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• • • Appendix - Rule C Table C1 Hydrologic Soil Group Si lit Textures* Gravel, _sand, sandy gravel, silLgraveL loamy sand, sandy loam Loam, silt loam Corresponding Unified Soil Classification** GW - We 11-gracled gravel or welL graded_gravel with sand graded GP - Poorlv araded gravel or poorly GM - Silty gravel or silty_gravel with sand SW - Well-graded sand or well- graded sandwith cmpl_ s p — Poorly graded sand or poorly graded sandwith Gravel SAL.-__.__...Siltysand or silty sand with _gravel 0.6 ML Silt OL - Organic silt or organic silt with sand or gravel _or gravelly organic silt Infiltration Rate Linches/hourl 0.3 Sandy_clay loam Clay, _clay loam, silty clay loam, sandy clay, silty clay GC - Clayey gravel or clayey gravel with sand SC - Clayey sand or clayey sand with gravel CL - Lean clay_or lean clay with sand or gravel or gravelly lean clay CH - Fat clay or fat clay with sand or gravel or gravelly fat clay OH - Organic clay or organic clay with sand or gravel or gravelly organic clay MH - Elastic silt or elastic silt with sand or gravel 02 Source: Minnesota Pollution Control Agency, Minnesota Stormwater Manual. Thirty guidance manuals and many other stormwater references were reviewed by the MPCA when it compiled the recommended infiltration rates. All of these sources use the following studies as the basis for their recommended infiltration rates: Rawls, Brakensiek and Saxton (1982): Rawls, Gimenez and r. 1 • • : • w- , • zi - 1 • : • . n. rban Hydrology for Small Watersheds (NRCS) The rates presented in this infiltration table use the information compiled from these sources as well as eight years of infiltration rates collected in various infiltration pces located in the South Washington Watershed District. *U.S. Department of Agriculture, Natural Resources Conservation Service, 2005. National Soil Survey Handbook, title 430-VI. (Online) Available: http://soils usda.gov/technical/handbook/. **ASTM standard D2487-00 DRAFT DOCUMENT 21