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i 4.3 GROUNDWATER MONITORING WELL INSTALLATION EF Three groundwater monitoring wells (MW-1, MW-2 and MW-3) were installed onsite on November 21 to 22, 1996. The wells were advanced to depths of 25 to 27 feet bgs. The wells are constructed of 2-inch diameter PVC and screened at 15-25 feet bgs (MW-2 and MW-3) and screened at 17-27 feet bgs (MW-1). The wells Ecasing, sandpack, seal and traffic boxes were constructed in accordance with County permit requirements. The screened section of each well consists of 0.010.machine slotted schedule 40 pvc. The j sand filter pack and bentonite seal were placed by the tremmie method through the annulus between the auger and casing as the auger was extracted from the borehole. During 1 construction of the filterpack,repeated soundings were made to check for bridging problems. The filter sand pack was brought up approximately 1 to 2 i cet above the top of the slotted casing. At this point, some initial pre-well development was performed to tighten the filter pack around the screen. The top of the filter pack was then sounded. If the sand level had fallen, additional sand was added to raise the filter pack up to its target height. Bentonite i chips were placed over the filter pack and hydrated with potable water. The bentonite seal was extended to approximately one-foot bgs. A locking, traffic-rated, protective well monument was then set in concrete slightly above existing grade. A typical monitoring well design has been included as Figure 4, and actual monitoring well construction details are included on the boring logs in Appendix B. The well casing elevations were surveyed to a common benchmark by designating the top-of- casing of well MW-1 as the benchmark with an assigned relative elevation of 37 feet. This assigned benchmark elevation corresponds approximatcly'tto the ground surface elevation above msl as based on USGS topographic maps. The groundwater well measurements are summarized on Table 3. 4 S L I. 1� 4.4 GROUNDWATER MONITORING WELL DEVELOPMENT Ej The groundwater monitoring well was developed in accordance with current EPA specified procedures which involved intermittent surging and bailing,to remove approximately 3 to 5 well volumes of water, as measured within the well casing below the groundwater surface. .f .4 4.5 GROUNDWATER SAMPLING AND PACKAGING di r Groundwater samples were collected from soil SB-1 using a hydropunch. The hydropunch sampler was pushed to the desired depth,and the rods were it approximately 8-inches to expose slotted PVC screen near the sampler tip. The hydropunch was allowed to sit for approximately 10 minutes, permitting groundwater infiltration into the hydropunch casing. JN 4M7-097-01 a«-96\arcmuca.ecs 42 =i