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E ' <br /> CONDOR EARTH TECHNOLOGIES INC. <br /> February 9, 1999 1125 N.Golden State Blvd. 188 Frank West Circle <br /> Suite G Suite I <br /> Turlock, CA 95381 Stockton, CA 95206 <br /> (209) 668-9234 (209) 234-0518 <br /> Mr. Philip Isorena FAX(209) 668-9248 FAX(209) 234-0538 <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> 3443 Routier Road, Suite A <br /> Sacramento, CA 95827-3003 <br /> RE: Proposed Modifications to Scope of Work in Approved Work Plan(dated June 23, <br /> 1997) and Addendum to Work Plan(dated May 11, 1998) for Standby Generator <br /> Diesel Supply Line Product Recovery System Installation and Monitor Well <br /> Installation,Pilkington Libbey Owens Ford,500 East Louise Avenue,Lathrop, <br /> California,San Joaquin County <br /> Dear Mr. Isorena: <br /> Introduction <br /> Pilkington Libbey Owens Ford(LOF)has been communicating with you regarding the discovery of,and <br /> responses to the discovery of,diesel fuel in soil and groundwater near an above ground fuel storage tank <br /> (AST)at the LOF site in Lathrop,CA. The AST supplied diesel fuel to a backup generator at the facility. <br /> A leak in an underground fuel pipeline associated with the AST was discovered in July 1996. In December <br /> 1998,LOF attempted to perform work that was approved by your department(correspondence dated June <br /> 16, 1998)to remove free-phase diesel, if present,by installing a series of gravel-filled trenches and a <br /> skimmer pump. Installation of the trenches,though attempted,was not possible due to the concentration of <br /> underground utilities and soil instability in the area of the proposed trenches. Approximately 50 lineal feet <br /> of trench was excavated at different times and locations in the area. Trenching was performed in areas with <br /> the lowest density of underground utilities;however,four different pipelines were exposed during the <br /> trenching. All trench walls failed before the bottoms of the trenches could be inspected for an <br /> accumulation of diesel and before gravel backfill could be placed. <br /> As a result of the difficulties encountered during attempts to install recovery trenches,further attempts to <br /> recover free-phase diesel from the site are not proposed at this time. Recovery of free-phase diesel, if <br /> present, is not proposed for the following reasons: <br /> 1. The source of the diesel release has been eliminated. The AST is now used for vehicle fueling only. <br /> The underground fuel pipeline that leaked is no longer in use. A new diesel AST was installed near the <br /> standby generator. <br /> 2. Recovery trench installation is not feasible using traditional excavation methods due to soil instability. <br /> 3_ Any type of trenching or excavation is not feasible without costly underground utility relocation, <br /> especially gravity drain sewer and stormwater pipelines. <br /> 4. A nearly flat groundwater gradient is anticipated based upon review of previous groundwater <br /> monitoring performed at the LOF site. Movement of the diesel plume is not expected to be <br /> significantly influenced by groundwater flow. <br /> ENVIRONMENTAL GEOLOGICAL ENGINEERING GEOTECHNICAL <br /> hftp:Nwww.condorearth.com <br />