SITE INFORMATION AND CORRESPONDENCE

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Ms. Jeanne Zolezzi April 12, 1996 Page 3 of 4 Our earlier review of published data on regional groundwater conditions indicated numerous wells throughout the Stockton area which have been impacted with high TDS and chloride levels, in addition to other inorganic contaminants related to both point and non-point (regional) sources. The eastern migration of high TDS/chloride groundwater into the Stockton area is documented in the California Department of Water Resources Bulletin No. 146 and has been related to intrusion of poor quality delta waters, industrial discharges and leakage from numerous unabandoned oil/gas wells. The closest known historical gas well is located approximately 2000 feet to the west. Therefore, it appears that the high TDS levels noted in wells on the Teichert property are probably not related to direct surface discharges from the subject site. More likely, the water quality impacts are due to infiltration of poor quality waters from elsewhere in the area. This is supported by the soil sampling results performed at the site which show TDS/chloride levels in soil samples declining to background at depths of about 15 feet. As noted in Attachment I, the sodium and chloride concentrations recorded in site soils are less than published values for naturally occurring soils in North America. Additionally, we are aware of other sites impacted by salt brines with higher levels of sodium and chloride which have been allowed by the Regional Water Board to remain in place. Since the shallowest historical groundwater depth in this area has been 35 feet below grade, it is most likely that the water chemistry of wells 6, 7, 8 and 9 is controlled by source factors elsewhere in the area. Favorable infiltration conditions would exist either where underground piping or sumps are located (such as the adjacent London property), or where surface water could pond, such as the topographic depression north of the site. The subject site is paved and boring logs indicate low permeability sediments above the groundwater surface. This further indicates that the hydraulic conditions at the site are not conducive to significant infiltration of water. In my experience at a number of other sites where groundwaters have been impacted by salt, the driving force (which resulted in impacted groundwater) has always been a continuous source of hydraulic head in the form of either a pond or waste line, not the periodic surface spillage of salty water nor infiltration of rainwater. This is consistent with the recognized fact that this geographical area is not a natural groundwater recharge area. Sampling has shown that the salt has not migrated below 15 feet. During a site inspection in September 1994, all visible crystalline salt had been removed. It should be noted, however, that after precipitation events capillary action may result in the formation of a white, salt film at the surface in some areas.