HomeMy WebLinkAboutDrainage Report - BLD Engineering / Geo-tech Reports - 12/21/2017 THESE PAS PAUST BE
IDU TH E JOB SITE
;M. R INSPECTION
Drainage Report
Shearer Logging & Single Family Residential Property
401 NE Timberline Drive
Parcel No. 12320-34-00030
Mason County, Washington
December 21, 2017
Project#17195
RECEIVED
JAN 0 8 2018
615 W. Aber Street
TO BE KEPT IN THE
Prepared For:
PARCEL FILE
Tom Shearer
PO Box 1959
Belfair, Washington 98528 G�Ptiti 'WA/ STy
Prepared By:
Envirotech Engineering, PLLC A
PO Box 984 BOA c SoEREo
Belfair, Washington 98528 �SS�oNALE�v�
Phone: 360-275-9374
I
TABLE OF CONTENTS
1.0 PROJECT DESCRIPTION..................................................................................................................1
2.0 EXISTING CONDITIONS...................................................................................................................2
2.1 TOPOGRAPHY AND GEOMORPHOLOGY.............................................................................................2
2.2 SURFACE DRAINAGE...........................................................................................................................2
3.0 INFILTRATION RATES/SOILS REPORTS....................................................................................3
3.1 SUBSURFACE CONDITIONS.................................................................................................................3
3.1.1 Groundwater...............................................................................................................................3
3.2 SOILS TESTING AND PROPERTIES......................................................................................................3
3.2.1 INFILTRATION RATES......................................................................................................................4
4.0 HYDROLOGIC/HYDRAULIC INFORMATION............................................................................5
4.1 HYDROLOGIC SUMMARY....................................................................................................................5
4.2 BEST MANAGEMENT PRACTICES.......................................................................................................5
4.3 DRAINAGE TRIBUTARY TO THE PROJECT..........................................................................................5
4.4 DRAINAGE SYSTEM BEYOND THE PROJECT......................................................................................5
4.5 CRITICAL AREAS—WELLS—SEPTICS-AQUIFERS...........................................................................6
4.6 FLOOD ANALYSIS................................................................................................................................6
5.0 FACILTY SIZING AND DOWNSTREAM ANALYSIS...................................................................7
5.1 INFILTRATION BASIN..........................................................................................................................7
5.2 VEGETATED FILTER STRIP.................................................................................................................7
5.3 ROOF DOWNSPOUT INFILTRATION....................................................................................................8
6.0 CONSTRUCTION SEQUENCE AND PROCEDURE......................................................................9
7.0 PERMANENT EROSION CONTROL AND SITE RESTORATION...........................................10
7.1 SURFACED DRIVEWAY...................................................................................................................... 10
7.2 TOPSOIL............................................................................................................................................10
7.3 PERMANENT SEEDING...................................................................................................................... 10
8.0 INSPECTION AND MAINTENANCE..............................................................................................12
9.0 CONTROL OF POLLUTANTS OTHER THAN SEDIMENTS.....................................................13
10.0 PROJECT ENGINEER'S CERTIFICATION................................................................................14
Appendices
Appendix A—Site Map
Appendix B—Hydrologic Information
Appendix C—Best Management Practices
1.0 PROJECT DESCRIPTION
Envirotech Engineering, PLLC (Envirotech) has completed this drainage report in conjunction
with the stormwater management plan for a residential property located at 401 NE Timberline
Drive, identified as parcel number 12320-34-00030 in Mason County, Washington. See the
Vicinity Map below for a general indication of the Project location.
Information pertaining to the Project was provided by the property owner, and observations from
a field visit by Envirotech. The proposed development is expected to consist of a new single
family residence, driveway and other ancillary features typical of this type of development.
Approximate site development with relation to existing site features are illustrated in the Site Map
in Appendix A.
The size of the property is 13.78 acres. It is anticipated that the residential structures will cover
approximately 6200 square feet (sf), and the driveways will encompass an additional 7050 sf in
size. The total proposed impervious surface area is 13,250 sf. The total land area that has already
been disturbed due to logging is approximately 3.00 acres. It is anticipated that additional land
disturbance will not result from the proposed development. Cut and fill quantities were
approximated to be 200 cubic yards (cy) and 200 cy, respectively. See the accompanying
stormwater management plans for an illustration of current and proposed site features.
I
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Project ' f
1 +
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Vicinity Map from Mason County Website
Envirotech Engineering,PLLC Shearer Drainage Report
PO Box 984 page 1 401 NE Timberline Drive
Belfair,Washington 98528 Parcel 12320-34-00030
360-275-9374 December 21,2017
2.0 EXISTING CONDITIONS
The Project is currently vacant land with few improvements such as a road. Clearing and light
grading is apparent. This includes past logging and stumping. The property is surrounded by rural
residential development. Timberline Drive extends along the north side of the property, and the
Union River and other water features on the south portion of the property.Vegetation on and near
the property consists primarily of 2nd growth firs, alders, and other trees and shrubbery common
to this area of the Pacific Northwest.
2.1 Topography and Geomorphology
Descending slopes exceeding 15% are located on and beyond the property. Average slope grades
are up to approximately 23%with a vertical relief of approximately 15 feet. Some steeper slopes
were observed,but negligible vertical height and influence on the project.
Ascending grades are generally located to the northwest of the planned development. This slope
is relatively minor within 300 feet of the Project, with no apparent slope grades of at least 15%.
The upland area of the property is situated on a gentle hillside.Landforms are primarily of glacial
origin with centuries of weathering overburden.Most of the property consists of alluvium.
2.2 Surface Drainage
The majority of the stormwater runoff originating upslope from the anticipated development is
expected to be minimal to moderate. Significant scour, erosion and sediment transport was not
apparent near the planned development. The Union River, stream and wetland on the property
have drainage issues,and is distant from the proposed project. There are no apparent water bodies
or wetlands located upslope from the planned development that would significantly influence the
Project.It appears that development will be at least 25 feet above the ordinary high water mark of
the Union River.
Envirotech Engineering,PLLC Shearer Drainage Report
PO Box 984 page 2 401 NE Timberline Drive
Belfair,Washington 98528 Parcel 12320-34-00030
360-275-9374 December 21,2017
3.0 INFILTRATION RATES/SOILS REPORTS
Information on infiltration rates and soil conditions pertaining to the Project was accomplished by
Envirotech. For complete details, see the Geological Assessment prepared for the Shearer
Logging and Single Family Residential Property,dated December 21,2017. Selected information
pertaining to the drainage aspect of the project is provided below.
3.1 Subsurface Conditions
The following subsurface conditions are estimated descriptions of the Project subgrade utilizing
information from the depth of penetration at all testing, sampling, observed and investigated
locations. Soils for this project were described utilizing the Unified Soil Classification System
(USCS). Using the USCS in conjunction with estimated relative densities and other anticipated
engineering properties of the soil, susceptibility for potential landslides, erosion and seismic
hazards may be assessed.
The Project is primarily composed of undisturbed, native soils,without indications of substantial
fill. However, some fill could be present. Competent bearing soils were encountered at 18 inches
below the existing ground surface in locations where the ground was probed. For engineering
purposes,these native soils consist of distinguishable layers,as presented below.
Soils within the upper 6 feet of natural ground were observed to be primarily moist, brown silty
sand with gravel(SM). Soils below the upper SM layer could be a conglomerate of sand, silt and
clay.This is based on nearby well reports, site geology,and/or knowledge of the general area.
According to the USDA Textural Classification System, the site soils are primarily classified as
sandy loam. Some pockets of gravelly soils was also observed. Soil structure may be described as
granular.
According to the "Soil Survey of Mason County," by the United States Department of
Agriculture, Soil Conservation Service (SCS), the site soils are described as Everett gravelly
loamy sand, with 5% - 15% slopes, Belfast silt loam, with 0 —3% slopes, and Indianola loamy
sand,with 5%to 15%slopes.
3.1.1 Groundwater
From the water well report(s)and knowledge of the general area,permanent groundwater
is at least 50 feet directly below the property at the building pad location. Surface seepage
or perched groundwater at shallow depths was not observed on-site, nor indicated on the
well reports.
3.2 Soils Testing and Properties
The soil samples obtained at the Project site during the field investigation were preserved and
transported for possible laboratory testing. Visual classification of soils was performed in the
field at all observed soil profiles. Visual classifications were performed in accordance with the
American Standards for Testing and Materials(ASTM D2488).
Envirotech Engineering,PLLC Shearer Drainage Report
PO Box 984 page 3 401 NE Timberline Drive
Belfair,Washington 98528 Parcel 12320-34-00030
360-275-9374 December 21,2017
The general results from the visual classification are presented above in the Subsurface
Conditions Section. Specifically, soils within the upper 4 feet in one testing location consisted of
approximately 12% gravel, 55% sand-sized soils, and 33% fines with no plasticity indicating a
very low content of clay within the fine fraction. Minor variations observed during the visual
classification of particle size content(i.e. gravel, sand, fines), or isolated pockets within the soil
stratification were insignificant in relation to the overall engineering properties of the soil.
Based on the fines content, erodibility of the site soils is considered to be moderate. However,
soils on disturbed slopes are more apt to erode than disturbed soils on flat ground. Based on the
fines content and fraction of clay within the fines content, settleability of the site soils is expected
to be moderate to fast. Permeability is expected to be high for this site due significance of
moderate density,poorly graded granular soils.
3.2.1 Infiltration Rates
According to the 2005 Stormwater Management Manual for Western Washington
prepared by the Washington State Department of Ecology Water Quality Program,
infiltration rates are determined per the USDA Textural Classification of the soils,and an
appropriate factor of safety. Based on the soils consisting predominantly of sandy loam,
and utilizing a factor of safety of 2, site infiltration for stormwater facilities should be
0.33 inches/hour.
3.2.2 Cation Exchange Rate
Water quality for this project is achieved by the soil subgrade beneath the sub-base water
storage area. The Cation-Exchange Capacity(CEC)of the soils, based on soil texture and
testing as provided above,the CEC ranges from a minimum of 15 to 40 meq/100g. Based
on the abundance of organic matter in the top soil,the CEC values may be much higher.
Envirotech Engineering,PLLC Shearer Drainage Report
PO Box 984 page 4 401 NE Timberline Drive
Belfair,Washington 98528 Parcel 12320-34-00030
360-275-9374 December 21,2017
4.0 HYDROLOGIC/HYDRAULIC INFORMATION
4.1 Hydrologic Summary
The Santa Barbara Urban Hydrograph (SBUH) method was utilized for estimating peak design
flows. The SBUH method is based on a runoff curve number approach, and uses Soil
Conservation Service (SCS) equations for computing soil absorption and precipitation excess.
This analysis is based on a Type 1 A rainfall distribution and a 24 hour storm duration.
The following design parameters were used for stormwater drainage design:
• Design storm for water quality,6mo-24hr(2.6 inches);
• Design storm for erosion control,2yr-24hr(3.6 inches);
• Design storm for stability, 100yr-24hr(7.0 inches);
• Hydraulic soil group `A'
• Curve Number of 98 for impervious areas; and,
• Curve Number of 36 for pre-existing conditions.
4.2 Best Management Practices
Best Management Practices(BMPs)for this project includes vegetated filter strips, storage basin,
infiltration pits, and gravel/ paved surfaced driveways/ parking areas. The proposed
developmental areas of the property are relatively flat. Stormwater originating from roofs will be
tight-lined to the infiltration gallery. Runoff from the primary parking areas will be sheet flowed
or channeled to a sheet flow location of a vegetated filter strip before full dispersion. Besides the
vegetated filter strip, permanent vegetation is required in all denuded areas. Storage is also
provided in order to compensate for the previous logging. Natural drainage patterns are to be
maintained to the maximum extents practicable.
4.3 Drainage Tributary to the Project
The upslope watershed is relatively small, and has low to slightly sloping grades. Stormwater
entering the site where the project will occur appears to be negligible.
4.4 Drainage System Beyond the Project
Most of the natural drainage from the site appears to be infiltrated on-site. Larger storms will
sheet flow and drain to the Union River. Some of this drainage will enter the stream and wetland
on the property prior to entering the Union River. Downstream drainage appears to follow the
river in a southerly direction for a distance of over 2 miles to the Hood Canal. This project is
within the Hood Canal watershed.
Off-site analysis and/or mitigation is not deemed necessary for this Project. This is based on the
scale of the proposed Project,and the expected low impact to downstream properties. This project
has been designed to retain all stormwater generated by new development during a 100-yr 24-hr
storm event.
Envirotech Engineering,PLLC Shearer Drainage Report
PO Box 984 page 5 401 NE Timberline Drive
Belfair,Washington 98528 Parcel 12320-34-00030
360-275-9374 December 21,2017
4.5 Critical Areas—Wells—Septics-Aquifers
Critical areas on this property include moderately hazard slopes, wetland, stream and the Union
river.A critical aquifer is not known to exist beneath the property.
This project is not anticipated to disturb any critical area, and special requirements are limited to
environmental buffers from the surface water and wetland.
Setback distances for stormwater retention/ detention facilities, as identified in the 2005
Stormwater Management Manual for Western Washington,were adhered to.
4.6 Flood Analysis
This project is situated near flood zones per FEMA flood mapping, and the property contains a
river that could influence the development. However, it is our opinion that the area of planned
development is above the base flood elevation. This is based on observing the Union River during
previous 100 year storms, and development is about 25 feet above the ordinary high water
elevation.
Envirotech Engineering,PLLC Shearer Drainage Report
PO Box 984 page 6 401 NE Timberline Drive
Belfair,Washington 98528 Parcel 12320-34-00030
360-275-9374 December 21,2017
5.0 FACILTY SIZING AND DOWNSTREAM ANALYSIS
Proposed facilities for this project include an infiltration basin, infiltration trench (pit), vegetated
filter strip and full dispersion. The following subsections provide design information for these
drainage features.
5.1 Infiltration Basin
The retention basin is designed to provide some compensatory storage for the excess of runoff
due to logging.
Other mitigation due to logging includes over 100 feet of flow path within full dispersion, and
mitigating over 13,000 sf of impervious which replaces some of the logged areas.
A trapezoidal storage basin was designed with the following parameters:
• 3:1 side slopes
• 150 feet bottom width
• 150 feet average length
• 0.5 feet in depth
5.2 Vegetated Filter Strip
The filter strip area located downslope from the driveway is sufficiently sized for treating
stormwater.
The vegetated filter strip naturally consists of the following parameters:
• Drainage area is less than 5 acres;
• Slope gradients of less than 10%;and,
• Filter strip length in excess of 5 feet.
Time of concentration was determined utilizing the equation T = Qn/(1.486 * y^1.667 * s^0.5),
where:
T=time of concentration,min.
Q=peak flow from the 6mo-24hr storm,cfs
n=Manning's factor
y=flow depth,ft
s=slope of filter strip,ft/ft
From the aforementioned hydrograph method, the peak flow was calculated during the 6 mo—24
hr design storm. Values of 0.5 and 0.1 were selected for the Manning's coefficient and hydraulic
radius, respectively. For filter strips, the flow depth is approximately equal to the hydraulic
radius. From the equation provided above,the time of concentration is approximately 15 minutes.
Velocity of stormwater on the filter strip, utilizing the standard Q=VA equation, is estimated to
be V=0.006 ft/sec.
Envirotech Engineering,PLLC Shearer Drainage Report
PO Box 984 page 7 401 NE Timberline Drive
Belfair,Washington 98528 Parcel 12320-34-00030
360-275-9374 December 21,2017
5.3 Roof Downspout Infiltration
Storm water runoff from the roof of the planned building will be directed to its own separate
infiltration facility.
Based on the governing storm water manual, the runoff from each 1000 sf of roof area shall be
directed to a standard 2 feet wide trench at 75 feet in length. The resulting trench infiltrative area
for the soils classification on-site is 930 sf, which excludes trench sides for conservative
purposes.
Envirotech Engineering,PLLC Shearer Drainage Report
PO Box 984 page 8 401 NE Timberline Drive
Belfair,Washington 98528 Parcel 12320-34-00030
360-275-9374 December 21,2017
6.0 CONSTRUCTION SEQUENCE AND PROCEDURE
The following includes the recommended construction sequence and procedure for project
development:
1. Delineate clearing and easement limits.
2. Construct all required temporary erosion control features.
p rY
3. Clear vegetation required for site development.
4. Perform initial earthwork and rough grading for constructing the roadway, driveways,
building pads, stormwater management facilities, etc. If necessary, exposed soils in stock
piles must be protected with plastic covering or County approved method.
5. Complete final grading of the subgrade, and materials placement per the plans and
specifications. This includes dredging sediments from temporary sediment facilities, if
necessary.
6. Maintain all temporary erosion and sediment control facilities, as needed, in order to
provide the required protection of downstream water quality. Additional temporary
erosion control shall be rendered throughout the duration of the project, if necessary.
7. Provide permanent erosion control in order to stabilize the project.
8. Remove temporary erosion sedimentation control facilities after construction is complete,
and the site is sufficiently stabilized.
Envirotech Engineering,PLLC Shearer Drainage Report
PO Box 984 page 9 401 NE Timberline Drive
Belfair,Washington 98528 Parcel 12320-34-00030
360-275-9374 December 21,2017
7.0 PERMANENT EROSION CONTROL AND SITE RESTORATION
Site restoration and permanent erosion control includes surfaced driveway, vegetation, topsoil,
and other standard protocol, if necessary. Specific details regarding permanent erosion are
illustrated on the drawing sheets.
All cut and fill slopes shall be stabilized according to the design plans. This includes temporary
stabilization when necessary, and permanent erosion control.
7.1 Surfaced Driveway
The gravel or asphalt surfaced driveway will be comprised of a 12 feet wide, 4-inch compacted
depth of aggregate overlying prepared subgrade or compacted fill, or equivalent pavement
section. The driveway will be sloped 2% in order to direct most of the stormwater runoff into the
adjacent filter strip.
7.2 Topsoil
Topsoiling should be used for this project for the basic vegetated filter strip. Earth cuts and
denuded areas may require topsoil in order to establish vegetation. The following specifications
for topsoiling are provided:
1.Topsoil should be used for this project due to highly dense exposed soils.
2. Topsoil should be placed on slopes not exceeding 2:1.
3. Stripping and stockpiling on-site soils shall only be permitted if topsoil is friable and loamy
(loam, sandy loam, silt loam, sandy clay loam,clay loam).
4. Stripping shall be confined to the immediate construction areas. A four to six inch stripping
depth is common, but depth may vary depending on the particular soil. All surface runoff control
structures shall be in place before stripping.
7.3 Permanent Seeding
The regenerative plan for this project includes permanent erosion control seeding in the disturbed
areas of the Project. Seeding specifications are provided in the construction plans, and
summarized below:
1. Before seeding, install needed surface runoff control measures such as gradient terraces,
interceptor dikes, swales, level spreaders and sediment basins.
2. The seed bed shall be firm with fairly fine surface,following surface roughening. Perform all
operations across or perpendicular to the slope.
3. Seeding mixture shall be as shown below,and shall be applied at the rate of 120 pounds per
acre.
Envirotech Engineering,PLLC Shearer Drainage Report
PO Box 984 page 10 401 NE Timberline Drive
Belfair,Washington 98528 Parcel 12320-34-00030
360-275-9374 December 21,2017
4. Seed beds planted between May 15 and August 15 will require irrigation and other
maintenance as necessary to foster and protect the root structure.
5. Seed beds planted between November 1 and April 30,armoring of the seed bed will be
necessary,(e.g.,geotextiles,jute mat, clear plastic covering).
6.Fertilizers are to be used according to suppliers'recommendations.Amounts should be
minimized, especially adjacent to water bodies and wetlands.
Use the following recommended seed mixture for erosion control,or a county approved alternate
seed mixture.
PROPORTIONS PURITY GERMINATION
NAME BY WEIGHT(%) N N
KENTUCKY BLUEGRASS (POA PRATENSIS) 15 85 80
PERENNIAL RYE(LOLIUM PERENNE) 30 95 90
CHEWING FESCUE 15 95 90
(FESTUCA RUBRA COMMUTATA)
(JAMESTOWN,BANNER, SHADOW, KOKET)
TALL FESCUE (FESTUCA ARUNDINCEA) 40 95 90
Envirotech Engineering,PLLC Shearer Drainage Report
PO Box 984 page 11 401 NE Timberline Drive
Belfair,Washington 98528 Parcel 12320-34-00030
360-275-9374 December 21,2017
8.0 INSPECTION AND MAINTENANCE
Erosion and sediment control inspection and maintenance schedules are provided in the
Construction Stormwater Pollution Prevention Plan for this project. This section provides
information pertaining to permanent stormwater management facilities.
An operation and maintenance schedule for all permanent stormwater facilities and BMP's are
provided under a separate cover titled "Operation and Maintenance Manual for Shearer Single
Family Residence." An operation and maintenance Declaration of Covenant will be required to
cover all privately owned and maintained stormwater facilities. Performance bonding, or other
appropriate instrument, shall be required for this project to ensure compliance with the standards
presented in this report.
Inspection, maintenance, and financial liability of all stormwater management facilities shall be
the responsibility of the current property owner. Currently, the property owner(s)is the following:
Tom Shearer
PO Box 1959
Belfair, Washington 98528
Envirotech Engineering,PLLC Shearer Drainage Report
PO Box 984 page 12 401 NE Timberline Drive
Belfair,Washington 98528 Parcel 12320-34-00030
360-275-9374 December 21,2017
9.0 CONTROL OF POLLUTANTS OTHER THAN SEDIMENTS
Upon completion of this project,the development is expected to render no more than 10 trips per
day of traffic. Potential source of pollutants may occur from spills, leaks, excessive usage,
ordinary usage,or vandalism of several pollutants including the following:
• Fuel
• Oil
• Solvent
• Degreaser
• Dust
• Pesticide
• Herbacide
• Fertilizer
• Other Chemicals
The aforementioned pollutants are not expected to be currently on-site. The potential sources may
be released into the stormwater due to development of the facilities, and/or future use of the
facilities.
Control of pollutants other than sediments include the following:
• All pollutants other than sediments shall be handled and disposed of in a manner
that does not cause contamination of stormwater.
• Cover, containment and protection from vandalism shall be provided for all
chemicals, liquid products, petroleum products, and non-inert wastes present on the
project site.
• Maintenance and repair of heavy equipment and vehicles involving oil changes,
hydraulic system drain down, solvent and de-greasing cleaning operations, fuel tank
drain down and removal, and other activities which may result in discharge or
spillage of pollutants to the ground or into stormwater runoff must be conducted
using spill prevention measures, such as drip pans. Contaminated surfaces shall be
cleaned immediately following any discharge or spill incident. Emergency repairs
may be performed on-site using temporary plastic placed beneath and, if raining,over
the vehicle.
• Wheel wash or tire bath wastewater shall be discharged to a separate on-site
treatment system or to the sanitary sewer, if available.
• Application of agricultural chemicals including fertilizers and pesticides shall be
conducted in a manner, and at application rates that will not result in loss of chemical
to stormwater runoff. Manufacturers' recommendations for application rates and
procedures shall be followed.
See the Best Management Practices for this development that should be adhered to after
construction is complete.
Envirotech Engineering,PLLC Shearer Drainage Report
PO Box 984 page 13 401 NE Timberline Drive
Belfair,Washington 98528 Parcel 12320-34-00030
360-275-9374 December 21,2017
10.0 PROJECT ENGINEER'S CERTIFICATION
I hereby state that this drainage plan for the Tom Shearer Logging and Single Family Residence
has been prepared by me or under my supervision and meets the standard of care and expertise
which is usual and customary in this community for professional engineers.
Please contact Michael Staten at 360-275-9374 if you have any questions, comments, or require
additional information.
Sincerely,
Envirotech Engineering
CLYb&S
WAS
110 43045
,P CISTf
�SS�CNALti�G`
Michael Staten,P.E.
Project Director
Envirotech Engineering,PLLC Shearer Drainage Report
PO Box 984 page 14 401 NE Timberline Drive
Belfair,Washington 98528 Parcel 12320-34-00030
360-275-9374 December 21,2017
APPENDIX A
SITE MAP
SCALE, 1 INCH = 200 FEET
0 100 200
,n
P1 r
���OR AY
\ � WELL
35 4y
a F Y SINGLE \
SEPM
FULL Si BESFFleSOI� �I'"! \P
J LTRA PET
FOR RUNOFF,
\ F'C
L — DRAG To6 PVC.S-04r.-ml \ 1
TCH
FULL DISPERSION RUNOFFDIVERSION ALL /
165 RrAM a
STREAM BUFFER
125'WETLAND
APM CLEARM BUFFER
Q, LOG
PAST
ti
4W CASEMENT
CATEGORY II
WETLAND
J
PROJECT/ OWNER/ LOCATION
SHEARER DRAINAGE PLAN
TOM SHEARER
401 NE TIMBERLINE DRIVE
PARCEL 12320-34-00030
MASON COUNTY WASHINGTON
ENGINEER,
ENVIROTECH ENGINEERING
PO BOX 984
BELFAIR, WASHINGTON 98528
360-275-9374
SITE MAP
APPENDIX B
HYDROLOGIC INFORMATION
Western Washington Isopluvial 100-year, 24 hour
124 123 122 121
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PRECIPITATION IN TENTHS OF A'! INCH 85 �
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Shaded area is applicable for design of infiltration BMPs
Figure 3.27 USDA Textural Triangle
Source: U.S. Department of Agriculture
3-74 Volume Ill—Hydrologic Analysis and Flow Control BMPs February 2005
Table 2.1 Hydrologic Soil Series for Selected Soils in Washin ton State
Soil Tye Hydrologic Soil Group Soil Type Hydrologic Soil Group
Cassolary C Mashel B
Cathcart B Maytown C
Centralia B McKenna D
Chehalis B McMurray D
Chesaw A Melbourne B
Cinebar B Menzel B
Clallam C Mixed Alluvial variable
Clayton B Molson B
Coastal beaches variable Mukilteo CID
Colter C Naff B
Custer D Nargar A
Custer,Drained C National B
Dabob C Neilton A
Delphi D Newberg B
Dick A Nisqually B
Dimal D Nooksack C
Dupont D Norma C/D
Earimont C Ogarty C
Edgewick C Olete C
Eld B Olomount C
Elwell B Olympic B
Esquatzel Orcas D
Everett Oridia D
Everson Orting D
Galvin D Oso C
Getchell A Ovall C
Giles B Pastik C
Godfrey D Pheeney C
Greenwater A Phelan D
Grove C Pilchuck C
Harstine C Potchub C
Hartnit C Poulsbo C
Hoh B Prather C
Puget D Solleks C
Puyallup B Spana D
Queets B Spanaway A/B
Quilcene C Springdale B
Ragnar B Sulsavar B
Rainier C Sultan C
Raught B Sultan variant B
Reed D Sumas C
Reed,Drained or Protected C Swantown D
Renton D Tacoma D
Republic B Tamvax D
Riverwash variable Tanwax,Drained C
Rober C Tealwhit D
Salal C Tenino C
Salkum B Tisch D
Sammamish D Tokul C
San Juan A Townsend C
Scarnman D Triton D
Schneider B Tukwila D
Seattle D Tukey C
Sekiu D Urbana C
Semiahmoo D Vailton B
Shalcar D Verlot C
Shano B Wapato D
Shelton C Warden B
Si C Whidbey C
2-12 Volume 111--Hydrologic Analysis and Flow Control BMPs February 2005
Table 2.2
Runoff Curve Numbers for Selected A ricultural,Suburban,and Urban Areas
Sources:TR 55,1986,and Stotmwater Management Manual,1992.See Section 2.1.1 for explanation)
CNs f h drologic soil group
Cover ryve and h drolo is condition. A B C D
Curve Numbers for Pre-Development Conditions
Pasture,grassland,or range-continuous forage for gracing:
Fair condition(ground cover 50%to 75%and not heavily grazed). 49 69 79 84
Good condition ound cover>75%and lightly or only occasional) grazed 39 61 74 80
Woods:
Fair(Woods are grazed but not burned,and some forest litter covers the soil). 60 73 79
Good(Woods are protected from grazing,and litter and brush adequately cover the soil). 30 55 70 77
Curve Numbers for Post-Development Conditions
Open space(lawns,parks,golf courses,cemeteries,landscaping,etc.)
Fair condition(grass cover on 50%-75%of the area). 77 85 90 92
Good condition(grass cover on>75%of the area) 68 80 86 90
Impervious areas:
Open water bodies:lakes,wetlands,ponds etc. 1 0 100 100 100
Paved Rarking lots roofs'-,driveways,etc. (excluding right-of-way) 9 98 98 98
Permeable Pavement(See Appendix C to decide which condition below to use)
Landscaped area 77 85 90 92
50%landscaped area/50%impervious 87 91 94 96
100%impervious area 98 98 98 98
Paved 98 98 98 98
Gravel includin right-of-way) 76 85 89 91
Dirt(including right-of-way) 72 82 87 89
Pasture,grassland,or range-continuous forage for grazing:
Poor condition(ground cover<50%or heavily grazed with no mulch). 68 79 86 89
Fair condition(ground cover 50%to 75%and not heavily grazed). 49 69 79 84
Good condition(ground cover>75%and lightly or only occasional) razed) 39 61 74 80
Woods:
Poor(Forest litter,small trees,and brush are destroyed by heavy grazing or regular burning). 66 77 83
Fair(Woods are grazed but not burned,and some forest litter covers the soil). 36 60 73 79
Good(Woods are protected from grazing,and litter and brush adequately cover the soil). 30 55 70 77
Single family residential': Should only be used for Average Percent
Dwelling Unit/Gross Acre subdivisions>50 acres impervious area3,4
1.0 DUiGA 15 Separate curve number
1.5 DU/GA 20 shall be selected for
2.0 DU/GA 25 pervious&impervious
2.5 DU/GA 30 portions of the site or
3.0 DUiGA 34 basin
3.5 DU/GA 38
4.0 DU/GA 42
4.5 DUiGA 46
5.0 DUiGA 48
5.5 DU/GA 50
6.0 DU/GA 52
6.5 DU/GA 54
7.0 DU/GA 56
7.5 DU/GA 58
PUD's,condos,apartments,commercial %impervious Separate curve numbers shall
businesses,industrial areas& must be be selected for pervious and
&subdivisions<50 acres computed impervious portions of the site
For a more detailed and complete description of land use curve numbers refer to chapter two(2)of the Soil Conservation Service's Technical
Release No.55 (210-VI-TR-55,Second Ed.,June 19861.
Composite CN's may be computed for other combinations of open space cover type,
'-Where roof runoff and driveway runoff are infiltrated or dispersed according to the requirements in Chapter 3,the average percent impervious
area may be adjusted in accordance with the procedure described under"Flow Credit for Roof Downspout Infiltration"(Section 3.1.1),and"Flow
Credit for Roof Downspout Dispersion"(Section 3.1.2).
3Assumes roof and driveway runoff is directed into streetistorm system.
4Ail the remaining pervious area(lawn)are considered to be in good condition for these curve numbers.
February 2005 Volume III—Hydrologic Analysis and Flow Control BMPs 2-15
for homogeneous soils. These rates not consider the effects of site
variability and long-term clogging due to siltation and biomass buildup in
the infiltration facility.
Table 3.7--Recommended Infiltration Rates
based on USDA Soil Textural Classification.
Estimated Long-
*Short-Term Term(Design)
Infiltration Correction Infiltration Rate
Rate(in./hr) Factor,CF (in./hr)
Clean sandy gravels and 20 2 10"
gravelly sands(i.e.,90%of
the total soil sample is
retained in the#10 sieve)
Sand 8 4 2***
Loamy Sand 2 4 0.5
�Q Sandy Loam 1 4 0.25
Loam 0.5 4 0.13
*From WEF/ASCE, 1998.
**Not recommended for treatment
***Refer to SSC-4 and SSC-6 for treatment acceptability criteria
Based on experience with long-term full-scale infiltration pond
performance, Ecology's Technical Advisory Committee(TAC)
recommends that the short-term infiltration rates be reduced as shown in
Table 3.7,dividing by a correction factor of 2 to 4, depending on the soil
textural classification. The correction factors provided in Table 3.7
represent an average degree of long-term facility maintenance,TSS
reduction through pretreatment,and site variability in the subsurface
conditions. These conditions might include deposits of ancient landslide
debris, buried stream channels, lateral grain size variability, and other
factors that affect homogeneity).
These correction factors could be reduced, subject to the approval of the
local jurisdiction,under the following conditions:
• For sites with little soil variability,
• Where there will be a high degree of long-term facility maintenance,
• Where specific, reliable pretreatment is employed to reduce TSS
entering the infiltration facility
In no case shall a correction factor less than 2.0 be used.
3-76 Volume 111—Hydrologic Analysis and Flow Control BMPs February 2005
APPENDIX C
BMP'S
BMPs for Description of Pollutant Sources: Landscaping can include grading, soil
Landscaping transfer,vegetation removal,pesticide and fertilizer applications, and
and Lawn/ watering. Stormwater contaminants include toxic organic compounds,
Vegetation heavy metals, oils,total suspended solids,coliform bacteria, fertilizers, and
Management pesticides.
Lawn and vegetation management can include control of objectionable
weeds, insects,mold,bacteria and other pests with chemical pesticides and
is conducted commercially at commercial, industrial, and residential sites.
Examples include weed control on golf course lawns, access roads,and
utility corridors and during landscaping; sap stain and insect control on
lumber and logs;rooftop moss removal;killing nuisance rodents;
fungicide application to patio decks, and residential lawn/plant care.
Toxic pesticides such as pentachlorophenol,carbamates, and
organometallics can be released to the environment by leaching and
dripping from treated parts, container leaks,product misuse, and outside
storage of pesticide contaminated materials and equipment. Poor
management of the vegetation and poor application of pesticides or
fertilizers can cause appreciable stormwater contamination.
Pollutant Control Approach: Control of fertilizer and pesticide
applications, soil erosion, and site debris to prevent contamination of
stormwater.
Develop and implement an Integrated Pest Management Plan(IPM) and
use pesticides only as a last resort. If pesticides/herbicides are used they
must be carefully applied in accordance with label instructions on U.S.
Environmental Protection Agency(EPA)registered materials. Maintain
appropriate vegetation,with proper fertilizer application where
practicable,to control erosion and the discharge of stormwater pollutants.
Where practicable grow plant species appropriate for the site, or adjust the
soil properties of the subject site to grow desired plant species.
Applicable Operational BMPs for Landscaping:
• Install engineered soil/landscape systems to improve the infiltration
and regulation of stormwater in landscaped areas.
• Do not dispose of collected vegetation into waterways or storm
drainage systems.
Recommended Additional Operational BMPs for Landscaping:
• Conduct mulch-mowing whenever practicable
• Dispose of grass clippings, leaves,sticks, or other collected vegetation,
by composting,if feasible.
February 2005 Volume IV- Source Control BMPs 2-23
• Use mulch or other erosion control measures when soils are exposed
for more than one week during the dry season or two days during the
rainy season.
• If oil or other chemicals are handled, store and maintain appropriate oil
and chemical spill cleanup materials in readily accessible locations.
Ensure that employees are familiar with proper spill cleanup
procedures.
• Till fertilizers into the soil rather than dumping or broadcasting onto
the surface. Determine the proper fertilizer application for the types of
soil and vegetation encountered.
• Till a topsoil mix or composted organic material into the soil to create
a well-mixed transition layer that encourages deeper root systems and
drought-resistant plants.
• Use manual and/or mechanical methods of vegetation removal rather
than applying herbicides,where practical.
Applicable Operational BMPs for the Use of Pesticides:
• Develop and implement an IPM(See section on IPM at end of BMW)
and use pesticides only as a last resort.
• Implement a pesticide-use plan and include at a minimum: a list of
selected pesticides and their specific uses;brands,formulations,
application methods and quantities to be used; equipment use and
maintenance procedures; safety, storage,and disposal methods;and
monitoring,record keeping,and public notice procedures. All
procedures shall conform to the requirements of Chapter 17.21 RCW
and Chapter 16-228 WAC(Appendix IV-D R.7).
• Choose the least toxic pesticide available that is capable of reducing
the infestation to acceptable levels. The pesticide should readily
degrade in the environment and/or have properties that strongly bind it
to the soil. Any pest control used should be conducted at the life stage
when the pest is most vulnerable. For example, if it is necessary to use
a Bacillus thuringiens is application to control tent caterpillars, it must
be applied before the caterpillars cocoon or it will be ineffective. Any
method used should be site-specific and not used wholesale over a
wide area.
• Apply the pesticide according to label directions. Under no conditions
shall pesticides be applied in quantities that exceed manufacturer's
instructions.
• • Mix the pesticides and clean the application equipment in an area
where accidental spills will not enter surface or ground waters, and
will not contaminate the soil.
2-24 Volume IV- Source Control BMPs February 2005
• Store pesticides in enclosed areas or in covered impervious
containment. Ensure that pesticide contaminated stormwater or
spills/leaks of pesticides are not discharged to storm drains. Do not
hose down the paved areas to a storm drain or conveyance ditch. Store
and maintain appropriate spill cleanup materials in a location known to
all near the storage area.
• Clean up any spilled pesticides and ensure that the pesticide
contaminated waste materials are kept in designated covered and
contained areas.
• The pesticide application equipment must be capable of immediate
shutoff in the event of an emergency.
• Do not spray pesticides within 100 feet of open waters including
wetlands,ponds, and streams,sloughs and any drainage ditch or
channel that leads to open water except when approved by Ecology or
the local jurisdiction. All sensitive areas including wells, creeks and
wetlands must be flagged prior to spraying.
• As required by the local government or by Ecology,complete public
posting of the area to be sprayed prior to the application.
• Spray applications should only be conducted during weather
conditions as specified in the label direction and applicable local and
state regulations. Do not apply during rain or immediately before
expected rain.
Recommended Additional Operational BMPs for the use of pesticides:
• Consider alternatives to the use of pesticides such as covering or
harvesting weeds, substitute vegetative growth, and manual weed
control/moss removal.
• Consider the use of soil amendments, such as compost,that are known
to control some common diseases in plants, such as Pythium root rot,
ashy stem blight, and parasitic nematodes. The following are three
possible mechanisms for disease control by compost addition(USEPA
Publication 530-F-9-044):
1. Successful competition for nutrients by antibiotic production;
2. Successful predation against pathogens by beneficial
microorganism; and
3. Activation of disease-resistant genes in plants by composts.
Installing an amended soil/landscape system can preserve both the plant
• system and the soil system more effectively. This type of approach
provides a soil/landscape system with adequate depth,permeability, and
organic matter to sustain itself and continue working as an effective
stormwater infiltration system and a sustainable nutrient cycle.
February 2005 Volume IV-Source Control BMPs 2-25
• Once a pesticide is applied, its effectiveness should be evaluated for
possible improvement. Records should be kept showing the
applicability and inapplicability of the pesticides considered.
• An annual evaluation procedure should be developed including a
review of the effectiveness of pesticide applications,impact on buffers
and sensitive areas(including potable wells), public concerns, and
recent toxicological information on pesticides used/proposed for use.
If individual or public potable wells are located in the proximity of
commercial pesticide applications contact the regional Ecology
hydrogeologist to determine if additional pesticide application control
measures are necessary.
• Rinseate from equipment cleaning and/or triple-rinsing of pesticide
containers should be used as product or recycled into product.
• The application equipment used should be capable of immediate
shutoff in the event of an emergency.
For more information, contact the WSUExtension Home-Assist Program,
(253) 445-4556, or Bio-Integral Resource Center(BIRC), P.O. Box 7414,
Berkeley, CA.94707, or the Washington Department of Ecology to obtain
"Hazardous Waste Pesticides"(Publication #89-41); and/or EPA to
obtain a publication entitled "Suspended, Canceled and Restricted
Pesticides"which lists all restricted pesticides and the specific uses that
are allowed. Valuable information from these sources may also be
available on the internet.
Applicable Operational BMPs for Vegetation Management:
• Use at least an eight-inch"topsoil" layer with at least 8 percent organic
matter to provide a sufficient vegetation-growing medium. Amending
existing landscapes and turf systems by increasing the percent organic
matter and depth of topsoil can substantially improve the permeability
of the soil,the disease and drought resistance of the vegetation,and
reduce fertilizer demand. This reduces the demand for fertilizers,
herbicides, and pesticides. Organic matter is the least water-soluble
form of nutrients that can be added to the soil. Composted organic
matter generally releases only between 2 and 10 percent of its total
nitrogen annually, and this release corresponds closely to the plant
growth cycle. If natural plant debris and mulch are returned to the
soil,this system can continue recycling nutrients indefinitely.
• Select the appropriate turfgrass mixture for your climate and soil type.
Certain tall fescues and rye grasses resist insect attack because the
symbiotic endophytic fungi found naturally in their tissues repel or kill
common leaf and stem-eating lawn insects. They do not,however,
repel root-feeding lawn pests such as Crane Fly larvae, and are toxic to
ruminants such as cattle and sheep. The fungus causes no known
2-26 Volume IV- Source Control BMPs February 2005
adverse effects to the host pla
nt t or to humans. Endophytic grasses are
commercially available and can be used in areas such as parks or golf
courses where grazing does not occur. The local Cooperative
Extension office can offer advice on which types of grass are best
suited to the area and soil type.
• Use the following seeding and planting BMPs,or equivalent BMPs to
obtain information on grass mixtures, temporary and permanent
seeding procedures,maintenance of a recently planted area, and
fertilizer application rates: Temporary Seeding, Mulching and Matting,
Clear Plastic Covering,Permanent Seeding and Planting, and Sodding
as described in Volu
me II).
• Selection of desired plant species can be made by adjusting the soil
properties of the subject site. For example, a constructed wetland can
be designed to resist the invasion of reed canary grass by layering
specific strata of organic matters (e.g., compost forest product
residuals) and creating a mildly acidic pH and carbon-rich soil
medium. Consult a soil restoration specialist for site-specific
conditions.
• Aerate lawns regularly in areas of heavy use where the soil tends to
become compacted. Aeration should be conducted while the grasses
in the lawn are growing most vigorously. Remove layers of thatch
greater than%-inch deep.
• Mowing is a stress-creating activity for turfgrass. When grass is
mowed too short its productivity is decreased and there is less growth
of roots and rhizomes. The turf becomes less tolerant of
environmental stresses,more disease prone and more reliant on outside
means such as pesticides, fertilizers and irrigation to remain healthy.
Set the mowing height at the highest acceptable level and mow at
times and intervals designed to minimize stress on the turf. Generally
mowing only 1/3 of the grass blade height will prevent stressing the
turf.
Irrigation:
• The depth from which a plant normally extracts water depends on the
rooting depth of the plant. Appropriately irrigated lawn grasses
normally root in the top 6 to 12 inches of soil; lawns irrigated on a
daily basis often root only in the top 1 inch of soil. Improper irrigation
can encourage pest problems, leach nutrients, and make a lawn
completely dependent on artificial watering. The amount of water
applied depends on the normal rooting depth of the turfgrass species
used,the available water holding capacity of the soil, and the
efficiency of the irrigation system. Consult with the local water utility,
Conservation District, or Cooperative Extension office to help
determine optimum irrigation practices.
February 2005 Volume IV-Source Control BMPs 2-27
i
Fertilizer Management.
Turfgrass is most responsive to nitrogen fertilization, followed by
potassium and phosphorus. Fertilization needs vary by site depending
on plant, soil and climatic conditions. Evaluation of soil nutrient
levels through regular testing ensures the best possible efficiency and
economy of fertilization. For details on soils testing, contact the local
Conservation District or Cooperative Extension Service.
• Fertilizers should be applied in amounts appropriate for the target
vegetation and at the time of year that minimizes losses to surface and
ground waters. Do not fertilize during a drought or when the soil is
dry. Alternatively,do not apply fertilizers within three days prior to
predicted rainfall. The longer the period between fertilizer application
and either rainfall or irrigation,the less fertilizer runoff occurs.
• Use slow release fertilizers such as methylene urea, IDBU, or resin
coated fertilizers when appropriate,generally in the spring. Use of
slow release fertilizers is especially important in areas with sandy or
gravelly soils.
• Time the fertilizer application to periods of maximum plant uptake.
Generally fall and spring applications are recommended, although
WSU turf specialists recommend four fertilizer applications per year.
• Properly trained persons should apply all fertilizers. At commercial
and industrial facilities fertilizers should not be applied to grass
swales, filter strips, or buffer areas that drain to sensitive water bodies
unless approved by the local jurisdiction.
Integrated Pest Management
An IPM program might consist of the following steps:
Step 1: Correctly identify problem pests and understand their life cycle
Step 2: Establish tolerance thresholds for pests.
Step 3:Monitor to detect and prevent pest problems.
Step 4: Modify the maintenance program to promote healthy plants and
discourage pests.
Step 5: Use cultural,physical,mechanical,or biological controls first if
pests exceed the tolerance thresholds.
Step 6: Evaluate and record the effectiveness of the control and modify
maintenance practices to support lawn or landscape recovery and prevent
recurrence.
For an elaboration of these steps refer to Appendix IV-F.
2-28 Volume IV- Source Control BMPs February 2005