SITE INFORMATION AND CORRESPONDENCE_FILE 1

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437 Miner Ave Page 2 On July 6, 1994, field work was initiated which consisted of the installation of three monitoring wells (U-1 - U-3) and the drilling of five soil borings(U-1 - U-M). The results were reported on September 21 , 1994 and indicated significant soil contamination up to 19,000 ppm TPH-gas and 140 ppm Benzene at 45.5 feet below ground surface from U-L drilled in the area of the former tanks that were removed in 1967. The laboratory noted that there were some holding time violations of the soil samples collected. When monitoring well, U-2, was developed a sample was collected on July 25, 1994 and submitted for a hazardous waste bioassay test. The results did not determine that the liquid was hazardous; however, two fish did die after 48 hours in the 100 ppm duplicate sample. On December 23, 1994, PHS/EHD requested that a work plan be submitted to define the extent of on site and off site soil and groundwater contamination. PHS/EHD provided this directive after reviewing the results of two groundwater sampling events which indicated significant contamination and that the groundwater gradient direction shifted from the west to the north. On July 19, 1995, field work was initiated which consisted of the installation of four monitoring wells, U-4 - U-8, and three soil borings, U-N - U-P. Soil boring, U-P, was subsequently converted into a vapor extraction well, UV-1. In summary, the soil and groundwater contamination which has been evidenced appears to be associated with the underground storage tanks which were removed in 1967, rather than the tanks which were removed in 1992, hence the statement was made in PHS/EHD's March 18, 1997 correspondence regarding the age of the release. Since the source of new contamination to the subsurface ended in 1967, the site does not appear to have naturally attenuated within a reasonable time period. Concentrations and Mass of Remaining Soil and Groundwater Contamination The vertical extent of soil and groundwater contamination beyond 45.5 feet (U-L) is unknown. At the time that U-L was drilled groundwater levels were measured between 47 and 50 feet bgs. As indicated earlier, significant concentrations of petroleum hydrocarbons were evidenced at 45.5 feet bgs. Also, the total depth of the monitoring wells are 55 feet bgs with screened intervals between 30 and 55 feet bgs (U-1 - U-3) or 35 and 55 feet bgs (U-4 - U-8). The most recent groundwater levels were measured between 31 and 33 feet bgs. Between 1994 and 1997, the groundwater level at this site has risen approximately 17 feet. Despite the dilution effect of this dramatic change in groundwater depth, concentrations of 39,000 ppb TPH-gas and 2,100 ppb benzene continue to be evidenced in samples collected from U-3 downgradient of the 1967 tank pit. Since the full vertical definition of the soil and groundwater contamination is not known, it is impossible to attempt to calculate the full volume and mass of the remaining contamination; however, based on an approximate vertical extent of 48 feet and lateral area of 80 feet by 80 feet GeoStrategies estimated that there was 8,900 cubic yards of contaminated soil with 56,819 pounds of TPH-gasoline. This contamination is the result of 30 years of natural attenuation. According to the Underground Storage Regulations: California Code of Regulations, Title 23, Division 3, Chapter 16, Article 11 §2724.(3) there is evidence that contaminated soils are or may be in contact with groundwater warranting a soil and groundwater investigation. The purpose of the investigation is to assess the nature and vertical and lateral extent of the release and to determine a cost-effective method of cleanup which will be reported in a Corrective Action Plan. An aspect of the development of a Corrective Action Plan is to perform a feasibility study to select and design the most cost-effective alternative (§2725).