 |
Oklahoma Administrative Code (Last Updated: March 11, 2021) |
 |
TITLE 252. Department of Environmental Quality |
|
Chapter 641. Individual and Small Public On-Site Sewage Treatment Systems |
|
Subchapter 12. Dispersal Fields |
SECTION 252:641-12-5. Evapotranspiration/absorption (ET/A) fields
Latest version.
- (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 highest point of the storage media in the ET/A field.(c) Minimum linear length. All ET/A fields must meet the minimum length requirements set forth in Appendix H, Figures 10 and 11. 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 ET/A field.(d) Trench length limitation. ET/A fields shall be constructed so that no sewage flows through more than a total of one hundred fifty linear feet (150') of perforated pipe in any given path.(e) Trench spacing. The trenches in an ET/A field shall be spaced at least eight feet (8') apart, center to center.(f) Trench width. All trenches in an ET/A field shall be twenty-four inches (24") wide.(g) Trench depth. Each trench in an ET/A field shall have a uniform depth of at least eighteen inches (18") and no more than twenty-four inches (24"). The bottom of the trenches shall be level.(h) Dispersal and storage. Each trench in an ET/A field shall contain a zone for the dispersal and storage of effluent comprised of perforated pipe and storage media.(1) Perforated pipe. The perforated pipe shall:(A) meet the minimum specifications listed in Appendix C; and(B) extend the entire length of the trenches.(2) Storage media. The storage media used shall:(A) be at least ten inches (10") deep and at least twenty-four inches (24") wide the entire length of the trench;(B) be installed with at least two inches (2") of the storage media above and two inches (2") of storage media below the perforated pipe;(C) be level:(i) in each trench; and(ii) across the ET/A field, unless installed in trenches of different elevations.(i) Retention structure. Retention structures must be used between trenches of different elevations in ET/A fields. When a retention structure is used:(1) the bottom of the outlet pipe of 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 ET/A fields:(1) the trenches shall be backfilled with at least six inches (6") of clean sand to within two inches (2") of the ground level;(2) the sand used to backfill the trenches shall be separated from the storage media by material that allows the flow of water but prevents the flow of sand; and(3) after a trench is backfilled with sand, two to four inches (2"-4") of sandy loam soil shall be mounded over the trench.(k) Layout examples. There are layout examples located in Appendix K, Figures 1, 2, and 4, Appendix L, and Appendix M, Figure 2.