HomeMy WebLinkAboutEngineered Stormwater, Erosion and Sediment Plan and Report 002352019651 Bachelor Road, Sequim, WA 99392
Jefferson County Parcel #f 002352019
Stormwater, Erosion, and Sediment Control Plan and Report
Prepared For
Terry Parks and Christine Clark
November 2015
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NORTHWESTERN TERRITORIES, INC.
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717 SOUTH PEABODY STREET. PORT ANGELES, WA 98362
Engineers ❑ Lend Surveyors O Geologists
Constmchon 0 Inspection D Malenals Teshw
(360(462-8491
Email:
NTI
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November 30, 2015
NORTHWESTERN TERRITORIES, INC.
717 SOUTH PEABOOy STREET, PORT ANGELES, WA 98362
Engineers C Land Sw Sym ❑ Geologists
Cons9ucgon Inspedion E Materials Testing
Phow: (360) 462-9491
EdAall: l4W
Mr. Terry Parks and Christine Clark
651 Bachelor Road
Sequim, WA 98382
Subject: STORMWATER, EROSION, AND SEDIMENT CONTROL PLAN AND REPORT FOR THE NEW
HOME ADDITION AT 651 BACHELOR ROAD; SEQUIM (GARDINER), WA 98382.
JEFFERSON COUNTY PARCEL Jt: 002352019
Dear Mr. Parks and Others Concerned,
1.0 BACKGROUND AND SCOPE OF WORK
NTI Engineering and Land Surveying (NTI) was requested by Terry Parks and Christine Clark to prepare a
Stormwater, Erosion, and Sediment Control Plan to mitigate stormwater runoff related to the proposed
house addition for the subject parcel. The 0.66 acre property has been assigned Jefferson County parcel
number 002352019 and it is located within the Northwest Quarter of Section 35, Township 30 N, Range
2 West, W.M., within Jefferson County, Washington. In July 2015, NTI completed a geotechnical review
of the proposed home addition and site and provided geotechnical recommendations for stormwater
management.
The house addition project proposed for the subject property includes the following:
ace Type
Effective Impervious Surface Area (square feet)
le family residence
1,400
ting garage
1,054
isting shed
96
Mdriveway
gravel driveway
4,356
oncrete parking
1,141
Tpervious Surface Area
8,047
d home addition
126
Reduction in gravel driveway area
389
Total Resulting Impervious Surface Area
7.794
2.0 STORMWATER PERMITTING REQUIREMENTS
Development projects within the jurisdiction of Jefferson County are required to prepare stormwater
control plans in accordance with the Department of Ecology's (DOE) 2012 Stormwater Management
Manual for Western Washington (SMMW W). The scope of engineering design requirements is generally
Stormwater, Erosion, Sediment Control Plan and 2015
Report
based on the total area of new impervious surfaces and total land disturbing activities. The Stormwater
Calculation Worksheet and Flow Chart for New Development provided by Jefferson County were
completed to determine the applicable engineering design requirements. These documents are located
in Appendix I of this report for reference. Since the resulting total impervious surface area proposed by
the project will be less than the existing total, this project is considered a "Small Project" per DOE
stormwater management requirements and thus only minimum requirement #2 of the DOE 2012
SMMW W must be met. This minimum requirement is discussed in more detail in Section 6 of this
report.
3.0 GEOTECHNICAL RECOMMENDATIONS PROVIDED BY INTI
The July 2015 NTI Geotechnical Report completed in regards to the proposed development actions
recommended that stormwater runoff from the residence be tightlined to a catch basin that is part of
the existing stormwater system for the garage site. A recommendation to direct surface runoff from the
existing gravel driveway to the catch basin was also provided. The purpose of directing surface runoff to
the Catch basin is to reduce the volume of runoff that is currently directed towards the rockery along the
east property line. These geotechnical recommendations have been incorporated into the stormwater
Control Plan shown in Appendix II of this report.
4.0 EXISTING STORMWATER MANAGEMENT SYSTEM AT THE SUBJECT PARCEL
The location(s) of existing stormwater conveyance lines, facilities, and natural drainage paths was
reviewed in the field so that an accurate stormwater site plan could be prepared for the new home
addition. An existing SR" diameter concrete culvert spans the middle of the property that collects
natural surface run-on from the west and discharges near the east property line. The discharge point
has a well -incised drainage path that has historically carried runoff to the shoreline on the north for
many years.
Stormwater runoff from the existing garage and concrete parking area is directed into a catch basin
system that has an outfall near the outlet of the concrete culvert mentioned above. During our site
review, the exact outfall location of stormwater pipes from the existing residence could not be found.
We suspect that the stormwater outlet pipe from the residence is located within close vicinity to the
residence and the east property line and is likely not connected to the existing Catch basin system.
Runoff from the existing gravel driveway is dispersed over grass vegetation within the site.
The configuration of the existing stormwater system can be seen in the project plans found in Appendix
11 of this report.
Stormwater, Erosion, Sediment Control Plan and 2015
Report
5.0 PROPOSED MODIFICATION OF THE EXISTING STORMWATER SYSTEM
We recommend that during construction of the home addition, that the existing stormwater pipes from
the residence be located and replaced with new piping that is tightlined to the existing catch basin and
stormwater system. Runoff from the addition should also be tightlined to the existing catch basin.
We also recommend that part of the gravel driveway approach nearthe residence be re -graded to direct
surface runoff towards a new curtain drain that will be connected to the existing catch basin. To make
room at the site for the new addition, we also recommend that the edge of the gravel driveway nearest
to the addition be moved about 5 -feet. This action also has the benefit of reducing the total impervious
surface area and should improve drainage conditions at the site. To help meet the geotechnical
recommendation for stormwater management, reclaimed gravel should be used to re -grade the gravel
driveway as mentioned above and as shown in the plans found in Appendix II of this report.
6.0 STORMWATER PLAN AND DESIGN REQUIREMENTS
Minimum requirement #2 of the DOE 2012 SMMW W has been followed to complete an Erosion and
Sediment Control Plan for the proposed project. Compliance with the minimum requirement is
summarized as follows:
Minimum Requirement #2— Construction Stormwater Pollution Prevention
To prevent erosion and discharge of sediment and other pollutants into receiving waters an Erosion and
Sediment Control Plan for the project has been developed and is included with the Stormwater Control
Plan in Appendix II. The 12 Elements of construction stormwater pollution prevention were considered
in developing the plan. Construction recommendations for meeting the goals of the 32 Elements of
construction stormwater pollution prevention are provided in this section.
Element#1: Preserve Vegetation/ Mark Clearing Limits
Before beginning land disturbing activities, including clearing and grading, the contractor shall
clearly mark all clearing limits. The clearing limits shall be kept to the minimal area necessary to
construct the proposed facilities.
The native top soil and natural vegetation must be retained in an undisturbed state to the
maximum degree practicable.
Element #2: Establish Construction Access
Access to the site is currently available from the existing gravel driveway. The existing gravel
surface should be sufficient to serve as a construction entrance.
Any sediment tracked off site onto roadways shall be cleaned thoroughly at the end of each day
or more frequently as necessary. Remove sediment from roads by shoveling, sweeping, or pick
Stormwater, Erosion, Sediment Control Plan and 2015
Report
up and transport the sediment to a controlled sediment disposal area. Afterwards, conduct
street washing if necessary.
Element 713: Control Flow Rates
Properties and waterways downstream of the project must be protected from erosion resulting
from increases in velocity of stormwater runoff from the project site. The permanent
stormwater facilities proposed should be constructed and made functional prior to completion
of site developments. These facilities should be protected from siltation during the construction
phase.
Element 714: Install Sediment Controls
The contractor is responsible for installing and maintaining effective erosion control and
sediment control BMP's to minimize the discharge of pollutants. These BMP's shall be
functional before land disturbing activities take place. Silt fencing should be installed per
instructions provided in the Temporary Erosion & Sediment Control Plan.
Elementt75: Stabilize Soils
Exposed and unworked soils shall be stabilized by application of effective BMP's that prevent
erosion.
Soils must not remain exposed and unworked for more than the time periods set forth below to
prevent erosion:
• During the dry season (May 1—Sept. 30): 7 days
• During the wet season (October 1—April 30): 2 days
Stabilize soils at the end of the shift before a holiday or weekend if needed based on the
weather forecast.
Stabilize soil stockpiles from erosion, protected with sediment trapping measures, and where
possible, be located away from storm drain inlets, and drainage channels.
The amount of exposed soil should be minimized as much as possible during construction
activity.
Element#6: Protect Slopes
The bluff at the north end of the property and the rockery near the existing home must be
protected from runoff and erosion throughout the construction period. Silt fencing and/or
straw wattles should be installed to protect these areas.
Stormwater, Erosion, Sediment Control Plan and 2015
Report
Element #7: Protect Drain Inlets
Catch basin inlets must be protected from sediment throughout the construction period. Catch
basin filters should be installed and maintained throughout the duration of the project to
protect the new stormwater system.
Element #8: Stabilize Channels and Outlets
There are no channels or outlets to stabilize as part of this project.
Element#9: Control Pollutants
The contractor shall install, implement, and maintain effective pollution prevention measures to
minimize the discharge of pollutants.
The contractor shall handle and dispose of all pollutants, including waste materials and
demolition debris that occur on-site in a manner that does not cause contamination of
stormwater.
Cover, containment, and protection from vandalism for all chemicals, liquid products, petroleum
products, and other materials that have the potential to pose a threat to human health or the
environment shall be completed by the contractor. On-site fueling tanks must include
secondary containment with 110% of the volume contained in the largest tank within the
containment structure. Double -walled tanks do not require additional secondary containment.
Conduct maintenance, fueling, and repair of heavy equipment and vehicles using spill
prevention and control measures. Clean contaminated surfaced immediately following any spill
incident.
Apply fertilizers and pesticides in a manner and at application rates that will not result in loss of
chemical to stormwater runoff. Follow manufacturer's label requirements for application rates
and procedures.
Adjust the pH of stormwater if necessary to prevent violations of water quality standards.
Assure that washout of concrete trucks is performed off-site or in designated concrete washout
areas only. Do not washout concrete trucks onto the ground, or into storm drains, open
ditches, streets, or streams. Do not dump excess concrete on-site, except in designated
concrete washout areas. Concrete spillage or concrete discharge to surfaces waters of the state
is prohibited.
Element#30: Control De -watering
Any required de -watering shall be maintained onsite with applicable BMP.
Stormwater, Erosion, Sediment Control Plan and 2015
Report
Element#11: Maintain BMPS
Maintain and repair all temporary and permanent erosion and sediment control BMPs as
needed to assure continued performance of their intended function in accordance with BMP
specifications.
Remove all temporary erosion and sediment control BMPs within 30 days after achieving final
site stabilization or after the temporary BMPs are no longer needed.
Element#12: Manage the Project
Inspect, maintain, and repair all BMPs as needed to assure continued performance of their
intended function.
Maintain and update the construction SWPPP.
7.0 THE LIMITATIONS OF THIS REPORT
This report has been prepared for the exclusive use of Terry Parks and Christine Clark for the proposed
residential home addition mentioned herein. The recommendations in the report apply only to the
property that was evaluated and they are not transferrable to other locations. The site evaluation and
recommendations contained in this report are based upon site conditions as they existed at the time of
our studies. During construction, if subsurface or other conditions are discovered that are significantly
different from those described in this report, NTI should be advised at once so that we may review the
conditions and reconsider our recommendations, where necessary. We recommend that a contingency
be established in the project budget and schedule to cover unexpected conditions.
Within the limitations of scope, schedule, and budget, our services have been executed in accordance
with generally accepted professional engineering principles and practice. This warranty is in lieu of all
others either expressed or implied.
Sincerely Yours,
NTI Engineering and Land Surveying
Trent T. Adams, EIT Justin Wilson, PE
Geotechnical Project Manager Principal Engineer
APPENDIX I - PERMITTING DOCUMENTS
FIGURE 5: NEW DEVELOPMENT
Start Here
Does the site have
Yes
See Redevelopment
35% or more of
Minimum
Requirements and
existing impervious
Flow Chart
coverage?
(Figure 2)
No
Does the project convert'/.
or acedapply
to the new impervious
acres or more of native
impces?surfaces
and converted
vegetation to lawn or
Does the project add No
landscaped areas, or
5,000 square feet or
convert 2.5 acres or more
Does the project have
more of new
of native vegetation to
landtdisturbing
impervious surfaces?
pasture?
activities of 7,000
Yes
Yes no
1
Doe;hha have
2,0t or
"LARGE" PROJECT
moreaced,All
Minimum Requirements
or acedapply
to the new impervious
impces?surfaces
and converted
pervious surfaces.
Yes
"MEDIUM" PROJECT
Does the project have
Minimum Requirements #1
landtdisturbing
throw #5 apply to the new
pp y Yes
activities of 7,000
and replaced impervious
square feet or more?
surfaces and the land
Baudon Fig. 12 from 2001 Ecology&ro w0lrMmgemenr Mannalfw Western Wash'nVo
ROJECT
mum
torrawater
ELRequimment#2,
vention
Baudon Fig. 12 from 2001 Ecology&ro w0lrMmgemenr Mannalfw Western Wash'nVo
4S�N �o DEPARTMENT OF COMMUNITY DEVELOPMENT
44w G� 621 Sheridan Scree, Pon Townsend, WT 98368
Td: 360.379.44501 Fax360.3794951
Web: .1u.i1flensm 19'/ 'ydevd,mmem
qSH] NO'S
STORMWATER CALCULATION WORKSHEET
Mwa
Penacr/APPUrAm NAME Home Addition - Terry Parks S Chris Clark
DETERMINING STORMWATER MANAGEMENT REOUIREMEWS: This stormwater calculation wormeet snoma De camprewo nrs to
classify the proposal as "small," "medium," or "large." The size determines whether a Stermwater Site Plan is required in
conjunction with a stand-alone stormwater management permit application, building permit application, Or other land use approval
application that involves stormwater review. The basic information will also be helpful for completing a Stormwater Site Plan, if
requir
=c.
PARCEL SIZE (I.E. SITE)
Size of parcel 0'66 acres An acre contains 43,560 square feet. Multiply the acreage by this figure.
Site of parcel in square feet 28,897 sq/ft
Land -disturbing activity is any activity that results in movement of earth, or a change in the existing soil cover (both vegetative and
non.vegetative) and/or the existing soil topography. land disturbing activities include, but are not limned to clearing, grading, filing,
excavation, and compaction associated with stabilization of structures and road construction.
Native vegetation is vegetation comprised on plant species, other than noxious weeds, that are indigenous to the coastal region of
the pacific Northwest and which reasonably could have been expected to naturally occur on the site. Examples include species such
as Douglas fir, western hemlock, western red cedar, alder, big -leaf maple, and vine maple; shrubs such as willow, elderberry,
salmonberry, and salal; herbaceous plants such as sword fern, foam flower, and fireweed.
LAND DISTURBING ACTIVITY CONVERSION OF NATIVE VEGETATION AND VOLUME OF CUTIFILL
Calculate the total area to be cleared. graded, filled,
excavated, and/or compacted for proposed development
project. Include in this calculation the area to be cleared for.
Construction site for structures 126 sglft
Drunfeld, septic tank, etc. 0
sq/ft
Well, utilities, etc. 0
SEIM
Driveway, packing, roads, etc. 389
sglft
Lawn, landscaping, etc.
Wit
Other compacted surface, etc.
sq/ft
Total Land Disturbance 515
sgMl
Answer the following two questions related to
conversion of native vegetation:
Does the project convert %acres or more of
native vegetation to lawn or landscaped areas?
Circle: Yes No
Does the pmject convert 2 Yz acres or more of
native vegetation to pasture?
Circle: Yes No
Indicate Total Volumes of Proposed:
Cut 5 Fin 5 (cutyd)
impervious surface is a hard surface that either prevents or retards the entry of water into the soil mantle as under natural
conditions prior to development. A hard surface area which causes water to run off the surface in greater quantities or at an
Increased rate of flow from the flow present under natural conditions prior to development. Common impervious surfaces include,
but are not limned to rooftops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt paving, gravel roads,
packed earthen materials, and oiled, macadam or other surfaces which similarly impede the natural infiltration of stormwater.
Somw,k�-REV.I W1 4
STORMWATER CALULATIONS — IMPERVIOUS SURFACE
NEW
Structures (all roof area) 126
Sidewalks 0
Patios
Solid Decks "+
(wlthout infiltration below)
Driveway, parking, roads, etc -369 sq/g
Other 0 sq/ft
Total New -263
TOTAL NEW +TOTAL EXISTING'
7,784
EXIS NG
Structures (811 roof area) 2,550
Sidewalks
Patios
Solid Decks
(without infiltration below)
Driveway, parking, roads, etc 5'497 sqm
Other 0 sqH[
Total Existing 8'047 sqtft
-This amount will be used to check trial IW coverage.
The following questions will help determine whether the proposed project is considered development or redevelopment.
DEVELOPMENT .REDEVELOPMENT
Divide the total existing impervious surface above by the size of the parcel and convert to a percentage: 28 %
Does the site have 35% or more ofxie sfinc impervious surface? Circle: Yes No
FURTHER INSTRUCnONS: If the answer is yes, the proposal is considered redevelopment and the attached Figure 2 should be used
to determine the applicable Minimum Requirements. If the answer is no, the proposal is considered new, development and the
attached Figure 1 should be used. At this juncture, the applicant should refer to the applicable Flow Chart to determine the
Minimum Requirements for stormwater management. DOD staff will help verify the classification of the project and the application
requirements.
For proponents of "small" projects who must comply only with Minimum Requirement #2—Construction Stormwater Pollution
Prevention—an additional submittal is not required. The proponent is responsible for employing the 12 Elements to control erosion
and prevent sediment and other pollutants from leaving the site during the construction phase of the project. Pick up the
Construction Stormwater Pollution Prevention (SWPP) Best Management Practices (BMPs) Packet. Proponents of "medium"
projects—those that must meet only Minimum Requirements #1 through #S—and for "large" projects—those that must meet all 10
Minimum Requirements—are required to submit a Stormwater Site Plan. DOD has prepared a submittal template of a Stormwater
Site Plan, principally for rural residential projects. Complete the template in the Stormwater Site Pian Instructions and Submittal
Template or prepare a Stormwater Site Plan using the step-by-step guidance in the Stormwater Management Manual.
APPLICANT SIGNATURE
By signing the Stormwater Calculation Worksheet I as the applicant/owner attest that the information provided herein is true and correct to the
best of my knowledge. 1 also certify that this application is being made with the full knowledge and consent of all owners of the affected
property.
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APPENDIX II - PROJECT PLANS
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