ARCHIVED REPORTS XR0008680 - Laserfiche WebLink

Home Browse Search

S E' C ® R 2 0 SITE HISTORY d` 21 Site Description , ' The site is located on the northeast corner of North EI Dorado Street and East Harding Way in Stockton, California (Figures 1 and 2) The site is a former 76 Unocal service station that dispensed gasoline and diesel fuel beginning in 1982 No fuel has been dispensed since the ' underground storage tanks (USTs) were removed in 1999 The surrounding land is a mix of commercial and residential properties There is a co-mingled plume study being done with the neighboring ARCO station located west of the site at 16 East Harding Way 22 Groundwater Monitoring Zone Classification ` Prior to the most recent vertical assessment conducted in November 2004 and April 2005, `shallow' and 'deep' were used to identify the groundwater monitoring zone for wells completed ° to depths ranging from 45 to 50 feet bgs (MW-1 through MW-4) and 79 to 83 feet bgs (MW-5 through MW-14), respectively However, the three wells installed as part of the most recent ' vertical assessment were completed to a depth of approximately 120 feet bgs, which is below *r 4 the previously termed 'deep' groundwater monitoring zone Therefore, 'shallow' and 'deep' will ; no longer be used to describe the groundwater monitoring zones and will be replaced by the A monitoring zone and the B monitoring zone, respectively The three new wells (MW-15 thourgh ' MW-17) installed to approximately 120 feet bgs are in the third groundwater monitoring zone, r� which will be classified as the C monitoring zoned ' 23 Previous Investigations On April 7, 1999, three 10,000-gallon capacity 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 bgs beneath the center of the western fuel tank Additional remedial activities included source removal of obviously impacted soil in the area beneath the former dispenser and product lines A concrete pad restricted the lateral extent of excavationfi 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 Maximum concentrations of total petroleum hydrocarbons as gasoline (TPHg) and total petroleum hydrocarbons as diesel (TPHd) were reported at 3,000 milligrams per kilogram (mg/kg) (PBB- 2@13') and 1,400 mg/kg (PBB-1@13'), respectively Following removal of the former station canopy, canopy footings and kiosk, additional over-excavation was completed in the dispenser area Over-excavation was terminated when obviously impacted soil was removed, the w ' 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 Historical maps of soil sample locations and areas of over-excavation are ' included in Appendix B, and historical sod analytical data is included in Table 2 On December 9 and 10, 1999, four groundwater monitoring wells (MW-1 through MW-4) were installed in the A monitoring zone to investigate the extent of petroleum hydrocarbons in soil and , groundwater beneath the site Monitoring well MW-1 was completed to 50 feet bgs, and ' monitoring wells MW-2 through MW-4 were completed to 45 feet bgs Petroleum hydrocarbons to • were not detected in any soil samples collected beneath the site Groundwater sampling of the Updated SCM 2005 doc 2 77CP 64409 0111105 y5� u� 4