SITE INFORMATION AND CORRESPONDENCE

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Former Valley Water Treatrra - 2 - • 26 February 2009 612 North Buena Vista Road, Stockton San Joaquin County Rationale for No Further Action Setting: The property at 612 North Buena Vista Road in Stockton, San Joaquin County (Site) (see Attachment 1 for location map) was formerly used as a water softening facility. The Site is bordered to the south by the Port of Stockton Deep Water Shipping Channel. Groundwater is approximately eight feet below ground surface, and is subject to tidal influence from the Shipping Channel. Groundwater flow is predominantly north-northeast. Groundwater monitoring results indicate some variation in chloride and TDS occurs seasonally, most likely from the influence of water from the Shipping Channel. Source: Leakage from a degraded brine pit caused salt impacts to soil and groundwater. Impacts are limited to the property boundary. The brine pit has been removed, contaminated soil excavated, and area repaved with asphalt. Actions: • Five groundwater monitoring wells were installed between 2005 and 2007. • In June 2007 the brine pit was removed and 975 cubic yards of salt-contaminated soil was excavated to below the water table. The Site has been paved with asphalt. • Groundwater monitoring in the five monitoring wells has continued quarterly. Extent Defined: Impacts to soil and groundwater were delineated horizontally. Concentrations of salt in soil were defined vertically to the water table at (93 mg/kg). Currently, chloride and TDS concentrations in the groundwater ranges from 1100 mg/L and 2500 mg/L, respectively, within the source area and from 83 mg/L (chloride) and 770 mg/L (TDS) in the down gradient wells. See Attachments 2 and 3 for analytical results and isocontour/site plan map. Estimated Residual Mass: The residual mass of chloride estimated to remain in the soil is 1 .85 pounds. Approximately 2400 pounds of dissolved salt is estimated to remain in the groundwater. Trend Analysis: Trend analyses for the two wells that are above background levels or water quality objectives are included in. Attachments 4 through 7. Chloride concentrations at the Site are predicted to reach water quality objectives by 2010. TDS concentrations will achieve background levels by 2011 . Threat to Groundwater: Site remedial activities have reduced the threat to groundwater quality by removing the source of salt impacts, and reducing infiltration from storm water.