7 Del. Admin. Code § 7103-19.0

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

Section 7103-19.0 - Evaluation of Potential Sites

19.1 Parties Involved. The word "wastewater" has negative connotations for most people with little knowledge of waste treatment. Rumors that a land treatment system is being proposed in a given area can cause an emotionally charged condition among residents of that area. Therefore, it is important to involve a number of people in the site selection process so an environmentally acceptable site will be selected, residents of the area can be educated about land treatment and lines of communication can be kept open.

19.1.1 A representative of local government should be involved early in the planning stage so he will be informed and can communicate with concerned residents. He can also determine if the proposed site is compatible with the local land use plan.

19.1.2 The county agricultural extension agent can assist in agronomic or forest recommendations for the site and perhaps can also provide with the help of state extension specialists an educational program for public meetings to inform area residents about land treatment.

19.1.3 The local SCS office can provide information on soils on the proposed site and can develop a soil map of the area if one is not available.

A representative of the Division of Water Resources, Water Pollution Control Branch must be involved. They will conduct a site inspection to determine if the site is suitable. This office will receive the permit application.

19.1.4 It is the responsibility of the waste generator and his consultant to coordinate the site evaluation and selection. Obviously, the land owner will be involved by offering the land for sale, lease or use.

19.2 Site Identification and Screening. Potential land treatment sites are identified using existing soils, topography, hydrogeology and land use data. Usually, land areas near where wastewater is generated are evaluated according to their land treatment suitability. A deductive approach is used in that, first, any constraints that might limit site suitability are identified. Some of the main factors to consider are current and planned land use, topography, soils, groundwater depth and quality, surface water sources, flooding hazard, and size of site required.

19.2.1 Eventually, for permit application the location of the site shall be indicated on topographic and soils maps.

19.3 Field Investigations. Although much of the preliminary screening of potential sites is based on existing field data available from an SCS county soil survey or other sources, some level of field investigation is necessary. This starts with a visual exploration of the site to identify any possible site limitations such as presence of wet areas, rock outcrops, and locations of streams. The visual exploration is normally followed by a site-specific field investigation to define assimilative capacities and other design related factors. However, the amount of additional field investigation needed will depend on the site characteristics and where uncertainty exists. Too little field data may result in using incorrect values for design while too much will result in unnecessarily high costs with little refinement in the design.

19.4 The allowable wastewater loading is often dependent upon the drainage characteristics of the site. The importance of evaluating the total pathway of movement of the wastewater from the soil surface to groundwater or surface water outlets is discussed in Chapter 4 under "Removal by Drainage." The field measurements needed to evaluate drainage will depend on the site characteristics. A deep soil with high permeability and low slope will be easier to evaluate than a soil with moderate slope and restrictive layers near the soil surface. The potential for groundwater mounding or perched water tables near the soil surface should also be evaluated. If applied properly, the USDA watershed model DRAINMOD can provide estimates of lateral migration of shallow groundwater. The EPA design manual (7) discusses methods for estimating hydraulic loading based on:

(a) vertical hydraulic conductivity of the most restrictive layer,

(b) limitation on percolate nitrate concentrations, and

(c) groundwater mounding near the surface. If the soil characteristics indicate that infiltration capacity of the soil surface may restrict hourly application rates of the sprinkler system, then the application rate must be reduced or a crop management scheme to enhance infiltration must be considered.

19.5 Again, requirements for field measurements will vary at each site, but an order of sequence of investigations that may occur as suggested in the EPA manual (7) is given in Table 1.

TABLE 1

Field Investigations in Typical Order of Testing and Information to Obtain

Field Test	Information to Obtain
1. Test pits and/or hand auger borings	Depth of profile, texture, structure, soil layers resticting percolation
2. Bore holes	Depth to groundwater, depth to impermeable layers.
3. Permeability	Expected minimum permeability of restrictive horizon.
4. Soil Chemistry	Specific data relating to crop and soil management, phosphorus and trace metal retention.

19.6 Although soils information from the SCS county soil surveys or previous farming or forestry records will indicate the productivity potential of the soil, soil samples must be taken from the site to determine soil chemistry and the soil's present status for growing the intended vegetation. From the results of the soil chemical analysis knowledge of vegetation and site management procedures and long-term erosion rates, the assimilative capacity for each of the important wastewater constituents can be determined.

19.7 The site should also be evaluated for land clearing requirements and possible drainage requirements. If land clearing is necessary, it should be done with minimal soil disturbance. Land should not be graded (e.g. to reduce slope) in land preparation because this will likely reduce permeability. If artificial drainage is necessary, the pollution impact of the drainage water discharge must be determined.

19.8 If a groundwater and/or surface water monitoring program is required for the particular system, monitoring points should be established early so background data can be collected before wastewater is applied.

7 Del. Admin. Code § 7103-19.0