ARCHIVED REPORTS XR0009533 - Laserfiche WebLink

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i IMass Balance of Gasoline The residual petroleum hydrocarbons are distributed between the vadose zone and the saturated zone as characterized by soil borings and groundwater monitoring wells installed in the vicinity of this release The available data suggest that the vadose zone contamination is Iconfined to a small area in the immediate area of the former fuel oil tanks, and does not constitute a material portion of the total contaminant mass The groundwater contamination has spread more extensively Vadose Zone Due to the very shallow groundwater, there is very little contaminant mass lying within the ' current vadose zone if the groundwater level falls, the portion of the total contaminant mass within the vadose zone will increase, but it currently is not a significant factor Saturated Zone The contaminant mass in the saturated zone is partitioned in to two phases, the portion ' adhering to the soil or absorbed phase, and the dissolved phase Dissolved Mass - Groundwater Measurement Method The mass of contaminant in the adsorbed phase was estimated by first contouring TPH-G ' concentrations from soil samples collected in the capillary fringe or near the groundwater surface (see Figure 2) The area of each contour was calculated by using the planimeter ' function of the drafting program used to create the figures (i e TurboCAD) Vertically, 5 to 8 foot-thick slices were considered for each contoured zone The volume of each slice was then computed and an average TPH concentration was estimated for each zone The slices ' were numbered from A to D with A being the shallowest Within each slice, the contaminated area was divided into zones based on the contaminant concentrations ' To compute the contaminant mass, the volume of each zone was converted into a total estimated weight of soil taking into consideration the porosity of the soil These calculations assume the average bulk density of the soil is 1 83 times that of an equal volume of water ' Computation yields the partial result that the soil weighs 113 lbs /c f The following table summarizes the volume of each zone and the average contaminant ' concentration in each Table AlA - Zone Volumes and Ave. TEPH Concentrations - Slice A—25'-33' ' Zone A Gross Net Area Volume (25'-33') Area A. �(A„*7ft) ' (each zone) 1 11,700 ppm 14sf 14sf 98cf 2 500 ppm 137 s f 123 s f 861 c f 3 50 ppm 380 sf 243 s f 1701 c f ' 4 5 ppm 1006 s f 626 s f 4382 c f t2937 Veneman Ave,#B240 Geo-Phase Environmental Inc Phone(209)569-0293 Modesto,CA 95356 Fax(209)569-0295 1