9.2 Soil & Site Evaluation and In Situ Soil Parameters (SPS 385, SPS 383.44)

Who does what (SPS 385.10)

A journeyman can't sign a soil report, but must recognize when a site or soil condition doesn't match the approved plan.

Number, type and depth of evaluations (SPS 385.20)

• At least 3 soil profile evaluation excavations are used to delineate the area for treatment or dispersal components that use in situ soil.
• For estimated flows of 1,000 gpd or less, at least one excavation per site must be a soil pit. For flows above 1,000 gpd, at least three must be soil pits.
• Application rates must be determined from soil pits. Horizon depth, color, texture, redoximorphic features and depth to groundwater or bedrock may come from pits or borings.
• Borings use a bucket auger, probe, split-spoon or Shelby tube at least 2 inches in diameter. A power auger may not be used.
• Pits must be big enough to enter and exit safely and describe the profile. OSHA excavation rules apply.
• Evaluate color only in good light, and thaw frozen soil before evaluating color, texture, structure or consistence.

Soil profile descriptions (SPS 385.30)

For application rates, each horizon is described by thickness, Munsell color, redoximorphic feature color, abundance, size and contrast, USDA texture with rock-fragment modifiers, structure (grade, size, shape), consistence, roots, boundary, and any saturated soil, groundwater, bedrock or fill.

Interpreting saturation. Redoximorphic features (mottles) are read as seasonal saturation. If they occur within 4 inches of an A horizon at the surface, of the bottom of fill, or of a buried A horizon, the highest seasonal saturation is taken as the ground surface. A CST may discount listed false indicators without a report, including fossilized patterns, residual sandstone colors, lime deposits and naturally gray glacial material. The CST must report each exemption used. Disputed cases go to a soil saturation determination under SPS 385.60.

Reports (SPS 385.40). Each page carries the CST's signature, identification number and date, unless the report is bound with a signed title sheet. The site's legal description must be given to within 40 acres.

In situ soil parameters (SPS 383.44)

Influent quality to a component consisting in part of in situ soil must not exceed these monthly averages:

Monthly averages use at least 6 samples on 6 separate days within 30 days. A facility can be designated "at-risk" and required to test.

Infiltrative surface location:

• At least 24 inches above the estimated highest groundwater and bedrock.
• At least 1 inch below finished grade.
• Systems designed from a recognized component manual need at least 6 inches of in situ soil credited in Table 383.44-3 within that separation.

Minimum depth of unsaturated soil for treatment (Table 383.44-3):

Application rates (Table 383.44-2). Maximum loading in gallons per square foot per day is set by texture, structure, grade and effluent strength. For example, with effluent over 30 mg/L BOD5, a fine sand (FS) is rated 0.5, and a sandy loam with weak blocky structure 0.4. Moderate to strong platy structure is limited to 0.2 even with clean effluent, and to 0 with stronger effluent. The highest-concentration parameter controls. Soil consistence stronger than firm, or any cemented soil, may not hold the infiltrative surface.

Pressure distribution is required where Tables 383.44-2 and 383.44-3 call for it. Each pressurized dose must be at least 5 times the void volume of the laterals.

Installation conditions (SPS 383.45)

1. Don't install in-soil components if the soil is frozen at or below the infiltrative surface.
2. Remove snow cover before excavating.
3. Moisture test: if soil at the infiltrative surface can be rolled into a 1/4-inch wire, stop. It is too wet and will smear.
4. Bed vessels and pipes per the product or plan approval.
5. In floodplains, tanks are watertight and vents end at least 2 feet above the regional flood level.
6. Effluent lines and forcemains have at least 12 inches of cover.