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Mr. Michael Inf ima <br /> Page 2 <br /> Prior to sampling, monitoring wells MW 1 through MW3 were purged of a minimum of three well <br /> casing volumes. During the purging process the physical parameters of temperature, pH and electrical <br /> conductivity were measured. Samples were collected after the physical parameters stabilized and <br /> 1001/o water level recovery. Purge water was contained in appropriately labeled DOT-approved 55- <br /> gallon drams, and is currently being stored onsite. Purge logs are included in Attachment A. <br /> Groundwater samples were delivered under chain of custody protocol to Argon Laboratories (FLAP <br /> #2359). Analysis consisted ofBTEX and MTBE using EPA method 8020, and TPHg and TPHd using <br /> modified EPA method 8015. <br /> GROUNDWATER ANALYTICAL RESULTS <br /> No detectable levels of TPHg, TPHd, BTEX, or MTBE were present in the samples collected from <br /> wells MWI and MW2. In the sample collected from MW3, benzene was detected at 1.3 parts per <br /> billion(ppb). TPHg was reported at a level of 140 ppb, TPHd was detected at a concentration of 600 <br /> ppb, and MTBE was present at a level of 230 ppb. Analytical results are summarized in Table 2. <br /> Attachment B contains laboratory reports and chain of custody documentation. <br /> �... CONCLUSIONS <br /> Groundwater levels at the site continue to rise, and a reversal in groundwater flow direction has <br /> occurred. Wells MW 1 and MW2 continue to show non-detectable levels of targeted analytes. <br /> Contaminant levels in well MW3 appear to be decreasing at a relatively rapid rate. The concentration <br /> of benzene in well MW3 is near the MCL; TPHg and MTBE levels have shown decreases of <br /> approximately 50 percent with each consecutive sampling event; and TPHd concentrations have <br /> decreased an order of magnitude. These decreases suggest significant attenuation within the area of <br /> concern is occurring. This is not unexpected given the minimal residual contaminant source. <br /> RECOMMENDATIONS <br /> The abrupt reversal in groundwater flow coupled with the rapid reduction in contaminant <br /> concentrations suggests that the installation of additional monitoring wells may be premature. <br /> Ground Zero recommends continuing groundwater monitoring and sampling for at least two <br /> additional quarters in order to confine contaminant concentrations, groundwater flow, gradient, and <br /> variations in water levels. The need for additional monitoring well(s) will be re-evaluated at that <br /> time. <br /> wooleey.chtlgmr12gm2000.doc <br />