SECTION 252:641-12-2. Conventional subsurface absorption fields

(a)   Location. All conventional subsurface absorption fields shall be:

(1)   located in the identified dispersal site; and

(2)   installed more than five feet (5') from the septic tank or aerobic treatment unit.

(b)   Fall. Unless a pump is utilized, there shall be a minimum fall of two inches (2") from the bottom of the outlet of the septic tank to the:

(1)   highest point of the storage media in the conventional subsurface absorption field; or

(2)   highest point of the sidewall openings of a chamber in the conventional subsurface absorption field.

(c)   Minimum linear length. All conventional subsurface absorption fields must meet the minimum length requirements set forth in Appendix H, Figures 1-5. If perforated pipe is used between distribution structures and installed in accordance with the trench requirements of this Section, it may be counted as part of the overall required length of the conventional subsurface absorption field.

(d)   Trench length limitation. Conventional subsurface absorption fields shall be constructed so that no sewage flows through more than a total of one hundred fifty linear feet (150') of perforated pipe or chambers in any given path.

(e)   Trench spacing. The trenches in a conventional subsurface absorption field shall be spaced at least eight feet (8') apart, center to center.

(f)   Trench width. All trenches in a conventional subsurface absorption field shall be twenty-four inches (24") wide.

(g)   Trench depth. Each trench in a conventional subsurface absorption field shall have a uniform depth of at least eighteen inches (18"), and no more than thirty inches (30"). The bottom of the trenches shall be level.

(h)   Dispersal and storage. Each trench in a conventional subsurface absorption field shall contain a zone for the dispersal and storage of effluent comprised of either perforated pipe and storage media, or chambers.

(1)   Perforated pipe with storage media. When perforated pipe and storage media are used to disperse and store effluent throughout the trenches, the following requirements shall apply:

(A)   Perforated pipe. The perforated pipe shall:

(i)   meet the minimum specifications listed in Appendix C.

(ii)   extend the entire length of the trenches.

(B)   Storage Media. The storage media shall:

(i)   be at least ten inches (10") deep and at least twenty-four inches (24") wide the entire length of the trench;

(ii)   be installed with at least two inches (2") of storage media above and two inches (2") of storage media below the perforated pipe;

(iii)   be level:

(I)   in each trench; and

(II)   across the dispersal field, unless installed in trenches of different elevations.

(2)   Chambers. When chambers are used to disperse and store effluent throughout the trenches, the chambers shall:

(A)   have a minimum bottom width of twenty-two inches (22");

(B)   have a minimum sidewall height of ten inches (10") with the sidewalls having evenly distributed open space. If the sidewall height is less than ten inches (10"), then the trench shall be backfilled with storage media to meet the ten-inch height requirement;

(C)   meet the most current IAPMO PS 63 standard;

(D)   extend the entire length of the trenches;

(E)   be level:

(i)   in each trench; and

(ii)   across the dispersal field, unless installed in trenches of different elevations.

(i)   Retention structure. Retention structures must be used between trenches of different elevations in conventional subsurface absorption fields. When a retention structure is used:

(1)   the bottom of the outlet pipe of a retention structure or the bottom of the outlet pipe of a chamber being used as a retention structure shall be ten inches (10") above the trench bottom; and

(2)   the line from the outlet of a retention structure to the next distribution point shall be constructed of solid pipe and shall be backfilled with compacted native soil.

(j)   Backfill. For conventional subsurface absorption fields:

(1)   the depth of the backfill shall be consistent and shall not vary more than four inches (4"); and

(2)   the backfill shall consist of at least eight inches (8") of topsoil.

(k)   Layout examples. There are examples of conventional subsurface system layouts in Appendix K, Figures 1, 2, and 4; examples of retention and distribution structures in Appendix L; examples of trench installation in Appendix M, Figures 1 and 2; and examples of chambers installed in trenches in Appendix N.

[Source: Added at 25 Ok Reg 2318, eff 7-11-08; Amended at 37 Ok Reg 1296, eff 9-15-20]