ARCHIVED REPORTS XR0001520 - Laserfiche WebLink

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gasoline, 38 4g11 of benzene, 310 4gA of toluene, 4 8 ofµg11 ethylbenzene and 6,800 µg/l of xylenes On January 5 and 6, 1999, Ramage Environmental conducted a preliminary investigation and evaluation which included the drilling of five on-site soil borings for soil sampling and analysis Three of the soil borings were converted to groundwater monitoring wells The newly installed wells were developed, surveyed, monitored and sampled on January 11, 1999 Soils encountered beneath the site consist of a fining-upward sequence of fine- grained siliciclastic sediments The depth to static groundwater beneath the site ranged from 39 31 to 40 34 feet bgs Groundwater flow was to the south-southeast at a gradient of 0 05 foot/foot A metal detection survey conducted at the site, on January 13, 1999, discovered strong metallic signals in the vicinity of the former UST excavation The metal may be drums of waste not accounted for from earlier site investigation activities and other material used to backfill the former UST excavation Soil and groundwater beneath the site have been impacted by significant concentrations of gasoline hydrocarbons In sod, the highest concentration of gasoline hydrocarbons was detected in the sample collected at 30 feet below ground surface (bgs) from the soil boring for MW-2 This sample, collected directly beneath the former UST excavation, contained 2,400 mg/kg of TPH-as-gasoline and detectable concentrations of toluene, ethylbenzene and xylenes Laterally, the extent of impacted soil appears to be limited to the footprint of the former UST excavation Vertically, the extent of impacted sod beneath the former UST excavation is defined at a depth of approximately 55 feet bgs, on the basis of soil samples collected for analysis from the previously drilled soil boring B-1 Groundwater in the three monitoring wells has been sampled on a quarterly basis The highest concentrations of gasoline hydrocarbons have been detected in MW-2, installed through the former UST excavation To date, the highest concentrations detected in groundwater include 130,000 µg/l of TPH-as-gasoline, 7,800 µgll of benzene, 64,000 µg/l of toluene, 6,100 µg11 of ethylbenzene, 35,000 µgll of xylenes, 2 6 µg11 of methyl tertiary butyl ether (MTBE), and 100 µg11 of tertiary butanol (TBA) The lateral extent of impacted groundwater is undefined to the north (upgradient), west and south (downgradient) of the former UST excavation However, the lateral extent is defined to the northeast of the former USTs by MW-1 Vertically, the possible impact to deeper groundwater-bearing zones has not been investigated 4