Failure Analysis of Large Septic Tank Systems

by Foppe B. DeWalle, Assoc. Prof.; Dept. of Environmental Health, Univ. of Washington, Seattle, Wash. 98195,

Serial Information: Journal of the Environmental Engineering Division, 1981, Vol. 107, Issue 1, Pg. 229-240

Document Type: Journal Paper


The differences in design criteria between single residence on-site sewage disposal systems and large on-site systems were evaluated. The allowed loading for large systems on coarse sand is 45% higher, while the actual loading based on 1970 Census data may be 213% higher, as compared to household systems. Surveys in the state of Washington show that most system failures are associated with impervious soil type, underdesign and age of the system. Calculations indicate a serious under-reporting of the number of failures of both small and large on-site systems, thereby underestimating a major public-health risk.

Subject Headings: Septic tanks | Load factors | Soil surveys | Failure analysis | Sewage | Coarse-grained soils | Sandy soils | Soil classification | Washington | United States

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