SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Mr. Ed Ralston -2 - 23 October 2007 Former Unocal Bulk Plant, Tracy• about nine feet bgs. Petroleum hydrocarbons and fuel oxygenates were not detected in any of the samples. The Domestic Well Report describes the sample results for the onsite water supply well. On 23 March 2007, ConocoPhillips collected a sample from the water hose connected to the hose bib after purging the water for two minutes and TPHd was detected at 140 pg/L. On 4 April 2007, ConocoPhillips collected a sample from the bib/tap after disconnecting the hose, sterilizing the tap, and purging the water for five minutes. TPHd was detected at 110 Ng/L; however, the analytical laboratory noted that the chromatograph was not typical for diesel. The laboratory also flagged the results because laboratory surrogate recoveries were not within the control limits, matrix spike precision for TPHd was not with in the control limits, and TPHd was detected in the method blank. On 16 April 2007 and 27 April 2007, ConocoPhillips collected samples from the bib/tap after the water was purged for 30 minutes which emptied the holding tank and allowed the pump to run. TPHd was not detected in these samples. On 1 October 2007, ConocoPhillips emailed Regional Water Board staff the August Results. Groundwater samples were collected on 29 August 2007 from wells U-8 and U-9 and analyzed for TPHd. TPHd was detected in U-8 and U-9 at 56 pg/L and 47 pg/L, respectively. Both results were flagged because of the 40 pg/L detection in the method blank. Historical Site data show that petroleum hydrocarbon concentrations are below or near detection limits, with the exception of the data with laboratory flags. Regional Water Board staff review of the case file shows that Regional Water Board staff requested a Closure Report in an 8 July 2005 email. By 30 November 2007, please prepare a Closure Request Report that complies with the No Further Action documentation requirements in the 16 April 2004 Appendix A Tri Regional Board Staff Recommendations for Preliminary Investigation and Evaluation of Underground Storage Tank Sites. If you have any questions regarding this letter, you may contact me at (916) 464-4819 or by email at ksheltonpwaterboards.ca.gov. KRISTI SHELTON Water Resources Control Engineer Aboveground Tanks Cleanup Unit cc: Ms. Margaret Lagorio, San Joaquin County Environmental Health Department, Stockton Ms. Diane Barclay, SECOR, Rancho Cordova