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EPdVjRQPlRl� <br /> E*f ON COMPANY, U.S.A. p �' 'rS RVQ AI.TII <br /> POST OFFICE BOX 4032.CONCORD,CA 94520-2032 93 SEp IS <br /> 2J Q8 <br /> I ONt�'�NTAUI.SENGSINEE VIC S p� <br /> SENIOR ENVIRO SLN &AL ENGINEER <br /> (510)246-8776 <br /> (510)246.8798 FAX <br /> September 13, 1993 <br /> Mr.Harlin Knoll <br /> Environmental Health Division <br /> 445 North San Joaquin Street <br /> Stockton,CA 95201 <br /> RE: Former Exxon RAS#7-3942;4444 North Pershing Avenue,Stockton,CA <br /> Dear Mr.Knoll: <br /> Attached for your review and comment is a report entitled Remediation Confirmation Sampling Results and Closure <br /> Recommendation for the above referenced site. This report,prepared by Aegis Environmental,Inc.,(Aegis)of <br /> Roseville,California,details the results of the confirmation soil borings completed at the site in June 1993. <br /> Soil analytical results for two of the three soil borings, SB-8 and SB-10,were below Practical Quantitation Reporting <br /> Limits(PQL)of 0.005 parts per million(ppm)for benzene,tolune,ethylbenzene, and total xylenes,(BTEX)and 1.0 ppm <br /> for total petroleum hydrocarbons as gasoline(TPHg)from depths of 6 feet below surface(fbs)to approximately 60 fbs. <br /> Only one sample from these two borings displayed results above the PQL for toluene,ethylbenzene, and total xylenes at <br /> levels of 0.062,0.0098,and 0.045 ppm at 6 fbs. It is Exxon's opinion that these results display the remedial effectiveness <br /> of the soil vapor extraction system employed at this site. <br /> The third soil boring analytical results, SB-9,display levels of TPHg below PQL to a depth of at least 11 fbs, and above <br /> PQL at depths of 16 to 36 fbs. At these sample depths,benzene was below PQL to at least 11 fbs, and was below <br /> detection limits of 0.2 ppm to 0.05 ppm,from 16 to 31 fbs. Toluene, ethylbenzene, and total xylenes ranged from below <br /> PQL to 2000 ppm from 6 to 41 fbs. Total xylenes reoccur,after a non-detect analysis at 41 fbs,between 0.0057 ppm to <br /> 0.022 ppm at depths of 51 to 57.5 fbs. However,in this boring,results for TPHg and BTE were below PQL from <br /> approximately 41 feet to 57.5 feet,which displays that over 16 feet of non-impacted or minimally impacted soil exists <br /> between the potential source area and groundwater. Also,SB-8 and SB-10,the two borings with either no impact or <br /> minor impact just below surface,are less than a 20 foot distance each from SB-9. Therefore,the area of remaining <br /> impact is believed to be remote and removable through overexcavation. <br /> It is Exxon's opinion that the existing area of impact in the soil is not a threat to groundwater. However,in an effort to <br /> expedite closure at this site for soil and groundwater,Exxon will be coordinating an excavation of soils in the area of <br /> SB-9 to a depth of approximately 25 feet. Using existing data,removal of soils impacted to this depth will remove the <br /> area of highest impact. This area prevented the successful implementation of a Leaching Potential Analysis for Gasoline <br /> using TPHg results(from the LUFT Manual in the Tri-Regional Board Recommendations). For levels of benzene just <br /> below the detection limits used for SB-9,(although they may not exist),the preliminary environmental fate analysis <br /> referenced above was successful in displaying further remediative efforts for this constituent would not be necessary. <br /> Therefore, it is Exxon's opinion that a minimal overexcavation effort should adequately remove the remote area of <br /> A DIVISION OF Ex ON CORPORATION <br /> of-Ii <br />