Laserfiche WebLink
Mr. Bob Fratto <br /> July 27, 1993 <br /> Page 6 <br /> A <br /> hydrocarbon constituents analyzed for. Groundwater analytical results are summarized in <br /> Table 3. <br /> DISCUSSION AND RECOMMENDATIONS <br /> A total of five soil borings were drilled and sampled for soil and/or groundwater around the <br /> open excavation to define the lateral and vertical extent of hydrocarbons in soil from the <br /> former underground storage tank. Four of the borings were drilled into groundwater, <br /> temporary wells were installed, and water level measurements and groundwater samples were <br /> collected. <br /> One soil sample, TW1-15-15.5, contained trace levels of benzene. TW1 is located on the <br /> north side of the excavation between the existing tank farm and the excavation. Soil has been <br /> visibly affected by hydrocarbons to approximately 43 feet in the vicinity of boring TW4, <br /> which was originated west of the excavation and extended to approximately 81 feet below <br /> ground surface beneath the center of the excavation. Some sur cial soil (upper 2 feet) in <br /> TW2 was documented as being hydrocarbon-affected. <br /> rte, Groundwater collected from TW4 did contained low levels of gasoline constituents. <br /> Hydrocarbons were not detected in the other groundwater samples analyzed. <br /> It is estimated that groundwater flows to the southwest under a very low hydraulic gradient. <br /> It is possible groundwater has been affected by releases at this site. Even though the oil <br /> stored within the former UST was viscous and relatively immobile and insoluble, free oil <br /> occurring as droplets and within fractures in the sediment was documented to approximately <br /> 33 vertical feet in TW4. Visible signs of soil discoloration extended to approximately 44 <br /> vertical feet in TW4. Due to the occurrence of fractured silt and clay and root traces, which <br /> may supply vertical migration pathways, hydrocarbon migration to groundwater cannot be <br /> completely dismissed. It is possible, but unlikely, migration occurred to and affected <br /> groundwater beneath the site. Hydrocarbon concentrations detected in groundwater from TW4 <br /> may be from an up-gradient off-site source. <br /> Based on the above discussion, further excavation of visibly hydrocarbon-affected soil will <br /> be necessary to remove the primary source area. At least three permanent groundwater <br /> monitoring wells should be installed to better quantify groundwater flow direction, hydraulic <br /> gradient, and to monitor groundwater quality. An upgrad.ient well would be helpful in <br /> defining a possible off-site hydrocarbon source. <br /> Brown and Caldwell 7603'vCORMPS 7603-01.L-1 <br /> Consultants <br />