ARCHIVED REPORTS_XR0007377 CASE 2

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' PHASE I1 ENVIRONMENTAL SOIL SAMPLING AT&T MICROWAVE RELAY FACILITY 90 WEST TURNER ROAD,SACRAMENTO,CALIFORNIA CONFIDENTIAL AND PRIVILEGED IV. CONCLUSIONS AND RECOMMENDATIONS The primary purpose of this investigation was to assess the lateral and vertical limits of diesel fuel Impacted soil and ' groundwater in the vicinity of a former UST and Its product piping To accomplish this goal, ATC's sampling plan was designed to evaluate the potential for soil and groundwater contamination from the past use of the Subject Property Based on the results of laboratory analyses of soil samples colleted as part of this Phase II investigation and analytical results from the previous UST removal investigation, diesel fuel contaminated soil appears to be laterally confined to the immediate vicinity of the former UST excavation m an area of approximately 25 feet long by 25 feet wide The lateral lints of diesel fuel impacted soil are presented in Figure 4 Soil boring B i encountered diesel fuel at a concentration of 490 ppm at a depth of 26 feet bgs, dust above the depth to groundwater Diesel fuel was not encountered in the soil bonngs surrounding the former UST (134, B5, B2, or B7) to a depth of 32 feet bgs Therefore, it is likely that diesel fuel is present in the soil in the depth Interval from 12 feet bgs (the depth of the slab beneath the ' former UST)to approximately 27 feet bgs (the depth to groundwater) Analytical results of groundwater samples Indicate that diesel fuel in the groundwater has migrated from the former UST excavation to the south and east The diesel fuel impacted groundwater appears to be laterally confined to an area approximately 60 feet long by 35 feet wide The lateral limits of diesel fuel impacted groundwater are presented in Figure 5 Diesel fuel is found at a maximum reported concentration of 150 ppb in boring B2 and attenuates to a ' concentration of 58 ppb in boring B3, 20 feet farther to the south State of California action levels for TPH in the soil do not currently exist However, the California Regional Water Quality Control Board uses TPH concentrations to prioritize cases for review The pnontization Ievel for Total TPH in soil is 100 ppm This level for TPH has been exceeded by the results indicated above and the case will likely be prioritized for review According to the Compilation of Water Quality Goals, March 1998 by the California Regional Water Quality Control Board, "diesel oil" has a taste and odor theshold of 100 ppb Additionally, the USEPA has a Suggested No-Adverse- Response Level (SNARL) for diesel oil of 100 ppb Groundwater sample 132-Water had a TPH-D concentration of ' 150 ppb and exceeded these water quality goals The one reported toluene concentration of 1 2 ppb did not exceed any posted water quality goals The Lawrence Livermore national Laboratory report on leaking UST cleanup indicated that passive bioremediation should be considered as the primary remediation tool in most cases once the fuel leak source has been removed The State Water Resources Control Board (SWRCB) issued a letter on December 8, 1995 suggesting that cleanup oversight agencies should require groundwater monitoring only in low risk cases where the fuel leak plume is stable In light of the limited nature and relatively low concentrations of the soil and groundwater contamination, ATC recommends that three groundwater wells be installed in the vicinity of the former UST in order to further define groundwater gradient and diesel fuel concentrations It is anticipated that after one year of monitoring, a nsk-based analysis will be performed on the site in order to obtain regulatory closure Additionally, research should be performed on the two groundwater production wells on site in order to determine the depth of the screened intervals and the potential for impact from the former UST 1 8