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' M LEEDSHILL•HERKENHOFF, INC, <br /> used at the site to analyze the head space above collected soil and water <br /> ' samples to detect possible contamination, and help select samples to be <br /> analyzed by the laboratory. <br /> ' 3.2 Groundwater Investigation <br /> ' The objectives of the groundwater investigation were to determine the local- <br /> ized direction of groundwater flow, determine whether the plume had moved <br /> off-site and obtain background water quality data. Although available data <br /> ' indicated groundwater direction was generally northerly, it was thought that <br /> this local groundwater direction may be influenced by the cones of depres- <br /> sion created by any or all of the three municipal wells located at Lincoln <br /> ' Village Center. It was also unknown whether an upper, shallow water bearing <br /> zone existed at this site. To provide information regarding direction of <br /> ' groundwater flow and background water quality data, the wells were located <br /> as follows: wells were placed near each of the operating dry-cleaning estab- <br /> lishment; one in the northwest corner and one in the southwest area of LVC. <br /> ' A third well was situated along the eastern edge of the property, and the <br /> fourth well was placed in-between the suspect leaky sewer line and LVMD #1. <br /> This well was installed in the area assumed to be within the contaminant <br /> ' plume to determine the degree of background contamination. Figure 3.4 shows <br /> the monitoring well placement. <br /> ' All four wells were constructed in June, 1988 using a hollow stem auger <br /> drilling rig with a 12-inch outside diameter bit. Three wells (MW#1, MW#2 <br /> ' and MW#3) were drilled to a depth of 60 feet. The depth was based on the <br /> first encountered water during construction of the wells. The fourth well <br /> (MW#4) was drilled to a depth of 70 feet, responsive to San Joaquin County <br /> Environmental Health's fifty foot seal requirement due to proximity to an <br /> existing sewer line. This fifty foot seal requirement was waived for the <br /> other three monitoring wells. An undisturbed sample, one and one half feet <br /> ' in length, was collected every five feet to define the geologic profile. <br /> These geologic logs are presented in Appendix B. <br /> ' Flush threaded Schedule 40 PVC casing (4-1/2 inch I.D. ) was used with No. 20 <br /> slotted screen. The screen was installed between 43 and 58 feet below grade <br /> 1 for the 60 foot wells and between 55 and 70 feet for the 70 foot well . A <br /> Lonestar #3 sand pack was placed into the annular space surrounding the well <br /> screen from the bottom of the well to above the top of the screened casing. <br /> 3-7 <br /> t <br />