ARCHIVED REPORTS XR0000608 - Laserfiche WebLink

Home Browse Search

' ;�oveinber 24, 1997 Page 3 contain nondetectable concentrations of TPI i-g and benzene; very low (0.012 to 0.022 ppm) concentrations of toluene and xylenes were reported in 2 of the 7 samples. Groundwater samples from Well MW-6 were reported to contain 980 ppb TPH-g and 9 ppb benzene. In May 1994, GTI drilled five borings (SB-1 through SB-5) onsite to further define the extent of hydrocarbons in soil in the areas of the eastern pump island, former USTs, and former used oil UST (GTI, June 28, 1994). Thirty seven soil samples collected from the borings were analyzed. The maximum concentrations of TPH-g and benzene (15,000 and 160 ppm) were reported in a sample from boring SB-4, in the former UST pit. Groundwater was reported at a depth of 43 feet bgs. In November and December 1995, GTI drilled four borings (SB-6, SB-7, SB-9, and MW-7), obtained groundwater "grab" samples from borings MW-7 and SB-9, and installed one groundwater monitoring well (MW-7) to further define the extent of hydrocarbons in soil and groundwater (GTI, January 25, 1996). GTI reported maximum concentrations of TPH-g and benzene (640 mg/kg and 1.4 mg/kg, respectively) in a soil sample from 40-112 bgs boring SB-9. Results of groundwater grab sampling indicated 1,900,000 ppb TPH-g in MW-7 and 260,000 ppb in boring SB-9. Benzene was reported as nondetectable in both groundwater grab samples. QUARTERLY MONITORING Quarterly monitoring has been ongoing at the site since March 1991. Historical groundwater gradient has been generally consistent to the south-southeast. Water levels have fluctuated in the wells from approximately 27 feet bgs recently to 47 feet bgs in 1992. Generally, groundwater levels have risen at the site since 1994. Blaine Tech Services, Inc. (Blaine) began monitoring at the site in November 1994; prior to that GTI performed the quarterly sampling. Nondetectable to low concentrations of hydrocarbons in Wells MW-3, MW-4, and MW-6 suggest that the hydrocarbon plume in groundwater has been defined in the areas north, northwest, and west of the former USTs. Hydrocarbon concentrations in Well MW-I, located west of the former USTs, have declined significantly over time. Ilydrocarbon concentrations in Well MW-5, southeast of the site, have been relatively consistent over time. The highest concentrations of hydrocarbons in groundwater were recently reported in Well MW-7, southeast(downgradient) of the site, in which TPH-g and benzene were reported at 6,400 and 230 ppb, respectively. During the most recent (third quarter 1997) sampling, MtBE was detected in Wells MW-2, and MW-7 (Blaine, September 30, 1997). SCOPE OF WORK The scope of work for the recent investigation included the installation of two (one onsite and one offsite) groundwater monitoring wells. A report of the results of the p 920-078.1 A/S01.G WRPT