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it FROM Ground 2erc Anal vs i e � PHONE NO. 209 838 9883 Feb. 15 2000 04:53PM P3 '• ,s k Mr.Harlin Knoll ! February 15, 2000 Page 2 of 4 had occurred. Sail boring locatior]s are shown on Figure 2_ Analytical results are summarized in Table 1, One 10,000-Sallon UST for storage or dieftl fuel ant I two 10,000 gallon USTs for the storage of gasoline and associated piping were removed under I terne t from PHSAEHD on January 21, 1999. Analytical results of sidewall soil samples and groundwater grab sample collected from beneath !I` the USTs indicated that elevated levels of petroleurn hydrocarbons were present in the soil and groundwater_ Sample locations are shown on Figure 2. Analytical results are summarized in Table 2. 2.2 Soil Boring Investigation In 7uly 1999, five direct push soil borings were ad oed along the perimeter of the former UST location to investigate the vertical and lateral extent of soil and groundwater contamination, and four hand augered soil borings were advanc*l to ' vestigate the lateral extent of shallow sail � contamination_ Soil boring locations are shown on Figure 2. Analytical resutts are sununarized in I Tables 3 and 4. I The results of this investigation were submitted to P 4S&HD in a report dated October 19, 1999. Based upon the localized contamination and its currm t accessibility, Ground Zero recommends the ,N implementation of remedial actions consisting of eKcz vation and limited groundwater extraction, as well as the installation of groundwater monitoring we 1s to further define the extent of gmundwater contamination. This "rkplan addendum address s proposed interim sail and groundwater remedial actions. The installation of groundwater monitoring wells will be scheduled upon completion of excavation and backfil ling activities anc have been addressed under separate cover. 0 2.3 Hydrogeological Setting The site is located in Thornton, California, approximately 5,140 feet southwest of the Mokeluinne River, the nearest body of surface water. Surface elevation at the site is i approximately eight feet above sea level, i Based on historical information provided by San Joaquin County Flood Control and Water .Conservation District and groundwater information cm a nearby site, groundwater beneath the site is expected to flare in a southwesterly direction. Groundwater was fid en xntered at a � depth of to 7 feet in the borings drilled on the prop y. 3.0 NATURE AND EXTENT OF CONTAA01S A"1 ION 3.1 Soil Contamination The data from the soil baring investigation combined with data previously obtained have largely defined the extent of soil contamination_ Soil contamination appears to be limited to depths between approximately 6 and 13 feet bgs and is genet ally Mound in the area immediately adjacent to CvAProta NGP.aUNbZ1FkM AN 9 EP-W ansa 2Nf etot4mwp.dae i i