ARCHIVED REPORTS_XR0005078 - Laserfiche WebLink

Home Browse Search

16 October 2006 AGE-NC Project No. 98-0520 Page 7 of 10 • Ethyl-benzene and m,p-xylene were reported in the samples collected from wells MW-3 and ' MW-5 at maximum concentrations of 860µg/I(MW-5)and 360 µg/1(MW-5).Toluene was also reported in the sample collected from well MW-3 at concentration of 2.1 µg/1. AGE concludes: ' TPH-g concentrations decreased this quarter in well MW-2 by 17%, but increased in wells MW-3 by 233% and MW-5 by 47%. The increase is a parently associated with the second highest ground water elevation levels recorded at the site. It should be'noted, only on-site ' wells MW-2, MW-3 and MW-5 have had reported detections of TPH-g since the sample from MW-1 was reported with a concentration of 200 µg11 of TPH-g in September 2005. • TPH-g concentrations have been reported at less than the detectable range in wells MW-1, ' MW-4, MW-6, MW-7, MW-8, MW-9 and MWA 0 for 3, 4, 19, 18, 13, 15, and 16 consecutive quarters, respectively. • The vertical extent of impacted ground water has been defined;TPH-g has not been detected in deep-screened well MW-6 since the well was installed in December 2001. Impacted ground water apparently does not extend to 45 feet bsg and beyond. • The lateral extent of TPH-g impacted ground water appears to be within the area defined by wells MW-4 (3 intermittent reports of detectable levels in last 16 quarters) and MW-7 through MW-10 (no reported detections since September 2002). • The lateral extent of TPH-g impacted ground water appears to be defined and not migrating.. Additionally,soil vapor extracted from soil vapor extraction well VW-I located in the center of the highest historical recorded concentrations of TPH-g at the site did not report a single detection of any constituent of concern as reported in the AGE-prepared Soil Vapor Extraction Pilot Test Report dated 22 December 2005. Apparently,hydrocarbons absorbed to soil in the vadose zone are either not present or not volatilizing and migrating upward through the soil. enzene has not been reported in the ground water monitoring well samples at or above th '� San Francisco Bay Regional Water Quality Control Boards Environmental Screening Level ' f 5.0 }zg/1 in the site's history and further, benzene has not been reported in any ground water sample since a concentration of 2.5 µg/l was reported in well MW-5 in September r' 2001. • Concentrations of TPH-g have steadily increased in monitoring well MW-5 for the past 3 quarters to the highest concentrations reported since February 2002. The increase in concentration of TPH-g in well MW-5 appear to be associated with the ncpth of ' the ground water table, which has�sed�-over feet dunng the past 3 quarters. Advanced GeoEnvironmentM,Inc. 1