HARWICH — The town plans to move forward this fall with an alum treatment in Hinckley's Pond. The 176-acre water body, the largest pond inside the limits of the town, has suffered several algae blooms and fish kills in recent years caused by excessive fertilization of those waters.
Natural Resources Department Director Heinz Proft was before the conservation commission last week with the proposal for an aluminum sulfate/sodium aluminate – alum – application to bind phosphorus which accumulates in the bottom of the pond, creating algae blooms that rob oxygen and lead to fish kills.
The blue/green algae blooms and fish kills have taken place in the pond in recent years, the most recent being two years ago, he said. Several years ago the pond had to be closed to swimmers and pets because conditions were so bad.
Blue/green algae is natural, but when driven by too much nutrients, density levels of the algae can be harmful to humans and animals. The cyanobacteria in such densities can create toxicity levels causing gastroenteritis, liver and kidney problems and even neurotoxicity issues. A routine state Department of Environmental Protection test of the pond on the day it was closed registered counts well in excess of an action level.
While there had been other algae and fish kills in the pond, that event raised concern about the water body's health. Proft said the town provided $30,000 to study conditions in the pond and to identify a means of addressing the problem. Excessive amounts of phosphorus entering the pond providing fertilization was identified as the cause, and the study recommended an alum treatment.
Proft said funding the treatment was an issue. Officials went to the community preservation committee twice seeking funding and got turned down. This past year, he said, Community Preservation Act funds were finally approved. Town meeting voted $650,000 for Hinckley's Pond remediation and improvements, which included $75,000 for better access, viewing platforms, a kiosk and picnic tables off the bike trail which runs past the pond. The alum project was estimated to cost in the $575,000 range.
Proft told the commission the biggest hurdle is using chemical treatment in the pond, but he said the benefit of alum is its safety. He pointed out it is used to clean drinking water ponds.
The plan is to do the application in late fall of this year, when there is little activity in and around the pond, with a deadline of mid December. The application process would take between 10 and 12 days. It could be done in March or June of next year, but apply the treatment during the herring migration will be avoided. Proft said bids have not yet been sought, but a draft request for proposals is being worked on.
Conservation Administrator Amy Usowski said she has worked on the permitting with Proft and it would be a conflict for her to offer recommendations to the commission. She said officials are waiting for a response from the state Natural Heritage and Endangered Species Program on the proposal, which is necessary before the commission can act. A response from the agency usually takes 30 to 60 days, she said.
Usowski said the commission will have to weigh the adverse impacts on the water body, wildlife, herring migration and bordering vegetated wetlands, all outlined in the study. The commission has to determine if this is the most technically appropriate alternative with the least adverse impact, she said, adding that the treatment won't solve the problem permanently due to septic discharges, including phosphorus, moving through groundwater from the approximately 20,000 acres surrounding the pond.
Proft noted the success of the alum treatment in Long Pond, which is connected to Hinckley's Pond by Princess Brook. The treatment was done by Harwich and Brewster and should last 20 years. There has not been a fish kill there since the application, he added.
Commission member John Ketchum questioned the 20-year duration of alum treatment, suggesting it might be only six to 10 years. He also said there could be potential health effects on wildlife, adding there is new technology using small bubbles to provide oxygen to the anoxic sediment in the pond.
Proft said depending on the dosage design for the pond, it can be “very safe.”
Commission member Stanley Pastuszak wanted to know if the treatment would have to be repeated in 20 years. Proft said alum bonds to the phosphorus now in the pond, but phosphorus traveling through groundwater will still enter the pond. There were questions about what is being done to reduce that. Stanley Selko asked why the pond sediment is being treated and not the runoff carrying the nutrients. He urged the town to take steps to address stormwater runoff. He also pointed out the Hinckley's Pond Association is working with landowners around the pond to reduce the use of fertilizers.
Ralph Anderson added that cranberry growers around the pond are holding back water and using less fertilizers on their bogs. He also said he has worked in the town's water sampling program over the past 18 years and those efforts are paying off.
Selko said there was an EPA study done by the University of Vermont that concluded alum application has a short-term adverse impact on benthic organisms, but they come back in greater numbers a few years after the treatment.
The new Cape Cod Tech building project will include changes that eliminate fertilizers from reaching the pond. But there was also discussion about the need to address stormwater runoff along a couple of roadways adjacent to the pond.
“The only way to get rid of it is to get rid of the food source,” commission member Mark Coleman said.
“We'll be adding the medicine to cure the ill,” Proft responded.
The Solar Bee oxygen generating system operating in Skinequit Pond would not be an appropriate solution for the much larger pond. Selko pointed out Hinckley's Pond is designated an FAA landing strip and Solar Bee structures would not be allowed on the pond.
“Our job is to look at the alternatives, it's a green pond now,” Conservation Commission Chairman Brad Chase said. “Alum will clean the pond. It will resolve the problems, but the question is are there better alternatives?”
Commission agreed a response from Natural Heritage is necessary before they can act on the proposal. Chase also said input will be needed from the state Division of Marine Fisheries. The commission agreed to continue the hearing until Nov. 7.
Proft asked if the RFP could be issued with the understanding the project would need the approval of the commission, so the project could get underway later this fall. The commission saw no problem with issuing a RFP.