310 C.M.R. 15.251 – Trenches

(1) Trench Design Specifications:
1. (a) Length (each trench) 100 feet maximum
2. (b) Width (each trench) 2 feet minimum
  3 feet maximum
3. (c) Effective Depth: shall be equal to the depth of the trench below the invert of the distribution pipe with a minimum of six inches up to a maximum of two feet.
4. (d) The minimum separation distance between any two trenches shall be two times the effective width or depth of each trench, whichever is greater, or where the area between trenches is designated as reserve area, three times the effective width or depth of each trench, whichever is greater.
5. (e) The effective leaching area shall be calculated using the bottom area and a maximum of two feet (per side) of side wall area for each trench.
(2) Trenches shall be situated, where possible, with their long dimension perpendicular to the slope of the natural soil. Where possible they shall follow the contour lines.
(3) Trenches constructed at different elevations shall be designed to prevent effluent from the higher trench(es) flowing into the lower trench(es).
(4) The area between trenches may be designated as system reserve area only where the separation distance between the excavation sidewalls of the primary trenches is at least three times the effective width or depth of each trench, whichever is greater.
(5) Distribution lines for soil absorption systems shall be constructed of either polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene (ABS), or high density polyethylene (HDPE). PVC pipe shall be schedule 40 General Purpose Sewer Pipe (ASTM D 1785), schedule 40 Drain, Waste and Vent Pipe (ASTM D 2665) or SDR 35 PVC Gravity Sewer Pipe and Drain Pipe (ASTM D 3034). ABS pipe shall be schedule 40 (ASTM F 628). HDPE pipe shall meet ASTM F 810 for Smoothwall Polyethylene Pipe for use in Drainage and Waste Disposal Fields. A material that meets an equivalent ASTM standard as a material specified in 310 CMR 15.251(5) may be substituted for that material.
(6) All connections and joints shall be mechanically sound and tight.
(7) Minimum diameter of each gravity distribution line shall be three inches.
(8) Gravitiy effluent distribution line outlet orifices shall be evenly spaced along two rows running the length of the line, on each side, midway between the invert and center-line which separates the upper and lower halves of the pipe, and orifices shall be no smaller than d inch and no larger than e inch in diameter.
(9) Gravity effluent distribution lines shall have a slope of 0.005 feet per foot along a straight line without bends and shall have ends capped or connected together by unperforated pipe of the same materials specifications.
(10) Distribution lines connecting the distribution box or pump chamber to the soil absorption system distribution lines shall be unperforated with water tight connections and joints.
(11) Effluent distribution lines exceeding 50 feet in length shall be connected and venting provided in accordance with 310 CMR 15.241.