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r) r� Additional Investigation to Define the Extent of Groundwater Contamination Quik Stop Market No 121 Page 4 From approximately 29 feet to 41 feet in monitoring wells MW-9 and MW-10, a light grey to grey brown dense sand was encountered In monitoring well MW-9, this granular material changed into a silty clay from a depth of 42 feet to approximately 49 feet, with localized calcium carbonate("hard pan") material The "hard pan" material appears to be an impediment to vertical contaminant migration From 49 feet to approximately 55 feet, a dense sand was encountered in both wells From approximately 55 to 63 feet, more silty clay was encountered Below 63 feet and extending to the bottom (76 feet) of MW-10, a very dense sand was encountered T he same conditions were encountered in MW-9 with the exception of a light grey to brown silty clay lens encountered between 67 and 70 feet MW-9 was completed to a depth of 75 feet A copy of the boring logs are attached in Appendix A During drilling of wells MW-9 and MW-10, it was not possible to determine where groundwater was first encountered due to the use of drilling fluid However, it is known from previous investigations conducted at the site, which included the use of a CPT rig, a shallow aquifer (A-Aquifer) and a deeper aquifer(B-Aquifer) were identified Monitoring wells MW-9 and MW-10 were installed in the B-Aquifer The depth-to-groundwater was measured on August 17, 2001 at a depth of 23 07 feet in MW-11, which is screened in the upper shallow aquifer(A Aquifer) The water level in the three . deep wells (MW-6, MW-9 and MW-10 )ranged from 28 38 feet below the top of the casing in MW- 10 to 29 05 feet in MW-9 It should be noted that all three deep wells are under hydrostatic pressure The three deep wells were left open for at least 30 minutes, in order to allow the water level in each well to stabilize The groundwater flow direction within the deep aquifer (B Aquifer) is calculated to be toward the southeast, at a gradient of approximately 0 015 feet per foot (Figure 2) Surveying A licensed land surveyor was retained to survey the monitoring wells accurately and to determine the elevation of each well casing The survey ensures accuracy so that the plot plans will portray the data in a manner useful for determining groundwater flow direction The survey included both horizontal and vertical measurements Elevation readings were measured to the nearest 0 01 foot and corrected to mean sea Ievel A copy of the survey measurements is attached in Appendix B Aquifer Pump Test and Analysis 4n July 26, 2001, CCI conducted an aquifer pump test in well RW-1 to evaluate the hydraulic characteristics of the shallow aquifer underlying the site RW-I is screened from 13 feet to 28 feet below grade (fbg) in clay, silty sand, and clayey sand units The well is completed at 28 feet bgs, in a clayey sand To determine the bottom of the aquifer, the boring log from MW-6, located approximately 35 feet away from RW-1 and completed to 75 fbg, was used The bottom of the aquifer was determined to lie at 41 fbg at the top of a clay unit i