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Water Quality Monitoring Report Forward Landfill contaminant and has rarely been detected in groundwater at Austin Unit wells. Results from the duplicate groundwater sample collected from well AMW-29 are presented along with the primary data in Table 3-2. The duplicate sample analyses yielded good correlation with quantifiable constituents having a RPD within 10 percent. Exceptions include cis-1,2-DCE, DCDFM, PCE, and TCE which had RPDs between 14 and 31 percent. Review of laboratory analysis dates and required holding times indicates that all samples were submitted and analyzed within the required holding times during the fourth quarter 2016. Based on the results of the laboratory blank and duplicate analyses, it is concluded that acceptable QA/QC procedures were exercised and the water quality samples collected from the Austin Unit appear to be representative of water quality at the site. 3.1.3 Groundwater Elevations and Contours Prior to purging and sampling, each well was sounded for water depth using a weighted electronic sounder, 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 Austin Unit are summarized in Table 3-6. The groundwater elevation data obtained during this quarterly monitoring period were used to generate the groundwater elevation contour map shown on Figure 3-1, which indicates that groundwater flows in a northeast direction with a hydraulic gradient varying from of 0.001 ft/ft. To calculate the approximate linear groundwater flow velocity for the site, 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 (CH21VI Hill 2000). An estimated groundwater flow velocity was calculated using Darcy's Law: Kic,» 0.001 sec — _/t — = [( 0.04 —) * ] * 2835 � 0.324 fi /day ne sec 0.35 on — day where: V= Groundwater flow velocity. K = Hydraulic conductivity of the water -bearing unit (0.04 cm/sec). i = Maximum hydraulic gradient: i � 0.001 during the fourth quarter 2016. ne= Effective porosity (ne = 0.35); an estimated value. The estimated maximum groundwater flow rate is calculated to be 0.324 feet/day (118 feet/year). 3.1.4 Detection Monitoring Program Field and laboratory results for the Austin Unit DMP wells for the fourth quarter 2016 are summarized in Table 3-1. Project No. 2016.0007 1 Water Quality Monitoring Report 11 January 2017