Pits, Galleries, or Chambers

(1) Pit, Gallery or Chamber design specifications: (a) Effective Depth - A maximum of two feet of sidewall depth below the invert of the inlet per unit shall be used when calculating the effective leaching area. (b) Surrounding Aggregate - 1 foot minimum per side. 4 feet maximum per side. (c) Separation Distance Between Units - two times the effective width or depth, whichever is greater. (2) Construction shall be of precast perforated concrete or interlocking concrete blocks laid dry with open joints in a manner to prevent displacement or as otherwise approved by the Department. (3) Each pit, gallery or chamber shall have a minimum of one inspection access cover per unit. For systems with a design flow greater than 2,000 gpd, the manholes shall be at least 24 inches in diameter with metal frames and covers to finished grade. (4) When two or more pits are used, the system shall be designed so that all pits function in parallel. (5) Two or more chambers or galleries connected in series shall constitute a chamber or gallery system. The application of 310 CMR 15.253(1)(c) (separation distance) shall be applied to adjacent chamber or gallery systems as a unit rather than to the individually connected chambers or galleries. (6) Inlets to chamber and gallery systems installed in trench configuration shall be provided at intervals not to exceed 20 feet. Chamber or gallery systems in bed configuration shall be provided with at least one inlet for every 40-foot square section. (7) when using pits, galleries, or chambers in a leaching bed or field configuration, the effective leaching area shall include only the bottom area, not the side walls.