Current through Register Vol. 56, No. 6, March 18, 2024
(a) Soil profile pits shall be excavated at the site of each proposed disposal field for the purpose of determining the suitability and distribution of soil types present at the site. Partial substitution for soil profile pits may be made using soil borings as outlined in (b) below.
(b) A minimum of two profile pits are required for each disposal field. A minimum of three soil borings may be performed in lieu of the second profile pit, provided that the soil horizons and substrata observed in the borings are not significantly different from those observed in the first profile pit.
(c) The location of soil profile pits and borings for disposal fields shall be as follows:
1. As shown in Figure 1 of Appendix A, profile pits shall be located at either end of the disposal field, within or no further than 15 feet beyond the boundaries of the disposal field.
2. In cases where a profile pit or part of a profile pit has been excavated within the boundaries of a proposed disposal trench or bed, the pit shall be backfilled after use in a manner that will not result in a major discontinuity with respect to soil horizonation, density or permeability in the soil below the disposal trench or bed.
3. When soil borings are substituted for the second profile pit these shall be located as shown in Figure 1 of Appendix A, at the approximate center of the disposal field and at corners opposite the profile pit. All soil borings shall be within the boundaries of the disposal field, or no further than 15 feet beyond the boundaries of the disposal field.
(d) When a seepage pit(s) is proposed, as allowed in 7:9A-7.6, a minimum of one profile pit or two soil borings shall be performed for each seepage pit. Profile pits shall be located within or no further than 15 feet from the proposed seepage pit. Borings shall be located on opposite sides of the seepage pit, no further than 15 feet from the seepage pit.
(e) Profile pits shall be prepared as follows:
1. Profile pits shall be excavated, if possible, to a minimum depth of 10 feet below the existing ground surface or to solid bedrock, where encountered. If the profile pit becomes unstable due to lack of soil cohesion or the presence of groundwater, or both, the pit may be terminated at a depth less than 10 feet and soil evaluation below the depth of the pit may be carried out by means of three or more soil borings, performed as prescribed in (f) below. The depth of the soil evaluation shall never be less than eight feet below the proposed level of infiltration.
2. When a seepage pit is proposed, the profile pit shall extend a minimum of eight feet below the bottom of the seepage pit or to solid bedrock, when encountered. In cases where the minimum required depth is deeper than that practically attainable using ordinary excavating equipment, soil borings should be used rather than a profile pit. Alternatively, borings may be used to extend the depth of profile pits beyond the range of the excavating equipment.
3. It is recommended that the sides of the profile pit be stepped and sloped as shown in Figure 2 of Appendix A, to prevent caving-in and to allow safe access to the upper portion of the pit. An undisturbed face, a minimum of one foot wide and extending from the top of the pit to a depth of five feet, shall be exposed by means of hand tools, for observation of the soil profile characteristics. Evaluation of soil properties below a depth of five feet may be accomplished by examination of samples removed by excavating equipment or by examination of three or more borings, performed as prescribed in (f) below.
4. It is recommended that persons performing soil evaluation not enter into portions of a soil profile pit which have been excavated to depths greater than five feet below the surrounding ground surface. It is the responsibility of persons performing or witnessing soil evaluation to comply with all applicable Federal, State and local laws and regulations governing occupational safety.
(f) Soil borings shall be performed as follows:
1. Soil borings shall be completed to a minimum depth of 10 feet below the existing ground surface or to solid bedrock, where encountered. In no case shall the depth of the borings be less than eight feet below the proposed level of infiltration. Where a seepage pit is proposed, the borings shall extend a minimum of eight feet below the bottom of the seepage pit or to solid bedrock, where encountered.
2. Soil borings shall be made in a manner that will provide a continuous sample of the soil profile without mixing the soil from different depths. Hand augers may be used provided that the hole remains open and does not slump.
(g) In soil profile pits and borings, the following characteristics of each recognizable soil horizon or substratum (not including rock substrata) shall be determined:
1. Depth and thickness of horizon;
2. Soil color, using the Munsell system of classification which includes an alpha-numeric symbol together with a descriptive color name;
3. Estimated soil textural class, using the USDA system of classification;
4. Estimated volume percentage of coarse fragment, if present;
5. Abundance, size and contrast of mottles, if present;
6. Soil structural class (soil profile pits only); and
7. Soil consistence.
(h) Soil profile characteristics shall be reported in log form, using terminology as prescribed in 7:9A-5.3.
