Site Evaluation and Selection

A critical step in land application of biosolids is finding a suitable site. The suitability of a site considered depends on the land application options being considered. Site characteristics of importance are topography, soil characteristics, soil depth to groundwater, and accessibility to critical areas. For the initial screening of potential sites, areas with following characteristics should be avoided (WEF, 1998):

• Steep areas with sharp relief

• Shallow soils

• Environmentally sensitive areas such as intermittent streams and ponds

• Rocky, nonarable land

• Wetland and marshes

• Areas bounded by surface water bodies without appropriate set backs

• Culturally sensitive lands, such as old cemeteries and burial grounds

Topography is important, as it affects the potential for erosion and runoff. Slopes up to 30% can be accommodated, depending on the types of biosolids and the method of application. Table 10.2 shows the slope limitations for land application of biosolids. Loamy soil of slow to moderate permeability with alkaline or neutral pH and a soil depth of 0.6 m (2 ft) or more is preferred. Because groundwater fluctuates on a seasonal basis in many areas, an acceptable minimum depth to groundwater is difficult to establish. At least 1 m (3 ft) to groundwater is preferred.

Ideal sites for land application of biosolids have deep silty loam to sandy loam soils; groundwater deeper than 3 m (10 ft); slopes at 0 to 3%; no wells, wetlands, or streams; and few neighbors (Metcalf & Eddy, 2003). The location of the treatment plant also determines whether suitable sites are available within a feasible hauling distance, a decision typically based on economic considerations. Agricultural practices and inclement weather in the area also have a considerable effect on site availability throughout the year. Because sites may be available only at certain times, substantially more acreage than is needed in a given year should be permitted to receive biosolids. Facilities for storing the biosolids for later use should also be considered.

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