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• <br /> . Mr. Ron Rowe <br /> Page 2 <br /> After a minimum of 3 well casing volumes were purged from well MWl and the pH, <br /> temperature, and electrical conductivity were allowed to stabilize, groundwater samples were <br /> collected. During the purging process the water level was drawn down below the top of the well <br /> screen to ensure representative sampling. The purge log is included in Attachment A. Purge <br /> water was stored on site in a 55 gallon container pending laboratory analysis. <br /> The samples were delivered under chain of custody to Argon Laboratories (FLAP #1873) and <br /> analyzed for TPHg using modified EPA method 8015 and BTEX/MTBE using EPA method <br /> 8020. TPHg and BTEX were nondetectable, and MTBE was detected at a concentration of 19 <br /> parts per billion. The table below shows cumulative groundwater analytical data. Laboratory <br /> reports are included in Attachment B. <br /> .Ate....... : ....... .... .... T E: ....... ..' ..... : ........ Tl H.9.... ...:.MTB . ... <br /> MW1 05/24/95 <0.5 5.2 18 85 850 -- <br /> 07/26/96 <0.5 <0.5 <0.5 <0.5 <50 19 <br /> Notes: <br /> . Results in parts per billion <br /> BTEX Benzene, Toluene, Ethylbenzene, total Xylenes <br /> TPHg = Total Petroleum Hydrocarbons as gasoline <br /> MTBE - Methyl tert-butyl ether <br /> -- = Not Analyzed <br /> < = Less than indicated detection limit <br /> Discussion and Recommendations <br /> The current analyses indicate only the most minor groundwater impact (19 ppb MTBE). This <br /> concentration is below the EPA Draft Lifetime Health Advisory of 20 to 200 ppb (RWQCB--San <br /> Francisco Bay Region, May 2, 1995). <br /> Previous investigation by Ground Zero defined the vertical and lateral extent of soil <br /> contamination at this site. The only significant area of petroleum hydrocarbon impacted soil is <br /> in the vicinity of MW 1 between depths of approximately 20.5 ft and 30.5 ft bgs. This is <br /> currently approximately 10 ft above groundwater (40 feet bgs), which suggests that the <br /> petroleum hydrocarbon concentrations detected in the groundwater samples collected from MWl <br /> in May 1995 may possibly be from an offsite source, or, alternatively, resulted from soil <br /> disturbance during well installation. <br /> The State of California owns a property at 601 East Miner Street. This site is located west of <br /> the subject site, and apparently had a leaking underground fuel tank. As a result, the State is <br /> • <br /> & \v \2qmI9 <br />