HomeMy WebLinkAboutStormwater Narrative 7.28.2022dawn cape engineerinq, Inc,
CIVINGINM 5 & I.ANP 5UMY05
939 MAIN 5f / k019 6A YMMOU1 POk9f, MA 02615
(508) 362-4 41 FAX (508) 362-9880
Date: 7/28/2022
To: Town of Yarmouth Conservation Commission
From: Daniel A. Oiala, PE, PLS down cape engineering inc.
Re: Joseph Gilmore, #150 South Street, Yarmouth, MA
STORMWATER SUPPLEMENTAL NARRATIVE ADDENDUM:
The following information is provided in response to the 7/19/2022 request for additional information
and is intended as an addendum to the original narrative provided with the stormwater permit, along
with the supplemental narrative dated 7/7/2022.
The line and grade of the grass lined swales are shown using spot grades and contour lines indicated on
the Site Plans. A supplemental sheet showing typical sections "Ald construction materials is included. If
the site specific conditions require, any areas which do not seed quickly and rut can be patched and
North American Green erosion control netting will be placed over fresh seed to help ensure
germination and stabilization of the swales.
Upon completion of the dwelling foundation the site shall be re -graded to match the proposed contours
shown on the site plan. This will include the drainage swales directing runoff into the rain garden
areas for infiltration. A cross section of the rain garden and typical grass swales are included in the
report, as is a detail and specifications for the roof drywells used to infiltrate the roof runoff. These
best management practices (BMP) will ensure that stormwater discharges are infiltrated on -site and
not directed toward the Bass River. The calculations indicating a 100 year storm is fully retained onsite
have been previously supplied, by infiltrating onsite, direct stormwater discharges to impaired water
bodies are eliminated, and majority of onsite runoff will be filtered by vegetation prior to entering the
aquifer.
Phosphorous uptake is most efficiently accomplished by the Low Impact Design (LID) specified using
vegetative cover which utilizes the Phosphorous for vegetative plant growth. To this end LID
stormwater solutions have been implemented including rain gardens and grass lined swales, which are
excellent for removing Total Suspended Solids (TSS), Nitrogen, and Phosphorous from
storm water flows. It is anticipated that using these BMW the design requirements of removal of 80%
TSS, 50% TP, and 30% TN will be met. Calculations using EPA's Region 1 BMP Accounting and
Tracking Tool are included in this report. Being a simple single family home fully utilizing LID
BMW's, the site should be found to be in full compliance with the local regulations.
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