HomeMy WebLinkAbout25 SUB 4 Drainage Narrative 6-19-25Indigo Land Design, LLC 860.388.9343 Phone 40 Elm Street, 2nd Floor 860.391.8854 Fax
Old Saybrook, CT 06475 jwren@Indigo-Land.com E-mail www.Indigo-Land.com
JUNE 19, 2025 Re: DeSautels 4-Lot re-subdivision 257 Chesterfield Road (Tax Map 29 Lot 66) Montville, CT 06370 DRAINAGE DESIGN NARRATIVE
This project is a proposed conservation re-subdivision at 257 Chesterfield Road in
Montville, Connecticut. The subject property encompasses approximately 16 acres, including
7.76 acres of wetlands concentrated along the northern boundary. The proposed development
includes the
re-subdivision of the subject property into four (4) residential building lots. All dwellings will
be serviced by public sanitary sewer and private wells.
The existing topography of the site generally slopes from south to north, directing surface
runoff toward the large on-site inland wetland. Site soils, as identified by the USDA NRCS Soil
Survey, are classified as Woodbridge fine sandy loam with 8–15% slopes. This soil type is
characterized as hydrologic group C/D, indicating moderate to slow infiltration potential and a
seasonally high-water table, particularly in undisturbed areas. These hydrologic conditions have
been considered in the sizing and selection of proposed stormwater management measures.
Although site work is conceptual at this stage, the plan includes paved driveways for each
proposed lot, ranging from approximately 1,300 S.F. to 2,100 S.F. of impervious coverage per lot
and house rooftop areas of approximately 1,800 square feet per house. For runoff mitigation
purposes, residential-scale rain gardens have been proposed for each lot. These rain gardens
are designed to capture and treat the first 1.3 inches of rainfall from the impervious areas of each
Lot, consistent with the guidance provided in the 2024 Connecticut DEEP Stormwater Quality
Manual. The rain gardens will promote infiltration, enhance groundwater recharge, and improve
water quality prior to discharge toward the adjacent wetland area.
In addition to these on-site stormwater measures, the plan accounts for an existing town
drainage pipe outlet located on proposed Lot 1. As part of this conceptual layout, the existing pipe
will be extended with approximately 50 lineal feet of 18-inch HDPE pipe and riprap outlet
protection, matched to the existing invert elevation. This extension is intended to better guide
concentrated flows away from the center of proposed Lot 1 and directed towards a stabilized
4-Lot re-subdivision 257 Chesterfield Road
Page 2 of 3
swale or overland sheet flow toward the natural inland wetland system. The extension will reduce
the potential for erosion and help maintain the existing hydrologic function of the site.
Although, no construction is proposed at this time, erosion and sedimentation control
measures are shown on the site plans. Once the project advances to permitting and construction;
site work shall include silt fence downgradient of disturbed areas, stone construction entrances
and temporary stabilized soil stockpile areas.
In summary, the proposed conservation re-subdivision at 257 Chesterfield Road has been
designed to minimize impacts to existing site hydrology and provide stormwater management
consistent with current regulatory standards. Stormwater runoff from new impervious surfaces will
be mitigated using rain gardens designed to treat the required water quality volume. The
extension of the existing drainage pipe will further ensure safe and controlled discharge to the
site’s natural inland wetland system. These measures, together with the site’s protected upland
and wetland buffers, demonstrate that the conceptual subdivision layout can be accommodated
without adverse impact to water resources or downstream properties.
Included below is a summary of water quality volume calculations for each of the 4
proposed Lots.
4-Lot re-subdivision 257 Chesterfield Road
Page 3 of 3
Proposed Lot 1: Proposed impervious coverage: Conceptual House: 1,800 S.F. Conceptual Paved Driveway: 1,300 S.F. Total Conceptual Impervious Area: 3,100 S.F. First 1.3 Inches of Stormwater Runoff: 3,100 S.F. * 1.3”/12” = 336 C.F. Conceptual Rain Garden Sizing: Top Contour Area = 314 S.F. Bottom Contour Area = 63 S.F. Conceptual Rain Garden Depth = 2 FT. Rain Garden Capacity = Avg. Area * Depth = (314 S.F. + 63 S.F.)/2* 2 FT. = 377 C.F. Conceptual Storage Volume 377 C.F. > First 1.3” of Runoff 336 C.F. – O.K. Proposed Lot 2: Proposed impervious coverage: Conceptual House: 1,800 S.F. Conceptual Paved Driveway: 1,300 S.F. Total Conceptual Impervious Area: 3,100 S.F. First 1.3 Inches of Stormwater Runoff: 3,100 S.F. * 1.3”/12” = 336 C.F. Conceptual Rain Garden Sizing: Top Contour Area = 314 S.F. Bottom Contour Area = 63 S.F. Conceptual Rain Garden Depth = 2 FT. Rain Garden Capacity = Avg. Area * Depth = (314 S.F. + 63 S.F.)/2* 2 FT. = 377 C.F. Conceptual Storage Volume 377 C.F. > First 1.3” of Runoff 336 C.F. – O.K. Proposed Lot 3: Proposed impervious coverage: Conceptual House: 1,800 S.F. Conceptual Paved Driveway: 2,100 S.F. Total Conceptual Impervious Area: 3,900 S.F. First 1.3 Inches of Stormwater Runoff: 3,900 S.F. * 1.3”/12” = 423 C.F. Conceptual Rain Garden Sizing: Top Contour Area = 314 S.F. Bottom Contour Area = 113 S.F. Conceptual Rain Garden Depth = 2 FT. Rain Garden Capacity = Avg. Area * Depth = (314 S.F. + 113 S.F.)/2* 2 FT. = 427 C.F. Conceptual Storage Volume 427 C.F. > First 1.3” of Runoff 423 C.F. – O.K. Proposed Lot 4: Proposed impervious coverage: Conceptual House: 1,800 S.F. Conceptual Paved Driveway: 1,450 S.F. Total Conceptual Impervious Area: 3,250 S.F. First 1.3 Inches of Stormwater Runoff: 3,250 S.F. * 1.3”/12” = 353 C.F. Conceptual Rain Garden Sizing: Top Contour Area = 314 S.F. Bottom Contour Area = 63 S.F. Conceptual Rain Garden Depth = 2 FT. Rain Garden Capacity = Avg. Area * Depth = (314 S.F. + 63 S.F.)/2* 2 FT. = 377 C.F. Conceptual Storage Volume 377 C.F. > First 1.3” of Runoff 353 C.F. – O.K.