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' GERAGHTY & MILLER, INC 2 <br /> ASSESSMENT OF IMPACTS <br /> ' The soil and groundwater at the site have been impacted by petroleum hydrocarbons stored <br /> at the facility Site investigations (beginning in 1989) have reported concentrations of total <br /> ' petroleum hydrocarbons (TPH) as gasoline (USEPA Method 8015, modified), benzene, <br /> toluene, cthylbenzene, and xylene (BTEX) compounds (USEPA Method 8020), and methyl <br /> tertiary butyl ether (MTBE) (m laboratory analyses conducted since June 1996) TPH is a <br /> ' mixture of hydrocarbons with no set toxicity value. Benzene is a known carcinogen. Toluene, <br /> ethylbenzene, and xylene have various acute and chronic effects with exposure The long-term <br /> ' health effects of MTBE are still being studied. Material Safety Data Sheets for these <br /> compounds will be provided upon request <br /> SITE HYDROGEOLOGY <br /> ' The site is underlain by interbedded clays, silts, and sands to a depth of 46 feet below <br /> ground surface (bgs), the total depth explored Depth-to-water measurements show significant <br /> ' seasonal variation, from approximately 10 to 17 feet bgs The direction of groundwater flow is <br /> to the northeast, towards the Swenson Park Golf Course <br /> PETROLEUM HYDROCARBONS IN SOIII. <br /> Petroleum hydrocarbons have been found in the soil during investigations at the site The <br /> ' highest concentrations of TPH as gasoline and BTEX in soil have been detected in samples <br /> collected between 15 and 20 feet bgs,in the zone of seasonal water-table fluctuation Although <br /> ' no holes were detected in the tanks removed in 1989, the former tanks and pump islands <br /> appear to be the primary source of subsurface contamination A graphic summary of maximum <br /> concentrations of petroleum hydrocarbons in soil for all monitoring wells, soil borings, and <br /> remediation wells is shown in Figure 2 <br /> ' Lateral delineation of hydrocarbons in soil (to non-detect levels) has been accomplished in <br /> all directions, except to the south (towards the ARCO service station) The maximum concen- <br /> tration observedof ward the southwest is 300 milligrams per kilogram (mg/kg) of TPH as <br /> gasoline in Soil Boring SB-2 No further lateral delineation is recommended <br /> A summary of analytical results from soil samples collected during all site investigations is <br /> included in Table 1 A short discussion of previous assessment activities at the site is <br /> presented in Attachment 1 Boring logs for all monitoring wells and soil borings completed <br /> Project No RC0309 010 <br />