HomeMy WebLinkAboutLog015
Section 9
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Beckett Point Sanitary Improvements
Stormwater Site Plan
Prepared for
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Jefferson County Public Utility District No. 1
230 Chimacum Road
Post Office Box 929
Port Hadlock, Washington 98339
Prepared by
Parametrix
5700 Kitsap Way, Suite 202
Bremerton, W A 98312-2234
360-377-0014
www.parametrix.com
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CITATION
Parametrix. 2005. Beckett Point Sanitary
Improvements
Storm water Site Plan. Prepared by Parametrix,
Bremerton, Washington. July 2005.
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Beckett Point Sanitary Improvements
Stormwater Site Plan
Jefferson County Public Utility District No. 1
. CERTIFICATION
By signing the Stormwater Site Plan, I as the applicant/owner/authorized representative attest
that the information provided herein is true and correct to tire best of my knowledge. I also
certify that this application is being made with the full knowledge and consent of all owners
of the affected property.
~~ //!:d-
Damon McAlister, P.E.
Project Manager
Date: S-/5/1
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Beckett Point Sanitary Improvements
Stormwater Site Plan
Jefferson County Public Utility District No. I
. TABLE OF CONTENTS
1. PROJECT .OVERVIEW ....................................................................................1-1
1.1 LOCATION ....... ........ ........................ .................. ......................... .......... ...... ..........1-1
1.2 EXISTrnG SITE CONDITIONS ...........................................................................1-1
1.3 DESCRIPTION OF CONSTRUCTION ACTNITIES .........................................1..2
1.3.1 Summary Conditions of the Existing Sewer System.................................... 1-2
1.3.2 Summary of Construction Activities ............................................................1-2
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2. CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN ..........2-1
2.1 SWPPP ELEMENTS.... ............. .............................. ............................................... 2-1
2.1.1 Clearing Limits ........ ........................................................... ..........................2-1
2.1.2 Construction Access .....................................................................................2-1
2.1.3 Flow ControL...... ................................................... ..................... ....... ...........2-2
2.1.4 Sediment Control..................................... .... ................................................. 2-2
2.1.5 Soil Stabilization........................................................... ................................2-2
2.1.6 Slope Protection. ........ ....... ....... ......... ................................ ....... ..................... 2-3
2.1.7 Drain Inlets Protection.................................................... .............................. 2-3
2.1.8 Channel and Outlet Stabilization..................................................................2-4
2.1.9 Pollutant Control...... .................................. .... ..................... ................. .........2-4
2.1.1 0 De-Watering Control............ ........................................................................ 2-4
2.1.11 BMP Maintenance and Inspection................................................................ 2-4
2.2 CONSTRUCTION SCHEDULE ........................................................................... 2-4
3. PERMANENT STORMWATER CONTROL PLAN ...........................................3.1
3.1 GENERAL ....... ........................ .... ........................... ............................................... 3-1
3.2 SOURCE CON'fROL OF POLLUTANTS............................................................3-1
3.3 PRESERVATION OF NATURAL DRAINAGE SYSTEMS AND
OUfF ALLS........... ....... .................. .... .... ...... ........................ ............. .....................3-1
3.4 ON-SITE STORMW ATER MANAGEMENT ......................................................-3-1
4. BMP-S ... ........ .... .................. .... ... .............. ................................... ........ ..............4-1
5. RE FE RE NeE S ....................................................................................1............ 5-1
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LIST OF FIGURES
1-1 Project Vicinity Maps ..................................;...........................................................1-3
1-2 Property Boundary...........................................................(5). ....r......;;.~..~u:..;.:...:!1-
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1-3 Project Site ~ .............................................................. ....+]'fu.....~ ........ .... ......... -
2-1 Surface Drainage ...... ......... ............. ..................... ............,.....)t .....~UG...~.'5...z0055
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Beckett Point Sanitary Improvements
Stormwater Site Plan
Jefferson County Public Utility District No. I
TABLE OF CONTENTS (CONTINUED)
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APPENDICES
A Relevant Project Plans
B Project BMPs
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Beckett Point Sanitary Improvements
Stormwater Site Plan
Jefferson County Public Utility District No, I
ACRONYMS
BMPs
Ecology
LOSS
ass
PUD No.1
SWMM
SWPPP
best management practices
Washington State Department of Ecology
large on-site septic
on-site septic
Jefferson County Public Utility District No. I
Stormwater Management Manual
Stormwater Pollution Prevention Plan
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1. PROJECT OVERVIEW
1.1 LOCATION
The Jefferson County Public Utility District No. 1 (PUD No.1) has retained Parametrix to
design a community sewage collection and large on-site septic (LOSS) system for the
shoreline community of Beckett Point. Beckett Point is located approximately six miles
southwest of Port Townsend, Washington on the east side of Discovery Bay (see Figure 1-1).
The Beckett Point property (see Figure 1-2) is owned by the Beckett Point Fisherman's Club.
The property is located on two Jefferson County parcels and includes approximately 83 acres.
Parcel Number 002231001 is located mainly in the southeast quarter of the northeast quarter
of Section 23, Township 30N, Range 2 West, W.M., Jefferson County, Washington. This
parcel consists mainly of a sand spit area where most of the sewage collection will occur.
Parcel Number 002242003 is located in the southwest quarter of the northwest quarter of
Section 24, Township 30N, Range 2 West, W.M., Jefferson County, Washington. It consists
mostly of an uplands area where the septic tanks and drainfields will be located. All land
surrounding the Beckett Point property is zoned Rural Residential. Figure 2 shows the
approximate property boundaries.
Individual lots on the property are leased. Currently the land is subdivided into approximately
165 lots. Of those lots, 102 are buildable and could potentially connect to the proposed LOSS
system. The majority of the developed lots are located on the sand spit, and several lots are
located on the hillside to the east of the sand spit.
1.2 EXISTING SITE CONDITIONS
The beach area, where the majority of the residences are located, is a large sand spit jutting
out into Discovery Bay and consists mainly of sandy, gravelly soils. A tidal lagoon lies in the
middle of the sand spit. A Wetlands Delineation and Ranking Report for the Beckett Point
Fisherman's Club was prepared by Pacific Rim Aquatic Environmental Sciences in August,
2000 (Brooks 2000). The report classified the lagoon and the area around the lagoon as a
palustrine Category IT wetland requiring a 50-foot buffer (Brooks 2000). Since the report was
prepared, the buffer for a Category n wetland has changed to 100 feet. An addendum will be
prepared for this report as part of this project.
Residents of the community have indicated that extreme high tides coupled with heavy
rainfall, mostly occurring during the winter months, can flood a portion of the area. Most of
the dwellings are built on stilts or raised foundations.
A bluff rises up from the eastern side of the beach area. Much of the bluff has slQP~ as high
as 70 percent and trees are sparse. The bluff and sand spit have been classified as a
"geologically hazardous area" by. Jefferson County. A Geologically Hazardous Area
Assessment and Recommendations report has been prepared by Myers Biodynamics, Inc. for
this project (Myers 2005). The eastern portion of the study area or uplands area is mainly
forest with slopes varying from zero to twenty percent. Please see the Myers Report for a
more complete description of.site topography. ' .
The only existing drainage facilities in the project. area are along Beckett Point Road and
Hillcrest Avenue, and consist of roadside drainage ditches, culverts and catch basins (see
Figure 1-3) . Only four catch basins have been located: one along Beckett Point Road in the
Olympic View area, one along the gravel/dirt access road in the Hill Park/Olympic View
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Beckett Point Sanitary Improvements
Stormwater Site Plan
Jefferson County Public Utility District No. I
area, and two along Beckett Point Road on the sand spit (Figure 1-3). The majority of the
rainwater runs off the road and infiltrates into the sandy/gravelly soils.
Under the direction of Parametrix, an aerial survey was conducted by DeGross Aerial
Mapping, Inc. of Kirkland, Washington in July 2004. Aerial photogrammetry was used to
develop contours in the beach area as well as the portion of the bluff area where trees are
sparse. The entire drainfield area was field surveyed by Parametrix.
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1.3 DESCRIPTION OF CONSTRUCTION ACTIVITIES
1.3.1 Summary Conditions of the Existing Sewer System
Currently, the residences of Beckett Point are served by individual on-site septic (OSS)
systems. The beach area consists of very sandy, well-draining soils. The majority of the OSS
systems are old and their condition and level of treatment are not well known and presumed
poor. The Beckett Point Fishennan's Club wishes to eliminate individual OSS systems and
establish a community sewage collection and treatment system, reducing potential pollution
to nearby surface waters. The PUD No. 1 will own, operate, and manage the two community
sewer systems.
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1.3.2 Summary of Construction Activities
This project will abandon the majority of the individual ass systems and construct a new
sewage collection and loss system. A small underground grinder pump station will be
installed at each home/cabin on the sand spit and the bluff. The grinder pump stations will
convey the sewage via shallow, small-diameter pressure pipelines to one of two central
underground pump stations located near the base of the bluff. Excavations in the sand spit
area will include trenching for the sewer service laterals from the residences to the pump
tions and from the pump stations to the force mains, trenching for the force main within
Belckett Point Road, and excavations will also be required for the underground pump stations.
~e grinder pump stations are approximately 40-inches in diameter at the base, 30-inches
from the top, and 6-feet tall. The construction activities will include surface restoration of all
ut~ty trenches and excavation.
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Two intermediate sewage pump stations will be constructed. The first pump station will be
lo~ted at a clearing on the hill along a dirt road in the Olyinpic View/Hill Park area. The
sePond pump station will be located in an old sand/gravel quany along Beckett Point Road at
one tiine Used by Beckett Point. Excavation will be required for the below-ground sewage
pUmp stations. Four large septic ~ and two dosing tanks will be located at the base of the
drainfieldS in the uplands area. Large excavations will be required for the septic tanks and
e~uent dosing tanks. Once the underground pump stations, septic tanks, and dosing tanks are.
---iMtalled, the excavations will be backfilled and surfaces restored to near pre-construction
conditions. .
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Construction activities for the drainfields will involve the clearing of approximately 5.9 acres
of forest in the uplands area, rough grading, and the installation of the drainfield piping. The
entire drainfield area will be hydroseeded oncethedrainfields are installed and tested. The
contract documents will state that the drainfield area must have an established vegetative
cover prior to contract completion.
The only new impervious surfaces for this project will be the circular tank covers for the
underground grinder pump stations, sewer inanhole covers, and septic tanks. The total surface
area of all the tank covers combined, and thus thl;} t9ta!,~Af ~e}V impervious surface, will
be less than 1,000 square feet. 'L. .... . .. .:::':"
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2. CONSTRUCTION STORM~JER'P()bbUTION PREVENTION
PLAN
This Construction Stormwater Pollution Prevention Plan (SWPPP) was completed in
accordance with Washington State Department of Ecology (Ecology) Stormwater
Management Manual (SWMM) for WestemWashington (August 2001) and Jefferson
County Department of Community Development guidelines. The purpose of this SWPPP is to
describe procedure to be used to prevent negative impacts to stormwater nmoff during
completion of construction activities.
2.1 SWPPP ELEMENTS
The Construction SWPPP consists of 12 elements per the Ecology SWMM Sections 3.1.1 and
3.2.3. These elements include best management practices (BMPs) that are critical in
preventing negative impact to stormwater from construction activities at the site. The
selection, installation, and maintenance of the correct stormwater and erosion control BMPs
will reduce the potential impact to site stormwater during construction. All BMPs will be
installed prior to start of construction activities.
The following sections describe the SWPP elements for the sewer system improvement
project at Beckett Point.
2.1.1 Clearing Limits
Minimal clearing will be required for installation of the new sewer lines and pump stations.
The majority of the sewage transport piping will be installed in the area of the existing utility
lines (water, telephone, media), which are located within or adjacent to existing gravel and
paved roadways.
The clearing limits associated with the proposed septic tank and drainfield are shown on the
project plans. The Drainfield Grading and TESC Plan and Temporary Erosion and
Sedimentation Control Details and Notes sheets of the project plans are located in Appendix
A. The limits of clearing will be marked in the field prior to the initiation of construction
activities. Orange barrier fencing and/or silt fencing (where applicable) will encompass the
entire drainfield area along the clearing limits. Vegetation within the drainfield footprint will
. be preserved, as appropriate. An approximate 50-foot buffer will be retained between the
property lines to the north and east and the drainfield clearing limits with the exception of the
construction entrance: This will both help negative impacts to any possible stormwater runoff
during construction activities and provide a greenbelt between surrounding property owners.
2.1.2 Construction Access
There will be one set access point for construction equipment and trucks used during
construction in the drainfield area. This access. will be off of Hillcrest Avenue, which is an
existing dead-end gravel/dirt road off of Beckett Point Road. A quarry spall entrance to the
construction area will be established as shown on the site plan (Figure 2-1). Hillcrest Avenue,
a County road, will also be maintained during and at. the conclusion of the LOSS. system
construction activities.
No specific construction access points will be required for the construction activities within
the sand spit. Construction activities will occur in individual lots and within or adjacent to
Beckett Point Road on the sand spit. Paved roadways used by trucks and equipment shall be
kept ,as clean as possible. Construction debris, ~~ ~~ocks shall be removed and
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Beckett Point Sanitary Improvements
Stormwater Site Plan
Jefferson County Public Utility District No. 1
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roadways swept clean at the end of each workday. All debris, dirt, mud, rocks, and other .
unsuitable organic material will be transported to a controlled disposal area located in or near
the drainfield area on the Beckett Point property.
2.1.3 Flow Control
Flow control will not be required for this project since there will be minimal increase in storm
runoff volwne. The only increases in impervious area will be the pwnp station, manhole, and
septic tank access covers. Exposed soil areas during the construction of the drainfield will be
protected as best as possible by using straw bail check dams, brush barriers, and silt fencing.
No sediment traps or other detention facilities are proposed.
2.1.4 Sediment Control
The need for sediment control during construction activities on the sand spit is anticipated to
be minimal since the exposed soil areas are to be limited to the width of the excavation
needed for pipe installation and installation of the grinder pwnp stations. The site topography
in this area is also relatively flat and well-draining, which will also help reduce potential soil
erosion.
During the construction of the LOSS systems (septic tanks, dosing tanks and drainfields), silt
fencing will be used "at the down-gradient edge of the site to reduce the amount of sediment
leaving the construction area. Straw bale check dams will be used in natural and/or man-made
conveyances.
The following Ecology-recommended BMPs will or may be used:
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BMP C232 - Gravel Filter Berm
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BMP C230 - Straw Bale Barrier
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BMP C231 - Brush Barrier
. BMPC233 - Silt Fence
Copies of these BMPs are included in Appendix B.
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2.1.5 Soil Stabilization
Exposed soil within the project footprint will be stabilized using effective BMPs that protect
the soil from erosion. Based on Ecology guidelines, the following criteria will be used:
· From October 1 through April 30, no soil will remain exposed for more than 2 days.
· From May 1 through September 30, no soil will remain exposed for 'more than 7
days.
These criteria may be altered based on forecasted weather conditions. The majority of the
proposed construction activities for this project are expected to occur during the dry months,
May 1 through October 31.
During the wet months, soil will be stabilized at the end of each week, if needed, based on
forecasted weather cOnditions. Berms or silt fencing will be constiucted around soil
stockpiles or the stockpiles will be covered following completion of daily' activities, as
needed, based on weather conditions. Bnish barriers and/or mulch shall. be used to protect
exposed soils while the drainfield area is wider construction.
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Slormwater Site Plan
Jefferson County Public Utility District No. 1
During dry months, dust control will be used, as needed, on exposed soil swfaces to reduce
airborne dust resulting from truck traffic or wind.
Following completion of construction activities, all exposed or impact soil areas (with the
exception of the drainfield area) will be returned to near pre-construction condition. This may
include re-vegetation, replacement of removed asphalt, etc. The entire drainfield area will be
hydroseeded upon completion and testing of the system. Hydroseeding shall occur ill mid to
late spring or early fall.
Recommended BMPs to be used for soil stabilization include the following:
. BMP C120 - Temporary and Permanent Seeding
. BMP Cl21 - Mulching
. BMP Cl22 - Nets and Blankets
. BMP Cl23 - Plastic Covering
. BMP C140 - Dust Control
. BMP C180 - Small Project Construction Stormwater Pollution Prevention
. BMP C231 - Brush Barrier
Copies of these BMPs are included in Appendix B.
2.1.6 Slope Protection
Impacts to exposed slopes are anticipated to be minimal. No open excavation will occUr on
the steep hillside other than in existing roadways. Trenching and excavation for manholes and
pwnp stations in the Olympic ViewlHill Park area will be protected with straw bale check
dams if necessary.
The drainfield area may be logged under a separate contract prior to the start of construction
of the sewer collection and treatment systems. The logging contractor will not clear and grub
the drainfield area and will leave stumps for the main contractor to remove. This is primarily
for erosion control between logging and constructin of the drainfields.
During construction of the drainfields, a combination of silt fencing, straw bale check dams,
and mulch or forest duff material will be used to protect slopes with exposed soil. A 50-foot
uncleared buffer will remain on. the down-gradient side of the drainfield area between the
area and Hillcrest Avenue, and also the adjacent property to the east.
2.1.7 Drain Inlets Protection
Storm drain inlets, catch basins, etc. located adjacent to constructions area or that. could
potentially be impacted by runoff from the construction site will be protected from receiving
sediment loads. Roadway surfaces will be kept clean' of Soil and sediments. Sediment and
street wash water will not be allowed to enter the storm drain system' without treatment to
remove silt and sediments. .
Recommended BMPs for projection of drain inlets include the fu~f 'f" t Jj IE
· BMP C220 - Storm Drain Inlet Protection r ~ r'
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Beckett Point Sanitary Improvements
Stormwater Site Plan
Jefferson County Public Utility Disuict No. I
2.1.8 Channel and Outlet Stabilization
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No temporary on-site conveyance channels are anticipated for this project. Therefore, channel
and outlet stabilization will not be necessary.
2.1.9 Pollutant Control
Petrolewn product leaks and spills will be contained before entering the storm drain system.
Contaminated surfaces will be cleaned immediately following discharge or spill. Leaking
equipment will be repaired or removed from site. All petrolewn products and chemicals used
onsite will be stored in appropriate containment areas and away from stormwater drainage
channels, catch basin, and other elements of the site storm drain system.
2.1.10 De-Watering Control
De-watering of pipe trenches and other excavations is not anticipated during construction.
Trenching and grinder pump excavations on the sand spit will most likely be coordinated
, with low tides. Should de-watering become necessary, the proposed method of disposal will
be discharged to the beach. If de-watering liquid is determined to be highly turbid or
contaminated, alternate methods of de-watering liquid disposal may include transport and
disposal at an off site facility.
2.1.11 BMP Maintenance and Inspection
BMPs shall be inspected daily (October - April) or weekly (May - September), and following
any runoff producing rainfall events. All inspections shall be docwnented and copies of .
completed forms shall remain on-site at all times. Any damage repair or maintenance
required will be completed before the end of the same workday in which it is disG<)vered.
During prolonged rainfall events BMPs shall be inspected daily. Additional BMPs may be
required as a result of increase stormwater runoff. Contractor shall implement additional
BMPs as site conditions dictate and/or as directed by the Project Engineer.
BMPs shall be removed following site stabilization or within 30 days of project completion.
Upon removal of the BMPs, the site and surrounding area will be cleaned and restored as
close to pre-constmction condition as possible. All removed material, collected seQiment, and
debris shall be disposed of at a controlled disposal area.
2.2 CONSTRUCTION SCHEDULE
Construction of the project is proposed for late spring, summer, and fall 2006. Contract
duration is 180 calendar days. The weather conditions during construction are expected to
vary from warm and dry to wet with moderate temperatures. Beckett Point lies in the
northeast comer of the "rain shadow" of the Olympic Mountain range and only experiences
an average annual rainfall of approximately 16 to 18 inches.
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Beckett Point Sanitary Improvements
Stormwater Site Plan
Jefferson County Public Utility District No. I
.
3. PERMANENT STORMWATER CONTROL PLAN
3.1 GENERAL
This Permanent Stormwater Control Plan was completed per the Ecology SWMM Section
3.1.5. The existing and developed site hydrological conditions are expected to be similar. No
significant additional impervious surfaces are proposed for this project other than the pump
station, manhole, and septic tank covers, and stormwater runoff volwne is not expected to
increase due to the proposed upgrades. Following construction, all disturbed areas will be
, restored to near pre-construction condition. Disturbed areas previously containing lawns,
landscaped areas, and unimproved surfaces will be compacted to 90 percent and hydroseeded
to restore vegetation. The drainfield area will also be hydroseeded once the construction of
the fields has been completed. The contract docwnents will require an established vegetative
cover over the drainfield area prior to the completion of construction. All other areas will be
restored to near pre-construction condition.
No new onsite facilities for stormwater conveyance and collection are proposed following
completion of this project.
Stormwater control after construction will remain the same as the existing conditions. The
proposed activities should not change the existing drainage patterns or discharge locations;
therefore, no changes in stormwater control, conveyance, or collection are necessary or
proposed.
. 3.2 SOURCE CONTROL OF POLLUTANTS
No source control will be necessary following project completion. All disturbed areas will be
returned to pre-construction conditions including re-vegetation of all soil areas exposed
during construction.
3.3 PRESERVATION OF NATURAL DRAINAGE SYSTEMS AND OUTFALLS
The natural drainage system and existing drainage basins (see Figure 2-1) at Beckett Point
will.not be altered by this project. All areas impacted by construction activities will be
returned to pre-construction condition, with the exception of the drainfield area which will be
hydroseed.ed upon completion.
3.4 ON-SITE STORMWATER MANAGEMENT
No additional stormwater management requirements are proposed following completion of
the proposed sewer system upgrades. The existing stormwater system at Beckett Point will
not require modification since. the post-development stormwater runoff volwne is not
anticipated to change as a result of construction.
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Beckett Point Sanitary Improvements
Stormwater Site Plan
Jefferson County Public Utility District No. 1
4. BMPS
· The following is a complete list of BMPs referenced in the previous sections and
included in Appendix B.
· BMP Cl20 - Temporary and Permanent Seeding
. BMP Cl21 - Mulching
. BMP Cl22 - Nets and Blankets
. BMP Cl23 - Plastic Covering
. BMP Cl40 - Dust Control
· BMP Cl80 - Small Project Construction Stormwater Pollution Prevention
. BMP C220 - Storm Drain Inlet Protection
. BMP C230 - Straw Bale Barrier
. BMP C231 - Brush Barrier
· BMP C232 - Gravel Filter Berm
. BMP C233 - Silt Fence
July 2005 I 256-1820-009
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5. REFERENCES
Beckett Point Sanitary Improvements
Stormwater Site Plan
Jefferson County Public Utility District No. 1
Myers Biodynamics, Inc. 2005. Geologically Hazardous Areas Assessment and
Recommendations, Beckett Point Wastewater Treatment System, Jefferson County,
Washington.
Washington State Department of Ecology 2005. Stormwater Management Manual
for Western Washington.
Brooks, K.M. 2000. Wetlands Delineation and Ranking Report: (as shown in Official
Record Map of Cape George Fisherman, Inc. Salmon Club). Pacific Rim Aquatic
Environmental Sciences, Port Townsend, Washington.
July 2005 I 256-1820-009
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APPENDIX A
Relevant Project Plans
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APPENDIX B
Project BMPs
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BMP C120: Temporary and Permanent Seeding
Purpose Seeding is intended to reduce erosion by stabilizing exposed soils. A
well-established vegetative cover is one of the most effective methods of
reducing erosion.
Conditions of Use
Design and
Installation
SpecifICations
February 2005
· Seeding may be used throughout the project on disturbed areas that
have reached fmal grade or that will remain unworked for more than
30 days.
· Channels that will be vegetated should be installed before major
earthwork and hydroseeded with a Bonded Fiber Matrix. The
vegetation should be well established (i.e., 75 percent cover) before
water is allowed to flow'in the ditch. With channels that will have
high flows, erosion control blankets should be installed over the
hydroseed. Ifvegetation cannot be established from seed before water
is allowed in the ditch, sod should be installed in the bottom of the
ditch over hydromulch and blankets.
· Retention/detention ponds should be seeded as required.
· Mulch is required at all times because it protects seeds from heat,
moisture loss, and transport due to runoff.
· All disturbed areas shall be reviewed in late August to early September
and all seeding should be completed by the end of September.
Otherwise, vegetation will not establish itself enough to provide more
than average protection.
· At final site stabilization, all disturbed areas not otherwise vegetated or
stabilized shall be seeded and mUlched. Final $bilization means the
completion of all soil disturbing activities at the site and the
establishment of a permanent vegetative cover, or equivalent
permanent stabilization measures (such as pavement, riprap, gabions
or geotextiles) which will prev(;mt erosion.'
· Seeding should be done during those seasons most co~ducive to
growth and will vary with the climate conditioIlSofthe region.
Local experience should be used to determine the appropriate .
seeding periods.
· The optimum seeding windows for we~m Washington are April 1
through June 30 arid September 1 through October 1. Seeding that
occurs between July 1 and August 30 will req~ irrigation until 7S
percent grass cover is established. Seeding that occurs between
October 1 and March 30 ~ require a mulch or plastic cover until
75 percent grass cover is established.
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· The seedbed should be firm and rough. All soil should be roughened
no matter what the slope. If compaction is required for engineering
purposes, slopes must be track walked before, seeding. Backblading or
smoothing of slopes greater than 4: 1 is not allowed if they are to be
seeded.
· New and more effective restoration-based landscape practices rely on
deeper incorporation than that provided by a simple single-pass
rototilling treatment. Wherever practical the subgrade should be
initially ripped to improve long-term permeability, infiltration, and
water inflow qualities. At a minimum, permanent areas shall use soil
amendments to achieve organic matter and permeability performance
defmed in engineered soilllandscape systems. For systems that are
deeper than 8 inches the rototilling process should be done in multiple
lifts, or the prepared soil system shall be prepared properly and then
placed to achieve the specified depth.
· Organic matter is the most appropriate form of "fertilizer" because it
provides nutrients (including nitrogen, phosphorus, and potassiwn) in
the least water-soluble form. A natural system typically releases 2-10
percent of its nutrients annually. Chemical fertilizers have since been
formulated to simulate what organic matter does naturally.
· In general, 10-4-6 N-P-K (nitrogen-phosphorus-potassiwn) fertilizer
can be used at a rate of 90 pounds per acre. Slow-release fertilizers .
should always be used because they are more efficient and have fewer
environmental impacts. It is recommended that areas being seeded for
~ landscaping conduct soil tests to determine the exact type and
quantity offertilizer needed. This will prevent the over-application of
fertilizer. 'Fertilizer should not be added to the hydromulch machine
and agitated more than 20 minutes before it is to be used. If agitated
too much, the slow-release coating is destroyed.
· There are nwnerous products available on the market that take the
place of chemical fertilizers. ' These include several with seaweed
extracts that are beneficial to soil microbes and organiSms. If 100
percent cottonseed meal is used as the mulch in hydroseed, chemical
fertilizer may not be necessary. Cottonseed meal is a good sourCe of
long-terttJ., slow-release, available nitrogen. .
· Hydroseed applications shall include a minimum of 1,500 pounds per
acre of mulch with 3 percent tackifier. Mulch may be made up of 100
percent: cottonseed meal; fibers made of wood, recycled cellulose,
hemp, and kenaf; compost; or blends of these. Tackifier shall be plant-
based, such as gu8.r or alpha plantago, or chemical-based such as
polyacrylamide or polymers. Any mulch. or tackifier product used
shall be installed per manufacturer's instructions. Generally, mulches
;~:so pound~.;~jertili7M are addOO at time or. .
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.
Volume 11- Construction Stormwstet Pollution Pl8vsntion
FebrosI)' 2005
.
· Mulch is always required for seeding. Mulch can be applied on top of
the seed or simultaneously by hydroseeding.
· On steep slopes, Bonded Fiber Matrix (BFM) or Mechanically Bonded
Fiber Matrix (MBFM) products should be used. BFM/MBFM
products are applied at a minimum rate of 3,000 pounds per acre of
mulch with approximately 10 percent tackifier. Application is made
so that a minimum of 95 percent soil coverage is achieved. Numerous
products are available commercially and should be installed per
manufacturer's instructions. Most products require 24-36 hours to
cure before a rainfall and cannot be installed on wet or saturated soils.
Generally, these products come in 40-50 pound bags and include all
necessary ingredients except for seed and fertilizer.
BFMs and MBFMs have some advantages over blankets:
· No surface preparation required;
· Can be installed via helicopter in remote areas;
· On slopes steeper than 2.5:1, blanket installers may need to be roped
and harnessed for safety;
. They are at least $1,000 per acre cheaper installed.
In most cases, the shear strength of blankets is not a factor when used on
slopes, only when used in channels. BFMs and MBFMs are good
alternatives to blankets in most situations where vegetation establishment
is the goal.
· When installing seed via hydroseeding operations, only about 1/3 of
the seed actually ends up in contact with the soil surface. This reduces
the ability to establish a good stand of grass quickly. One way to
overcome this is to increase seed quantities by up to 50 percent
· Vegetation establishment can also be enhanced by dividing the
hydromulch operation into two phases:
1. Phase 1- Install all seed and fertilizer with 25-30 percent mulch
and tackifier onto soil in the first lift;
2. Phase 2- Install the rest of the mulch and tackifier over the first lift.
.
.
. An alternative is to install the mulch, seed, fertilizer, and tackifier in one
lift. Then, spread or bloW' straw over the top of the hydromulch at a rate of
about 800-1000 pounds per acre. Hold straw in place with.a standa,rd
tackifier. }loth of these approaches will increase cost moderately bUt will
greatly improve and enhance vegetative establishment".The iner :\
may be offset by the reduced need for: r. ~.__ ___ L~-, rl)
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2. Reapplication of mulch . I '\ \ \ AU G - 5 2005 \I"
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This technique works with standard hydromulch (1,500 pounds per acre
minimum) and BFM/MBFMs (3,000 pounds per acre minimum).
..
· Areas to be permanently landscaped shall provide a healthy topsoil
that reduces the need for fertilizers, improves overall topsoil quality,
provides for better vegetal health and vitality, improves hydrologic
characteristics, and reduces the need for irrigation; This can be
accomplished in a number of ways:
Recent research has shown that the best method to improve till soils is
to amend these soils with compost. The optimum mixture is
approximately two parts soil to one part compost. This equates to 4
inches of compost mixed to a depth of 12 inches in till soils. Increasing
the concentration of compost beyond this level can have negative
effects on vegetal health, while decreasing the concentrations can
reduce the benefits of amended soils. Please note: The compost should
meet specifications for Grade A quality compost in Ecology
Publication 94-038.
· . Areas that will be seeded only and not landscaped may need compost
or meal-based mulch included in the hydroseed in order to establish
vegetation. Native topsoil should be re-installed on the disturbed soil
surface before application.
. Seed that is installed as a temporary measure may be installed by hand
. . if it will be covered by straw, mulch, or topsoil. Seed that is installed
as a permanent measure may be installed by hand on small areas
(usually less than I acre) that will be covered with mulch, topsoil, or
erosion blankets; The seed mixes listed below include recommended
mixes for both temporary and permanent .seeding. These mixes, with
the exception of the wetland mix, shall be applied at a rate of 120
powdsper acre. This rate can be reduced if soil amendments or slow-
release fertilizers are used. Local suppliers or the local conservation
district should be consulted for their recommendations because the
appropriate mix depends on a variety of factors, including location,
exposure, soil type, slope, and expected foot traffic. Alternative seed
mixes approved by the local authorltymay be U$ed.
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Volume 11- Construction Stormwater Pollution Prevention
February 2005
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February 2005
50
98
5
92
5
98
Perennial rye blend
Lolium erenne
Chewings and red fescue blend
Festuca rubra var. commutata
or Festuca rubra
30
98 . 90
% Germination
90
90
85
90
% Germination
90
This turf seed mix in Table 4.3 is for dry situations where there is no need
for much water. The advantage is that this mix requires very little
maintenance.
% Germination
90
Dwarf tall fescue (several varieties)
Festuca arundinacea var.
Dwarf perennial rye (Barclay)
LP/ium erenne var. bard
Red fescue
Festuca rubra
Colonial bentgrass
oatis tenuis
30
98 90
20
98 90
5
98 90
Table 4.4 presents a mix recommended for bioswa1es and other
intermittently wet areas.
% Germination
90
1001S
92
85
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The seed mix shown in Table 4.5 is a recommended low-growing,
relatively non-invasive seed mix appropriate for very wet areas that are
not regulated wetlands. Other mixes may be appropriate, depending on
the soil type and hydrology of the area. Recent research suggests that
bentgrass (agrostis sp.) should be emphasized in wet-area seed mixes.
Apply this mixture at a rate of 60 pounds per acre.
.
% GerminatioD
Tall or meadow fescue 90
Festuca arundinacea or
Festuca elatior
Seaside/Creeping bentgrass 10-15 98 85
A ostis alustris
Meadow foxtail 10-15 90 80
Ale curus atensis
Alsike clover 1-6 98 90
Tri olium bridwn
Redtop bentgrass 1-6 92 85
A ostis alba
* Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix
The meadow seed mix in Table 4.6 is recommended for areas that will be
maintained infrequently or not at all and where colonization by native
plants is desirable.' Likely applications include rural rmid and utility right-
of-way.' Seeding should take place in September or very early October in
order to obtain adeqUate establishment prior to the winter months. The
appropriateness of clover in the mix may need to be considered, as this can
be a fairly invasive species.. If the soil is amended, the addition of clover
may not be necessary.
.
Table 4.6
MeadoW Seed Mix
%W
20
% Germination
85
70
98 90
10
98
90'
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Volume 11- Construction Stonnwster Pollution Prevention
FebRISI}' 2005
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February 2005
· After adequate cover is achieved, any areas that experience erosion
shall be reseeded and protected by mulch. If the erosion problem is
drainage related, the problem shall be fixed arid the eroded area
reseeded and protected by mulch.
· Seeded areas shall be supplied with adequate moisture, but not watered
to the extent that it causes runoff.
51
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Volume 11- Constroction Stonnwater Pollution Prevention
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BMP C121: Mulching .
Purpose The purpose of mulching soils is to provide immediate temporary
protection from erosion. Mulch also enhances plant establishment by
conserving moisture, holding fertilizer, seed, and topsoil in place, and
moderating soil temperatures. There is an enormous variety of mulches,
that can be used. Only the most common types are discussed in this
section.
Conditions of Us~ As a temporary cover measure, mulch should be used:
· On disturbed areas that require cover measures for less than 30 days.
· As a cover for seed during the wet season and during the hot summer
months.
· During the wet season on slopes steeper than 3H: 1 V with more than 10
feet of vertical relief.
· Mulch may be applied at any time of the year and must be refreshed
periodically.
Design and
Installlltion
SpecifICations
For mulch materials, application rates, and specifications, see Table 4.7.
Note: Thicknesses may be increased for disturbed areas in or near
sensitive areas or other areas highly susceptible to erosion.
Maintenance
Standards
Mulch used within the ordinary high-water mark of surface waters should
be selected to minimize potential flotation of organic matter. Composted
organic materials have higher specific gravities (densities) than straw,
wood, or chipped material.
· The thickness of the cover must be maintained.
· Any areas that experience erosion shall be remulched and/or protected
with a net or blanket. If the erosion problem is drainage related, then
the problem shall be fixed and the eroded area remulched.
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Volume 11- Construction Stormwater Pollution Prevention
February 2005
. Table 4.7
Mulch Standards and Guidelines
Mulch AppUcatiOD
Material uali Standards Rates Remarks
Straw Air-dried; free from 2"-3" thick; 5 Cost-effective protection when applied with adequate
\D1desirable seed and bales per 1000 sf thickness. Hand-application generally requires greater
coarse material. or 2-3 tons per thickness than blown straw. The thickness of straw may be
acre reduced by half when used in conj\D1ction with seeding. In
windy areas straw must be held in place by crimping, using a
tackifier, or covering with netting. Blown straw always has
to be held in place with a tackifier as even light wincls will
blow it away. Straw, however, has several deficiencies that
should be considered when selecting mulch materials. It
often introduces and/or encoW'ages the propagation of weed
species and it has no significant long-term benefits. Straw
should be used only if mulches with long-term benefits are
unavailable locally. It should also not be used within the
ordinary high-water elevation of surface waters (due to
flotation).
Hydromulch No growth Approx. 25-30 Shall be applied with hydromulcher. Shall not be used
inhibiting factors. lbs per 1000 sf without seed and tackifier unless the application rate is at
or 1500 - 2000 least doubled. Fibers longer than about 0/...1 inch clog
lbs per acre hydromulch equipment. Fibers should be kept to less than %
inch.
Composted No visible water or 2" thick min.; More effective control Can be obtained by increasing
Mulch and dust during approx. 100 tons thickness to 3". Excellent mulch for protecting final grades
. Compost handling. Must be per acre (approx. unti11andscaping because it can be directly seeded or tilled
purchased from 800 lbs per yard) into soil as an amendment. Composted mulch has a coarser
supplier with Solid size gradation than compost. It is more stable and practical
Waste Handling to'use in wet areas and during rainy weather conditions.
Permit (unless
exempt).
01ipped Site Average size shall 2" minimum ' This is a cost-effective way to dispose of debris from
Vegetation ' be several inches. thickness clearing and grubbing, and it elimm9tes the problems
Gradations from associated with burning. Generally, it should not be used on
fines to 6 inches in slopes above approx. 10% because of its tendency to be
length for texture, transported by nmoff. It is not recommended within 200
variation, and feet of surface waters. If seeding is expected shortly after
interlocking mulch, the decomposition of the chipped vegetation may tie
properties. up nutrients important to grass establishment.
Wood-based No vist'ble water or 2" thick; approx. This material is often called "hog or hogged fueL" It is
Mulch dust during 100 tons per acre usable as a material for Stabilized Construction Entrances
handling. Must be (approx. 800 lbs; (BMP CI0S) and as a mulch. The use of mulch ultimately
purchased from a per cubic yard) improves the organic matter in the soil. Special caution is
supplier with a Solid advised regarding the ~ and composition of wood-
Waste Handling based mulches. Its preparatiOn typically does not provide
Permit or one any weed seed control, so evidence of residual vegetation in
exempt from solid its composition or known inclusion of weed plants or seeds
waste regulations. should be monitored and prevented (or minimi7'.ed).
.
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Volume 11- Constnlction Stonnwater Pollution Prevention
-4=.'21-
Purpose
BMP C122: Nets and Blankets
.
Conditions of Use
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Erosion control nets and blankets are intended to prevent erosion and hold
seed and mulch in place on steep slopes and in channels so that vegetation
can become well established. In addition, some nets and blankets can be
used to permanently reinforce turf to protect drainage ways during high
flows. Nets (commonly called matting) are strands of material woven into
an open, but high-tensile strength net (for example, coconut fiber matting).
Blankets are strands of material that are not tightly woven, but instead
forma ,layer of interlocking fibers, typically held together by a
biodegradable or photodegradable netting (for example, excelsior or straw
blankets). They generally have lower tensile strength than nets, but cover
the ground more completely. Coir (coconut fiber) fabric comes as both
nets and blankets.
Erosion control nets and blankets should be used:
· To aid permanent vegetated stabilization of slopes 2H: IV or greater
and with more than 10 feet of vertical relief.
· For drainage ditches and swales (highly recommended). The
application of appropriate netting or blanket to drainage ditches and
swales can protect bare soil from channelized runoff while vegetation
is established. Nets and blankets also can capture a great deal of
sediment due to their open, pc.lrous structure. Synthetic nets and
. blankets can be used to permanently stabilizechamiels and may
provide a cost-effective, environmentally preferable alternative to
riprap. 100 percent synthetic blankets manufactured for use in ditches
may be easily reused as temporary ditch liners.
, Disadvantages of blankets include:
· Surface preparation required;
· On slopes steeper than 2.5: 1, blanket installers may need to be roped
and harnessed for safety;
· They cost at least $4,000-6,000 per acre installed
Advantages of blankets include:
· Can be installed without mobilizing special equipment;
. Can be installed by anyone with minimal training;
. Can be installed in stages or phases as the project progresses;
· Seed and fertilizer can be hand-placed by the installers as they
progress down the slope;
· Can be installed in any weather;
· There are numerous types of blankets that can be designed with
various parameters in mind Those parameters include: fiber blend,
mesh strength, longevity, biodegradability, cost, and availability.
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Volume 11- Construction Stonnwater Pollution Ptevsntion
February 2005
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Design and
Installation
SpecifICations
February 2005
· See Figure 4.4 and Figure 4.5 for typical orientation and installation of
blankets used in channels and as slope protection. Note: these are
typical only; all blankets must be installed per manufacturer's
installation instructions.
'. Installation is critical to the effectiveness of these products. If good
ground contact is not achieved, runoff can concentrate under the
product, resulting in significant erosion.
· Installation of Blankets on Slopes:
1. Complete final grade and track walk up and down the slope.
2. Install hydromulch with seed and fertilizer.
3. Dig a small trench, approximately 12 inches wide by 6 inches deep
along the top of the slope. .
4. Install the leading edge of the blanket into the small trench and
staple approximately every 18 inches. NOTE: Staples are
metal,"lr' -shaped, and a minimum of 6 inches long. Longer
staples are used in sandy soils. Biodegradable stakes are also
available.
5. Roll the blanket slowly down the slope as installer walks
backwards. NOTE: The blanket rests against the installer's legs.
Stap.es are installed as the blanket is unrolled. It is critical that the
proper staple pattern is used for the blanket being installed. The
blanket is not to be. allowed to roll down the slope on its own as
this stretches the blanket making it impossible to maintain soil
contact. In addition, no one is allowed to walk on the blanket after
it is in place. .
6. If the blanket is not long enough to cover the entire slope length,
the trailing edge of the upper blanket should overlap the leading
edge of the lower blanket and be stapled. On steeper slopes, this
overlap should be installed in a small trench, stapled, and CQvered
with soil.
· With the variety of products available, it is impossible to cover all the
details of appropriate rise and installation. Therefore, it is critical that
the design engineer consults the manufacturer's information and that a
site visit takes place in order to insure thatthe product specified is
appropriate. Information is also available at the following web sites:
1. WSDOT: http://www.wsdOt.wa.gov/eesc/environmentaV
2.
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Maintenance
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· Jute matting must be used in conjunction with mulch (BMPC121). .
Excelsior, woven straw blankets and coir (coconut fiber) blankets may
be installed without mulch. There are many other types of erosion
control nets and blankets on the market that may be appropriate in
certain circumstances.
· In general, most nets (e.g., jute matting) require mulch in order to
prevent erosion because they have a fairly open structure. Blankets
typically do not require mulch because they usually provide complete
protection of the surface. '
· Extremely steep, unstable, wet, or rocky slopes are often appropriate
candidates for use of synthetic blankets, as are riverbanks, beaches and
other high-energy environments. If synthetic blankets are used, the
soil should be hydromulched first.
· 100 percent biodegradable blankets are available for use in sensitive
areas.. These organic blankets .are usually held together with a paper or
fiber mesh and stitching which may last up to a year.
· Most netting used with blankets is photodegradable, meaning they
break down under sunlight (not UV stabilized). However, this process
can take months or years even under bright sun. Once vegetation is
established, sunlight does not reach the mesh. It is not uncommon to
find non-degraded netting still in 'place several years after installation.
This can be a problem if maintenance requires the use of mowers or
ditch cleaning equipment. In addition, birds and small animals can
become trapped in the netting.
· Good contact with the ground must be maintained, and erosion must
not occur beneath the net or blanket.
· Any areas of the net or blanket that are damaged or not in close contact
with the ground shall be repaired and stapled.
· If erosion occurs due to poorly controlled drainage, the problem shall
be fixed and the eroded area protected.
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Volume 11- Construction Stonnwater Pollution Prevention
February 2005
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Longitudinal Anchor Trench
Tennlnal Slope and Channel Anchor Trench
initiai Channel Anchor Trench Inlermlttent Check Slot
NOTES:
1. Cleek a10Ia to be C01IItrucfIed per III8Il1Ifilclur apecificatIoas.
2. 81lIkiD& or ItIpIiDg IayoutperllllDllfAclurer 1pCClficIdou.
. Figure 4.4 - Channellnstallallon
Slope Sl.Iface shall be smooth before
plaCement for proper soil contact.
Stapling pattern as per
manufaCturer's recommendallons.
If there isa berm at the
top of s101l8. anchor
upslope of the berm.
Anchor In 6"x6ft min. Trench
and staple at 12" Intervals.
Mn. 6ft overlap.
Staple CMlI'Iaps
InlllC. 5" epac::Ing.
~ material ckrtM1 to a level :A'
the end l.I'lCIer ..ft and 8l8pIe at 12" r
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Ume, fertilize, and seed before . -. - -:::....__ .
Planting of shrubs, trees, etc. s oCcur
after In8laIIafIon. J - - n
Do not lIIretch bIanketsImatti~s tight .
allowthe rOIls to mold to any lneglJaities.
For slopes less than 31-1: 1Y, rOIls '
may be placed In horizcntaIlIIrIps.
Figure 4.6 - Slope Installation
February 2005
Volume 11- Construction stotinwatsr Pollution Prevention
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Purpose
Conditions of
Use
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Plastic covering provides immediate, short-term erosion protection to
slopes and disturbed areas.
· Plastic covering may be used on disturbed areas that require cover
measures for less than 30 days, except as stated below.
· Plastic is particularly useful for protecting cut and fill slopes and
stockpiles. Note: The relatively rapid breakdown of most polyethylene
sheeting makes it unsuitable for long-term (greater than six months)
applications.
· Cle~ plastic sheeting can be used over newly-seeded areas to create a
greenhouse effect and encourage grass growth if the hydroseed was
installed too late in the season to establish 75 percent grass cover, or if
the wet season started earlier than normal. Clear plastic should not be
used for this purpose during the summer months because the resulting
high temperatures can kill the grass.
· Due to rapid runoff caused by plastic sheeting, this method shall not be
used upslope of areas that might be adversely impacted by
concentrated runoff. Such areas include steep and/or unstable slopes.
· While plastic is inexpensive to purchase, the added cost of installation, .
maintenance, removal, and disposal make this an expensive material,
up to $1.50-2.00 per square yard.
· Whenever plastic is used to protect slopes, water collection measures
must be installed at the base of the slope. These measures include
plastic-covered berms, channels, and pipes used to covey clean
rainwater away from bare soil and disturbed areas. At no time is clean
runoff from a plastic covered slope to be mixed with dirty runoff from
a project. '
· Other uses for plastic include:
1. Temporary ditch,liner;
2. Pond liner in temporary sediment pond;
3. Liner for bermed temporary fuel storage area if plastic. is not
reactive to the type of fuel being stored; , '
4. Emergency slope protection during heavy rains; and,
5. ,Temporary drainpipe ("elephant tnmk") used to direct water.
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Volume 11- Construction stormwater Pollution Prevention
February 2005
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Design and
Installation
SpecifICations
Maintenance
Standards
. Febtuary 2005
· Plastic slope cover must be installed as follows:
1. Run plastic up and downslope, not across slope;
2. Plastic may be installed perpendicular to a slope if the slope length
is less than 10 feet;
3. Minimum of 8-inch overlap at seams;
4. On long or wide slopes, or slopes subject to wind, all seams should
be taped;
5. Place plastic into a small (12-inch wide by 6-inch deep) slot trench
at the top of the slope and backfill with soil to keep w~ter from
flowing underneath;
6. Place sand filled burlap or geotextile bags every 3 to 6 feet along
seams and pound a wooden stake through each to hold them in
place;
7. Inspect plastic for rips, tears, and open seams regularly and repair
immediately. This prevents high velocity runoff from contacting
bare soil which causes extreme erosion;
8. Sandbags may be lowered into place tied to ropes. However, all
sandbags must be staked in place.
· Plastic sheeting shall have a miirimum thickness'ofO.06 millimeters.
· If erosion at the toe of a slope is likely, a gravel berm, riprap, or other
suitable protection shall be installed at the toe of the slope in order to
reduce the velocity of runoff.
· Tom sheets must be replaced and open seams repaired.
· If the plastic begins to deteriorate due to ultraviolet radiatio~ it must
be completely removed and replaced.
· When the plastic is no longer needed, it shall be completely removed.
· Dispose of old tires appropriately.
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Volume 11- Construction stonnwater Pollution Prevention
4-27
BMP C140: Dust Control
.
Purpose Dust control prevents wind transport of dust from disturbed soil surfaces "-
onto roadways, drainage ways, and surface waters.
Conditions of Use · In areas (including roadways) subject to surface and air movement of
dust where on-site and off-site impacts to roadways, drainage ways, or
surface waters are likely.
Design and
InstaUation
Specifications
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,. Vegetate or mulch areas that Will not receive vehicle traffic. In areas
where planting, mulching, or paving is impractical, apply gravel or
landscaping rock.
· Limit dust generation by clearing only those areas where immediate
activity will take place, leaving the remaining area(s) in the original
condition, if stable. Maintain the original ground cover as long as
practical.
· Construct natural or artificial windbreaks or windscreens. These may
be designed as enclosures for small dust sources.
· Sprinkle the site with water until surface is wet. Repeat as needed. To
prevent carryout of mud onto street, refer to Stabilized Construction
Entrance (BMP CI05).,
· Irrigation water can be used for dust control. Irrigation systems should .
be installed as a first step on sites where dust control is a concern. .
· Spray exposed soil areas with a dust palliative, following the
manufacturer's instructions and cautions regarding handling and
application. Used oil is prohibited from use as a dust suppressant.
Local governments may approve other dust palliatives such as calcium
chloride or PAM.
· PAM (BMP C126) added to water at a rate ofO.5Ibs. per 1,000
gallons of water per acre and applied from a water truck is more
effective than water alone. This is due to the increased infiltration of
water into the soil and reduced evaporation. In addition, small soil
particles are bonded together and are not as easily transported by wind.
Adding PAM may actually reduce the quantity of water needed for
dust'cootrol, especially in eastern Washington. SinCe the wholesale
cost ofP AM is about $ 4.00 per pound, this is an extremely cost-
effective dust control method.
Techniques that can be used for unpaved roads and lots include:
· . Lower speed limits. High vehicle speed increases the amount of dust
stirred up from unpaved roads and lots.
· Upgrade the road surface strength by improving particle size, shape,
and mineral types that make up the ,surface and base materials. . .
Volume 11- Construction Stonnwater Pollution Prevention
Febroary 2005
.
.
.
, Maintenance
Standards
February 2005
· Add surface gravel to reduce the source of dust emission. Limit the
amount offme particles (those smaller than .075 mm) to 10 to 20
percent.
· Use geotextile fabrics to increase the strength of new roads or roads
undergoing reconstruction.
· Encourage the use of alternate, paved routes, if available.
· Restrict use by tracked vehicles and heavy trucks to prevent damage to
road surface and base.
· Apply chemical dust suppressants using the admix method, blending
the product with the top few inches of surface material. Suppressants
may also be applied as surface treatments.
· Pave unpaved permanent roads and other trafficked areas.
. Use vacuum street sweepers.
· Remove mud and other dirt promptly so it does not dry and then turn
into dust.
. Limit dust-causing work on windy days.
· . Contact your local Air Pollution Control Authority for guidance and
training on other dust control measures. Compliance with the local Air
Pollution Control Authority constitutes compliance with this BMP.
Respray area as necessary to keep dust to a minimum.
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Volume 11- Construction Stonnwater Pollution Prevention
4-41
BMP Ci80: Small Project Construction Stormwater Pollution Prevention
Purpose To prevent the discharge of sediment and other pollutants to the maximum
extent practicable from small construction projects.
Conditions of Use
Design and
Installation
SpecifICations
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On small construction projects, those adding or replacing less than 2,000
square feet of impervious surface or clearing less than 7,000 square feet.
· Plan and implement proper clearing and grading of the site. It is most
important only to clear the areas needed, thus keeping exposed areas
to a minimum. Phase clearing so that only those areas that are actively
being worked are uncovered.
Note: Clearing limits should beftagged in the lot or area prior to
initiating clearing.
· Soil shall be managed in a manner that does not permanently compact
or deteriorate the final soil and landscape system. If disturbance and/or
compaction occur the impact must be corrected at the end of the
construction activity. This shall include restoration of soil depth, soil
quality, permeability, and percent organic matter. Construction
practices must not cause damage to or compromise the design of
permanent landscape or infiltration areas.
· Locate excavated basement soil a reasonable distance behind the curb, .
such as in the backyard or side yard area. This will increase the .
distance eroded soil must travel to reach the storm sewer system. Soil
piles should be covered until the soil is either used or removed. Piles
should'be situated so that sediment does not run into the street or
adjoining yards.
· Backfill basement walls as soon as possible and ~ grade the lot.
This will eliminate large soil mounds, which are highly erodible, and
prepares the lot for temporary cover, which will further reduce erosion
potential.
· Remove excess soil from the site as soon as possible after backfi11ing.
This will eliminate any sediment loss from surplUs fill.
· If a lot has a soil bank higher than the curb, a trench or berm should be
installed moVing the bank several feet behind the curb. This will
reduce the occurrence of gully and rill erosion while providing a
storage and settling area for storm water.
· The construction entrance should be stabilized where traffic will be
leaving the construction site and traveling on paved roads or other
paved areas within 1,000 feet of the site.
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4-55
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· Provide for periodic street cleaning to remove any sediment that may
have been tracked out. Sediment should be removed by shoveling or
sweeping and carefully removed to a suitable disposal area where it
will not be re-eroded.
· Utility trenches that run up and down slopes must be backfilled within
seven days. Cross-slope trenches may remain open throughout
construction to provide runoff interception and sediment trapping,
provided that they do not convey turbid runoff off site.
4-56
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Volume 11- Construction Stonitwster Pollution Prevention
February 2005
BMP C220: Storm Drain Inlet Protection
Purpose
Conditions of Use
Type of Inlet
Protection
Dro Inlet Protection
Excavated drop inlet
protection
Block and gravel drop
inlet protection
Gravel and wire drop
inlet protection
Catch basin filters
Curb Inlet Protection
Curb inlet protection
with a wooden weir
Block and gravel curb
inlet protection
.
To prevent coarSe sediment from entering drainage systems prior to
permanent stabilization of the disturbed area.
Where storm drain inlets are to be made operational before permanent
stabilization of the disturbed drainage area. Protection should be provided
for all storm drain inlets downslope and within 500 feet of a disturbed or
construction area, unless the runoff that enters the catch basin will be
conveyed to a sediment pond or trap. Inlet protection may be used
anywhere to protect ~e drainage system. It is likely that the drainage
system will still require cleaning.
Table 4.9 lists several options for inlet protection. All of the methods for
storm drain inlet protection are prone to plugging and require a high
frequency of maintenance. Drainage areas should be limited to 1 acre or
less. Emergency overflows may be required where stormwater ponding
would cause a hazard. If an emergency overflow is provided, additional
end-of-pipe treatment may be required.
Table 4.9
Storm Drain Inlet Protetion
Applicable for
Paved! Earthen
. Surfaces
Emergency
Overflow
Conditions of Use
.'
Yes,
temporary
flooding will
occur
Yes
Earthen
Applicable for heavy flows. Easy
to maintain. Large area
Requirement: 30' X 30'/acre
Paved or Earthen
Applicable for heavy concentrated
flows. Will not pond.
Applicable for heavy concentrated
flows. Will pond. Can: withstand
traffic.
Fre uent mamtenance re uired.
No
Yes
Paved or Earthen
Small capacity Paved
overflow
Yes
Used for sturdy, more compact
installation.
Sturdy, but limited filtration.
Paved
Culvert Inlet Protection
Culvert inlet sediment
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Volume 11- Construction.Stonnwater Pollution Prevention
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FebruarY 2005 '
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Design and
Installation
Specijlcations
Februaly 2005
Excavated Drop Inlet Protection - An excavated impoundment around the
storm drain. Sediment settles out of the stormwater prior to entering the
storm drain.
· Depth 1-2 ft as measured from the crest of the inlet structure.
· Side Slopes of excavation no steeper than 2: 1.
· Minimum volume of excavation 35 cubic yards.
· Shape basin to fit site with longest dimension oriented toward the
longest inflow area.
· Install provisions for draining to prevent standing water problems.
· Clear the area of all debris.
· Grade the approach to the inlet unifonnly.
· Drill weep holes into the side of the inlet.
· Protect weep holes with screen wire and washed aggregate.
· . Seal weep holes when removing structure and stabilizing area.
· It may be necessary to build a temporary dike to the down slope side
of the structure to prevent bypass flow.
Block and Gravel Filter - A barrier formed around the storm drain inlet
with standard concrete blocks and gravel. See Figure 4.14.
· Height I to 2 feet above inlet.
· Recess the first row 2 inches into the ground for stability.
· Support subsequent courses by placing a 2x4 through the block
opening.
· Do not use mortar.
· Lay some blocks in the bottom row on their side for dewatering the
pool.
· Place hardware cloth or comparable wire mesh with %-inch openings
. over all block openings.
· ,Place gravel just below the top of blocks on slopes of2:1 or flatter.
· An alternative design is a gravel donut.
. Inlet slope of 3: 1.
· Outlet slope of2:1.
· I-foot wide level stone area between the structure and the inlet.
· Inlet slope stones 3 inches in diameter or larger.
· OUtlet slope use gravel %- to %-inch at a mjni~~ 1bi~ of l-i-- r\\
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Volume 11- Construction Stonnwater Pollution pmvehuori'
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Plan View
A
.
Drain
Grate
Concrete
Block
,
Gravel
Backfill
Wire Screen or '
Filter Fabric
.
Noles: .
1. Drop inlet sediment barriers are to be used for smaD. nearly level drainage areas. (less than 5%)
2. Excavate a basin of sufllcIent size adjacent to the drop Inlet
3. the top of the structure (ponding height) must be well below the gromJ.d elevation downslope to prevent
runoffftom bypassiIig the iD1et. A temporary dike may be necessary on the dowalope side of the structure.
Figure 4.'14 - Block and Gravel Filter
Gravel and Wire Mesh Filter - A gravel barrier placed over the top of the
inlet. This structure does not provide an overflow.
· Hardware cloth or comparable wire mesh with ~-inch openings.
· Coarse aggregate.
r ~; \.l Y j ~ \f\\ \ · Height I-foot or more, 18 inches wider than inlet on all sides.
rR~~~-:-~--~l\). ~m:,::e~:~ondm::'::'::'~':ll .:5:L
. , \, ~ . ~ U G - c \ ~ If more than one strip of mesh is necessary, overlap the strips; 111 !Q t
, , ,.~~d~,_'d--'- . \ Place coarse aggregate over the wire mesh.
· The'depth of the gravel should be at least 12 inches over the entire '.
inlet opening and extend at least 18 inches on all sides.
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Catchbasin Filters - Inserts should be designed by the manufacturer for
use at construction sites. The limited sediment storage capacity increases
the amount of inspection and maintenance required, which may be daily
for heavy sediment loads. The maintenance requirements can be reduced
by combining a catchbasin filter with another type of inlet protection.
This type of inlet protection provides flow bypass without overflow and
therefore may be a better method for inlets located along active rights-of-
way.
· 5 cubic feet of storage.
· Dewatering provisions.
· High-flow bypass that will not clog under normal use at a construction
site.
· The catchbasin filter is inserted in the catchbasinjust below the
grating.
Curb Inlet Protection with Wooden Weir - Barrier formed around a curb
inlet with a wooden frame and gravel.
· Wire mesh with ~-inch openings.
· Extra strength filter cloth.
· Construct a frame.
· Attach the wire and filter fabric to the frame.
· Pile coarse washed aggregate against wire/fabric.
· Place weight on frame anchors.
Block and Gravel Curb Inlet Protection - Barrier formed around an inlet
with concrete blocks and gravel. See Figure 4.14.
· Wire mesh with ~-inch openings.
· Place two concrete blocks on their sides abutting the curb at either side
of the inlet opening. These are spacer blocks.
· Place a 2x4 stud through the outer holes of each spacer block to align
the front blocks.
· Place blocks on their sides across the front of the inlet and abutting the
spacer blocks.
· Place wire mesh over the outside vertical face.
· Pile coarse aggregate against the wire to the top of the barrier.
Curb and Gutter Sediment Barrier - Sandbag or rock berm (riprap and
aggregate) 3 feet high and 3 feet wide in a horseshoe.shape. See Figure
4.16.
· Construct a horseshoe shaped berm, faced with coarse aggregate if
. using riprap, 3 feet high and 3 feet wide, at least T. ~ from~~~~. ;f iF
· =:~o::t~~..::ro.-:~te~~ ~ u: ~
' , AUG - 5 2005 lWI
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Volume 11- Construction Stonnwater Pollution Prevention;
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Maintenance
Standards
· Catch basin filters should be inspected frequently, especially after
storm events. If the insert becomes clogged, it should be cleaned or
replaced.
· For systems using stone filters: If the stone filter becomes clogged
with sediment, the stones must be pulled away.from the inlet and
cleaned or replaced. Since cleaning of gravel at a construction site
may be difficult, an alternative approach would be to use the clogged
stone as fill and put fresh stone around the inlet.
· Do not wash sediment into storm drains while cleaning. Spread all
excavated material evenly over the surrounding land area or stockpile
and stabilize as appropriate.
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Volume 11- Construction StOlTlJwater Pollution Prevention
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Plan View
Back of Sidewalk
A
Back of Curb
Section A - A
Curb Inlet
Catch Basin
NOTES:
1. Use block and gravel type sediment barrier when curb Inlet is Iocaled In genUy sloping street segment,
where water can pond anc/ allow secllment to separate tom nmlf. ~"" "'-m
2. Barrier shall allow for overflow from severe storm event. , , , r r I
3. Inspect barriers and remove ~lment after each storm event. Sediment and grave/ m ,be ~ed___!...~_...:::,_ _ i
fran the traveled way immediately. ",\ l i I
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figure 4.15 - Block and GnlYeI Curb Inlet p_on' AUG - 5 200, ! I~I
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FebnJary 2005
Volume 11- Construction Stonnwater Pollution ,Prevention '
4-87
Plan View
.l Back of Sidewalk
RUNOFF
RUNOFF
Back ofeurb
NOTES:
1. Place curb type sediment barriers on gently sloping street segments, where water can pond and allow
sediment to separate from runoff.
2. Sandbags of either burlap or woven 'geotex,tile' fabric, are filled with gravel, layered and packed tightly.
3. Leave a one sandbag gap in the top row to provide a spillway for overflow.
4; Inspect baaiers and remove sediment after each stoJm event Sedimentand gravel must be removed from
the traveled way immediately.
FI ure 4.16 - Curb and Gutter Bamer
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Purpose
BMP C230: Straw Bale Barrier
Conditions of Use Below disturbed areas subject to sheet and rill erosion.
· Straw bales are among the most used and least etTectiveBMPs. The
best use of a straw bale is hand spread on the site.
· Where the size of the drainage area is no greater than 1/4 acre per 100
feet of barrier length; the maximum slope length behind the barrier is
100 feet; and the maximum slope gradient behind the barrier is 2: 1.
· ,Where effectiveness is required for less than three months.
· Under no circumstances should straw bale barriers be constructed
in streams, channels, or ditches.
· Straw bale barriers should not be used where rock or hard surfaces
prevent the full and uniform anchoring of the barrier.
Bales shall be placed in a single row, lengthwise on the contour, with ends
of adjacent bales tightly abutting one another.
All bales shall be either wire-bound or.string-tied. Straw bales shall be
installed so that bindings are oriented arOlmd the sides rather than along
the tops and bottoms of the bales in order to prevent deterioration of the
bindings.
· The barrier shall be entrenched and backfilled. A trench shall be
excavated the width of a bale and the length of the proposed barrier to
a minimum depth of 4 inches. The trench must be deep enough to
remove all grass and other material that might allow underflow. After
the bales are staked and chinked (filled by wedging), the excavated '
soil shall be backfilled against the barrier. Backfill soil shall conform
to the ground level on the downhill side ~d shall be built up to 4
inches against the uphill side of the barrier. '
· Each bale shall be securely anchored by at least two stakes or re-bars
driven through the bale. The first stake in each bale shall be driven ,
toward the previously laid bale to force the bales together. Stakes or
re-bars shall be driven deep enough into the ground to securely anchor
the bales. Stakes should not extend above the bales but instead should
be driven in flush with the top of the bale for safety reasons.
· The gaps 'between the bales shall be chinked (filled by wedging) with
s1raw to prevent water from escaping ~es. r.oom.s1raw
. ~==~~.w.::r~. '. ,.~~~-JnYI
. m order not to separate the bales. i I \1 i . t, Ii 1.1./
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Volume 11- Construction stonnwaler Pollution Pre~nfiOfr^~ ._~,,- -'-'--4-89"
Design and
Installation
SpecifICations
.
To decrease the velocity of sheet flows and intercept and detain small
amountS of sediment from disturbed areas of limited extent, preventing
sediment from leaving the site. See Figure 4.17 for details on straw bale
barriers. '
'.
FebnJaty 2005
Maintenance
Standards
· Straw bale barriers shall be inspected immediately after each tunoff-
producing rainfall and at least daily during prolonged rainfall.
· Close attention shall be paid to the repair of damaged bales, end runs,
and undercutting beneath bales.
· Necessary repairs to barriers or replacement of bales shall be
accomplished promptly. '
· Sediment deposits should be removed after each runoff-producing
rainfall. They must be removed when the level of deposition reaches
approximately one-half the height of the barrier. ,
· Any sediment deposits remaining in place after the straw bale barrier
is no longer required shall be dressed to conform to the existing grade,
prepared and seeded.
· Straw bales used as a temporary straw bale barrier shall be removed
after project completion and stabilization to prevent sprouting of
unwanted vegetation.
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Volume 11- Construction Stonnwater Pollution Prevention
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Section A - A
I ....'
r(105-1oam)
Ponding Height
Section B - B
7,.
A,
Plan
BI~
NOTES:
1. The straw bales shall be placed on slope contour.
2. Bales to be placed in a row with 1he ends tightly abutting.
3. Key in bales to prevent erosion or flow under bales.
~1/
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Embed Straw Bale
4" (100mm) Minimum
into Soli
Angle Stake Toward
Previous Bale to
Provide TIght Fit
Figure 4.17 Straw Bale Barrier
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Volume 11- Construction Stonnwater Pollution Prevention
4-91
Purpose
BMP C231: Brush Barrier
Conditions of Use
Design and
Installation
SpecifICations
Maintenance
Standards
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The purpose of brush barriers is to reduce the transport of coarse sediment
from a construction site by providing a temporary physical barrier to
sediment and reducing the runoff velocities of overland flow.
· Brush barriers may be used downslope of all disturbed areas of less
than one-quarter acre.
· Brush barriers are not intended to treat concentrated flows, nor are
they intended to treat substantial amounts of overland flow. Any
concentrated flows must be conveyed through the drainage system to a
sediment pond. The only circwnstance in which overland flow can be
treated solely by a barrier, rather than by a sediment pond, is when the
area draining to the barrier is small.
· Brush barriers should only be installed on contours.
· Height 2 feet (minimum) to 5 feet (maximum).
· Width 5 feet at base (minimum) to 15 feet (maximum).
· Filter fabric (geotextile) may be anchored over the brush berm to
enhance the filtration ability of the barrier. Ten-ounce burlap is an
,adequate alternative to filter fabric.
· Chipped site vegetation, composted mulch, or wood-based mulch (hog
fuel) can be used to construct brush barriers.
· A 100 percent biodegradable installation can be constructed using 10-
ounce burlap held in place by wooden stakes. Figure 4.18 depicts a
typical brush barrier.
· There shall be no signs of erosion or concentrated runoff under or
around the barrier. If concentrated flows are bypassing the barrier, it
must be expanded or augmented by toed-in filter fabric.
· '.The dimensions of the barrier must be maintained.
Min. 5' wide brush banier with
max. 6" diameter ~ debris.
A1tematively topsoil stripPlngs
may be used to fbrm the barrier.
.5\
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Figure 4.18 - Brush Barrier
Volume 11- Construction stonnwater Pollution Prevention
February 2005
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BMP C232: Grav.1 Filter Berm
Purpose
Conditions of Use
Design and
Installation
SpecifICations
Maintenance
Standards
February 2005
A gravel filter berm is constructed on rights-of-way or traffic areas within
a construction site to retain sediment by using a filter berm of gravel or
crushed rock.
Where a temporary measure is needed to retain sediment from rights-of-
way or in traffic areas on construction sites.
· Berm material shall be % to 3 inches in size, washed well-grade gravel
or crushed rock with less than 5 percent fines.
. Spacing of berms:
- Every 300 feet on slopes less than 5 percent
- Every 200 feet on slopes between 5 percent and 10 percent
- Every 100 feet on slopes greater than 10 percent
· Berm dimensions:
- 1 foot high with 3: 1 side slopes
- 8 linear feet per 1 cfs runoffbased on the 10-year, 24-hourdesign
storm
· Regular inspection is required. Sediment shall be removed and filter
material replaced as needed.
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Volume 11- Construction Stonnwater Pollution Ptevention
4-93
BMP C233: Silt Fence
.
Purpose Use of a silt fence reduces the transport of coarse sediment from a
construction site by providing a temporary physical barrier to sediment
and reducing the runoff velocities of overland flow~ See Figure 4.19 for
details on silt fence construction.
Conditions of Use Silt fence may be used downslope of all disturbed areas.
· Silt fence is not intended to treat concentrated flows, nor is it intended
to treat substantial amOlmts of overland flow. Any concentrated flows
must be conveyed through the drainage system to a sediment pond.
The only circumstance in which overland flow can be treated solely by
a silt fence, rather than bya sediment pond, is when the area draining
to the fence is one acre or less and flow rates are less than 0.5 cfs.
· Silt fences should not be constructed in streams or used in V-shaped
ditches. They are not an adequate method of silt control for anything
deeper than sheet or overland flow.
Joints In filter fabriC shall be spliced at '
posts. Use staples, wire rings or
equivalent to attach fabric to posts
I
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II
2")(2" by 14 Ga. wire or
equivalent_if standard
strength Taboo used
Alter fabric
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1"1:. 6' max - - - ;-y ,-",- Minimum 4"x4" trench
,U / l\;Sackfjll trench wUh native soil
Post spacing may be Increased or 314"-1.5" washed gravel
to 8' If wire backing Is used
2")(2" wood posts, steel fence
posts, or equivalent
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Figure 4.19 -Silt Fence
, Design and
Installation
Specijications
· Drainage area of 1 acre or less or in combination with sediment basin
in a larger site.
· Maximum slope steepness (normal (perpendicular)to fence line) 1:1.
/1) 1:~_~L_-.1~ iml := ;:::1811 ~ow paIh leugth to 1he ftmce of 100 feel
,\ l'! d! I.:
I , ,\ ! ! . } ~i 1)e geotextile used shall meet the following standards. All geotextile
'I . I ' ~ i properties listed below are minimum average roll values (i.e., the test
~-...~,. .." ..", ' resUlt for any sampled roll in a lot shall ~~etQr.e~ceed., the values .
shown in Table 4.10):
, ...51.
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Polymeric Mesh AOS
(ASTM04751)
Table 4.10
Geotextlle Standards
0.60 nun maximum for slit film wovens (#30 sieve). 0.30
nun maximum for all other geotextile types (#50 sieve).
0.15 nun minimum for all fabric types (#100 sieve).
0.02 sec- minimum
Water ,Permittivity
(ASTMD4491)
Grab Tensile Strength
(ASTM D4632)
180 Ibs. Minimum for extra strength fabric.
100 lbs minimum for standard strength fabric.
Grab Tetisile Strength 30% maximum
(ASTM D4632)
Ultraviolet Resistance . 70% minimum
(ASTM 04355)
· Standard strength fabrics shall be supported with wire mesh, chicken
wire, 2;.inch x 2-inch wire, safety fence, or jute mesh to increase the
strength of the fabric. Silt fence materials are available that have
synthetic mesh backing attached.
· Filter fabric material shall contain ultraviolet ray inhibitors and
stabilizers to provide a minimum of six months of expected usable
construction life at a temperature range ofooF. to 120oF.
· 100 percent biodegradable silt fence is available that is strong, long
lasting, and can be left in place after the project is completed, if
p~tted by local regulations.
· Standard Notes for construction plans and specifications follow. Refer
to Figure 4.19 for standard silt fence details.
The contractor shall install and maintain temporary silt fences at the
locations shown in the Plans. The silt fences shall be constructed. in
the areas of clearing, grading,. or drainage prior to starting those
activities. A silt fence shall not be considere4 temporary if the silt
fence must fUnction beyond the life of the contract The, silt fence
shall prevent soil carried by nmoff water from going beneath, through,
or over the top of the silt fence,. but shall allow the water to pass
throUgh the fence.
The .minimum height of the top of silt fence shall be 2 feet and the
maximum height shall be 2~ feet above the originalgrolUld surface.
The geotextile shall be sewn together at the point of manufacture, or at
an approved location as determined by the Engineer, to form geotextile
lengths as required. All. sewn seams shall be located at a SUPPOrt post.
Alternatively, two sections of silt fence can be overlapped, provided
the Contractor can demonstrate, to the sa1W'actioft~, tJ1at. re-~""
, ::soev:=~~~o::;~:~~:d~=rft.,o~"i.i;=-;h:g~- L \) ~j,rr~,ii
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to.."""._..",.. ... '. ,.".,.'-."...."'.,~.,,_.,-"'._c._'...._..d.'-.,.......~_, _.J
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The geotextile shall be attached on the up-slope side of the posts and .
support system with staples, wire, or in accordance with the
manufacturer's recomniendations. The geou,xtile shall be attached to
the posts in a manner that reduces the potential for geotextile tearing at
the staples, wire, or other connection device. Silt fence back-up
support for the geotextile in the fonn of a wire or plastic mesh is
dependent on the properties of the geotextile selected for use. If wire
or plastic back-up mesh is used, the mesh shall be fastened securely to
the up-slope of the posts with the geotextile being up-slope of the
mesh. back-up support.
The geotextile at the bottom of the fence shall be buried in a trench to
a minimum depth of 4 inches below the ground surface. The trench
shall be backfilled and the soil tamped in place over the buried portion
of the geotextile, such that no flow can pass beneath the fence and
scouring can not occur. When wire or polymeric back-up support
mesh is used, the wire or polymeric mesh shall extend into the trench a
minimum of 3 inches.
The fence posts shall be placed or driven a minimum of IS inches. A
minimum depth of 12 inches is allowed if topsoil or other soft
subgrade soil is not present aild a minimum depth of IS inches cannot
be reached. Fence post depths shall be increased by 6 inches if the
fence is located on slopes of3:1 or steeper and the slope is
perpendicular to the fence. If required post depths cannot be obtained,
the posts shall be adequately secured by"racing or guying to prevent
overturning of the fence due to sediment loading.
Silt fences shall be located on contour as much as possible, except at
the ends of the fence, where the fence shall be turned liphill such that
the silt fence captures the runoff water and prevents water from
. flowing around the end of the fence. .
If the fence lllust cross contours, with the exception of the ends of the
fence, gravel check ~ placed perpendicular to the back of the fence
shall be used to minimi7'.e concentrated flow and erosion along the
back of the fence. The gravel check dams shall be approximately 1-
foot deep at the back of the fence. It shall be continued perpendiculai
to the fence at the same elevation until the top of the check dam
intercepts ~e ground surface behind the. fence. The gravel check dams
shall consist of crushed surfacing base course, gravel backfill for
walls, or shoulder ballast. The gravel check dains shall be located
every 10 feet along the fence where the fence must cross contours.
The slope of the fence line where contours must be crossed shall not
be~tban 3:1. .
, ,
Wood, steel or equivalent posts shall be used. Wood posts shall have
minimum dimensions of 2. inches by 2 inches by 3 feet minimum
length, and shall be free of defects such as knots,sp]its,Ot80vges.
VoIlIIIIe 11- ConsIrocIIon StonnwsIer PoIutJon ~:f~~.~
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Steel posts shall consist of either size No.6 rebar or larger, ASTM A
120 steel pipe with a minimum diameter of l-inch,U, T, L, or C shape
steel posts with a minimum weight of 1.35 lbs.lft. or other steel posts
having equivalent strength and bending resistance to the post'sizes
listed. The spacing of the support posts shall be a maximum of 6 feet.
Fence back-up support, ifused, shall consist of steel wire with a
maximum mesh spacing of 2 inches, or a prefabricated polymeric
mesh. The strength of the wire or polymeric mesh shall be equivalent
to or greater than 180 lbs. grab tensile strength. The polymeric mesh
must be as resistant to ultraviolet radiation as the geotextile it supports.
· Silt fence installation using the slicing method specification details
follow. Refer to Figure 4.20 for slicing method details.
The base of both end posts must be at least 2 to, 4 inches above the top
of the silt fence fabric on the middle posts for ditch checks to drain
properly. Use a hand level or string level, ifnecessary, to mark base
points before installation.
Install posts 3 to 4 feet apart in critical retention areas and 6 to 7 feet ,
apart in standard applications. '
Install posts 24 inches deep on the downstream side of the silt fence,
and as close as possible to the fabric, enabling posts to support the
fabric from upstream water pressure.
Install posts with the nipples facing away from the silt fence fabric.
Attach the fabric to each post with three ties, all spaced within the top
8 inches of the fabric. Attach each tie diagonally 45 degrees through
the fabric, with each puncture at least 1 inch vertically apart. In .
addition, each tie should be positioned to hang on a post nipple when
tightening to prevent sagging.
Wrap approximately 6 inches of fabric around the end posts and secure
with 3 ties.
No more than 24 inches of a 36-inch fabric is allowed above ground
level.
The rope lock system must be used in all ditch check applications. '
The installation should be checked and corrected for any deviation
before compaction. . Use a flat-bladed shovel to tuck fabric deeper into
the ground ifnecessary. '
Compaction is vitally.important for.effective results. Compact the soil
immediately next to the silt fence fabric with$t wheel of the
tractor, skid steer, or roller exerting at least 6 ~ ~ square hlCh;,;2:--
Comp~ct the upstream. side first and then eac ~twietr:~.9~ 1 !~W
four trips. " I I" {I
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Volume /1- Construction Stonnwater Pollution Pl8vfirition' '~''''';-,-"~9?~,,J
Maintenance
Standards
· Any damage shall be repaired immediately.
· If concentrated flows are evident uphill of the fence, they must be
intercepted and conveyed to a sediment pond.
· Itis important to check the uphill side of the fence for signs of the
fence clogging and acting as a barrier to flow and then causing
chamelization of flows parallel to the fence. If this occurs, replace the
fence or temove the trapped sediment.
· Sediment deposits shall either be removed when the deposit reaches
approximately one-third the height of the silt fence, or a second silt
fence shall be installed.
· If the filter fabric (geotextile) has deteriorated due to ultraviolet
breakdown it shall be re laced.
.
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Figure 4.20 - Silt Fence Instanltlon by Slicing MtIIlod'
.
, 4-98
Volume 1I-.ConstnJctionstormwater Pollution Prevention
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February 2005