Site evaluation is the process of evaluating the characteristics of a particular site to determine certain related features for design purposes. The main objective of a site evaluation, which is sometimes also referred to as a soil evaluation, soil test, or percolation "perc" test, is to determine the feasibility of the site and soil for subsurface wastewater disposal. Although some refer to it as a "perc" test, this method which involves filling a hole with water and timing the percolation rate into the soil profile, is no longer part of the site evaluation process in the state of Maine, but still used in the state of New Hampshire.

Soil characteristics are determined by examination of a soil test pit dug by hand, by shovel or auger, or by some type of earth excavating machine, to evaluate both the texture of the soil and any restrictions in the soil profile that would be considered a limiting factor. The texture of the soil is determined by the percentage of certain particle sizes of either sand, silt, or clay in the mineral part of the soil. The coarser textured soil types, such as sands and gravels, allow water to pass through them more readily whereas the finer textured soil types, such as silts and clays, allow water to pass through them much more slowly. Restrictions in the soil profile can include bedrock, or hardpan, a restrictive layer formed in basal glacial till, fine-textured sediments, or occasionally in sandy soils from iron cementation. Another limiting factor also includes groundwater, which is either an apparent water table or a seasonal water table generally "perched" above either bedrock or any hardpan layer which is apparent mostly in the Spring runoff season or other times of heavy precipitation.

These soil factors, as well as other design parameters, such as design flows, are used to determine disposal field size and planned elevation for a septic system, which needs to have a certain separation distance between the bottom of the disposal field and any limiting factor. Other site features including size of lot, setback distances to varied features, and slope are also used to determine system location and system type.

The photos included show a soil profile, and the use of a soil auger.