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APPENDIX A <br /> • PROJECT BACKGROUND <br /> (continued) <br /> May 1990 : The average depth to ground water was determined to be <br /> approximately 57 . 5 fbg. The approximate ground water gradient <br /> across the site at this time was reported by WCC to be 0. 008 foot <br /> per foot toward the west. Alton Geoscience's interpretation of <br /> WCC's ground water elevation data shows the ground water gradient <br /> to have been actually toward the north. <br /> May 4 and 11, 1990: Ground water samples collected from , <br /> Monitoring Wells MW-6 through MW-9 were analyzed fot total <br /> petroleum hydrocarbons and BTEX. Results of laboratory analysis <br /> revealed concentrations of TPH in water samples collected from <br /> MW-8 ( 1, 900 ppb) and MW-9 (3 , 400 ppb) , and benzene in water <br /> samples collected from MW-7 (1. 5 ppb) , MW-8 (200 ppb) , and MW-9 _ <br /> (60 ppb) . Monitoring well MW-5 was dry <br /> March 1991; Alton Geoscience was retained by Caltrans to conduct <br /> supplemental ground water monitoring and sampling to determine <br /> the status of the existing monitoring wells onsite. <br /> May 1991: Monitoring Wells MW-1 through MW--9 were monitored and <br /> MW-7 , MW-8 , and MW-9 were sampled for TPH-G and BTEX. Monitoring <br /> Wells MW-1 through MW-6 were dry. Depth to ground water in MW-7 <br /> through MW-9 averaged approximately 65 fbg. Water samples from <br /> MW-9 had detectable concentrations of TPH-G at 2 , 100 ppb and BTEX <br /> constituents up to 310 ppb. No TPH-G and BTEX constituents were <br /> detected in the water samples from MW-7 and MW-8 . <br />