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HomeMy WebLinkAbout25SITE2 - TE Comments 04-17-2025Page 1 of 2 April 17, 2025 CLA Engineers, Inc. | 317 Main Street, Norwich CT 06360 | 860.886.1966 | www.claengineers.com April 17, 2025 Meredith Badalucca, Assistant Planner Town of Montville 310 Norwich-New London Tpke., Uncasville, CT 06382 Via Email: mbadalucca@montville-ct.org RE: Site Plan Application 25SITE2 Review 145 Route 32 & 18 Powerhouse Road (“Madison Place”) CLA-7873G Dear Meredith: CLA Engineers, Inc. (CLA) has received the application materials for the above referenced project as emailed to our office and located on the Town Form Repository: https://www.townofmontville.org/form-repository/25-site-2-145-route-32-multi-family- development/ CLA has performed a review of the application documents and offer the following comments: Engineering Report Previous Comment #2: The existing condition Drainage Area “A” travel time: The sheet flow component appears to be longer than 100’ and the slopes appears to less than 8.8%, potentially in the range of 2.5-3%. This should be reviewed. And recalculated. Applicants Response: Response: Please see page 54 in the Engineering Report. The first 100 feet has been calculated utilizing the Sheet Flow criteria. The remainder of the flow path has been calculated using concentrated flow per standard practice. The entire segment slope has been calculated based on the aggregate slope between the beginning high point and the ending point of concern. New Comment - In our opinion the sheet flow length for this watershed travel path is longer than the 100’ used in the calculations. Please see attached SK1 an excerpt of the DA-EX watershed map from the Engineering Report. In our opinion the sheet flow component would extend to the top of slope at approximately contour 105, adding another ±60 to the sheet flow component. Limiting this length to 150’ would not be unreasonable in accordance with the DOT Drainage Manual Section 6.C.4 (attached). - An aggregate slope should not be used for the entire travel path time of concentration calculation. The actual slope of the land for each segment of the travel path should be used. In this case, sheet flow is the largest component of the time of concentration, and the actual land slope is approximately 2% vs the 8.8% used in the calculations. Using the actual land slope may substantially change the calculations. CLA Engineers, Inc. Civil Structural Survey 317 MAIN STREET NORWICH, CT 06360 (860) 886-1966 (860) 886-9165 FAX Page 2 of 2 April 17, 2025 CLA Engineers, Inc. | 317 Main Street, Norwich CT 06360 | 860.886.1966 | www.claengineers.com Previous Comment #3: The existing and post development travel times are identical in the calculations but are depicted differently in the mapping. Actual ground slopes should be used in the calculations. Applicants Response: While there is minor grading in some areas, the aggregate slopes from each endpoint do not change from the pre existing to post existing development conditions. New Comments - Please see the comment above regarding using the actual land slope for each segment when calculating travel times. - Please see attached SK1 and SK2, excerpts from DA-EX and DA-PR indicating two different flow path length for the travel flow path. These differences are not reflected in the calculations (See highlighted summaries attached). - As shown on SK1 and SK2 there appears to be a substantial difference in ground slope for each of the sheet flow components. As previously noted, in this case the sheet flow is the largest component in the time of concentration calculation, and land slope will have impact to those calculations. The concern with the times of concentration calculations is that the existing conditions peak stormwater flow rates may be lower than calculated in the Report and the post development may be higher than calculated in the Report; therefore, additional subsurface storage may be needed. All other previous comments have been addressed. Thank you for the opportunity to provide this review. Please feel free to call me at our office or email khaubert@claengineers.com with any questions. Very truly yours, CLA Engineers, Inc. Kyle Haubert, P.E.