Draft Report: Water Demand Still Outstrips Capacity

CHATHAM – A draft report shared with the water and sewer advisory committee last week had some surprising findings: the town will need to develop more drinking water sources and still could need regular water restrictions in order to keep meeting peak summertime demand, even with two recently completed wells near Mill Pond.

The report suggests that in the summertime, the water system would be severely challenged if there is a house fire, and would be stressed if wells need to be taken offline for maintenance or because of pollution.

Weston and Sampson, the town’s water and wastewater consultant, compiled water use and pumpage data from 2020, 2021 and 2022 to try and predict the town’s drinking water needs, Water Program and Discipline Leader Leah Stanton told the committee on Feb. 12. The sample included various demand conditions, with 2020 being a normal year, 2021 a year with greater than normal precipitation, and a very dry year in 2022 when mandatory water restrictions were imposed. Predicting water use isn’t simple, Stanton said.

“It depends on population growth, it depends on conservation, it depends on outdoor watering restrictions,” she said. Determining the peak capacity of the water system means adding up the maximum pumping limits permitted by the state’s Water Management Act, and then essentially cutting that number in half. “What you can withdraw from the sources in the summertime is about 50 to 60 percent of your permitted withdrawal,” Stanton said. That’s because the Cape’s aquifer is shallow and takes time to recharge. “What’s tough in Chatham, and for many communities like you, is that when demands are highest, the groundwater table is the lowest. It’s like a double-whammy,” she said.

Including Wells 10 and 11, the new ones at Mill Pond, all of the wells in town together can produce about 4.1 million gallons per day (mgd) in July. The typical maximum day demand ranges from 3.45 mgd to 4.00 during peak usage.

“Do you have enough water? You don’t really have enough. There’s not a lot of margin in there,” she said. The study also considered what happens if the town’s top-producing well is offline for maintenance or because of some emergency, like the discovery of pollutants. In that scenario, the town’s production is 3.58 mgd.

Committee Chair Jeff Colby noted that his group had not yet seen the draft report. “Are you anticipating making a recommendation to the town as far as additional water supply?” he asked. “I think that’s really the crux behind this report, this study, is do we have enough water supply to meet our needs for Chatham?” Stanton said the presentation was meant as a precursor to more detailed discussions that will ultimately lead to recommendations.

“Basically, if you do not do watering restrictions, you will continue to need more water. When we first started looking at this, I was thinking you probably had enough water supply. Then after we started cranking these numbers, you almost can’t have enough water supply for the way the people in Chatham are using water,” she said. “If you want to be able to continue to sell water the way that you have historically – which is up for discussion with the new regulatory climate – you will need more sources. And for every new source that you put into service, you can expect to get roughly 50 to 60 percent of its permitted withdrawal out of it in the summertime.”

The town had relied on occasional voluntary water restrictions until 2022, when the discovery of per- and polyfluoroalkyl substances (PFAS) forced two wells offline. Mandatory restrictions were put in place, including a ban on outdoor watering, and the reduction in water consumption was sufficient to keep the town’s water system functioning.

Deputy Public Works Director Tom Barr said it’s clear that the water system would be strained if a well went down again. “That’s not counting any other kind of issue that may happen, like a fire,” he said. Industry standards say that storage tanks should be kept at least at 75 percent capacity at all times in case of a fire, which can consume around 600,000 gallons of water at once.

“If you have that happen in the summertime, you’re 100 percent correct,” Stanton said. “We’re going to have a hard time getting our tanks back full again.” It’s evidence that Chatham doesn’t have enough water capacity for peak usage.

“It wasn’t super clear to me until we started kind of looking at this data, if I’m being honest with you,” she said. “The reason why you all have water right now, and the reason you all have enough water, is because you had done the pre-work for the water supply wells. If you did not have wells 10 and 11 right now, things would be looking a lot different.” She said Chatham needs to focus on finding new water sources.

Conservation is key, Barr said, and so is the development of new sources. But providing that the town can find suitable locations for them, it’s more complicated than just digging new wells, he said.

“Most of these areas that we looked at back in like 1996, there were a lot of issues with water quality. Right out of the gate, we’re probably adding iron and manganese removal, which is going to increase the price,” he said. “And then we don’t even know with those areas if there’s the potential of PFAS. We would have to test that beforehand too,” he said.

Responding to a question from Colby, Stanton said the study did consider population changes, but used predictions by the Metropolitan Area Planning Council that show the town’s population declining somewhat in the next few decades. Colby said he’s not sure about those predictions. While the town experienced a spike during the pandemic, “it didn’t really go down as some of us expected. So I think, being conservative, you would build in that [population numbers are] flat, if not growing a little bit,” she said.

Select board member Dean Nicastro said the town hopes to create around 200 new housing units in the next five years. “There is a very ambitious effort to bring younger families, single professional people and working people into Chatham over the next decade,” he said. “I don’t know, but I think it’s something you need to take into account.”

Stanton said an additional 1,000 residents would be expected to consume about 6,500 gallons per day, or .06 mgd.

“It’s nothing,” she said. The real challenge is for Chatham to flatten the drastic seasonal increase in water usage. “The summer impact is huge,” Stanton said. While population growth is important, “I don’t think that’s what’s going to tip your water supply system,” she said.

Committee member Ann Ryan asked how quickly the town could respond, should more contamination be found that takes another well offline.

“We could respond pretty quickly. We did that at Well 5,” Stanton said. A temporary treatment vessel now removes PFAS, allowing the well to be brought online in the summertime, and a permanent treatment system is being completed. If PFAS were discovered in another well during times of peak demand, the town would need to decide whether to shut down the source or operate it while it is out of compliance with water quality standards.

“Water with PFAS is a lot better than...no water,” Stanton said.

“I don’t see relying on conservation,” committee member Debbie Aikman said. “It seems to me we’re going to have to start talking seriously about another well. I don’t see any way around that,” she said.

“We agree,” Stanton replied.

The water and sewer advisory committee was expected to continue its discussion at an upcoming meeting.