ARCHIVED REPORTS XR0006187 - Laserfiche WebLink

Home Browse Search

1 15 September 2005 AGE-NC Project No 98-0465 Page 6 of S Analytical results of ground water samples are summarized in Table 2 The laboratory report(CTEL ' Project No CT214-054152),quality assurance/quality control report,and chain of custody forms are included in Appendix E Documents confirming the upload of laboratory electronic deliverable format (EDF) files and depth to water measurements to GeoTracker are included in Appendix F 4.0. CONCEPTUAL SITE MODEL ' ,The site is located on essentially flat land that is developed into t a convenience store and fueling facility,the majority of the ground surface is covered by asphalt(Figure 2) Based on data collected ' to date from soil borings and monitoring well installations, AGE has developed a conceptual site model for the'release, migration and distribution of the contaminants in the subsurface (Figure 5) ' Site assessment activities to date identified the area where subsurface soil appears to be impacted by petroleum hydrocarbons, soil is impacted at the former UST location and appears to be confined to the former UST pit/over excavation area Laboratory analysis of soil samples collected from ' beneath the former USTs detected total petroleum hydrocarbons quantified as gasoline and diesel (TPH-g and TPH-d, respectively) at concentrations up to 300 mg/kg (milligrams per kilogram) Volatile aromatic compounds benzene, toluene, ethylbenzene, and xylenes (BTEX) were detected ' • at concentrations up to 0 29 mg/kg,methyl tertiary-butyl ether(MTBE)was detected in soil samples at concentrations up to 0 54 mg/kg ' Soil impact at the former UST release area does not appear to extend significantly beyond the tank pit After removal of the overburden and tanks, samples collected from the side walls were non- detect for TPH-g and TPH-d with the exception of sample TK-1 S MTBE was detected at very low concentrations in samples D-1, D-2, TK1-S, TK1-N, TK2-S and TK2-N The concentrations of MTBE were all less than 10 mg/kg ' Between July 2000 and April 2005, twenty ground water monitoring events were performed at the site to monitor dissolved petroleum hydrocarbon concentrations in ground water and to characterize ' groundwater flow direction and gradient on the site Since initiation of the groundwater monitoring program,ground water elevations have ranged from approximately 5 to 10 feet below mean sea level and the ground water flow has been consistently towards the,north to northwest at low hydraulic ' gradients TPH-g and/or MTBE have been detected in water samples collected from wells MWA through MW-4 at concentrations as high as 1,100 µg/1 TPH-g and 1,200 µg/l MTBE The MTBE concentrations have been declined suddenly at the site since initiation of ground water extraction at ' the Sanchez Property site (northwest and down-gradient) during the first quarter of 2005 At the present time the hydrocarbon impacted ground water 1s laterally and vertically defined in all ' directions, ground water is defined to the north by monitoring well MW-2, in the south by boring 13-5, to the west by borings B-2 and B-3, to the east by monitoring well MW-4 and boring B-4 Advanced GeoEnvironmental,Inc I