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r Ms Mary Meays Page 4 <br /> April 13, -1994 <br /> Likewise, the concentrations of BTEX compounds previously detected in ground <br /> . water at Site 1 in MW-5 also decreased significantly, the concentration of benzene <br /> decreased from 1 1 ppm to 0 23 ppm Similarly, at Site 2, the concentration of TPH <br /> detected in ground water in MW-1A decreased from 50 ppm in April 1993 to 3 9 <br /> ppm in January 1994, and the concentration of benzene decreased from 16 ppm to <br /> 13 ppm <br /> RECOMMENDATIONS <br /> The significant reductions in concentrations of chemicals in ground water at both <br /> sites is an indication of both the effectiveness of the ground water extraction <br /> remediation employed and the continued degradation of chemical constituents in <br /> ground water with time Because the concentrations of chemicals in ground water <br /> have decreased significantly over time and the extent of the chemicals is very <br /> limited at both sites, we propose that no further ground water remediation is <br /> necessary The source of chemicals to ground water has been eliminated (site soils <br /> were successfully remediated in October 1993), and the residual concentrations of <br /> chemicals present in ground water (TPH and BTEX) pose no significant threat to <br /> human health and the environment or the local ground water quality Also, no <br /> significant migration of chemicals in ground water has been observed over time, <br /> and migration does not seem to be a significant issue Local ground water is not <br /> used as drinking water, and we do not anticipate that the local ground water will <br /> ever be used as drinking water We, therefore, propose to conduct an additional <br /> four quarters of ground water monitoring at both sites to monitor the reduction in <br /> chemical concentrations over time These four quarterly sampling events are <br /> scheduled for April, July, and October 1994, and January 1995 Based on the <br /> sample results from these four events, an evaluation of the ground water <br /> conditions at the sites will be made to determine whether or not additional <br /> monitoring is necessary <br /> Thank you for your assistance in this matter If you have any questions regarding <br /> this report or the project, please call the undersigned at (510) 946-0455 <br /> Sincerely, <br /> ERM-WEST, INC <br /> Mark E Ransom, P E Gary B Fritze <br /> Project Director Project Manager <br /> GBF/gbf/1572 10 <br /> cc Kim Brandt - Catellus Development Corporation <br />