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Austin Road Landfill Appendix D Contaminant Plume Characterization Report Aquifer Test Methods Background Monitoring The initialP hase of the aquifer testing consisted of a pretest monitoring of water levels in each observation well. One of the wells,MW-12(Figure 1-2),was also used throughout the five aquifer test phases to identify local trends in the water table surface. As shown on Table D-1,well MW-12 is located the greatest distance from either extraction well yet it is close enough to the test site that fluctuations in its water levels should be representative of larger-scale influences affecting the entire study area. Identifying ambient(background)water level trends,as represented by the water level data in MW- 12, is important because the aquifer test analysis methods assume there are no fluctuations in the water table surface other than those produced by pumping from the test wells EW-1 and EW-2. To meet this assumption,the regional background fluctuations must be removed from the data sets of the aquifer test observation wells as a pre-evaluation data correction. Regional/background fluctuations in the water table in the vicinity of the ARL are likely caused by changes in barometric pressure,infiltration of rainfall into the aquifer,and from pumping of nearby wells. Pretest water level measurements from the observation wells showed similar trends to each other, verifying that regional factors affected the aquifer in the vicinity of the ARL site in a consistent manner. The pretest water level data also indicated that well MW-12 generally was representative of the background fluctuations,and could be used for this purpose throughout the remaining test phases. Recovery n inPhases As mentioned in Section 2.3,the ARL aquifer test was designed to cause minimal disturbance to the operation of the site's groundwater remediation system. This was accomplished by turning off each extraction well,in sequence,and then turning them back on in sequence. In terms of the aquifer test,this meant that the recovery phase of each well occurred first then was followed by the pumping phase. The following summarizes the different test phases,their starting time and duration: Test Phase Event . tar Date.Time Recovery-1 EW-1 off December 4,11:10 am 5650 min Recovery-2 EW-2 off December 8,9:20 am 5680 min Pumping-1 EW-1 on December 12,8:00 am 4380 min Pumping-2 EW-2 on December 15,9:00 am 4430-5840 min The test phases continued until a sufficient change in water levels were recorded in a majority of the observation wells,as determined through repeated review of water level data while the tests were being conducted. Extraction well operations were controlled by the onsite remediation system operator,Dennis Young. Water level measurements were collected from the Trolls during each test phase on a logarithmic scale starting at a 0.005 minute measurement interval and gradually increasing until reaching a CDM Camp Dresser&McKeeD-3 W:\REPORTS\STOCKTO~LPLUME.OMPPO.WPD CS OZO City of Stockton 199 SO 0855-0006