Analysis Suggests Pond Property Housing Will Not Affect Drinking Water

BREWSTER – Senior Hydrologist Mark Nelson of Horsley Witten Group told the select board Monday that future development within Zone II water supply areas is unlikely to significantly impact the town’s drinking water supply, a finding that contrasts with recent Brewster Conservation Trust concerns over affordable housing at the Sea Camps pond property.

 Nelson’s presentation was a snippet of the newly updated integrated water resource management plan (IWRMP), which was requested by the Brewster Ponds Coalition after they found limited references to wastewater in the previous plan. 

 The main takeaway: If done carefully and in the right location, development on the pond property won’t threaten the town’s drinking wells. 

 Most of the conversation centered upon the Zone II capture area. Nelson said Zone II is a protective area around public drinking supply wells. It marks the area where if contamination gets into the groundwater, it could potentially impact the drinking water in the town’s wells. 

 Zone II is intentionally conservative. It assumes that wells are pumping at max capacity, with little to no recharge from rain. Being in a Zone II does not automatically mean development will contaminate the wells, Nelson said. 

 Using an updated model from the previously used 1990s map, Nelson found that even though part of the land falls inside the broad Zone II map, most wastewater from future housing there would likely not flow toward Brewster’s wells, especially if septic or wastewater systems are placed strategically.

 Nelson said the model he used is the exact same model that was the basis for much of the Brewster Conservation Trust’s supplemental information in their town meeting petitions seeking to prevent development on the pond parcel. 

 In an effort to simplify the complexities of the science behind the hydrology report, Select Board Chair Mary Chaffee sought to reframe the conversation and help define terms. 

 The town has five drinking water wells, each protected by a Zone I area where development is prohibited, she said. 

 “The Zone II area is a state of Massachusetts-approved line on a map marking the likely capture area where water in the ground is being drawn down into our well and being pumped,” she said. 

 Nelson said it is specifically rainwater that falls and soaks into the ground, moves to the well and is being pumped at the maximum permitted rate. A Zone II is determined over a course of 180 days, maxing out the size of the cone of depression that surrounds the well, which is where water is drawn down into the pump. 

 In the specific case of Brewster’s Zone II area, there is a groundwater divide along Route 137, where water on the east flows toward Pleasant Bay and on the west flows toward Long Pond. 

 Concerns are that housing development on the pond property would lead to sewage and contaminants that could pollute the town’s drinking water. 

 Nelson said that is unlikely due to three reasons: Existing water quality is strong, nitrogen levels in wells are very low and current development in surrounding areas hasn’t significantly harmed wells. He also said the proposed housing could be designed to avoid groundwater contamination risks. 

 Select Board Member Pete Dahl questioned the likelihood of potential Per- and polyfluoroalkyl substances, or PFAS, entering the area. Nelson said the key to forecasting potential PFAS contamination is looking at the nitrogen levels, since that is a common sign that septic waste is entering groundwater.

 “Seeing very low nitrogen means that there’s very limited septic system effluent making its way to these drinking water wells,” he said. “If you’re only seeing very low levels of nitrogen, it’s an indicator that the other contaminants really aren’t there.” 

 After initial discussions with Nelson, the select board reiterated that the findings don’t automatically mean housing will be built on the property. Although drinking water may not be a barrier, there is still more information needed from the feasibility study before use of the land for housing will go back to residents at town meeting. 

 The science presented Monday suggested that building some housing on the Sea Camps Pond parcel may be possible without endangering Brewster’s drinking water, as long as wastewater is properly located and managed — but more study is still required before any final decision.

 “The findings from the analysis is that fundamentally, there isn’t a risk to our drinking water… in terms of the data that we have available now,” said Town Manager Peter Lombardi. 

 Later in the meeting, the select board unanimously voted to bring an article to town meeting after completion of the Sea Camps pond property housing feasibility study.  

 “There is zero chance of any type of proposed housing initiative without town meeting determination that it should proceed,” said Chaffee.