ARCHIVED REPORTS XR0008689 - Laserfiche WebLink

Home Browse Search

SECOR www secor com INTERNATIONAL 3017 Kilgore Road Suite 100 S E C ® R INCORPORATED Rancho Cordova CA 95670 916$61-0400 TEL 916-881-0430 FAX 1 February 26, 2004 Mr Mike Infurna San Joaquin County Public Health Services FEB 304 East Weber Avenue Stockton, California RE Work Plan for Vertical Assessment Former 76 Service Station 4409 1502 North El Dorado Street Stockton, California I SECOR Project No 77CP 64409 03 0001 Dear Mr Infurna This letter, prepared by SECOR International Incorporated (SECOR) on behalf of ConocoPhillips, , presents a work plan for vertical assessment of soil and groundwater at the subject site (Figures 1 and 2) The proposed assessment involves the advancement of drilling and Installation of three groundwater monitoring wells onsite This work plan has been prepared In response to the San Joaquin County Environmental Health Department letter dated January 2, 2004 (Attachment A) The purpose of the proposed work is to install three deep monitoring wells and to delineate the vertical a extent of petroleum hydrocarbons in groundwater beneath the site This work plan includes a brief discussion of site background, proposed scope of work, and schedule ' SITE BACKGROUND On April 7, 1999, three 10,000-gallon capacity underground storage tanks (USTs), which contained gasoline and diesel fuel, were removed from the site Excavation dimensions were approximately 35 feet by 40 feet by 15 feet deep Initial remedial activities Included source removal of obviously impacted soil to a depth of approximately 18 feet below ground surface (bgs) beneath the center of the western fuel tank Additional remedial activities included source removal of obviously Impacted o soil in the area beneath the former dispenser and product lines A concrete pad restricted the lateral extent of excavation During excavation of impacted soil, unidentified fiberglass piping was found Additional excavation and sampling was completed on April 8, 1999 to remove the unidentified piping Samples were collected from the bottom and sidewalls of the excavated area Following removal of the former station canopy, canopy footings and kiosk, additional over-excavation was y completed in the dispenser area Over-excavation was terminated when obviously impacted soli was removed, the structural Integrity of the sidewalk was endangered, or groundwater was encountered A total of approximately 1,707 tons of soil was transported off-site for disposal at the Forward Landfill in Manteca, California '' On December 9 and 10, 1999, four groundwater monitoring wells (MW-1 through MW-4) were T Installed to investigate the extent of petroleum hydrocarbons in soil and groundwater beneath the site Well MW-1 was completed at 50 feet bgs, and wells MW-2 through MW-4 were completed at 45 feet bgs Petroleum hydrocarbons were not detected in any soil samples from beneath the site Groundwater sampling from the new wells was initiatedlon January 5, 2000 Concentrations of total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and xylenes (BTEX), and methyl tertiary butyl ether (MtBE) were generally not detected in the wells, with the exception of minor concentrations of benzene and/or MtBE (EPA Method 8260) detected in wells MW-3 and MW- 4 Initial depth to water was approximately 28 to 29 feet bgs The direction of groundwater flow was