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• <br />• <br />• <br />Appendix A <br />Table 1 <br />Hydrologic <br />Soil Group .. <br />Sol l <br />Textures* <br />Corresponding Unified Soil <br />Classification ** . ' <br />Infiltration Rate <br />[inches/hour] <br />1.6 <br />A <br />Gravel, sand, <br />sandy gravel, <br />silty gravel, <br />loamy sand, <br />sandy loam <br />GW — Well- graded gravel or well - <br />graded gravel with sand <br />GP — Poorly graded gravel or poorly <br />graded gravel with sand <br />GM — Silty gravel or silty gravel with <br />sand <br />SW — Well- graded sand or well- <br />graded sand with gravel <br />SP — Poorly graded sand or poorly <br />graded sand with gravel <br />0 8 <br />B <br />Loam, silt <br />loam <br />SM — Silty sand or silty sand with <br />gravel <br />0.6 <br />ML — Silt <br />OL — Organic silt or organic silt with <br />sand or gravel or gravelly organic silt <br />0.3 <br />C <br />Sandy clay <br />loam <br />GC — Clayey gravel or clayey gravel <br />with sand <br />SC — Clayey sand or clayey sand with <br />gravel <br />0.2 <br />D <br />Clay, clay <br />loam, silty <br />clay loam, <br />sandy clay, <br />silty clay <br />CL — Lean clay or lean clay with sand <br />or gravel or gravelly lean clay <br />CH — Fat clay or fat clay with sand or <br />gravel or gravelly fat clay <br />OH — Organic clay or organic clay <br />with sand or gravel or gravelly <br />organic clay <br />MH — Elastic silt or elastic silt with <br />sand or gravel <br />< 0.2 <br />Source: Minnesota Pollution Control Agency, Minnesota Stormwater Manual. Thirty <br />guidance manuals and many other stormwater references were reviewed by the MPCA <br />when it compiled the recommended infiltration rates. All of these sources use the <br />following studies as the basis for their recommended infiltration rates: Rawls, Brakensiek <br />and Saxton (1982); Rawls, Gimenez and Grossman (1998); Bouwer and Rice (1984); and <br />Urban Hydrology for Small Watersheds (NRCS). The rates presented in this infiltration <br />table use the information compiled from these sources as well as eight years of <br />infiltration rates collected from various infiltration practices in the South Washington <br />Watershed District. <br />* U.S. Department of Agriculture, Natural Resources Conservation Service, 2005. <br />National Soil Survey Handbook, title 430 -VI. (Online) Available: <br />http: / /soils.usda.gov /technical /handbook /. <br />** ASTM standard D2487 -00 <br />P110 <br />