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Applied Geotechnology Inc. 5.0 SITE INVESTIGATION 5.1 Existing Monitor Well Evaluation Three previously installed monitor wells, MW-1, MW-2, and MW-3 were evaluated to determine if they were still suitable for monitoring ground- water quality and water levels. The locations of these wells are shown on Figure 3 . MW-1 was vandalized and was unsuitable for water level measure- ments or sampling. MW-2 contained insufficient water for sampling and appeared unreliable for measuring groundwater levels. MW-3 provided suf- ficient groundwater during sampling and was thought to provide accurate water level measurements. Based on this evaluation, four additional borings were completed as monitor wells to accurately describe site sub- surface conditions. MW-1 and MW-2 were abandoned in accordance with California regulations under a San Joaquin County Department of Environmental Services Permit. Abandonment included extracting the stainless steel well points, drilling out the old boring beyond its original depth, and grouting the boring to the surface. 5.2 Subsurface ExDloration Subsurface conditions were explored by advancing four borings with a ( Mobile-357 hollow stem auger drill rig. These borings were completed as monitor wells. Monitor well locations were selected to assess groundwater conditions downgradient of the former USG Interiors facility. Monitor i wells were generally placed around the site perimeter to assess groundwater I� quality to depths of approximately 20 feet below ground surface. Details of our field exploration are provided in Appendix B. Monitor well boring logs and well construction details are provided in Appendix C. Monitor well locations are shown on Figures 1 and 3. C Soil samples were collected every 2-1/2 feet using a split barrel sampler. The samples were examined and logged according to the Unified Soil Classification System (USCS) as shown in Appendix C. Reference points on each well were surveyed by AGI to the nearest 0.01-foot; wells were sur- veyed to an assumed datum of 100 feet. 5.3 Chemical Analysis 5.3.1 Groundwater Groundwater samples were collected from each monitor well and submitted to Analytical Technologies Inc. (ATI) of Renton, Washington for chemical test- IL ing. Monitor wells were developed prior to sampling; groundwater sampling procedures are discussed in Appendix B. -15-