ARCHIVED REPORTS_XR0008888 - Laserfiche WebLink

Home Browse Search

' 10 December 2001 ro AGE NC Project No 95-0143 ' 3 Page 2 of 10 ' From September to November 1995, five additional monitoring wells (MW-10, MW-14, MW-15, MW-16 and MW-17)were installed on and near the site Petroleum hydrocarbons were not detected in any of the soil samples analyzed Procedures and findings were summarized in the Quarterly ' Report - December 1995, dated 29 January 1996, prepared by AGE In April 1999, 11 horizontal vapor recovery wells, 5 vertical vapor extraction wells and 23 air ' sparging wells were installed at the site A thermal/catalytic oxidizer soil vapor extraction(S VE) unit and an in-situ air sparging (IAS) unit were subsequently installed north of the car wash canopy Details of the SVE/IAS system installation were reported in Quarterly Report-May 1999, dated 30 ' July 1999 and Quarterly Report - August 1999, dated 05 October 1999, both prepared by AGE Operation of the SVE/IAS system was initiated in November 1999 and continued until November 2000 The SVE system was shut down due to a significant decrease in hydrocarbon concentrations ' in soil gas drawn from the vadose zone The decrease in hydrocarbon concentrations coincided with an increase in ground water elevation that may have "drowned"the portion of vadose zone in which ' the extraction wells were screened Approximately 830 gallons of petroleum hydrocarbons were extracted during operation of the SVE system � . On 15 and 16 March 2001, five soil borings (MW-22, MW-23, MW-24, EW-3 and EW-4) were advanced at the site Borings MW-22, MW-23 and MW-24 were completed as 2-inch ground water monitoring wells,borings EW-3 and EW-4 were completed as 4-inch ground water extraction wells ' Extraction wells EW-3 and EW-4 were installed to address hydrocarbon-impacted ground water at the site and to induce draw-down in local ground water Draw-down of local ground water would increase vadose zone and enhance SVE performance at the former UST pit location Procedures and t results of the well installation were sumrnanzed in AGE's Quarterly Report -- First Quarter 2001, dated 30 May 2001 ' 3.0. GROUND WATER AQUIFER PUMPING TESTS 1 An 8-hour step draw-down aquifer pumping test and a 24-hour constant rate aquifer pumping test were performed at the site on 30 May 2001 and 17--15 July 2001, respectively Wells screened in the upper water zone (EW-3, EW-4, MW-3, MW-7, MW-9, VW-1, VW-2 and VW-4)were utilized as ' observation wells during both tests Table 1 summarizes well construction specifications Based on previous subsurface investigations, AGE informally identified the upper water zone as being a significant interval of porous, coarser-grained sand and silty sand separated from lower water zones ' by less permeable silty clay/clayey silt and silt layers The bulk of the impacted water is believed to be within the sandy unit Generally, the upper water zone was identified at depths between 15 feet ' (first encountered ground water) and 35 feet bsg • ' Advanced GeoEnvironmental,Inc