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Wetter Is Better?
completed animal waste retention ponds in
Goshen County, Wyoming (NRCS photo — click to enlarge) |
Wetter is better? For those involved in the construction of waste
storage ponds and treatment lagoons, that means a well designed, fully
functional soil liner that meets minimum admissible thresholds. The
influence of initial water content at which a sample is molded affects the
hydraulic conductivity. When saturated, permeability can vary by several
orders of magnitude if the initial water content is changed a few percentage
points. Soils compacted above optimum moisture content (wetter) generally
have lower permeabilities than when compacted dry of optimum moisture content
for the same density. This has been well documented in literature, as well as in
tests taken at NRCS’s geotechnical laboratories in Lincoln, Nebraska and Fort
Worth, Texas based on results using state-of-the-art flexible-wall permeameters.
This is a much different recommendation than in testing of road fill or dams
where compaction characteristics are perhaps of greater importance than the
moisture content at which the soil is molded. Appendix 10d in Part 651 of
the Animal Waste Management Field Handbook provides excellent guidelines and
design considerations when using a compacted soil liner.
Your contact is Jody Kraenzel,
NRCS civil engineer, at 402-437-5337, ext. 113.
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