SECTION 252:641-3-4. Soil profile description

(a)   Test hole requirements. Test holes may be augered borings, continuous core borings, or excavated pits.

(1)   Borings. If borings are used, three test holes shall be placed in the proposed dispersal site at the approximate corners of an isosceles triangle having two (2) sides fifty feet (50') long and one side seventy-five feet (75') long. If the dispersal field will cover an area larger than ten thousand square feet (10,000 ft), then one additional test hole shall be used for each additional five thousand square feet (5,000 ft). Additional test holes shall not be placed within fifty feet of any other test hole and shall be located between fifty to seventy-five feet (50-75') from one of the other test holes. The DEQ may approve or require alternative configurations. Borings shall allow for the classification of the soil in six-inch intervals and shall be bored to a minimum depth of forty-eight inches (48") or until one of the following is encountered first:

(A)   a layer that is impervious to boring;

(B)   a six-inch interval classified as a Group 5 soil; or

(C)   water saturated soil.

(2)   Pits. If excavated pits are used, three (3) pits shall be placed in the proposed dispersal site at the approximate corners of an isosceles triangle having two (2) sides fifty feet (50') long and one side seventy-five feet (75') long. If the dispersal field will cover an area larger than ten thousand square feet (10,000 ft), then one additional test hole shall be used for each additional five thousand square feet (5,000 ft). Additional test holes shall not be placed within fifty feet of any other test hole and shall be located between fifty to seventy-five feet (50'-75') from one of the other test holes. The DEQ may approve or require alternative configurations. Pits shall:

(A)   have a depth of a minimum of forty-eight inches (48"), unless rock or water saturated soil is encountered at a shallower depth;

(B)   be a minimum of thirty-six inches (36") wide and sixty inches (60") long; and

(C)   have one end sloped or stepped to allow for entry.

(b)   Identification of limiting layers. The shallowest limiting layer encountered in the test holes shall be the limiting layer for the entire dispersal site. The following are considered limiting layers and shall be identified by depth on DEQ Form 641-581SP, "Report for On-Site Sewage Treatment:"

(1)   a layer that is impervious to boring;

(2)   a six-inch interval classified as a Group 5 soil; and

(3)   water saturated soil.

(c)   Verifying limiting layers using pits. Limiting layers may be verified using an excavated pit. The results of the pit(s) shall override the results of borings completed in the same proposed dispersal site.

(d)   Classifying soil intervals. For each test hole, the soil group for each six-inch interval between the surface and the bottom of the test hole shall be identified using the guidelines found in the "DEQ/OSU Soil Classification Manual" and classified as one of the soil groups in Appendix B.

(e)   Determining the soil group for the separation range. The soil group for the separation range establishes the required vertical separation between the dispersed effluent and the limiting layer. The separation range consists of the three (3) six-inch intervals above the interval containing a limiting layer or, if no limiting layer was identified, the separation range shall be the three (3) six-inch intervals above the bottom of the test hole. To determine the soil group for the separation range:

(1)   Select the test hole in the dispersal site with the lowest clay content in the separation range; and

(2)   Identify and record the most prevalent soil group in the separation range for that test hole.

(f)   Identifying dispersal field options. Based on the soil group identified in (e) of this Section, use Appendix A, Figure 1 to identify suitable dispersal fields along with their minimum separations distances from the limiting layer.

(g)   Sizing the dispersal field(s). Each suitable dispersal field shall be sized as follows:

(1)   Determining sizing range. Select the test hole in the dispersal site with the highest clay content in the sizing range for the chosen dispersal field. The applicable sizing range for each type of dispersal field is as follows:

(A)   Conventional subsurface absorption fields. The sizing range for conventional subsurface absorption fields is the three (3) six-inch intervals between twelve inches (12") and thirty inches (30").

(B)   Low pressure dosing fields. The sizing range for low pressure dosing fields is the three (3) six-inch intervals between twelve inches (12") and thirty inches (30").

(C)   ET/A fields. The sizing range for ET/A fields is the three (3) six-inch intervals between twelve inches (12") and thirty inches (30").

(D)   Shallow extended subsurface absorption fields. The sizing range for shallow extended subsurface absorption fields is the three (3) six-inch intervals between six inches (6") and twenty-four inches (24").

(E)   Drip irrigation fields. The sizing range for drip irrigation fields is the three (3) six-inch intervals between ground level and eighteen inches (18").

(F)   Spray irrigation fields. The sizing range for spray irrigation fields is the three (3) six-inch intervals between ground level and eighteen inches (18").

(2)   Identifying soil group in sizing range. Determine the most prevalent soil group in the sizing range for the test hole selected in (1) of this subsection;

(3)   Sizing dispersal field. Based on the soil group identified in (2) of this subsection, size the dispersal field using the charts in Appendix H, Figures 3 and 5-22; and

(4)   Sizing additional dispersal field options. Repeat (1) through (3) of this subsection for each dispersal field option.

(h)   Information to be reported. After completion of the soil profile, the soil profiler shall submit an accurate, completed DEQ Form 641-581SP to the local DEQ office.

[Source: Added at 16 Ok Reg 1895, eff 6-11-99; Amended at 19 Ok Reg 45, eff 8-17-01 (emergency); Amended at 19 Ok Reg 1027, eff 6-1-02; Amended at 21 Ok Reg 1618, eff 6-11-04; Amended at 25 Ok Reg 2318, eff 7-11-08; Added at 28 Ok Reg 1278, eff 7-1-11; Amended at 29 Ok Reg 1053, eff 7-1-12; Amended at 37 Ok Reg 1296, eff 9-15-20]