HomeMy WebLinkAboutMiscellaneous - Exception (470)'Guidelines for the Design and Installation of Impervious Barriers
INTRODUCTION:
Title 5, 310 CMR 15.255, addresses the construction of systems in fill. An
impervious barrier is required for systems constructed in fill when the designer can not
provide the minimum 15 foot horizontal distance between the edge of the top of the two
inch layer of washed stone (peastone) cover over the soil absorption system, and the top
of the sideslope. For a system constructed in fill, 310 CMR 15.255 requires slope
stabilization, such as a concrete retaining wall, when the sideslopes to a soil absorption
system are steeper than 3:1 (horizontal: vertical). Section 310 CMR 15.211(1)[4] requires
slope stabilization when systems are located in an area adjacent to a naturally occurring
downhill slope steeper than 3:1. When a naturally occurring downhill slope adjacent to a
system is steeper than 3:1, Title 5 requires stabilization in accordance with accepted
engineering practice which may include installation of a concrete retaining wall designed
in accordance with 310 CMR 15.255(2)(a) through (g),
TEXT:
Impervious Barriers:
Pursuant to 310 CMR 15.255(2), an impervious barrier is required for a system
constructed in fill when the designer can not provide a minimum distance of 15 feet
between the edge of soil absorption system and the top of the side slope. Impervious barriers
must also be incorporated into the design when a minimum 15 -foot horizontal distance
cannot be provided between the edge of the soil absorption system and an adjacent naturally
occurring downhill slope. (see Figure 1)
Less than 15'
Top Elevation of SAS 1 O O O
Soil Absorption System
Impervious Barrier
4
N
N
3:1 slope > Fill or Naturally Occurring
I Pervious Material
1' minimum 'N' Naturally Occurring
10' minimumJ1 Pervious Material
6" minimum
Figure 1: Impervious Barrier
Finished