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Excavation Remediation Report Advanced Environmental Concepts,Inc. w 5.0 GROUNDWATER MONITORING WELL INSTALLATION AND SAMPLING w In order to evaluate the groundwater condition beneath the property following completion of the remedial excavation and to calculate the hydraulic gradient beneath the site, a total of 3 groundwater monitoring wells were installed, developed, and sampled in accordance with AEC's August 1998 "Confirmation Water Sampling Work Plan". San Joaquin County approved the workplan prior to implementation and provided oversight of the procedures. The following sections describe methods and procedures performed and results of laboratory analyses of samples collected during the post-remedial excavation groundwater assessment. 5.1 Boring Locations and Methods Borings identified as W-1, W-2, and W-3 were positioned within the south, east, and north areas of the remedial excavation limits, respectively. Figure 8 illustrates the positioning of these borings. w The borings were completed as groundwater monitoring wells in order to provide analytical data for evaluation of groundwater conditions following the completion of the remedial excavation �,. procedures and water depth information for hydraulic gradient calculations. The borings were advanced using a Mobile B-61 Drill Rig equipped with an 8-inch diameter, continuous flight auger in accordance with ASTM Method D 1452-80 for soil investigations and `" sampling by auger borings. The augers were steam cleaned prior to drilling and between each boring in order to minimize potential cross-hole or downhole contamination. Soil lithoiogy and other visual data was recorded on field boring logs in accordance with the Unified Soil Classification 4.0 System for visual description and identification of soils. 5.2 Soil Sampling/Analyses V Soil samples were collected through the auger into 1.5-inch diameter by 6-inch long brass sleeves driven in a split spoon sampler by a 140-pound hammer with a 30-inch drop, in accordance with r. ASTM Methods D 1586.84 for split-barrel sampling of soil and D 1587-83 for thin-walled tube sampling of soils. The brass sleeves and sampler were washed in an Alconox solution and double rinsed in clean de-ionized water prior to each use. Soil samples were driven at the estimated capillary fringe(11 feet BGL)within each boring in order to evaluate conditions of soil at or near the soil/groundwater interface. The blow counts, sample recovery, and lithology were recorded on the field logs. Soil samples were sealed with teflon tape, capped, labeled, placed in a cooler with frozen blue ice, and transported to Baseline Onsite Analysis, a California Certified Laboratory under Chain- of-Custody protocol for analysis. Laboratory results are presented in Table 9. Laboratory reports and Chain-of-Custody documentation are contained within Appendix B. Ago w L Project: AEC 96C-1707 10 •ENVIRONMENTAL CONCEPTS WITH DESIGN W MIND - 4400 ASHE ROAD.*206 • BAKERSFIELD.CA 93313 8051831.1646 FAX 805/831-1771 I.r