The next phase of the site and system selection process involves field surveys to confirm map data and then field testing (as needed) to confirm site information or to provide the data needed for design. This preliminary procedure includes an estimate of capital cost so the sites identified in previous steps can be evaluated economically. A concept and a site are then selected for final design. Each site evaluation must include the following information:
• Property ownership, physical dimensions of the site, and current and future land use
• Surface and groundwater conditions — location of any wells as well as use and quality of groundwater, surface waters, drainage and flooding problems, depth and fluctuations in depth to groundwater, ground-water flow direction
• Characterization of the soil profile to a depth of 5 ft (1.5 m) for SR and most biosolids systems and to a depth of 10 ft (3 m) for SAT and pond systems, as well as both physical and chemical properties
• Agricultural crops — history of cropping, yields, fertilizers used and amounts applied, tillage and irrigation methods and rates of irrigation, end use of crops
• Forest site — age and species of trees, commercial or recreational site, irrigation and fertilizer methods, vehicle access to and within the site
• Reclamation site — existing vegetation, historical causes for disturbance, previous reclamation efforts, and need for regrading or terrain modification
Investigation of SAT sites requires special consideration of the topography and of soil type and uniformity. Extensive cut-and-fill or related earthmoving operations not only are expensive but can also alter the necessary soil characteristics through compaction. Sites with significant and numerous changes in relief over a small area are not the best choice for SAT. Any soil with a significant clay fraction (>10%) would generally exclude SAT basin construction if fill is required by the design. Extremely nonuniform soils over the site do not absolutely preclude development of a SAT system, but they do significantly increase the cost and complexity of site investigation.
A sequential approach to field testing to define the physical and chemical characteristics of the site soils is presented in Table 2.13. In addition to the site test pits and borings, examination of exposed soil profiles in road cuts, borrow pits, and plowed fields on or near the site should be part of the routine investigation. Backhoe test pits to a depth of 10 ft (3 m) are recommended, where site conditions permit, in each of the major soil types on the site. Soil samples should be obtained from critical layers, particularly from the layer being considered as the infiltration
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