Camposeo_Coles_Meadow_Rd_20220705.pdfCOSTA CONSULTING ENGINEERS, INC.
104 MOODY ST.
LUDLOW, MA 01056
TEL: 413-583-4377 FAX: 413-583-4486
WWW.COSTACONSULTINGENGINEERS.COM 7/5/22 Northampton Conservation Commission
City Hall
210 Main St; Room 11 Northampton, MA 01061 Attention: Sarah Lavalley
Re: Coles Meadow Road Driveway Parcel 08-070-001 Erosion Northampton, MA CCE File No. 450
Dear Sarah, Costa Consulting Engineers (CCE) performed erosion and stability analysis of the proposed driveway at Parcel 08-070-001 located on Coles Meadow Road in Northampton, Massachusetts. The analyses were in accordance with the information shown on Pages (drawings) Nos. 1 and 2 of
3, prepared by Environmental Planning Associates and CCE, latest revision on 7/5/22. The fill materials considered are as follows: M1.03.0 Type B (mass fill) – natural sand and gravel mixture
M2.01.7 Dense Graded Crushed Stone (road bed surficial fill) – bedrock crushed into stone and sand-size particles, 2” Crushed Stone (side slope surficial fill) – bedrock crushed into open-graded, nearly uniform-sized particles.
The road bed and side slopes were analyzed for potential surface erosion generated by sheet flow, using standard engineering practice methods in accordance with NRCS TR-55. In this instance, the calculated runoff velocities on this proposed driveway are below the threshold of erosion specified in design manuals. The permissible velocities were obtained from the Virginia Department of Transportation drainage design manual (January 2021).
The side slopes were analyzed for sloughing, with potential slip planes occurring along:
• The surficial 2” crushed stone and fabric interface,
• The lower mass gravel and fabric interface, and
CCE# 450 7/5/22
Coles Meadow Road Driveway Page 2 Erosion
COSTA CONSULTING ENGINEERS, INC. • 104 MOODY ST. • LUDLOW, MA 01056
• The mass gravel-gravel interface.
The analyses account for all M 1.03.0 Type B gravel and M 2.01.7 Dense Graded Crushed Stone
fill being placed and compacted to a minimum of 95 percent of its maximum dry density. The filter fabric will extend at least 1 foot into the roadbed along the interface between the surficial dense graded crushed surface stone and the lower mass gravel fill. These conditions will provide support to the side slopes and secure the fabric's placement. The analyses results indicate that the proposed
design shown on Pages 1 and 2 have adequate factors of safety to prevent sloughing and sliding
If you have any questions, please contact CCE. Very truly yours,
COSTA CONSULTING ENGINEERS, INC. By: _____________________________________
George L. Costa, P.E; President