SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Shell Oil Products US page 2 Station #204-7524-4, 3011 W. Ben Holt Drive, Stockton. Before SJCEHD can concur with Cambria that the down gradient extent of the MtBE plume is defined, additional monitoring for trend analysis will be needed as it is not practicable to install well further down gradient (Cal-Trans). A concentration over-time trend that supports Cambria's attenuation conclusion hopefully should be apparent after another annual sampling period has passed. In order to partially validate the SCM and delineate the MtBE plume in the undefined northwest quadrant, SJCEHD will require an additional, shallow, monitoring well to be installed northwest of MW-5. Shell is to take immediate steps to secure access to this parcel and submit a work plan to SJCEHD during 2004. Data collected from this well's installation should be included in an updated SCM. To verify the break down of MtBE as Cambria has suggested, SJCEHD will require additional sampling procedures to be followed to support attenuation conclusions. Although there have been many modifications to the quarterly sampling events in the past, the following changes to the monitoring well sampling protocol are to be incorporated: • Core Wells: Monitoring wells MW-1, MW-2, MW-5, MW-6, and MW-10, 11, & 12 are to be sampled for TPHg (TPPH), BTEX, MtBE, TBA, Ethanol, Acetone and 1,2-DCA, quarterly by EPA Method 82608. Detections limits for TBA and the oxygenates should not be greater than 5.0 ug/I or 0.5 ug/l, respectively, and BTEX detection limits should not exceed 0.5 ug/l. TPPH detection limit should be 50 ug/l. Detection limits higher than these with the results reported as non-detect or"<", will be carefully evaluated and may not be accepted as meeting SJCEHD requirements. • Peripheral Wells +: On an annual basis (once a year) ALL monitoring wells for this site are to be sampled for the constituents noted above as well as DIPE, EtBE, EDB, Methanol, and TAME by EPA Method 8260B. It is hoped that the data from these wells for this next period will support Cambria's conclusions, meet the characterization requirements, and define the contamination adequately enough to allow SJCEHD to concur that no additional work is warranted. Donna Heran, REHS, Director Emental Healt Division Michael J. Infurna Jr., Senior REHS Nuel C. Henderson Jr. LOP / Site Mitigation Unit IV LOP / Registered Geologist MI/ c: CVRWQCB —James L. Barton, Sacramento. c: Cambria— Joe Neely, PO Box 259, Sonoma, CA., 95476.