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1.6 Groundwater, Surface Water, and Vadose Zone Monitoring Systems <br /> Water quality is monitored in accordance with WDR Order No. 5-01-176 and the monitoring <br /> program approved by the RWQCB (Figure 2). <br /> 1.6.1 Groundwater <br /> The present groundwater monitoring network consists of seven monitoring wells. These wells <br /> monitor both the deep aquifer and the shallow aquifer. <br /> Shallow Aquifer Monitoring <br /> Three wells (SB-1, MW-4 and MW-5)monitor the shallow,perched aquifer. Well SB-1 is an <br /> up-gradient well, whereas wells MW-4 and MW-5 are down-gradient. <br /> Deep Aquifer Monitoring <br /> Deep aquifer monitoring wells MW-6 and MW-7 were installed in 2003. Well MW-7 is up- <br /> gradient to well MW-6. These wells replaced the previously installed deep aquifer wells MW-1, <br /> MW-2 and MW-3, which became dry in 1990. The direction of the flow of groundwater in the <br /> deep aquifer was determined by monitoring the three original deep aquifer wells. <br /> 1.6.2 Surface Water <br /> When flowing, Corral Hollow Creek is sampled upstream of the waste management facility at <br /> background monitoring point SW-1, and downstream at monitoring point SW-2. Samples are <br /> collected after the first storm of the rainy season that produces significant flow and semi- <br /> annually thereafter when water is flowing. <br /> 1.6.3 Vadose Zone Soil Gas <br /> Vadose zone soil gas wells GW-1 through GW-7 are multi-probe wells originally installed to <br /> monitor the subsurface concentration of combustible gases near the property boundary. These <br /> wells are monitored for combustible gas quarterly, and a selected probe from each well is <br /> sampled for VOCs (EPA Method TO-14) semiannually. <br /> Corral Hollow EMP WP.DOC 1-3 February 28,2007 <br />