Soil Absorption Systems

(1) On-site subsurface sewage disposal systems shall be located in an area where there is at least a four foot depth of naturally occurring pervious soil below the entire area of the soil absorption area and reserve area unless a variance is issued in accordance with the provisions of 310 CMR 15.415(2). The four foot stratum must be free of impervious and unsuitable materials. (2) Effluent from any component of an on-site sewage disposal system shall not be disposed of by direct discharge to any waters of the Commonwealth, unless in compliance with a permit issued pursuant to 314 CMR 3.00 (surface water permitting) or 314 CMR 5.00 (groundwater permitting). (3) Soil absorption systems shall be designed as an integral part of the system. Septic tank effluent is to be distributed throughout the soil absorption system by means of effluent distribution lines so that the effluent can migrate through the underlying soil column under unsaturated flow conditions. All soil absorption systems shall achieve the following objectives of the soil treatment process: (a) maximum stabilization of organic wastes in the effluent; (b) removal of pathogenic organisms, nutrients, and particulates; (c) recharge of the ground-water table with adequately treated effluent with minimal attendant pollution of the groundwater; and (d) disposal of the effluent without discharge to the ground surface or the creation of any nuisance. (4) The minimum area for the design of a soil absorption system shall be determined by the results of the site evaluation set forth in 310 CMR 15.100 through 15.107 and in accordance with the appropriate long-term acceptance rate criteria specified in 310 CMR 15.242 (effluent loading rates). Area requirements increase by 50% when garbage grinders are installed and the system shall be upgraded to meet such requirements prior to the installation of a garbage grinder. (5) All soil absorption systems designed to serve single family dwellings, including but not limited to single family condominiums and cooperatives, shall be designed to serve a minimum of three bedrooms, unless a deed restriction limiting use to two bedrooms is granted to the local Approving Authority. (6) Absorption trenches should be used whenever possible. (7) No driveway, parking or turning area or other impervious area shall be located above a soil absorption system, except where restrictions on the use of the land make it unavoidable. In such cases, the soil absorption system shall be vented to the atmosphere in accordance with 310 CMR 15.241. (8) The bottom of each soil absorption system shall be excavated to a level grade. If the removal of stones or boulders is required, creating localized depressions, filling to grade with the excavated naturally occurring pervious soil or material in compliance with 310 CMR 15.255 is acceptable. (9) The soil placed as backfill over the soil absorption system shall be a minimum of nine inches, excluding topsoil, placed in lifts and sufficiently compacted to prevent depressions due to settling which may intercept or collect surface water runoff above the system. Backfill must be clean and free of stones and boulders greater than six inches in size. Tailings, clay or similar materials are prohibited. (10) Final cover above the system shall be stabilized and graded to reduce infiltration of surface water and minimize erosion. Finish grade shall have a minimum slope of 0.02 feet per foot. (11) Surface drainage shall be directed away from the soil absorption system. (12) For systems with a design flow of 2,000 gpd or greater, the separation distance to the high groundwater elevation required by 310 CMR 15.212 shall be determined by adding the effect of groundwater mounding to the high groundwater elevation as determined pursuant to 310 CMR 15.103(3). (13) All soil absorption systems shall have a minimum of one inspection port consisting of a perforated four inch pipe placed vertically down into the stone to the naturally occurring soil or sand fill below the stone. The pipe shall be capped with a screw type cap and accessible to within three inches of finish grade.