(A) Applicants for sewage treatment system permits, site, or subdivision approval will be required to submit soil test data derived from soil borings and percolation tests for each proposed site or installation. The minimum testing shall be that necessary to verify suitable conditions for 2 complete soil treatment systems. Large systems designed for 1,200 gallons per day or more shall require a hydrogeologic investigation in accordance with § 157.39(G)(3).
(Prior Code, Ch. 506 § 9.1)
(B) All testing shall be conducted in accordance with the requirement of this chapter and shall be done by qualified personnel, certified under the MPCA training and certification program and licensed by the MPCA.
(Prior Code, Ch. 506 § 9.2)
(C) All proposed sites for sewage treatment systems shall be protected by fence or other methods as necessary to avoid excavations, construction equipment, or other traffic that could affect the soil conditions.
(Prior Code, Ch. 506 § 9.3)
(D) For subdivision testing, enough soil borings must be done to assure that suitable soils exist for each lot for long-term sewage treatment. Percolation tests are not required unless the permeability cannot be estimated or there is reason to believe the soil is not original or has been compacted.
(Prior Code, Ch. 506 § 9.4)
(E) Complete testing on each individual lot will be required prior to permit issuance independent of any prior approved subdivision testing. A minimum of 4 satisfactory soil borings outlining an area of 5,000 square feet are required. Larger areas may be required where conditions of use, soils, topography, or vegetation require.
(Prior Code, Ch. 506 § 9.5)
(F) Where soil tests require a mound, testing and design must clearly show suitable area for installation of 2 complete mounds. Where site conditions are such that the only backup mound will likely be disturbed, the Department at its discretion, may require both mounds to be constructed at once.
(Prior Code, Ch. 506 § 9.6)
(G) Soil borings shall be made as follows:
(1) Borings shall be by auger or excavation and shall be staked and protected until notification that the field evaluation has been completed. Flite augers which are continuous or disturb extracted soil samples are not allowed. Borings shall be made to a depth of at least 3 feet deeper than the bottom of the proposed system or until bedrock or water table is encountered, whichever is less.
(2) Any evidence of disturbed or compacted soil must be disclosed and may result in the prohibition of utilizing that test area.
(3) Particular effort shall be made to determine the highest known water table by recording the first occurrence of mottling observed in the hole, or if mottling is not encountered, the open holes in clay or loam soils shall be observed after standing undisturbed a minimum of 16 hours, and depth to standing water, if present, shall be measured.
(Prior Code, Ch. 506 § 9.7)
(H) A soil description shall be written for each soil observation at the proposed site. Soils should be evaluated under adequate light conditions with the soil in a moist state and including the following:
(1) The depth of each soil horizon measured from the ground surface. Soil horizons are differentiated by changes in soil structure, soil texture, soil color, mottling, bedrock, or any other characteristic which may affect water percolation or treatment of effluent.
(2) The soil matrix and mottled color described per horizon by the Munsell Soil Color Charts, 1992 revised edition, which is incorporated by reference. This document is available from Macbeth Division, Kollmorgan Instruments Corporation, Munsell Color, PO Box 230, Newburgh, New York 12551-0230. It can be found at the Minnesota State Law Library, Judicial Center, 25 Constitution Avenue, St. Paul, MN 55155. This document is not subject to frequent change.
(3) The soil texture described using the United States Department of Agriculture (USDA) soil classification system as modified here:
Clay | = | Clay, sand clay, silty clay |
Clay loam | = | Clay loam, sandy clay loam, silty clay loam |
Loam | = | Loam |
Sandy loam | = | Sand loam |
Silt loam | = | Silt loam, silt |
Loamy sand | = | loamy sand |
Coarse sand | = | coarse sand |
(Medium) sand | = | (Medium) sand |
Fine sand | = | Fine and very fine sand |
(Prior Code, Ch. 506 § 9.8)
(I) After soil borings have outlined the minimum area suitable soils, percolation tests shall be made. The only exception to this requirement is for sand soils clearly in the 5 MPI range. The design for sizing of systems in such soils shall be 1.27 square feet per gallon. The requirements for percolation tests are:
(1) Each test hole shall be 6 to 8 inches in diameter, have vertical sides, and be bored or dug to a depth of the bottom of the proposed individual sewage treatment system. Soil texture description shall be recorded noting depths where texture changes occur.
(2) The bottom and sides of the hole shall be carefully scratched to remove any smearing and to provide a natural soil surface into which water may penetrate.
(3) All loose material shall be removed from the bottom of the test hole and 2 inches of 1/4-inch to 3/4-inch gravel shall be added to protect the bottom from scouring.
(4) The hole shall be carefully filled with clear water to minimum depth of 12 inches over the soil at the bottom of the test hole and maintained for no less than 4 hours. Failure to adequately saturate the test hole may result in rejection of the test.
(5) The soil shall then be allowed to swell for at least 16 but no more than 30 hours. In sandy soils, the saturation and swelling procedure shall not be required and the test may proceed if 1 filling of the hole has seeped away in less than 10 minutes.
(6) Measure the percolation rate as follows:
(a) In sandy soils, adjust the water depth to 8 inches over the soil at the bottom of the test hole. From a fixed reference point, a drop in water level shall be measured in inches to the nearest 1/16-inch at approximately 10-minute intervals. Measurement can also be made by determining the time it takes for the water level to drop 1 inch from an 8-inch reference point. If 8 inches of water seeps away in less than 10 minutes, a shorter interval between measurements shall be used, but in no case shall the water depth exceed 8 inches. The test shall continue until 3 consecutive percolation rate measurements vary by a range of no more than 10%.
(b) In other soils, adjust the water depth to 8 inches over the soil at the bottom of the test hole. From a fixed reference point, the drop in water level shall be measured in inches to the nearest 1/16 inch at approximately 30-minute intervals, refilling between measurements to maintain an 8-inch starting head. The test shall continue until 3 consecutive percolation rate measurements vary by a range of no more than 10%. The percolation rate can also be made by observing the time it takes the water level to drop 1 inch from an 8-inch reference point if a constant water depth has been maintained for a least 4 hours prior to the measurement.
(7) Calculate the percolation rate by dividing the time interval by the drop in water level to obtain the percolation rate in minutes per inch. The percolation rates which are within the 10% provision determined for each test hole shall be averaged to determine the final percolation rate for that hole.
(8) The slower final percolation rate for all holes within the soil treatment area shall be used for design.
(9) A percolation test shall not be run where frost exists below the depth of the proposed soil treatment system.
(Prior Code, Ch. 506 § 9.9)