SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Mr. Ken Gillies • • Gillies Trucking 3931 Newton Road, Stockton Page 4 of • Revising the TPH-d sorbed mass estimate; • Estimating and modeling the TPH-d transfer or flux rate from impacted soil to groundwater in the First Riverbank Aquifer; • Modeling the likely effect on groundwater in the Modesto Aquifer (approx. 25 to 55 feet bsg) and its fate and transport should groundwater rise into the Modesto Formation (approx. 25 to 58 feet bsg) again; and • Delineating the lateral extent of impacted groundwater in the First Riverbank Aquifer sand (approx. 58 to 70 feet bsg). Approximately 50,000 pounds of TPH-d are in soil (EHD's roughly revised estimate) that appears to be subject to leaching to groundwater through migration of rainwater or periodic immersion in groundwater. Figure 4 of the QR shows the Modesto channel sand (approx. 25 to 55 feet bsg) locally in contact with the underlying First Riverbank channel sand (approx. 55 to 70 feet bsg), while Figure 5 shows the First Riverbank channel sand (approx. 58 to 80 feet bsg) locally in contact with the underlying Second Riverbank channel sand (approx. 75 to 95 feet bsg). Thus, groundwater migrating through the impacted soil has potential lateral and vertical migration pathways. This appears to pose a significant risk to groundwater in this area that has been reported to have more than 30 water supply wells within 2,000 feet of the petroleum fuel release. This risk must be adequately addressed before site closure can be properly considered. Questions or comments may be directed to Nuel Henderson by mail (address on letterhead), or by telephone at (209) 468-3436. Donna Heran, REHS, Director Environmental Health Division Nuel C. Henderson, Jr., PG Margaret Lagorio, REHS Unit IV - Site Mitigation Unit IV Supervisor cc: James L.L. Barton — CVRWQCB Victor Cherven — UEC Clyde Hebbron - UEC Mark Owens — State Cleanup Fund Mr. Richard Pombo — Member of Congress