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Mr. Paul Korenovsky ES-6067 <br /> June 20, 2018 Page 10 <br /> The total correction factor applied to the measured infiltration rates was 0.315. The resulting <br /> design/long-term infiltration rates ranged from 0.3 to 0.9 iph; however, based on overall soil <br /> variability and the relatively shallow depth to dense native soils, a design infiltration rate of 0.3 <br /> iph is recommended. The limited infiltration facilities should apply the following: <br /> • Design Infiltration Rate 0.3 iph <br /> Soil Types and Site Variability <br /> We conducted USDA textural analyses of representative soil samples collected at the PIT <br /> areas. The majority of the infiltration surface consists of gravelly sandy loam soils. The <br /> variability of the soils in terms of fines contents ranged from about 16 to 34 percent. <br /> Water Quality Characteristics <br /> Per the 2014 SWMMWW, infiltration facilities that are to be used as treatment facilities must <br /> have infiltrating soils with certain chemical characteristics that will adequately remove target <br /> pollution. In general, soils must have a cation exchange capacity (CEC) of at least 5 <br /> milliequivalents per 100 grams and organic matter (OM) content of at least 1 percent to be <br /> considered suitable for treatment. <br /> We analyzed two representative soil samples for OM and CEC using an outside laboratory. All <br /> samples contained OM of between 3.4 to 3.9 percent and CEC values between 6.9 and 7.9 <br /> meq/100g at infiltrating depths. The laboratory test results are attached. The soil deposits on <br /> this site are relatively consistent and the values for OM and CEC are representative of the site. <br /> Additional Recommendations <br /> In the event that limited infiltration facilities would comprise adjacent residential structures or <br /> threaten existing below-grade basements, the proposed limited infiltration facilities should be <br /> considered infeasible. Additionally, we recommend incorporating emergency overflow <br /> provisions into the infiltration design. If an emergency overflow cannot be provided, infiltration <br /> should not be considered feasible. <br /> In our opinion, the results of the infiltration analysis correlate with the soil and groundwater <br /> conditions observed at the test sites. This opinion does not cover unforeseen or changed <br /> conditions. ESNW should observe the infiltration construction activities to confirm soil <br /> conditions are as anticipated and to provide supplemental recommendations, as necessary. <br /> Earth Solutions NW,LLC <br />