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w Ld 'GeofogicidTecFinics Inc. V Page 3 Former Moresco Property Site Characterization Report Project No.251.2 October 11, 1996 2.4 SUBSURFACE INVESTIGATION �. Between April 1995 and June 1996, a series of soil borings were advanced through and surrounding the former tank excavation to provide a better understanding of the site's vadose zone and how its geology may have affected the transport of petroleum hydrocarbons and its attenuation processes. Soil samples were analyzed to evaluate the vertical and horizontal extent of the contamination, and to determine site specific fate and transport characteristics. 2.1 Soil Boring Installation On June 17 - 18, 1996 V&W Drilling, Inc. of Rio Vista mobilized hollow stem auger and wire line sampling equipment. Geological Technics Inc. personnel supervised the drilling of three soil borings to a total depth ofl 00 feet below ground surface (bgs): r' I. S13-5 Iocated approximately 35 feet north of the former UST location, 2. SB-6 Iocated approximately 28 feet east northeast of the former UST, and 3. SB-7 located adjacent to the south edge of the former UST location (Figure 2). During drilling, soil samples were collected for geological and analytical evaluation at 5 foot intervals starting at five feet bgs to the total depth of each boring. In SB-7, a SimulProbe multiphasic sampling tool was employed at five discrete depths to collect soil and collocated soil gas samples. All soil samples were sealed with aluminum foil, capped, labeled and placed in a cooler at 4° Celsius for transport to the laboratory following Chain of Custody protocol. LO 2.2 SimulProbe Sampling r.. The SimulProbe is a relatively new tool on the market which has demonstrated it's ability to provide correlative data between soil cores and the surrounding matrix fluid; either groundwater or soil gas. The SimulProbe is designed to recover a soil core and a representative fluid sample from the same interval thus allowing correlation and assessment of the sorbed and dissolved or gaseous phase fraction of contaminants. This correlation is useful in calculating mass balance and for calibrating reconnaissance techniques (i.e. soil gas sampling). The SimulProbe was chose for it's capability in the soil gas collection mode. We �- were interested in evaluating the gaseous phase component for risk assessment purposes and as a more definitive solution for a mass balance calculation. We also collected atmospheric gas samples at depth (oxygen and carbons dioxide) to evaluate if aerobic biodegradation is Lo occurring or if it is limited by excessive CO2 or insufficient 02 levels. During this investigation the SimulProbe tool was employed at selected lithologic intervals to collect soil cores and a collocated in-situ soil gas sample. At the desired sampling interval the SimulProbe sampling tool was attached to the wire-line down hole hammer and advanced 18" into undisturbed sediments. A light back-hammer motion exposes the sample collection screen which opens a conduit via one-time use disposable Teflon tubes to the sampling L- chamber. The sampling chamber is vented to the surface via a length of Teflon tubing. An oil-less vacuum pump is used to purge the stagnant sample chamber and line volumes before an air sample is collected in a one liter capacity Tedlar bag.