ARCHIVED REPORTS XR0001845 - Laserfiche WebLink

Home Browse Search

a wooden plug in lieu of the drill bit for collection of samples below 55 feet bgs The hole was then reentered 0 and drilled below the flowing sand zone where the wooden plug was knocked out of the auger string and replaced by a standard drill bit Approximately twice the normal time was required to drill, complete, and sample these soil borings and subsequent monitoring wells because of the flowing sand problem Figure 11 is a map that depicts the areal distribution of petroleum hydrocarbon constituents in the soil at the site above 45 feet bgs The distribution of the petroleum constituents at the site is greatest along the south- central portion of the site where the former USTs were located and under the former dispensers It is estimated that the significant core area of the petroleum hydrocarbon areal extent is approximately 5,700 square feet and that an underlying source contaminant mass of approximately 9,400 cubic yards is present beneath and adjacent to the former UST pit and dispenser locations It is estimated that the contaminant mass has the following estimated petroleum hydrocarbon constituent concentrations benzene (1 to 10 mg/kg), toluene (2 to 50 mg/kg), ethylbenzene (2 to 15 mg/kg), xylene (5 to 220 mg/kg), TPH-gas (10 to 2, 100 mg/kg) Oxygenate compounds were all reported as below analytical laboratory detection limits with the exception of very minor concentrations of MTBE ( Photo Ionization Device(PID) readings from the field instrument indicated the presence of organic vapors ranging in concentration from 0 to I0,000 ppmv PID readings generally correlated directly with analytical laboratory data soil sample results but were greatly elevated over actual analytical laboratory results In all cases, the field instrument indicated the presence of organic vapors at concentrations that would have suggested significantly higher laboratory analytical results from associated soil samples This is very likely the result of a degraded and old petroleum hydrocarbon release The presence of petroleum hydrocarbons in the soil at locations immediately below and adjacent to the former USTs suggests that migrating shallow groundwater has been the primary transport mechanism for hydrocarbon impacts to soil 4,3 Groundwater Conditions The groundwater gradient at the site flows historically to the south or southwest(San Joaquin County,2000) Figure 5 depicts the area-groundwater flow in the immediate vicinity of the site according to groundwater data collected in support of the city of Lodi investigation (Environmental Forensics, 2002) Quarterly groundwater monitoring events at the 521 North Cherokee Lane site during April,July,and November,2003 indicate a groundwater surface at a surface elevation on site from 6 to 8 feet msl with a flow direction to the MaW\D TnvmonmenWa PannuTemcotiRew MLSAR1203 wN Page 21