7301 HARDESON RD 2019-01-11 - Laserfiche WebLink

Cadman,Inc. August 31,2018 Page 4 The 4,000-gallon water truck used to supply water to PIT-2 and PIT-3 was refilled two times (approximately 12,000 gallons) in order to complete the PITs. In PIT-2, 79 stages were analyzed with a repeated head drop of 0.2 feet(Figure 4).The final stage of the testing period was used to estimate the measured infiltration rate for PIT-2. This is a conservative analysis method. The field measured infiltration rate at the end of the testing period was 42.1 inches per hour(in/hr). In PIT-3, seven stages were analyzed with a repeated head drop of 0.2 feet (Figure 6). The final stage of the testing period was used to estimate the measured infiltration rate for PIT-3.The field measured infiltration rate during the final stage of the testing period was 1.10 in/hr. Recommended Design Infiltration Rates Measured infiltration rates from the PITs,including PIT-1 which was completed in 2017 and used as the design infiltration rates for the Hardeson Pond facility, are summarized in Table 1. TABLE 1. MEASURED AND RECOMMENDED DESIGN INFILTRATION RATE - HARDESON POND Measured Infiltration Rate Design Infiltration Location (in/hr) Rate(in/hr) PIT-1 4.7 1.6 PIT-2 42.1 14.2 PIT-3 1.1 0.4 The design infiltration rate is determined by applying correction factors to the measured infiltration rate. The correction factors account for uncertainties in site variability and number of tests, testing method, and long-term reductions in permeability due to plugging from biological activity and accumulation of fines. Table III-3.3.1 of the 2014 SWMMWW describes the correction factors to be used to estimate design infiltration rates. Table III-33.1 Correction Factors to be Used With In-Situ Saturated Hydraulic Conductivity Measurements to Estimate Design Rates Issue Partial Correction Factor Site variability and number of locations tested CFv=0.33 to 1.0 Test Method . Large-scale PIT . CFt=0.75 . Small-scale PIT . =0.50 . Other small-scale(e.g.Double ring,falling head) . =0.40 . Grain Size Method . =0.40 Degree of influent control to prevent siltation and bio-buildup CFm=0.9 Total Correction Factor,CFT=CFv x CFt x CFm • CF0 accounts for site variability and number of locations tested. A CF„ of 0.75 was used for consistency with previous PITs. • CFt is determined based on the test method.The CFt for small-scale PIT testing is 0.50. • CFm accounts for the degree of influent control to prevent siltation and bio-buildup and is 0.9. The total correction factor CFT for the PITs is 0.338. When applied to the measured infiltration rates of 4.7, 42.1 and 1.1 in/hr,the design infiltration rates for the Hardeson Pond are 1.6, 14.2 and 0.4 in/hr,respectively. GEOENGINEERS Foe No.7087-028-02