1. (1) Any system where fill is required to replace topsoil, peat or other unsuitable or impervious soil layer above the requisite four feet of naturally occurring pervious material is a system constructed in fill. Any system constructed in fill which extends either wholly or partially above natural grade for the purpose of complying with 310 CMR 15.212 (depth to groundwater) is a mounded system. All soil absorption systems constructed in fill shall be sized using the soil class of the underlying naturally occurring pervious material.

2. (2) The finished side slopes of a mounded system shall not be steeper than 3:1 (horizontal:vertical). A minimum 15 foot horizontal separation distance shall be provided between the soil absorption area and the adjacent side slope as measured from the edge of the top of the two inch layer of c to ½ inch washed stone aggregate or geotextile fabric cover. The toe of the slope shall be a minimum of five feet from any property line, or a swale or other drainage system directing runoff away from the adjacent property shall be installed. Adjustments to the above horizontal separation may be allowed if a suitable impervious barrier is installed to prevent potential sewage breakout. The impervious barrier shall meet the following requirements:

   1. (a) the impervious barrier shall be designed by a Massachusetts Registered Sanitarian or a Massachusetts Registered Professional Engineer.
   2. (b) construction of the impervious barrier shall be supervised by the designer.
   3. (c) prior to issuance of a Certificate of Compliance, the applicant shall submit to the Approving Authority an as-built plan prepared and certified by the designer that the impervious barrier has been constructed in accordance with the approved design plan.
   4. (d) the elevation of the top of the impervious barrier shall be no lower than the "breakout" elevation, which is the elevation of the top of the two inch layer of c inch to ½ inch washed stone aggregate cover.
   5. (e) the recommended distance from the impervious barrier to the edge of the soil absorption system closest to the barrier should be at least ten feet.
   6. (f) where a retaining wall to stabilize the slope is required and also is proposed as an impervious barrier, in addition to meeting the requirements in 310 CMR 15.255(2), it shall be constructed of suitable structural material and be designed by a Massachusetts Registered Professional Engineer.

3. (3) Fill material for systems constructed in fill shall consist of select on-site or imported soil material. The fill shall be comprised of clean granular sand, be free from organic matter and deleterious substances, and shall not contain Remediation Waste as that term is defined in 310 CMR 40.0000. Mixtures and layers of different classes of soil shall not be used. The fill shall not contain any material larger than two inches. A sieve analysis, using a #4 sieve, shall be performed on a representative sample of the fill. Up to 45% by weight of the fill sample may be retained on the #4 sieve. Sieve analyses also shall be performed on the fraction of the fill sample passing the #4 sieve, such analyses must demonstrate that the material meets each of the following specifications:

   SIEVE SIZE EFFECTIVE % THAT MUST

   PARTICLE SIZE PASS SIEVE

   # 4 4.75 mm 100% # 50 0.30 mm 10% - 100% #100 0.15 mm 0% - 20% #200 0.075 mm 0% - 5%

A plot of the sieve analyses of the portion of the sample passing the #4 sieve shall fall on or between the lines on the following graph:

1. (4) If required by the Approving Authority, a minimum of one representative sample shall be taken from the in-place fill for a system serving a single family residence and tested for compliance with the grain size distribution specification. One soil test per pit per removal day shall be required for systems with design flows of 2,000 gpd or more.
2. (5) Where fill is required to replace unsuitable or impermeable soils, the excavation of the unsuitable material shall extend a minimum of five feet laterally in all directions beyond the outer perimeter of the soil absorption system to the depth of naturally occurring pervious material as required by 310 CMR 15.240 (soil absorption systems) and replaced with fill material meeting the specifications of 310 CMR 15.255(3).
3. (6) Prior to placement of the fill, which shall be stockpiled at the edge of the excavation and filled in gradually, the bottom surface of the excavation shall be scarified and relatively dry. Fill shall not be placed during rain or snow storms. If the groundwater elevation is above the elevation of the bottom of the excavation, the excavation shall be dewatered prior to placement of the fill.