ARCHIVED REPORTS XR0001845 - Laserfiche WebLink

Home Browse Search

(1) Surveying the existing monitoring well casing locations and establishing vertical and horizontal coordinates,(2)submitting the site into the Geotracker program database,(3)completion of a geophysical survey, (4)drilling and sampling of eight soil borings to 50 feet bgs,(5)drilling,sampling,and completion of three additional monitoring wells to 60 feet bgs to further delineate the groundwater petroleum hydrocarbon extent Significant findings of the investigation are as follows (l) soil and groundwater at the site have been impacted by petroleum hydrocarbon compounds The exclusive source of this contamination has been from this site (2)The geophysical survey suggests no additional tanks or pipelines are present at the site that have not already been removed or identified (3)The subsurface soil conditions beneath the site are primarily fine to coarse-grained sand with interbedded silty sand or silt beds that may approach several feet in thickness (4)Petroleum hydrocarbon contamination in the soil and groundwater is in the form of gasoline fuel Significant concentrations of benzene, ethylbenzene, and 1,2-DCA compounds are present in the groundwater beneath the site at concentrations that exceed State of California Maximum Contaminant Levels (MCL's)for water quality (5)Oxygenate compounds do not appear to be present in the soil as a principal contaminant mass Minor concentrations of MTBE an TBA are present in both soil and groundwater at the site (6) Soil contamination appears to be present from a depth of 10 feet bgs to about 50 feet bgs beneath the former UST and dispenser locations Horizontal extent of the soil petroleum hydrocarbon contamination has been identified to the north and northwest The horizontal extent of soil petroleum hydrocarbon contamination has not been delineated to the southwest,south,or southeast (7) Regional groundwater flow at the site has been historically to the south and southwest with a gradient of about 15 feet per mile (8) Groundwater petroleum hydrocarbon contamination extent beneath the site has been delineated to the northwest to northeast within the 1 st water bearing zone The horizontal extent of the petroleum hydrocarbon contaminated groundwater has not been identified in the down or cross-gradient flow direction to the southwest to southeast A preliminary site conceptual model based on the available data suggests the following (1) source contaminant mass is primarily on site and is approximately 9,400 cubic yards This source area is located beneath and adjacent to the former UST pit and dispenser locations (2)The contaminant soil mass extends over approximately 5,700 square feet which forms the primary source area This contaminant mass has the following estimated petroleum hydrocarbon constituent concentrations benzene(1 to 10 mg/kg), toluene M=\D 1EnwonmenWTannarrex=olR +SAR1zos wpd Page 2