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Water Quality Monitoring Report Forward Landfill The groundwater elevation data obtained on August 19, 2015, were used to generate the groundwater elevation contour map shown on Figure 2-1 for the third quarter 2015 monitoring period, which indicates that groundwater beneath the majority of the Forward Unit generally flows to the southwest at an average hydraulic gradient of 0.001, while groundwater beneath the northeastern corner of the Forward Unit flows to the northwest at an average hydraulic gradient of 0.004 ft/ft. To calculate the approximate linear groundwater flow velocity for the Forward Unit, conservative assumptions were used, including a hydraulic conductivity of 875 gallons per day per square foot (0.04 cm/sec) and an estimated effective porosity of 35 percent (CH2M Hill, 2000). An estimated groundwater flow velocity was calculated using Darcy's Law: Ki cm 0.004 sec— ft V = —= [(0.04—)* ]*2835 = 1.30 ft l day ne sec 0.35 cm — day where: V= Groundwater flow velocity. K= Hydraulic conductivity of the water-bearing unit (0.04 cm/sec). i= Hydraulic gradient: i=0.004 at the site during the third quarter 2015. ne= Effective porosity (ne=0.35); an estimated value. The maximum groundwater flow rate is calculated to be 1.30 feet per day (473 feet/year). 2.1.4 Detection Monitoring Program Field and laboratory results for the Forward Unit groundwater monitoring wells for the third quarter 2015 monitoring period are summarized in Table 2-2. Non-Statistical Data Analysis The California Non-Statistical Data Analysis Method (CNSDAM) was performed for VOCs detected less than 10 percent of the time in background samples. Under the CNSDAM, a measurably significant indication of release occurs in a given sample when: two or more VOCs exceed their respective Method Detection Limits (MDLs); or one or more VOCs equals or exceeds its respective practical quantitation limit (PQL). During the third quarter 2015 monitoring period, non-statistical indications of a release were identified at well MW-16 as a result of a quantifiable concentration of diisopropyl ether (DIPS); and at well MW-17 as a result of quantifiable concentrations of chloroform and carbon tetrachloride. In a letter dated August 13, 2015, similar concentrations of these VOCs were reported to the RWQCB for the second quarter 2015 and confirmed in retest samples collected on July 29, 2015. It should be noted that these confirmed VOCs are M:\2015.0014\FA 3Q15.docx 6