310 C.M.R. 15.242 – LTAR - Effluent Loading Rates

(1) The effluent loading rates set forth below are adjusted to account for the long term acceptance rate (LTAR) of the proposed soil absorption system. The LTAR is limited in large part by both the texture of the most hydraulically restrictive soil layer included within the four- foot zone beneath the proposed soil absorption system and the formation of a biomat based on the strength of effluent applied to the soil. As such the effluent loading rates have been based on the strength of typical settled sanitary sewage and may be adjusted proportionately downward if the proposed effluent strength is determined by the local Approving Authority or the Department to exceed that of typical sanitary sewage. Soil textural classes and soil types comprising the classes are defined in 310 CMR 15.243 and 310 CMR 15.244 based upon the general soil classification used by the U.S. Department of Agriculture.
1. (a) The following effluent loading rates apply:
  EFFLUENT LOADING RATE gpd/sq.ft (cm/day)
PERC. RATE SOIL CLASS (min./inch) CLASS I CLASS II CLASS III CLASS IV
(cid:35)5 .74 (3.0) 0.60 (2.5) - - 6 0.70 (2.9) 0.60 (2.5) - - 7 0.68 (2.8) 0.60 (2.5) - - 8 0.66 (2.7) 0.60 (2.5) - - 10 - 0.60 (2.5) - - 15 - 0.56 (2.3) 0.37 (1.5) - 20 - 0.53 (2.2) 0.34 (1.4) - 25 - 0.40 (1.6) 0.33 (1.3) - 30 - 0.33 (1.3) 0.29 (1.2) - 40 - - 0.25 (1.0) - 50 - - 0.20 (0.8) 0.20 (0.8) 60 - - 0.15 (0.6) 0.15 (0.6)
1. (b) The effluent loading rates set forth below may be used in place of those listed above at 310 CMR 15.242(1)(a) when the effluent from a septic tank, installed in compliance with 310 CMR 15.223, is distributed over the soil absorption system using pressure distribution designed in compliance with 310 CMR 15.254(2). However, the effluent loading rates set forth below cannot be used in conjunction with reductions to the soil absorption system approved under 310 CMR 15.280 through 15.289 or 310 CMR 15.404 through 15.405.

SEPTIC TANK EFFLUENT LOADING RATE WITH PRESSURE DISTRIBUTION

gpd/sq.ft (cm/day)

PERC. RATE SOIL CLASS (min./inch) CLASS I CLASS II CLASS III CLASS IV

10 - 0.63(2.6) 15 - 0.61(2.5) 0.41(1.7) 20 - 0.58(2.4) 0.37(1.5) 25 - 0.44(1.8) 0.36(1.4) 30 - 0.38(1.6) 0.33(1.3) 40 - - 0.29 (1.2) 50 - - 0.25 (1.0) 0.25 (1.0) 60 - - 0.20 (0.8) 0.20 (0.8)