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Water Quality Monitoring Report Forward Landfill 2.1.3 Groundwater Elevations and Contours Prior to purging and sampling, each well was sounded for water depth using a weighted electronic sounder to an accuracy of 0.01 foot, and the static water level was recorded on a Well Data Sheet (Appendix F). The groundwater elevations were calculated for each well by subtracting the depth-to-water measurement from the top-of-casing reference elevation. The current groundwater elevation data for the Forward Unit is summarized in Table 2-3. The groundwater elevation data obtained on August 15, 2017, were used to generate the groundwater elevation contour map shown on Figure 2-1 for the third quarter 2017 monitoring period, which depicts groundwater beneath the northeastern corner of Forward Unit generally flowing to the east-northeast at an average hydraulic gradient of 0.003 ft/ft, while groundwater beneath the remainder of Forward Unit flows to the south-southeast at an average hydraulic gradient of 0.003 ft/ft, potentially controlled by agricultural well pumping on adjacent properties south of the Forward Unit. To calculate the approximate linear groundwater flow velocity for the Forward Unit, conservative assumptions were used, including a hydraulic conductivity of 2SS feet per day (CDM, 1997) and an estimated effective porosity of 35 percent. An estimated groundwater flow velocity was calculated using Darcy's Law: Alk Ki ft 0.003 V = —_ (255 )*- = 2.19ftlday ne day 0.35 where: V=Groundwater flow velocity. K=Hydraulic conductivity of the water-bearing unit(255 ft/day). i=Average hydraulic gradient:i=0.003 during the third quarter 2017. ne=Effective porosity(ne=0.35);an estimated value. The maximum groundwater flow rate is calculated to be 2.19 feet per day(798 feet/year). 2.1.4 Detection Monitoring Program Field and laboratory results for the Forward Unit groundwater monitoring wells for the third quarter 2017 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 Project No.SO17.1030 I Water Quality Monitoring Report 6 October 2017