SITE INFORMATION AND CORRESPONDENCE

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RI/FS Report Review -2- 5 July 1991 DDRW, Tracy of the site and the investigations of the waste management units (WMUs) . However, most of this work may be deferred to the FS or to the remedial design phases. Site-wide Ground Water Monitoring Program The RI Report indicates that there has been no site-wide quarterly ground water monitoring program at Tracy. The existing water level data base is inadequate to determine whether there are seasonal variations in the ground water flow direction and gradients, to assess the pumping influence of off-site agricultural supply wells (the Raspo wells) , to assess hydraulic interactions between the horizons or to assess plume movement throughout the aquifer through time. The only available ground water level data in the RI Report are from 1986, 1988 and 1990. Ground water levels appear to have been measured monthly during 1986, and only sporadically in 1988 and once in September 1990. Tracy needs to develop a comprehensive site-wide ground water level monitoring program. A monthly ground water level monitoring program for a period of one year is always preferable as a baseline, however consistent quarterly water level measurements are acceptable. Without development of an adequate hydraulic data base and a better understanding of the hydraulics of the system, the effectiveness of a ground water remedial measure at design capacity is jeopardized. The existing water quality data base is primarily for VOCs, although analytical results exist for purgeable aromatics, organochlorine pesticides and polychlorinated biphencs (PCBs) and heavy metals. The existing water quality data base indicates that ground water may have locally elevated concentrations of cadmium, chromium, lead, mercury, nickel and zinc. These concentrations need to be confirmed. The water quality data base generally does not include analyses for general minerals. Analyses for t�-se constituents are needed to not only type the different water bearing horizons, but :re necessary information for operation and maintenance of the IRM and are needed for decisions regarding disposal . Tracy needs to expand the water quality monitoring program to include additional analyses for other potential waste constituents for wells installed in the future and to include general minerals analyses for a representative number of existing wells for the site-wide RI/FS. In order to be in compliance with the 10 July 1992 submittal date for a site-wide well monitoring program, Tracy must submit a comprehensive monitoring plan as soon as possible. The existing ground water quality data indicate that the off-site private supply wells may have concentrations which exceed the drinking water standards for some VOCs, including TCE. The last off-site water quality sampling of these Bells was conducted in 1987. The well monitoring program needs to be expanded to include monitoring of the specific off-site private supply wells which are in or downgradient of the plume. This monitoring frequency may need to be performed on a quarterly basis. Southern Portion of the Site The RI has not focused on potential soil and ground water contamination in the southern portion of the site. Hydrogeologic investigations of the southern end of the site have generally not been conducted. The cross-sections do not extend across the southern portion of the site, therefore the horizons identified in the northern portion of the site have not been identified as existing in the southern portion of the site.