7 Del. Admin. Code § 7103-62.0

Current through Register Vol. 28, No. 4, October 1, 2024

Section 7103-62.0 - Required Design Considerations

62.1 Suitability of Sites for Wastewater Irrigation

62.1.1 Location

62.1.1.1 There are two, often contradictory, requirements for slow rate land treatment sites: proximity to the wastewater source and a large tract of suitable land. Additional considerations are a moderate degree of isolation, ease of access, availability of utilities and protection from flooding. Wastewater irrigation systems can be developed on agricultural land and forests. The Department will also consider wastewater irrigation of golf courses, cemeteries, green areas and parks. Special preapplication treatment requirements may apply to such systems (see subsection 64.7.2.2 and 64.7.2.3).

62.2 Topography

62.2.1 Due to equipment limitations and erosion potential, maximum slopes for wastewater spray fields are generally limited to 7 percent for row crops, 15 percent for forage crops and 30 percent for forests. Sloping sites are preferred over flat sites because lateral subsurface drainage occurs which makes ponding and extended saturation of the soil less likely. Depressions must be carefully evaluated in the design.

62.3 Soils

62.3.1 In general, soils with a USDA Soil Conservation Service permeability classification of moderately slow (.02 to 0.6 inches/hour) or more are suitable for wastewater irrigation. However, groundwater and drainage conditions must also be suitable. Soils which are poorly drained, have high groundwater tables or restrictive subsurface soil layers are generally not suitable for slow rate treatment without drainage improvements.

62.4 Hydrogeology

62.4.1 Hydrogeologic characteristics of the site shall be investigated by a Professional Geologist registered in the State of Delaware and submitted as part of the design report. This information can be obtained from published literature or from on-site field investigations. The hydrogeologic report shall contain a description of the geologic and hydrogeologic characteristics of the site including:

62.4.1.1 Stratigraphy;

62.4.1.2 Lithology of the water table aquifer;

62.4.1.3 Hydrologic properties of the water table aquifer, including horizontal and vertical hydraulic conductivity, groundwater flow gradient, water table elevations, and a determination of the depth to seasonal high groundwater table including an estimate of seasonal variations;

62.4.1.4 Elevation interval and lithology of the uppermost, laterally extensive confining unit;

62.4.1.5 Lithology, elevation interval and hydrologic properties of the uppermost confined aquifer;

62.4.1.6 Identification of any facilities, such as nearby high capacity irrigation wells, that do or may potentially influence groundwater flow characteristics;

62.4.1.7 An assessment of the effects on groundwater flow at the land treatment site, if any, that may be caused by nearby activities;

62.4.1.8 Identification of any activities adjacent to the land treatment site which do or may potentially contaminate groundwater at the land treatment site, and a description of such activities and associated potential contaminants.

7 Del. Admin. Code § 7103-62.0