of them at
properly approved disposal sites.
Any spillage of chemicals or other hazardous materials shall be immediately reported to Jefferson
County and the Washington State Department of Ecology.
Minimum Requirement #4: Preservation of Natural Drainage Systems and Outfalls. The
existing site consists of undulating sloping terrain with a bluff sloping down to the shoreline. Most of
the property is covered with trees with a brush understory. This native vegetation and current natural
drainage to the bay will be maintained as much as possible onsite. A vegetative buffer will be
maintained between the steep bluff and the shoreline high water mark, which will be composed of
native vegetation. A native vegetation buffer will also be maintained in the area of the Type 4
stream.
Minimum Requirement#5: Onsite Stormwater Management. All stream corridors and shoreline
areas will be protected from disturbance (BMP T5.20). Roadway grading will be integrated into
natural topography as much as possible to minimize the grading volumes and utilize existing
drainage systems (BMP T5.21). All stormwater onsite will be infiltrated or utilized onsite. This will
include runoff from roofs directed to a raingarden and dispersion trench for infiltration. In addition,
runoff may be collected in cisterns or an onsite re-circulating ornamental waterfall and stream feature.
Minimum Requirement#6: Runoff Treatment. The new pollution-generating impervious surfaces
(parking areas) will exceed the 5,000 square foot threshold requiring treatment. Thus, treatment
facilities are required for runoff from these paved areas. Runoff from these paved areas will be
directed to a raingarden, a bioinfiltration swale or compost amended soil areas for treatment and
infiltration. Figure 6 shows a typical raingarden section.
Minimum Requirement #7: Flow Control. Flow control facilities are required if the stormwater
discharges directly into freshwater. This site is located along the shoreline, and therefore would
discharge directly into salt water. However, to prevent seawater intrusion all stormwater must be
infiltrated onsite to the maximum extent possible. Due to these issues, flow control is not required
onsite.
The site will utilize compost amended soils, a raingarden and dispersion trench, and a bioinfiltration
swale to reduce flowrates and infiltrate as much stormwater onsite as possible. A raingarden with an
overflow dispersion trench will be used to collect roof runoff. Runoff that cannot be infiltrated in the
raingarden section will overflow into a dispersion trench. The trench will slowly release the
stormwater runoff via "weep" holes into existing vegetation in order to maintain the natural drainage
onsite. Figures 6 and 7 show a typical raingarden detail and dispersion trench detail.
Minimum Requirement #8: Wetlands Protection. This requirement only applies to stormwater
being discharged directly into a wetland, either directly or indirectly. There are no wetlands onsite.
Westall Property—Gradingemit
Stomiwater Management Technical Memorandum
Page4of4
Minimum Requirement #9: Watershed Planning. This site is located next to a shoreline and --
therefore must meet any shoreline requirements. To prevent seawater intrusion, all stormwater must
be infiltrated or utilized onsite. There are no other known specific basin or watershed concerns. The
LID design standards that will be used for impervious surfaces will limit the impact of stormwater
flows, both in quantity and quality. These include compost amended soils, a raingarden, and a
bioinfiltration swale.
Minimum Requirement #10: Operation and Maintenance. The project stormwater facilities
requiring special maintenance are the raingardens. Specific operation and maintenance guidelines
for these are in the attachment of this memorandum.
References
Hielema, Eric,1996. Hydrologic Simulation of the Klahanie Catchment, King county, Washington,
With and Without a Landscape Consisting of Soil Amended with Compost. Masters Thesis submitted
to the College of Engineering, University of Washington. Seattle, Washington.
Harrison, R.B., M.A. Grey, C.L., 1997: Field Test of compost Amendment to Reduce Nutrient Runoff.
Prepared for the City of Richmond, College of Forestry Resources, University of Washington, Seattle,
Washington.
CIT.) 3
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DESIGNED M. WESTALL RESIDENCE SHEET'
IL BUE 9-71-06 t om.
DRAM BY: R. KOWA DATE 9-14-01III. 2020 ENGINEERING,Inc.
CHECKED BY: M. BUEIRER DATE 9-14-06 FIGURE 6
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1.THIS DISPERSION TRENCH
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1 } 1 L__-•
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FOLLOW CONTOURS OF SITE. OPTION,TYP.)—\ I
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(2)1/2"0 HOLES AT 12"C/C(MIN.) 't,�s111 a1.s1rs,
4.WASHED ROCK SHALL BE CLEAN 4;`114' 4%1'1! CLEAN OUT WYE FROM PIPE
3/4"-1-1/2"0 ,'4j0 IV 14, TYP.
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TRENCH SHALL BE 30' 4 %1t
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6. 18"(MIN.)#4 REBAR TO BE PLACED AT 1 Kitts"!
CENTER OF LEVEL SPREADER AND @ „-,• Kt,'•59;i�4 1 2"x 1 2"CATCH BASIN
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ENGINEER:
DESIGNED M. 8VENRER M. EXIEHRO? DATE 9-11-06 , WESTALL RESIDENCE SHEET:
DRAWN BY:Y.R. KOPKA DATE: 9-11-08 /ol` )(`; 2020 ENGINEERING,Inc.
CHECKED BY: N. EA ENRER DATE: 9-11-06 .; FIGURE 7
PRaL NO: st5whp '\,, DISPERSION TRENCH
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MAINTENANCE REQUIREMENTS
WESTALL RESIDENCE DRAINAGE FACILITIES 4_
RAINGARDENS(BIORETENTION)
• The flow entrances to the raingarden shall be inspected periodically and after large storm events.
Soil, plant material and/or mulch shall be replaced if any erosion has occurred. Mulch in the
raingardens serving parking lots shall be replaced annually due to the heavier pollutant loading.
• The catch basins within the raingardens shall be inspected annually, or after any extreme storm
event (2-inches or greater within 24 hours). If sediment or debris accumulates more than 12
inches in the bottom of the catch basin,it shall be removed to an approved disposal location. Any
debris blocking catch basin grates shall be immediately cleared.
• Ongoing weeding, watering as necessary, erosion and sediment control, and replacement of dead
plant material shall be provided for a minimum of three years after installation to achieve an 80
percent survival rate of all plantings. The site vegetation shall be trimmed only as necessary to
maintain the aesthetic appearance of the sites and to keep the raingarden free of leaves and other
accumulated dead vegetation. Poisonous or nuisance vegetation within the raingarden shall be
removed. Slope areas that are bare shall be revegetated and any eroded areas or holes shall be
filled and regraded prior to revegetation.
• If vegetation falls below the 80 percent level, new vegetation shall be planted to bring the total
percentage back up to that level or higher. Added vegetation types shall be changed as necessary
if it is determined that the original planting scheme is unable to survive at the 80 percent level over
an extended period.
• Any accumulated sediment shall be removed immediately, in order to maintain functional capacity
and adequate freeboard,and disposed of at an approved location.
• No nutrients or pesticides shall be applied to the raingardens.
STORMWATER POLLUTION
PREVENTION PLAN
for
Westall Property
Prepared for
James Westall
c/o Skookum
385 Benedict St.
Port Townsend, WA 98368
September 2006
Prepared by
.�
.
E NJ G I N E ER I N G
2020 ENGINEERING, Inc.
700 Dupont Street
PO Box 1621,Bellingham,WA 98227
(360) 671-2020 Fax(360) 671-0322
Westall Property-SWPPP 1 September,2006
• •
PROJECT DESCRIPTION
This project involves the construction of a residential area consisting of five buildings
and associated walkways, parking areas and driveways.
The purpose of this SWPPP is to provide guidance to the owner/contractor and the
owner/contractor's dedicated erosion control lead in minimizing erosion and
sedimentation problems due to this project. The owner/contractor is responsible to
implementing all appropriate measures to meet County, State and Federal guidelines
regarding water quality. This SWPPP, in conjunction with the civil plans by 2020
Engineering, Inc., describes the minimum starting measures to implement. However,
additional measures may be needed based on the actual onsite performance of BMPs
and the schedule and techniques used by the contractor. Contact information is
provided below, and should be amended as appropriate.
Proiect Owner:
Civil Engineer: 2020. Engineering, Inc.
P.O. Box 1621
Bellingham, WA 98227
Phone: (360) 671-2020
Contractor: DEC 1 - ': } w.�
1
cVi:x-OPi.'[NT
Erosion Control Lead Person:
Phone:
Email:
Fax:
A copy of this SWPPP, a list of the appropriate contact persons, and copies of
completed inspection forms shall be maintained onsite at all times during the project.
Westall Property-SWPPP 2 September,2006
r i
EXISTING CONDITIONS
Location. The project is located in on the Quimper Peninsula, south of Port Townsend
in Section 17, Township 29 North, Range 1 West, W.M. Jefferson County, Washington.
Topography. The entire area encompasses approximately 6 acres, with the project
site covering approximately 1.4 ac. The site slopes generally from west to east, with
slopes from approximately 10 to 30%.
Land Cover and Soils. The land is currenl.ly undeveloped. The underlying soils are
characterized in general as a sandy loam or silt loam. The site has mostly hydrologic
group "Type C" soils, as described by the SCS Soils Manual for Jefferson County Area,
Washington. The property lies along the Port Discovery shoreline.
Structures and Utilities. It is the contractor's responsibility to locate any onsite and
adjacent utilities. The one-call utility locate number is 1-800-424-5555. There is a
former railroad grade through the west end of the property.
Onsite Drainage Description. The majority of current surface runoff sheetflows down
the ridge to the shoreline over native vegetation areas and is either infiltrated or flows
offsite into Port Discovery.
Contributing Offsite Areas. Due to the slopes and the location of Highway 20, no
stormwater runoff will flow onto the site from offsite areas.
Downstream Conveyance. Any stormwater runoff that is not detained onsite travels
southeast off of the site to Port Discovery.
`f
I
I
Westall Property-SWPPP 3 September,2006-7--1
• •
PROPOSED CONDITIONS
The scope of work is to grade building pads for each of the five buildings, and the associated
walkways, parking areas, and driveway access to Highway 20. As much native vegetation as
possible will be maintained in order to limit stormwater runoff and infiltrate any runoff that is produced.
Landscaped areas will use amended soil to increase the infiltration and retention of water in the
existing soils. Amended soils are existing soils with 4 inches of Grade A composted tilled into them
to a depth of 8 to 12 inches. In areas where topsoil has been removed during earthwork activities, a
compost soil blend consisting of 2/3 sand and 1/3 compost shall be applied on the ground surface at
a depth of 12 inches to provide topsoil for lawn and landscape areas.
Westall Property-SWPPP 4 September,2006
•
EROSION AND SEDIMENTATION CONTROL
Temporary erosion and sedimentation controls (TESC) and Best Management Practices-.-
(BMPs) will be used to mitigate potential erosion and sedimentation due to construction
activities. A detailed summary of the suggested minimum aicf sio�i sed sr ehtatioh `\;
control elements follows below:
Element#1
Mark Clear Limits1,111
•
;, +�:r niTJ
Prior to beginning land-disturbing activities, including clearing and grading, all work
limits shall be marked. Areas to be marked include the roadway areas and their
associated drainage facilities (infiltration trenches). Either wood lath stakes or painted
ground surfaces may be used to mark the limits.
Element #2
Establish Construction Access
Any new construction access points required off of Highway 20 shall have stabilized
quarry spall construction entrances (BMP C105) meeting Jefferson County standards.
In addition, the adjacent roadway areas shall be cleaned at the end of each day, with
swept up materials deposited in a controlled onsite sediment disposal area, or an
approved offsite disposal location.
Element #3
Control Flow Rates
Temporary sediment traps or ponds (BMP C240 or BMP C241) shall be built if
necessary to collect any surface runoff during construction to prevent sediment laden
runoff from reaching offsite areas, streams or other water bodies. Siting of the traps or
ponds shall be at locations where overflow can discharge into existing vegetated areas.
Element #4
Install Sediment Controls
The owner/contractor shall endeavor to maintain any natural vegetation in as
undisturbed condition as possible. Where work is performed, the following BMPs may
be used to control runoff:
• Straw Bale Barrier (BMP C230). Use as a temporary emergency measure, as straw
bales do not last long under heavy flow conditions.
• Silt Fence (BMP C233). Place silt fence parallel to contours between work areas
Westall Property-SWPPP 5 September,2006
• •
and protected areas, and around exposed infiltration surfaces under construction.
• Straw Wattles (BMP C235). Place where surface flow begins to channelize, to slow
runoff and allow sedimentation.
• Sediment Trap (BMP C240). Construct as needed to prevent dirty runoff from
reaching the wetland or offsite areas.
Element#5
Stabilize Soils
Any exposed soils unworked for a significant: period shall be stabilized using effective
cover BMPs. Between October 1 and April 30, no exposed and unworked soils shall
remain unstabilized for more than two days. Between May 1 and September 30, no
exposed and unworked soils shall remain unstabilized for more than seven days. Soils
planning to be exposed and unworked for greater than one month shall be temporarily
seeded (BMP C120) or sodded (BMP C124), with adequate protection provided to
stabilize the soil until the vegetation is established. Stockpiles and areas exposed for
shorter periods may be stabilized using appropriate measures from the following BMPs.
• Nets and Blankets (BMP C122)
• Plastic Covering (BMP C123)
• Surface Roughening (BMP C130) 1 ; �.
• Gradient Terraces (BMP C131)
• Dust Control (BMP C140) I�
;; - :1\,.....„-,.
Element#6
I \\I
Protect Slopes :_vt- `0 ff
Steep slopes or landslide hazard areas shall have a undisturbed vegetated buffer to
protect them. The buffer shall follow requirements set forth in the land use permit. On
stockpiles and ditches or temporary embankments, appropriate measures from Element
#5 shall be used to minimize erosion.
Element#7
Protect Drain Inlets
Any drain inlets (catch basins) shall be protected by placing storm drain inlet protection
(BMP C220) at each catch basin. Each basin shall be inspected weekly, and daily
during significant storm events. Inlet protection shall be cleaned or replaced prior to the
accumulation of six inches of sediment.
Westall Property-SWPPP 6 September,2006
3 VI:
•
Element#8
Stabilize Channel and Outlets
Any outlets from temporary or permanent stormwater pipes or facilities!shall be armored ,EVEiLF�:LENI
with rocks or quarry spalls to prevent scour and erosion (BMP C209).
Element#9
Control Pollutants
All potential pollutants, including but not limited to wash water, human wastes,
chemicals, oils, fuels, vehicular lubrication and cooling fluids, miscellaneous trash and
waste materials, demolition debris, pesticides, herbicides, and fertilizers shall be
handled in such a manner to prevent contamination of stormwater. Stored hazardous
materials shall be protected from vandalism, covered, and have spill containment in
place, including plastic or other ground cover to minimize the opportunity for any spilled
materials to infiltrate into the porous soils.
Any spillage of hazardous materials into surface waters or into the ground shall be
immediately reported to Jefferson County, the Washington State Department of
Ecology, and other appropriate state or federal authorities, and immediately contained.
Pesticides, herbicides or fertilizers shall not be applied during or immediately prior to
expected precipitation events, and application shall follow the manufacturer's
recommendations.
Element#10
Control De-Watering
De-watering water from trenches or other excavations shall be discharged across
undisturbed vegetation areas, to allow dispersal and infiltration, or into previously
constructed temporary sediment traps (BMP C240). De-watering water shall not be
allowed to discharge directly onto offsite areas, except as approved by the offsite
owners.
Element#11
Maintain BMPs
All temporary and permanent erosion and sediment control BMPs shall be maintained
repaired and enhanced as necessary to assure continued performance of their intended
functions. Except as previously noted, all BMPs shall be inspected at a minimum on a
weekly basis, and during or immediately following a significant storm event (any storm
exceeding 0.5 inches rainfall within 24 hours, or 2.0 inches of rainfall within 7 days).
Within 30 days of final site stabilization or when no longer applicable, temporary BMPs
shall be removed from the site. Any accumulated debris and sediments shall be
disposed of at an approved onsite or offsite location, and each BMP site itself shall be
permanently stabilized.
Westall Property-SWPPP 7 September,2006
• • •
Element#12
Manage the Project
The grading work shall begin only after any needed temporary sedimentation and
erosion control BMPs have been put in place. Soil disturbance shall be avoided during
precipitation events, and priority shall be placed on maintaining existing vegetation in
work areas as long as possible.
The owner/contractor's erosion control lead shall follow the previous elements of this
SWPPP, the erosion control requirements from the plans, and any requirements of
County, State and Federal agencies. If circumstances require additional BMPs beyond
those recommended in this SWPPP to prevent construction caused contaminated runoff
from leaving the project site or contaminating the onsite infiltration facilities, it is the
owner/contractor's responsibility to implement those additional BMPs.
Note that the proposed raingarden and dispersion trench areas are infiltration
facilities. Thus, a priority of the contractor shall be to prevent silt, sediment or
debris laden water from reaching the infiltration surfaces of these facilities
throughout construction of the facilities and the rest of the site, so that the
permanent functionality of the infiltration facilities are not impaired.
The erosion control lead shall also keep a weekly log of BMP inspections, noting any
problems, repairs performed, or additional BMPs used. A sample weekly inspection
form is attached on the following page. Copies of this SWPPP and completed
inspection forms shall be maintained onsite at all times during the project.
The owner/contractor shall be aware that the Washington State Department of Ecology
has the authority to levy significant fines against the project owner if runoff exceeding
allowed contaminant levels due to any onsite or project activity is found to be
discharging from the project site.
SWPPP DRAWINGS
• Approved Civil Drawings with TESC Information (by 2020 Engineering, Inc., to be
attached upon approval by Jefferson County)
-----7—.\::
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Westall Property-SWPPP 8 September,2006
• •
SAMPLE SWPPP INSPECTION FORM
WEEK STARTING: ,
Name of Erosion Control Lead:
Weather Comments:
Condition of Site and BMPs:
Exposed Soils:
Silt & Construction Limit Fencing:
Quarry SpaII Entrances:
Adjacent Roadways and Properties
Catch Basin Protection:
Sediment Traps and Ponds:
Stockpiled Materials:
Other BMPs:
Repairs Made:
New BMPs Installed:
Other Comments:
Westall Property-SWPPP 9 September,2006 ��,
''_'_ Y'NTJ
S
SECTION II—EROSION AND SEDIMENT CONTROL PLAN
Sediment and erosion control measures may be depicted on the master land use application plot plan,a stormwater site plan,and/or a
separate Construction SWPPP site plan. This is a checklist to ensure that the following are depicted on a site plan:
1. General.
a. Vicinity Map
b. Jefferson County Approval Block
c. Erosion and Sediment Control Notes
2. Site Plan.
a. Legal description of subject property.
b. North arrow.
c. Indicate boundaries of existing vegetation (e.g.,tree lines,pasture areas,etc.).
d. Identify and label areas of potential erosion problems..
e. Identify FEMA base flood boundaries and Shoreline Management boundaries(if applicable).
f. Show existing and proposed contours.
g. Indicate drainage basins and direction of flow for individual drainage areas.
h. Label final grade contours and identify developed condition drainage basins.
i. Delineate areas that are to be cleared and graded.
j. Show all cut and fill slopes indicating top and bottom of slope catch lines.
3. Conveyance Systems.
a. Designate locations for swales,interceptor trenches, or ditches.
b. Show all temporary and permanent drainage pipes,ditches,or cut-off trenches required for erosion&sediment control.
c. Provide minimum slope and cover for all temporary pipes or call out pipe inverts.
d. Shows grades,dimensions,and direction of flow in all ditches,swales,culverts and pipes.
e. Provide details for bypassing off-site runoff around disturbed areas.
f. Indicate locations and outlets of any dewatering systems.
4. Location of Detention Best Management Practices(BMPs). Identify location of detention BMPs.
5. Erosion and Sediment Control Facilities.
a. Show the locations of sediment trap(s),pond(s), pipes and structures.
b. Dimension pond berm widths and inside and outside pond slopes.
c. Indicate the trap/pond storage required and the depth,length,and width dimensions.
d. Provide typical section views through pond and outlet structure. _ ,
e. Provide typical`details of gravel cone and standpipe,and/or other filtering devices. ,i; ,' '1 r' r-`~,
t,,
f. Detail stabilization techniques for outlet/inlet. j
g. Detail control/restrictor device location and details. I,
h. Specify mulch and/or recommended cover of berms and slopes. i .1 - 1 _.
F
i. Provide rock specifications and detail for rock check dam(s),if applicable. 1
j. Specify spacing for rock check dams as required. _i
k. Provide front and side sections of typical rock check dams.
I. Indicate the locations and provide details and specifications for silt fabric. -- - - ---------
m. Locate the construction entrance and provide a detail.
6. Detailed Drawings. Any structural practices used that are not referenced in the Ecology Manual should be explained and
illustrated with detailed drawings.
7. Other Pollutant BMPs. Indicate on the site plan the locations of BMPs to be used for the control of pollutants other than
sediment(e.g.,concrete wash water).
8. Monitoring Locations. Indicate on the site plan the water quality sampling locations to be used for monitoring water quality on
the construction site. Sampling stations should be located upstream and downstream of the project site.
stormwater site plan template—rev.10/1/2003 11
• •
STRATUM GROUP
1451 Grant Street, Bellingham, WA 98225
Phone(360)714-9409
January 3, 2007
Bill Irvine
1980 Cape George Road
Port Townsend, WA 98368
Re: Geology Review of Stormwater Plan
MLA#: MLA06-00651, Case#: BLD06-00678
Jefferson County, Washington
Dear Mr. Irvine:
I received a memo from Michele Farfan of Jefferson County Department of Community
Development regarding the stormwater plan for the proposed development at Warren Westfall's
property. Jefferson County requested that I review the stormwater plan for consistency with my
geology evaluation of the property that was completed in November 2003.
I have reviewed the stormwater plans for the site prepared by 2020 Engineering and spoke with
the Jennifer Ramsey the project manager at 2020 Engineering regarding the stormwater plan. The
stormwater plan will disperse stormwater runoff on the site in a manner consistent with the
recommendations I made in my November 2003 report.
Buildings 1, 2 and 5 and driveway areas will discharge stormwater in a dispersed manner into
areas of amended soil and into existing natural swales with existing natural infiltration. Building
4 will discharge stormwater into a raingarden with and subsequently into a dispersion trench and
onto an existing gravel road drainage route that will convey water to the base of the slope where
it will infiltrate behind into the ground behind the old railroad grade on the west side of the
property. The stormwater plan drawing indicates that Building 3 will direct its storm water into
the raingarden planned between Buildings 3 and 4.
The only change I recommend is that half the stormwater from Building 3 be directed towards a
dispersion trench located south of Building 3 towards the existing natural infiltration area.
Stratum Group appreciates the opportunity to be of service to you. Should you have any
questions regarding our reconnaissance please contact our office at(360) 714-9409.
Sincerely yours, �.
Stratum Group 'pt Was j
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Dan McShane, M.Sc., L.E.G. JAN - $ 2007
t ^'t L .Y:
Licensed Engineering Geologist
k Engineering G •, . �„
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