Results of the private well sampling found that eight wells were contaminated with detectable levels of tetrachloroethylene (PCE) or methyl tertiary butyl ether (MtBE). Four wells were contaminated with PCE and four wells with MtBE. The concentration of PCE ranged from 2 to 95 micrograms per liter (ug/l, or parts per billion) with three of the four samples exceeding the 5.0 ug/l safe drinking water standard. The three residences which exceeded the drinking water standard have recently connected to the municipal water supply in Wilmington. MtBE ranged from less than 1 to 70 ug/l. The drinking water guideline in Massachusetts for MtBE is currently set at 70 ug/l. Letters have been issued by DEP and the Board of Health to all homes with detectable levels of volatile organic compounds (VOCs) recommending that they connect to the municipal water supply or install a properly designed home water filtration device.

Results of the private well sampling are presented in the table below. The approximate locations of each well are indicated on the attached map labeled "Wilmington, Private Well Sampling, Kelly Hill".

Discussion, Kelly Hill
The Kelly Hill and Main Street areas are located along the headwaters of the Ipswich River Basin. Surface water drainage in the Kelly Hill neighborhood flows in an easterly-southeasterly direction towards Mill Brook. Mill Brook is culverted across Main Street near the north end of Sweetheart Plastics (see attached map "Wilmington Surface Water Flow") and merges with Maple Meadow Brook and Lubbers Brook in East Wilmington, between Concord and Lowell Streets, to form the confluence of the Ipswich River.

The neighborhoods in the area of Kelly Hill have grown steadily through the years since initially being developed in the 1950s. The entire area is served by private septic systems. The majority of the residences of the area are served by the municipal water supply, although as stated above, 30 private drinking water wells were reported to be in use in the summer of 1999.

Groundwater contamination with PCE was found in the Kelly Hill area in four bedrock wells ranging in depth from 300' to 710'. The two PCE contaminated wells on Birch Road are located within 200 feet of each other, while the other two wells are several hundred feet away. Several wells within this area had no VOC contamination, indicating the PCE is not continuous throughout the bedrock aquifer. As observed with PCE, MtBE was also found in several wells and absent in others. It should be noted, however, that 8 of 13 private wells sampled had detectable levels of PCE or MtBE, indicating that groundwater contamination, although not continuous, is a widespread problem within the bedrock aquifer of Kelly Hill.

A review of the files for the contaminated "21E" sites located in proximity to the private wells has identified several sites with documented releases of PCE and MtBE located between 1000 and 4500' away (see attached maps "Wilmington, Main Street 21E Sites with MtBE" and "Wilmington, 21E Sites with PCE Contamination"). The study area is located within the headwaters of the Ipswich River basin with the general direction of surface water flow to be in an easterly direction along Lubbers Brook to the north and Mill Brook to the south. Overburden material composed mainly of the highly conductive glacial outwash deposits of loose sand and gravel were found during site investigations to range between 30-50' deep in the lowland areas. Groundwater flowing through this material will generally move toward surface water areas and eventually discharge to the nearby brooks and Ipswich River. While several sites are located along Main Street with the same contaminants as the private wells, the surface water and groundwater flow is in an easterly direction away from the Kelly Hill neighborhoods, which are located upgradient and west of Main Street. Dissolved groundwater contaminants from the Main Street sites ultimately flow east. It should be noted, however, that the depth to bedrock is generally not too deep and groundwater contamination that reaches bedrock could flow and migrate through its cracks and fractures. Depending on the orientation of the fractures, and the bedrock strike and dip, groundwater contaminants in proximity to the private wells could conceivably migrate in a westerly direction. Additional data considered during the assessment of this investigation include the fact that although TCE was not found in any of the private well data, TCE was found to have the highest concentration of groundwater contaminants in the Main Street area, with over 400 mg/l TCE at the JJT site located at 315-319 Main Street). TCE was observed at over 400 mg/l in the sand and gravel overburden deposits

It should also be noted that the entire Kelly Hill neighborhood has had private septic systems since first being developed in the 1950s. Until recently, many commercially available septic system cleaners contained chlorinated solvents. The bedrock aquifer may have received PCE through discharges of cleaners containing PCE being poured into private septic systems.

The presence of MtBE in the bedrock aquifer at Kelly Hill is not likely the result of gasoline releases from one of the listed 21E sites as the direction of surface and groundwater flow is east, away from the private wells. Due to the common use of gasoline, incidental spillage from automobiles and/or small gasoline engines (such as lawn mowers) is more likely the source of the MtBE contamination in the bedrock aquifer. Due to the depth into bedrock where MtBE has been detected, and the possibility of multiple small sources of gasoline, it is not technically or economically feasible to pinpoint the area(s), which may have contributed to the presence of MtBE in bedrock at Kelly Hill.

Recommendations, Kelly Hill

Efforts should be made by DEP and the Town of Wilmington to encourage all owners of private wells in the Kelly Hill area to connect to the municipal water supply as the bedrock aquifer is contaminated with VOCs.