1. (a) The required minimum liquid capacity of a septic tank for an ISDS serving a residence, residential structure, or senior housing shall be determined in accordance with this section, except as allowed in Env-Wq 1008.01.
2. (b) A residence or senior housing unit with up to 4 bedrooms shall have a minimum septic tank liquid capacity of 1,250 gallons.
3. (c) For each additional bedroom over 4 and up to 12 bedrooms in a residence or senior housing unit, the liquid capacity of the septic tank shall be increased by 250 gallons.
4. (d) For each additional bedroom over 12 bedrooms in a residence, the liquid capacity of the septic tank shall be calculated using the following formula: Liquid Capacity (gal) = 2,000 gallons + (0.70 x daily flow).
5. (e) For each additional bedroom over 12 bedrooms in a senior housing complex, the liquid capacity of the septic tank shall be calculated using the following formula: Liquid Capacity (gal) = 2,000 gallons + (0.70 x 2 x daily flow).
6. (f) For a multi-unit residential structure or structures, or a multi-unit senior housing complex, that have 12 or less bedrooms total, the first unit in the structure that has the least number of bedrooms and not more than 4 bedrooms shall have a minimum septic tank liquid capacity of 1,250 gallons, and each additional bedroom in the first unit or in additional units shall increase the total liquid capacity of the septic tank or tanks by 250 gallons provided that the structure(s) share a septic tank or tanks.
7. (g) For a multi-unit residential structure or structures that have more than 12 bedrooms total, but not more than 45 bedrooms total, and that share a septic tank or tanks, each additional bedroom over 12 bedrooms per structure and less than 45 bedrooms total shall be calculated using the following formula: Liquid Capacity (gal) = 2,000 gallons + (0.70 x daily flow).
8. (h) For a multi-unit senior housing complex that has more than 12 bedrooms total, but not more than 45 bedrooms total, and that share a septic tank or tanks, each additional bedroom over 12 bedrooms per structure and less than 45 bedrooms total shall be calculated using the following formula: Liquid Capacity (gal) = 2,000 gallons + (2 x 0.70 x daily flow).
9. (i) For a multi-unit residential structure or structures with greater than 45 bedrooms total, the volume in gallons shall be equal to the daily flow gallons per day.
10. (j) For a multi-unit senior housing complex with greater than 45 bedrooms total, the volume in gallons shall be equal to 2 times the daily flow gallons per day.

11. (k) If a garbage grinder is or will be used in the residence, structure, or a multi-unit structure, a note shall be placed on the plan indicating the location of the garbage grinder(s), and:

    1. (1) The liquid capacity of the septic tank for a residence or structure shall be increased by 50%; or
    2. (2) The flow from each unit proposing to use a garbage grinder in a multi-unit structure shall be increased by 50%, and the liquid capacity of the septic tank shall be increased accordingly.

12. (l) Subject to (n), below, where raw sewage is pumped directly into the septic tank, whether or not a garbage grinder is or will be used, then:

    1. (1) The liquid capacity of the septic tank shall be twice the liquid capacity otherwise required by this section or Env-Wq 1010.02, as applicable; and
    2. (2) The pumped sewage shall be connected to an additional septic tank if one is used to meet the required tank capacity in this section, or to the first chamber of the first tank if multiple compartment tanks are used to meet the requirements of Env-Wq 1010.12.
13. (m) When raw sewage is pumped from plumbing fixtures that are below grade to the building’s gravity-fed ISDS piping that is hydraulically upstream of the septic tank, no increase in the total liquid capacity of the septic tank shall be required if the sewage from the below-grade plumbing fixtures will be pumped by a sewage pump capable of handling 2-inch or greater solids.

14. (n) When raw sewage is pumped from plumbing fixtures that are below grade to the building’s gravity-fed internal piping and the sewage pump provisions in (l), above, do not apply, then the total liquid capacity of the septic tank shall be increased by at least 250 gallons if:

    1. (1) Only one septic tank is used; or
    2. (2) A separate septic tank that has a minimum liquid capacity of 1,000 gallons is used to receive the raw sewage being pumped and will connect hydraulically upstream of the primary septic tank for the structure.
15. (o) For a one-bedroom residential unit that shares a septic tank with a single-family residence, the liquid capacity shall be the capacity required for the single-family residence plus 375 gallons for the one-bedroom unit.

Source. (See Revision Notes #1 and #2 at chapter heading for Env-Wq 1000) #11184, eff 10-1-16; ss by #14486, eff 2-1-26, EXPIRES: 2-1-36