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• <br />0 <br />Everett Dental Office - TIR <br />C-.rni inr WAtar <br />April 2017 <br />The soil sample was collected during the wet -season. No groundwater seepage was <br />observed. It should be noted that groundwater levels vary seasonally with rainfall and <br />other factors. <br />Hydraulic Restrictive Layer <br />The test pits were excavated to a total depth of 5.0 ft. There was no restrictive layer or <br />hardpan clay at this depth. <br />EPA Fallinp, Head Infiltration Test <br />Infiltration tests were conducted at the site following the EPA Falling Head test <br />methodology by our staff on March 17, 2017. Data from all three test pits were analyzed <br />and the most limiting measured percolation rate was used to determine the <br />recommended design infiltration rate as outlined below. <br />Measured percolation rate <br />time interval =10 minutes <br />minimum water level drop = 1.75 inches <br />measured percolation rate = 10.5 inches/hour <br />The soils encountered at 3 to 4 feet below grade in the proposed infiltration area and the <br />results of the infiltration test are consistent with (medium) sand to the USDA textural <br />analysis recommendations per Table 3.7 of the DOE Stormwater Manual, Volume III, <br />page 3-76. <br />Table 3.7 -- Recommended Infiltration Rates <br />based on USDA Soil Textural Classification. <br />Estimated Long - <br />*Short -Term <br />Term (Design) <br />Infiltration <br />Correction <br />Infiltration Rate <br />Rate (in.lhr) <br />Factor, CF <br />(in.lhr) <br />Clean sandy gravels and <br />-)0 <br />? <br />10`s <br />gravelly sands (i.e., 90% of <br />the total soil sample is <br />retained in the #10 sieve) <br />Sand <br />8 <br />4 <br />- *** <br />Loanry Sand <br />? <br />4 <br />0.5 <br />Sandy Loam <br />1 <br />4 <br />0?5 <br />Loani <br />0.5 <br />4 <br />0.13 <br />"From WEF ASCE. 1998. 1 <br />The Concept Group <br />