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s Gem€nl Petro ra hit lnvesti P,flons (Mr.Craig Wright). During the assessment,three underground storage tanks were Identified(two diesel 5,000 and 10,000 gallons;and ane 1,000 gallon gasoline tank). The 1,000 gallon leaded gasoline tank was removed In April of 1989 with additional excavations of the former tank pit during January of 1990. During tho initial excavation of the tank,Jeff M€ller,of Western Meter,Stockton collected two snmples from each end of the tank and submitted the samples under chain-of-custody protocol to California Water Labs of Modesto. Laboratory analysis of soil samples taken below the excavated gasoline tank indicated the presence of TPH-G (up to 200 ppm)and aromatic hydrocarbon(BTX&E)ranging from N,D.10 5.6 ppm(predominately xylene). Total Lead was also analyzed with results within natural soil abundance levels. Additional excavation and sampling of the pit was performed on 23 May 1989 by Troy . 'hams, Universal Englneering and transported under chain-of-custody protocol to Precision Analytical Laboratory in Richmond, Laboratory analysis Indicated - TPH•G concentrations of 124 ppm. Soil samples were collected from all excavations and stockpiles(10 cu. yds.) on 10 January 1990 by George Reed, Universal Engineering, and analyzed by Preclslon Analytical of Richmond, Indicated the presence of TPH-G (N.D. to 90 ppm), TPH-D (N.D, to 100 p�m,)�anz aro tic hydrocarbons from N.D. -0.7 ppm. D€esO contamination was suspected to be derived fr'bm tt+.e excavationnt � equipment since diesel was not store In the tank. Sol)removed from the gasoline excavation was stockpiled and aerated until N.D.values were obtained. In June 1969,two diesel tanks(5,000 and 10,000 gallons)were removed,sampled by George Reed,Universal Engineering;and transported under chaln-of-custody protocol to Groundwater Technology Laboratory In Concord. Laboratory analysis of soil samples taken below the excavated diesel tanks Indicated no soil contamination for TPN-D. The excavations were backfilled and re-surface with concrete In June 1990. D. SUMMARY OF FINDINGS Subsurface conditions were Investigated by drilling one boring in the location shown in Figure 2(Site Plan). Boring placement was designed to Intercept possible contamination which laterally and vertically migrated -- from the removed underground gasoline storage tank. At the request of Ms. Darlene Reuss,the proposed boring site was moved to the present location in the assumed downgradlent direction from the previously excavated gasoline underground storage tank. Boring 1 was drilled to a final depth of 50 feet below grade, J with soil sampling at 5-foot Intervals and/or at major changes in lithol ogles. Collected samples ware analyze "�'� for TPH(as gasoline)and BTX&E. Laboratory analysis were performed by Superior Analytical Laboratories, °r Inc.a DOHS approved laboratory. The laboratory data indicated that all samples exhibited concentrations below the analytical detection limits(1 ppm)for TPH (as gasoline). Results for BTX&E constituents were` variable,ranging from not detected at 5.0`(Sample#90481-1-1)to maximum concentration of 37 ppb(xylane) /k` In sample 90481-1-9. Low levels of BTX&E contamination are thought to be the result of pre-existing groundwater contaminatlon from an off-site sources and not the result of vertical mlgratlon of contaminates aC6, /'� derived from the on-site excavated gasoline underground tank. c� "'�y/ -- --II:-FiELD INVESTIGATIONS—--- A. NVESTIGATIONS A. DATA REVIEW We reviewed available geologic and hydro!oglc information relative to the site from the California D!vislon of Mines and Geology(CDMG),U.S.Gecioglcat Survey Professional Papers,and pervious reports pertaining to the site.Pertinent references are listed in references at the beginning of this report. 2