Further sampling of water from the six groundwater wells (wells 10, 11, 17, 18A, 19 and 22) was conducted in 1986 by the MDEP. These samples were analyzed for the presence of VOCs. No VOCs were detected in four of the six wells (wells 10, 11, 17, and 22). One VOC, chloroform, was detected in well 18A at a maximum concentration of 1.9 ppb (Refer to Table 1) which was below the MMCL of 100 ppb. TCE was again detected in well 19 at a maximum concentration of 12 ppb. This concentration is above the MMCL of 5 ppb. Sampling of well 19 conducted one year later, found both TCE (detected at 11 ppb) and TCA
(detected at 2 ppb).
Scituate Town Hall is described by the Scituate Water Department as the very first location to receive finished water containing water from Well 19. A water sample was obtained from a utility sink in the Town Hall in 1986 and analyzed for the presence of VOCs. TCE was detected at a concentration of 6.9 ppb, exceeding the MMCL of 5 ppb (Refer to Table 1). Following these sampling results, the town of Scituate hired an environmental consulting firm, Camp, Dresser, and McKee, Inc. (CDM), to investigate the contamination at well 19.
Additional sampling activities were conducted by CDM in 1988 to further evaluate the nature and extent of TCE contamination in well 19. Eighteen groundwater-monitoring wells were installed in the vicinity of well 19. Specifically, 14 shallow monitoring wells were installed at depths ranging from 30 to 50.5 feet below ground surface and four deep monitoring wells were installed at depths ranging from 45 to 90 feet below ground. These wells were screened for the presence of VOCs. Based on the screening results, samples from 11 of the monitoring wells were sent to the laboratory for confirmatory VOC analysis. A second round of sampling was conducted for three monitoring wells to confirm results, and a third round of sampling included seven samples to evaluate temporal changes (i.e., changes over time) in VOC concentrations found in the monitoring wells (CDM 1988).
The results indicated that TCE was detected in the three deep monitoring wells installed around well 19 at concentrations ranging from 30 to 58 ppb, exceeding the MMCL of 5 ppb. PCE was also detected in these monitoring wells at concentrations ranging from 2.6 to 9.3 ppb. The maximum concentration of PCE (9.3 ppb) exceeded the MMCL for PCE (5 ppb). VOCs including toluene, PCE, and carbon tetrachloride also were detected in the shallow monitoring wells installed around well 19. The maximum concentration of toluene detected was 32 ppb, below the MMCL of 1,000 ppb. The maximum concentration of PCE detected
(5 ppb) was equal to the MMCL (5 ppb). Carbon tetrachloride (11-12 ppb) was detected at a concentration exceeding its MMCL (5 ppb).
As part of the CDM investigation, water samples from well 19 and Scituate Town Hall were obtained and collected on a monthly basis. Six samples were collected from both of these locations between June and November 1988. Results of the analysis indicate that TCE was detected in well 19 during all six sampling rounds at concentrations ranging from 6.4 to 13.0 ppb. TCE was detected in water from the Town Hall during five sampling rounds at concentrations ranging from 2.5 to 9.6 ppb. The highest concentrations of TCE in water from Town Hall, 6.9 and 9.6 ppb, were detected in 1986 and 1988, respectively (refer to Table 1).
Between the years 1991 and 1998, quarterly sampling of well 19 was conducted. During this time period, the data reviewed indicated that the maximum detected concentration of TCE was 6.2 ppb. This maximum concentration is slightly higher than the MMCL for TCE of 5 ppb1. More recent sampling conducted in 1999 detected TCE in well 19 at a maximum concentration of 2 ppb, below the MMCL of 5 ppb. Thus, it appears that TCE in well 19 continues to be detected, although at slightly lower concentrations (e.g., < 7 ppb), in the testing conducted in the 1990s versus the concentrations detected in the 1980s (e.g., < 20 ppb).
1 When a water supply is sampled and analyzed for chemicals several times per year, MDEP determines compliance with MMCLs by calculating a running annual average of all samples taken during a one-year period and comparing that value to the MMCL.
Based on the results of the CDM investigation, several possible sources of groundwater contamination were identified. Because of the proximity of the town municipal complex to well 19, and the known use of chlorinated solvents and degreasers discharged at the complex, CDM concluded that the source of well 19 contamination was most likely the municipal complex (CDM 1988). Several source areas were identified at the municipal complex, including an area of underground storage tanks, a vehicle maintenance area, a materials storage area, and sewage facilities. Of the monitoring wells installed in the vicinity of well
19, the highest concentrations of TCE were detected in the wells installed at the materials storage area behind the school bus parking lot and at the school bus parking lot and maintenance area. According to the CDM investigation, a contamination plume in the groundwater originates near the materials storage area and moves southwest toward well 19
(CDM 1988). However, the boundaries of the plume are not well defined due to the limited number of sampling locations.