ARCHIVED REPORTS_XR0012668 - Laserfiche WebLink

Home Browse Search

Addendum to Work Plan September 13, 1989 Former Texaco Service Station, Manteca, California AGS 3$053-2 r� other pertinent site features, are shown on the Generalized Site Pian, Plate P-2. The samples were collected with a hand-operated percussion sampler, which we used to drive a clean brass sleeve into the native soil beneath the locations of the former lines. Each sleeve was removed from the sampler and promptly sealed with aluminum foil, plastic caps, and tape. The samples then were labeled and placed in iced storage. The field geologist initiated a Chain of Custody Record and accompanied the samples to the analytical laboratory. A copy of this record is attached to this addendum. The samples were analyzed at Mobile Chem Labs, Inc., of Lafayette, California, which is certified by the State of California to perform the analyses requested (Hazardous Waste Testing Laboratory Certificate No. 195). The samples were analyzed for total petroleum hydrocarbons (TPH) as gasoline and diesel by Environmental Protection Agency (EPA) modified Method 8015 and for benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) by EPA Method 8020. The results of analyses are summarized in Table 1 and indicate that no detectable hydrocarbon contamination exists in the soil sample collected from between the former tank cavity and dispenser islands. TPH as diesel was detected. however, at 6,900 parts per million (ppm) and TAH as gasoline at 10 ppm beneath the former dispenser islands. These results indicate that treatment of contaminated soil beneath the former dispensers W' is necessary at this site. We propose that the contaminated soil beneath the dispenser islands be removed by excavation, in conjunction with the re-excavation of the former tank cavity, which is described in our work plan. Excavation beneath the former dispensers should proceed vertically to the extent of hydrocarbon contamination or to the ground- water surface(approximately 23 feet below grade). The horizontal extent of contamination should be limited to the north and south by the lack of subjective evidence of hydrocarbon contamination or by the site building and sidewalk. The excavation should proceed to the limits of subjective evidence of soil contamination related to the former dispensers to the east and west. The approximate limits of the proposed excavation are shown on Plate P- 2 Mobile Chem Labs will be onsite to verify the condition of the base and sidewalls at the limits of the excavation and to analyze one soil sample for approximately every 25 cubic yards of soil that is removed by excavation as stated in our work plan. Laboratory analyses and sampling methods will be performed as we proposed in our work plan. After receiving analytical results of the soil removed by excavation, we will evaluate alternatives to treat or dispose of the soil. If aeration is chosen, we will contact the San Joaquin Air Pollution Control District for authorization to proceed within aeration requirements. If soil samples collected._at._the_..limits-.of-.the--excavation-indicate--that-soil--contamination — --- ---- remains in the subsurface, Applied GeoSystems recommends that a feasibility study be conducted to evaluate the most appropriate method to mitigate the soil. -- 2 AV pA901 GeaSystems --