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■1 .y Additional Investigation to Define the Extent of Groundwater Contamination . Quik Stop Market No 121 Page 3 Monitoring Well Construction Monitoring wells MW-9, MW-10 and MW-11 were constructed using 2-inch diameter, schedule 40 polyvinyl chloride (PVC) well casings Ten to 20 feet of 0 020-inch screen were used to construct each well The annulus between each casing and borehole was backfilled with number 3, aquarium sand to 2 feet above the screen interval A bentonite clay spacer, at least 1 foot thick, was placed above the sand pack, and cement grout was pumped from above the bentonite to the surface A watertight,locking,vault box caps each well A copy of each well construction schematic is attached in Appendix A Well Development and Sampling On August 17,2001,monitoring wells MW-9,MW-10 and MW-11 were developed with a vacuum pump to (a) remove residual silts and clays left from the drilling, and (b) improve the hydraulic conductivity between the wells and the natural formation In addition, CCI tagged the water level and collected a water sample from on-site deep well MW-6 so that a groundwater gradient could be established within the B-aquifer at the subject site After development, the wells were allowed to recharge to within 80 percent of static water level, enabling CCI to collect a representative water sample All water collected during well development was placed in the on-site holding tank, located on the northwest side of the site A summary of groundwater purge data is summarized in Table 1 Subsurface Conditions As previously stated, three additional groundwater wells were placed at selected locations in the vicinity of the Quik Stop Market in an effort to further investigate the lateral and vertical extent of petroleum hydrocarbon contamination at the site Monitoring wells MW-9 and MW-10 were placed on the southwest and northwest sides of the site (Figure 2) Monitoring well MW-II was placed on the northeast side of the site, near the drive-way entrance to the site Subsurface conditions at these three locations were explored to depths ranging from 30 to 76 feet The subsurface conditions encountered in the site wells were found to be composed of alternating layers of silty sand and sand, with some silty clay and clay from the surface to approximately 30 feet in well MW-11 The material was found to be dense,with localized areas of hard material consisting of clay and sand The soil conditions encountered in MW-I1 are consistent with subsurface conditions encountered in the other shallow site wells The subsurface conditions encountered in deep monitoring wells MW-9 and MW-10 matched the Cone Penetration Test (CPT) log information collected during pervious investigations at the subject . site