ARCHIVED REPORTS_XR0002783 - Laserfiche WebLink

Home Browse Search

i 3.0 CONCLUSIONS AND RECOMMENDATIONS During the fourth quarter of 1997, groundwater was monitored and samples were collected from all five original groundwater monitoring wells and the two vapor extraction wells (VW-1 and VW-2) with screen intervals coinciding with current groundwater levels ' The depth-to-groundwater beneath the site ranged from 47 81 feet Below ground surface (bgs) in MW-1 to 49 18 feet bgs in MW-5 The groundwater elevation beneath the site ranged from 30 81 feet below mean sea level (MSL) in MW-1 to 31 09 feet below MSL in MW-5 Groundwater levels have dropped an average of 1 94 feet since groundwater levels were last measured on August 13, 1997 The groundwater gradient was calculated at 0 003 foot/foot in a northerly direction Since ' May 1992, the groundwater elevation in MW-1 has risen 18 42 feet As a result, the groundwater table has risen above the screen intervals in monitoring wells MW-1, MW-2, MW-3, MW-4 and MW- 5 As such, the groundwater monitoring and sampling results from these wells may not reflect groundwater table conditions Accordingly, groundwater from these five wells had not been sampled since April 1996 To evaluate the possible presence of oxygenate compounds in groundwater beneath the site, all five groundwater monitoring wells and VW-1 and VW-2 were sampled during this quarterly sampling event Groundwater sampled from VW-2 continued to contain the highest concentrations of gasoline hydrocarbons (5,700 ppb of TPH-as-gasoline, 370 ppb of benzene, 1,300 ppb of toluene, 230 ppb of ethylbenzene, 1,000 ppb of xylenes and 1,700 ppb of MTBE) Gasoline hydrocarbons were also detected at lower concentrations in VW-1, MW-1, MW-2, MW-3 and MW- 5 Monitoring well MW-4 was the only well without detectable concentrations of gasoline ' hydrocarbons MTBE was the only oxygenate detected MTBE was detected in VW-2 at 1,700 ppb, MW-3 at 1,400 ppb, MW-2 at 230 ppb and in VW-1 at 60 ppb The volatile organic compound 1,2- Dichloroethane was also detected in MW-3 at 230 ppb, VW-2 at 190 ppb, MW-2 at 120 ppb and in VW-1 at 14 ppb These concentrations of 1,2-Dichloroethane exceed the Maximum Contaminant Level (MCL) of 0 5 ppb Neither MTBE nor 1,2-Dichloroethane was detected in MW-1, MW-4 and MW-5 Carbon Disulfide was detected in MW-5 at 11 ppb The three drums of wastewater designated A, B and C did not contain detectable concentrations of TPH-as-gasoune, BTEX or MTBE Neither TPH-as-gasoline nor BTEX was detected in any of the drummed wastewater samples, however, MTBE was detected in the three drums of wastewater designated D, E and F at 6 ppb and in the three drums of wastewater from MW-2 at 55 ppb 5