TM 5-814-3/AFM 88-11, Volume III
c. Subsurface sand filters. Septic tank effluent can also be applied to subsurface sand filters. Subsurface
explorations are always necessary. Clogging and installation costs are significant disadvantages. Where recir--
culatory sand filters on used dose rate may range between 3-5 gallons per day per square foot, Consult EPA
Manual No.625/1-80-012, Harris et al., 1977, and Ronaye et al., 1982, for appropriate procedures for site
evalua-tion and design parameters.
d. Percolation tests. In the absence of groundwater or subsoil information, subsurface explorations are
necessary. This investigation may be carried out with shovel, posthole digger, or solid auger with an
extension handle. In some cases the examination of road cuts or foundation excavations will give useful
information. If subsurface investigation appears suitable, percolation tests should be made at typical points
where the disposal field is to be located. Percolation tests determine the acceptability of the site and serve
as the basis of design for the liquid absorption. Percolation tests will be made as follows (fig 6-4).
6-4
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