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. Mr. George Takemori Project OF90-002.07 <br /> April 30, 1999 <br /> Page 4 <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> The results of the groundwater sampling events indicate that dissolved hydrocarbons have <br /> been delineated and appear to be isolated beneath the former USTs and dispenser islands. <br /> During the previous seven sampling events, benzene was not detected in groundwater <br /> monitoring wells, with the exception of well AS-1, which contains a relatively low <br /> concentration. During this sampling event, benzene was detected at 55 ppb in MW-13. In <br /> general, TPHG and benzene are isolated to two wells and the source area has been removed <br /> during the tank removal activities at the site. <br /> It was Pinnacle's opinion that natural biodegradation would further reduce residual and <br /> dissolved petroleum hydrocarbons at the site as presented in the August, 1996 report <br /> titled "Second Quarter 1996 Status and Closure Report". As shown from recent <br /> analytical results, natural biodegradation has continued to degrade petroleum <br /> hydrocarbons at the site. Therefore, due to the removal of residual hydrocarbons via <br /> excavation and remediation, the decline of dissolved hydrocarbons, and the process of <br /> natural biodegradation, it is Pinnacle's opinion that no further action is warranted at the <br /> site. Pinnacle recommends closure for the site. <br /> DOCZ.i1WELiiT D:STRIDU70M <br /> We recommend copies of this report to be forwarded to the following: <br /> Ron Rowe <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> P.O. Box 388 <br /> Stockton, California 95201-0388 <br /> Elizabeth Thayer <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> 3443 Routier Road, Suite A <br /> Sacramento, California 95827-3098 <br /> Cl'1E:ITEFCHER-11STOCKTOMQTRLYISTKNQ199.DOC-9511sg:1 �GafsLc <br />