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4.0 First Semester 1996 Groundwater Monitoring and Sampling <br /> ' 4.1 Monitoring <br /> The first semester 1996 groundwater monitoring data were collected on March <br /> ' 27, 1996 Monitoring activities included measuring the groundwater elevations in all <br /> nine of the onsite monitoring wells shown on Figure 4-1 Groundwater <br /> ' measurements were taken using an electronic groundwater depth meter Dissolved <br /> oxygen was measured in MW-1, MW-4, MW-5, MW-8, and MW-9 using a field <br /> meter Free product was not observed in any of the onsite monitoring wells Depth <br /> ' to groundwater and well depth measurements were recorded for each monitoring <br /> well and are listed in Table 1. The groundwater elevations were approximately 7 <br /> ' feet higher than the elevations recorded during the fourth quarter 1995 monitoring ! <br /> event <br /> ' Data collected were used to determ.me groundwater flow direction and gradient <br /> as shown on Figure 4-2 The general groundwater flow direction in the vicinity of <br /> the underground storage tank is to the northeast at an average hydraulic gradient of <br /> 0 020 foot/foot This is different from the typical southwest flow direction from <br /> t, previous quarterly monitoring events However, the high groundwater levels and <br /> ' gradient toward the northeast are consistent with conditions reported in the first <br /> quarter 1995 monitoring report Waste Science will continue to monitor the <br /> groundwater flow direction and gradient during subsequent monitoring events to <br /> ' determine if there are seasonal variations <br /> ' 4.2 Sampling <br /> Field groundwater monitoring data (conductivity and temperature) and <br /> groundwater elevation data were used to determine the volume of purge water to be <br /> removed from each monitoring well prior to sampling (Field samples were not <br /> ' analyzed for pH because the pH meter was inoperable during the first semester field <br /> event. Subsequent semester monitoring events will again collect pH data as a part <br /> of sampling ) Samples were collected after physical parameters stabilized and a <br /> minimum of three well volumes of water had been removed Purge water and other <br /> investigation-denved wastes (IDW) were placed in Department of Transportation <br /> (DOT) approved 17E/H drums <br /> 96R7 East Say Municipal Utility District <br /> 4042960011stsem gw 3 Stockton Service Center-First Semester 1996 <br />