Septic Separation Memo 8-21-23T REYNOLDS ENGINEERING | CIVIL ENGINEERS | PLANNING, DESIGN, AND PERMITTING SERVICES
152 MAPLEWOOD TERRACE, FLORENCE, MA 01062 | PHONE: 413-387-8078 | FAX: 413-727-3477
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To: Northampton Dept. of Public Works, Attn. Doug McDonald
From: Terrence Reynolds P.E.
Subject: 332 Turkey Hill Road Septic separation to proposed rain garden
Date: 8/21/2023
This is to confirm the required separation distance between the proposed residential septic system and
the proposed rain garden. Concerns were brought to the attention of this office regarding the 10’
separation between the proposed leach field and the rain garden and it was agreed that a confirmation of
the allowable separation per title V and structural BMP of the Stormwater Handbook was needed. After
reviewing the Title V regulations, it was determined that the minimum separation to open surface and
sub-surface drains is 10’. No estimated ground water was observed during the evaluation of the
stormwater/septic test pits. Additionally, an impervious barrier is specified between the leach field and
rain garden preventing any lateral effluent flow from entering the rain garden sub-drain. In the
Stormwater Handbook structural BMPs, Rain Gardens have no listed separation. The rain garden is
designed to provide enhanced water quality and runoff control but does not provide any appreciable
infiltration. If the rain garden were designed to infiltrate into the subgrade it could be interpreted that it
would need to meet the separation specified for infiltration basins which is 50’ for soil absorption
systems. Since it is not designed to infiltrate, we believe the 50’ separation is not applicable and the 10’
separation is appropriate.