HomeMy WebLinkAbout2009.07.22 - Molotsky Wetland Delineation and Enhancement Plan Addendumd
Michael B. Dawson
MOLOTSKY ADDENDUM
July 22,2OOg p 1of 4
1. INTRODUCTION
A Wetland Delineation and Enhancement Plan was submitted to the city of Port T6wnsend for
the Molotsky Addition project on June 26,2009.4' drainage plan was requestedfor t}lle3_5J' -
square foot iAAition and is providedbelow along with revisions to the Site Plan (Figure 7 in the
original report) and plan and sec[ion views of the drarnage plan (Figure 8).
1.1. Drainage Plan
The Molotsky property consists of a8.32-acre (362,371square-foot) parcel with an existing
single-family residenci 33 by 43 feetin area and abarn 47 by 53 feet in area. In addition there is
a gtaveldrive 20 by 30 feet in size and two concrete patios (6by 20 and 15 by 20 feet in size).
T[e total existing impervious sruface is 4,930 square feet, or 1.36% of the total proper$ area-
The proposed addition adds 352 square feet of impervious surface bring$g the total to 5,282
square feet or 1.460/o of the total property area.
The Department of Ecology Stormwater Management Manual for Western W1s!in49n-
(Ecology 2005) was used ai guidance in developing the drainage plan. Section 3.1 of Volume
itt dir*rt.s roof downspout conffols. Since a seasonally high water table exists onsite that may
reach within three feet pf the finished gtade, a dispersion trench system is proposed for
handling roof runoff. For single-family lots grcater than22,000 square feet and for downspouts
draining less than 700 square feet, one 2-footby lO-foot dispersion trench is indicated' One
conditijn for using dispersion trenches is that greater than25 feet of vegetated flowpath mustbe
present between the trench outlet and any wetland. Wefland A lies 30 to 60 feet downslope of
the proposed trench outlet on a gradual slop€. This should provide more ttran adequate
vegetated flowpath for dispersal of the anticipated runoff.
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1,419House
2,491Barn
600Drive
420Patios
1.36%4,930Totalexisting
O.1lo/o352Proposed addition
1.46%5,282New total
Molotsky Addendum, 2009-07'22 p,2 of 4
The addition roof will be a simple gable with aidge running east-west. Gutters along the north
and south rooflines Will each drain to a downspout at the eastern corners. Downspouts will be
connected directly to 4-inch corrugated solid pipe buried in a shallow trench in the setback to
the east of the addition. The two pipes will converge in a wye to a 6-inch catch basin and then
drain to 4-inch perforated pipe in the dispersion trench. The trench will be constructedby Bernt
Ericsen Excavating to the details specified in the plan and section drawings (Figure 8). The
dispersion trench will drain east towards the wetland buffer. No other impervious qurfaces,
structures, roads o( steep slopes exist on3ite downslope of the'dispersion area.
Michael B. Dawson
Wetland Biologist
2. REFERENCES
Ecology 2005. Stormwats Management Manualfor Western Washington, VoL I-V Ecology
Publication #5-1,0-29 through 5-10-33. Olympia, Washington. wwW,9c.y,Wa;gov/
programs /wq/stormwater/manual.html
MichaelB.Dawspn@gma.il,com . 1361 51* Street . Poft Townsend . WA 98368 . 360-385'1773
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Figure 7. Site Plan - Revised July 2009
Molotsky Addend um 2009107 122
Buffer reduction and enhancement
Michael B. Dawson
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ridge
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L76 sf
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Figure 8. Drainage Plan and Section
Molotsky Addendum 20091 07 122
Michael B. Dawson