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Water Quality Monitoring Report <br /> Forward Landfill <br /> downgradient (north) of the Austin Unit with an average hydraulic gradient of 0.002 <br /> ft/ft,while an east to southeast gradient was noted underneath the Austin Unit. <br /> To calculate the approximate linear groundwater flow velocity for the site, conservative <br /> assumptions were used, including a hydraulic conductivity of 875 gallons per day per <br /> square foot (0.04 cm/sec) and an estimated effective porosity of 35 percent (CH2M Hill <br /> 2000). An estimated groundwater flow velocity was calculated using Darcy's Law: <br /> Ki cm 0.002 sec— ft <br /> V = —_ [(0.04—)* ]*2835 = 0.648 ft/day <br /> ne sec 0.35 cm —day <br /> where:V= Groundwater flow velocity. <br /> K= Hydraulic conductivity of the water-bearing unit (0.04 cm/sec). <br /> i= Hydraulic gradient: i=0.002 at the site during the second quarter 2016. <br /> ne= Effective porosity(ne=0.35); an estimated value. <br /> The maximum groundwater flow rate is calculated to be 0.648 feet/day (237 feet/year). <br /> 3.1.4 Detection Monitoring Program <br /> Field and laboratory results for the Austin Unit DMP wells for the second quarter 2016 <br /> are summarized in Table 3-1. <br /> Non-Statistical Data Analysis <br /> During the second quarter 2016 monitoring period, the CNSDAM was performed for <br /> VOCs detected in the DMP wells. As shown in Table 3-1, non-statistical indications of a <br /> release were identified at well AMW-6 as a result of a quantifiable concentrations of <br /> PCE (2.2 µg/L), and a trace-level concentrations of DCDFM and trichloroethene (TCE). <br /> Forward had previously requested that well AMW-6 be reclassified as a CAP well, since <br /> similar concentrations have been historically measured in this well. Trace-level <br /> concentrations of PCE were also measured in wells AMW-2 and AMW-12. <br /> Concentration Limit Thresholds <br /> In accordance with RWQCB Order No. 115-2014-0006, the routine inorganic monitoring <br /> data obtained from the Austin Unit DMP wells during the second quarter 2016 <br /> monitoring period were compared to intrawell concentration limits (CLs) established for <br /> each well. Details on the statistical analysis for the established CLs are presented in <br /> Appendix G of the fourth quarter 2014 Water Quality Monitoring Report for the <br /> Forward Landfill (GLA, 2014). As summarized in Table 3-3, the following CLs were <br /> exceeded during the second quarter 2016 monitoring period. <br /> M:\2016.0007\FA 2Q16.docx 11 <br />