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437 East Miner <br /> December 1997 <br /> Page 2 <br /> As stated in the above referenced feasibility study,"the highest concentrations of TPH-g were detected <br /> in the boring U-L at 45 feet bgs (19,000 ppm)". It was not reported that the vertical extent of this <br /> contamination remains undefined. PHS/EHD has stated in correspondence dated January 3, 1994, <br /> November 4, 1994,December 23, 1994, June 3, 1997, and June 25, 1997 that the vertical extent of <br /> the hydrocarbon contamination has not been defined. PHS/EHD focussed regulatory efforts,during <br /> the years of 1995, 1996,and 1997,towards Unocal performing a vapor extraction feasibility test when <br /> the highest concentrations identified to date were above the water table level;however,compliance <br /> was never achieved.The point of defining the vertical and horizontal extent of the soil and <br /> groundwater contamination is to comply with the Health and Safety Code and Underground Storage <br /> Regulations and to prepare a corrective action plan which addresses the contamination which resulted <br /> from the operation of former underground storage tanks. Unocal has not demonstrated willingness to <br /> comply with the California Laws and Regulations. <br /> The vertical and lateral extent of soil and groundwater contamination has not been delineated. Until <br /> such time as the full extent of the soil and groundwater contamination is determined,it is premature to <br /> conclude that the plume is not migrating. Already,the groundwater plume has migrated off site <br /> impacting groundwater beneath neighboring properties. <br /> The work plan to complete the investigation should have included soil borings on site to define the <br /> extent of on site contamination and to install air sparge and vapor extraction wells to perform the <br /> required feasibility study. The above referenced feasibility study failed to include at least two <br /> alternatives for restoring or protecting the beneficial uses of the groundwater which has been impacted <br /> as a result of the operation by Unocal of former underground storage tanks. <br /> PHS/EHD has observed that as groundwater levels have risen,resulting in a longer column of water <br /> within monitoring wells,that samples collected from these wells may not be representative of <br /> groundwater contamination levels due to dilution effects. Wells which have been installed with <br /> proper screened intervals,in plume conditions similar to this site conditions,have evidenced <br /> significantly higher levels of groundwater contamination. <br /> Should Unocal wish to evaluate natural attenuation as one of the remedial alternatives,additional <br /> monitoring wells will be required which are screened discretely to monitor the full vertical and lateral <br /> extent of groundwater contamination. <br /> If you have any questions please contact me at (209) 468-0337. <br /> Donna Heran,REHS,Director <br /> Environmental He ivision <br /> Mary Meays,Senior REHS Marga REHS <br /> Site Mitigation Unit Supervisor <br /> cc: David Irey,San Joaquin County Deputy District Attorney <br /> cc: Pat Anderson,CVRWQCB <br /> cc: Sherri Kirk,Starsky&Kirk,601 University Ave.Ste. 245,Sacramento CA 95825-6708 <br /> cc: Peter Niemiec,Unocal Corporation,376 S. Valencia Ave. Brea CA 92823 <br /> cc: Stephen Carter,GeoStrategies 3164 Gold Camp Ste.240,Sacramento CA 95670 <br /> cc: Sutter Office Center,2001 Union Street Ste.300,San Francisco CA 94123 <br />