HomeMy WebLinkAbout24SUB2-Stormwater Report
WENTWORTH CIVIL
ENGINEERS LLC
177 West Town Street
Lebanon, Connecticut 06249
Tel. (860) 642-7255
Fax. (860) 642-4794
Email: Wes@WentworthCivil.com
March 6, 2024 – Revised May 28, 2024
Sara Lundy, Chair
Montville Planning & Zoning Commission
310 Norwich-New London Tpke
Uncasville, CT 06382
Re: Black Ash Estates Re- Subdivision
Black Ash Rd. and
Old Colchester Rd.
Montville, CT
Dear Sara:
I am writing to you in regards to your above referenced 13 lot subdivision.
The subdivision layout has been designed to minimize potential onsite and
offsite drainage impacts due to development.
The lot design encourages overland sheet flow in three major directions (see
attached Overall Drainage Map for reference). The western portion of the site
slopes to a large onsite wetland system that drains southerly via culverts under
Black Ash Road. Similarly, the central portion of the site also drains to a
large onsite wetland that also discharges southerly via culverts under Black
Ash Road. The eastern portion of the site slopes southeasterly towards
abutting properties that front on the north side of Black Ash Road.
Design elements included in the creation of this development include
minimizing impervious areas, maximizing wooded areas, keeping wetlands
and upland review areas undisturbed and in their existing vegetated state.
Other low impact design elements include and encouraging runoff via
overland sheet flow and maximizing infiltration within these areas. All
proposed roof downspouts are to discharge into underground infiltration
drywells. All storm runoff from driveway areas are to be treated in infiltration
trenches or rain gardens. These Low Impact Development design features
will treat pollutants, maximize infiltration, retain runoff and discourage point
discharges of storm water runoff.
Per town engineer recommendations, the following measures have been added
to the design plans:
Lot 9. All proposed activity is north of existing stonewall that
runs east to west through the lot and is the highpoint of the site.
All developed areas on this lot will drain to the north and west,
away from abutting properties.
Lot 10. Grading notes have been added along the western
property line to ensure that drainage runoff from developed areas
will slope to the south towards Lot 9 onsite wetlands.
Lot 11. The rain garden for Lot 11 driveway has been increased
in size to retain up to a 10 year (5.5” precipitation) 24 hour storm
event. A proposed stonewall has been added along the southern
property line to further retain and diffuse runoff from the
developed portion of this lot.
Lot 12. The rain garden treating driveways serving Lots 11 & 12
has been increased in size to retain up to a 10 year (5.5”
precipitation) 24 hour storm event. A proposed stonewall has been
added along the downslope side of the rain garden to provide
additional runoff retention and diffuse any runoff from the
developed portion of this lot. The existing stonewall along the
southern property line will continue to diffuse and retain runoff
sheet flow during larger storm events.
Lot 13. The rain garden for Lot 11, 12 & 13 driveway has been
increased in size to retain up to a 10 year (5.5” precipitation) 24
hour storm event.
The re-subdivision design plans include a site specific erosion and
sedimentation control plan, design calculations for rain gardens and
infiltration trenches, and a long term operation and maintenance plan for these
design elements.
It is my professional opinion that the development of this project as designed
will not result in any significant impacts to drainage runoff onsite or offsite.
If you have any comments or questions, please do not hesitate to contact me.
Sincerely,
Wesley J. Wentworth
P.E. , Soil Scientist
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