In 2021, MPSLA learned that an important water quality indicator in McGrath Pond is higher than in the other Belgrade Lakes. Further, the trend of the data over time shows this indicator has been rising slowly but steadily in McGrath Pond since the 1970s, with no sign of tapering off. Salmon Lake has some elevation also, which is not surprising, as it receives much of its water from McGrath Pond. The MPSLA Water Quality Committee has been investigating to find the cause.

Most Maine lakes have been sampled for basic water quality parameters since the early 1970s. One of them is Specific Conductance (SC), a measure of the water’s ability to conduct an electric current. A high reading results from many ions in the water and can indicate the presence of contaminants, although that’s not always the case. A high reading means that there are dissolved elements or molecules in the water (other than H2O), whether their source is natural or artificial.

A review of both historic and recent data from the McGrath Pond sampling station at the deepest point in the lake indicates something about the possible source of high SC in the pond. Here, the level does not fluctuate substantially during the course of the year, telling us that deicing chemicals washing off the roads are not the primary cause. The multi-decade SC increase is likely related to groundwater entering the lake because the year-in, year-out steady readings indicate a constant rather than seasonal source.

Last spring, we acquired a SC meter and used it to measure seven streams entering McGrath Pond. These streams convey surface-water runoff in wet weather. During dry periods, groundwater at the top of the water table seeps into the streambeds, maintaining a small flow. Measuring monthly from May to October 2022, we found that streams on the east side of the McGrath Pond have average SC readings about three times those of streams on the west and north sides (see map graphic).

This information leads us to focus on the Oakland solid waste facility on the east side of Town Farm Road, which included the town’s open landfill until about 1990, when it was capped to minimize the infiltration of rainfall and snow melt. Water percolating through a landfill will pick up contaminants, and that “leachate” carries the contaminants into the groundwater. Although the landfill cap reduced the creation of new leachate, it’s possible that leachate formed during landfilling decades ago, made its way downhill, through the bedrock and overlying soil, and has been gradually reaching the lake.

Twelve property owners provided us with laboratory test results for their potable wells, and those data show good quality water in the deep groundwater on both sides of the pond, down 200 to 300 feet. So, we believe the high SC water entering McGrath Pond is likely coming from shallow groundwater — and some surface water — in the eastern watershed.

Based on the information gathered so far, there’s a need for further testing to determine what environmental impacts, if any, these inputs have on the lake, streams and nearby potable wells that are less than 200 feet deep. Our next step is to sample the lake, streams, and groundwater for elements and compounds that are typically found in landfill leachate, including PFAS (“forever chemicals”).

So far, we have benefited from existing data, a donated meter, and volunteer efforts, with no direct cost to MPSLA. The next steps will require funding because the laboratory tests are rather expensive, and we will seek town and DEP assistance as we move forward.

Just as this article goes to press, we’ve learned that Maine DEP has conducted sampling in McGrath Pond focusing on landfill-specific contaminants. The preliminary results indicate PFAS compounds in McGrath Pond waters at just over nine parts per trillion (ppt), about one- half the state safe drinking water limit of 20 ppt. DEP has also measured PFAS compounds in fish flesh from McGrath Pond and found levels of concern in black crappie and large-mouth bass. We expect to learn more details from DEP in the coming weeks.

As for MPSLA’s sampling program going forward, once we have all the information, we will consult with Maine DEP and the town of Oakland before deciding on the best course of action.