7 Del. Admin. Code § 7103-63.0

Current through Register Vol. 28, No. 3, September 1, 2024

Section 7103-63.0 - Soil Investigations

63.1 General

63.1.1 Each design development report shall include a detailed soils investigation report which contains details on the field investigations conducted by a person who is registered as a Professional Soil Scientist with the American Registry of Certified Professionals in Agronomy, Crops and Soils (ARCPACS) depicting soils conditions on the site. Soil investigations for land treatment differ greatly from investigations for foundations, road and other civil engineering works. As a result, different investigative and testing methods are required. The land treatment soil investigation must characterize the permeability and chemical properties of the surface 5 to 10 feet of the soil profile. It must verify Soil Conservation Service soil mapping. It must also determine the elevation of the seasonal high groundwater, establish the groundwater flow direction and gradient, and identify any subsurface conditions which may limit the vertical or lateral drainage of the land treatment site. The number of soil samples necessary to supply all of this information will be dependent on the nature of the particular site. As a minimum however, the Department requires that at least one sample be taken for every 5 to 10 acres of each soil series to confirm the Soil Conservation Service mapping and to provide a sufficient number of undisturbed soil samples. The specific information required for design is outlined in Table 202-2.

63.2 Saturated Hydraulic Conductivity Testing

63.2.1 Saturated vertical hydraulic conductivity testing is required for the most limiting horizon (i.e., horizon with lowest saturated conductivity) of each major soil series present. The most limiting soil horizon shall be determined from soil survey information and on-site observations. A minimum of three (3) tests for each major soil series shall be performed. These test results will be compared with the values published by SCS. If the values are not comparable, additional testing is recommended. Testing for saturated horizontal hydraulic conductivity may be necessary when subsurface drainage systems are planned or when lateral subsurface drainage is the predominant drainage mechanism for the land treatment site. Less intensive conductivity testing may be conducted when hydraulic loading is much less than site capacity.

63.2.2 Acceptable methods for saturated hydraulic conductivity testing are listed in Table 302-1. Field testing is preferred over laboratory testing methods. The Department will accept laboratory approaches only when field testing is not possible. Percolation tests as performed for septic tank drain fields are not acceptable.

63.2.3 Use of the hydraulic conductivity values to determine design percolation rates is discussed in Section 3.0.

63.3 Soil Chemical Testing.

63.3.1 The pH, cation exchange capacity, phosphorus adsorption and percent base saturation, of each soil series must be determined from samples taken from the A and B horizons. These chemical tests determine the retention of wastewater constituents in the soil and the suitability of the soil for different cover crops. A minimum of three (3) samples for each major soil series shall be taken. Testing for soil nutrients (nitrogen, phosphorus and potassium) and agronomic trace elements shall be included if appropriate for the vegetative management scheme.

63.3.2 Soil chemical testing should be in accordance with Methods of Soil Analysis published by the American Society of Agronomy, Madison, Wisconsin. Other methods, properly documented, may be accepted upon approval by the Department.

7 Del. Admin. Code § 7103-63.0