12/19/2001 Env Bd Packet - Laserfiche WebLink

Home Search

Infiltration Basins Infiltration Rate The soils of a prospective site are an important consideration when determining the suitability for infiltration. County soil surveys are useful for preliminary screening of a site for soil infiltration rate. The Natural Resource Conservation Service (formerly the Soil Conservation Service) Soil Group is found in the National Engineering Handbook. Conservative estimates of infiltration rates for a range of hydrologic soil groups (A through D) have been developed for some Minnesota authorities and are shown below (Riley - Purgatory -Bluff Creek Watershed District, 1999). Soil Group Rate (in/hr) A 0.38 B 0.23 C 0.1 D 0.03 Max. Water Depth (ft) 2 1.4 0.6 0.2 If these estimates are deemed too conservative for the site, a geologic investigation of the specific site should be conducted to verify higher infiltration rates. Infiltration rates should be measured in situ according to the stan- dards presented in: • Annual Book of ASTM Standards, 1997, Section 4, Vol 4.08, Soil and Rock (I): Designation D 3385 -94, Standard Test Method for Infiltration Rate of Soils in Field Using a Double -Ring Infiltrometer, pp 331 -337. • Annual Book ofASTMStandards, 1998, Section 4, Vol 4.09, Soil and Rock (II): Designation D 5093 -90, Standard Test Method for Field Measurement and Infiltration Rate Using a Double -Ring Infiltrometer with a Sealed -Inner Ring, pp 87 -92. • Johnson, A.I., 1963, "A field method for measurement of infiltration," United States Geological Survey, Water- Supply Paper, W 1544 -F, p. F1 -F27. The depth of water within the infiltro -ter should be maintained at the following depths: Hydrologic Soil Type Water Depth (Inches) A 18 B 9 C 4 D 1 Notes on alternative infiltration measurement methods: • Alternative methods other than reference standards should use a double -ring apparatus and be acceptable to local authorities. Metropolitan Council / Barr Engineering Co. 3 -161