Tisbury develops Lake Tashmoo denitrification plan

The targeted watershed management plan now goes to the state for review.

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Tisbury is sending a targeted water management plan for Lake Tashmoo to the state for review.

Tisbury has a plan to tackle nitrogen levels in Lake Tashmoo, but it still needs state approval.

The Tisbury Select Board unanimously approved on Wednesday, July 26, to accept and send a targeted watershed management plan for Lake Tashmoo, as presented by water resources consultant Scott Horsley, to the state for review.

The plan is designed with steps to maintain and restore Lake Tashmoo’s environment, particularly through nitrogen load reduction, over a 20-year period. Although there are various sources of nitrogen loading in Tashmoo, 75 percent of it comes from septic systems (76 percent from Tisbury, 23 percent from West Tisbury, and 1 percent from Oak Bluffs). The percentage was based on 2010 load numbers from the Massachusetts Estuaries Project (MEP) that showed 9,154 kilograms of nitrogen entered the Tashmoo watershed a year. The MEP threshold for Lake Tashmoo is 6,244 kilograms of nitrogen a year. 

The load amount increased to 9,831 kilograms of nitrogen a year in 2023, which is projected to rise to 10,605 kilograms of nitrogen a year by 2043 if nothing changes — a slight increase from the projected 10,510 kilograms of nitrogen a year by 2043 projected when the data was presented in May

“Things are going to get a little worse before they get better,” Horsley said. “This is what all the towns I’ve worked with on the Cape and Islands [see]. We wait, things are going to get worse.” 

Additionally, Horsley showed a projection of the number of septic systems that are anticipated to be added between 2020 and 2023 and contribute to the nitrogen load in Lake Tashmoo: seven systems in Oak Bluffs, adding 45 kilograms of nitrogen a year; 110 systems in West Tisbury, adding 684 kilograms of nitrogen a year; and 156 systems in Tisbury, adding 296 kilograms of nitrogen a year. Horsley said West Tisbury is anticipated to have a higher load output because it doesn’t have the types of regulations Tisbury has in place. 

Some of the proposed changes in the plan for Tisbury include upgrading septic systems to more innovative and alternative (I/A) systems, to cluster wastewater treatment at the Lake Street Park area, retrofitting stormwater systems at West Spring Street, making a sewer connection in the State Road area (B2 district), and creating a fertigation well, a type of irrigation system, at Mink Meadows. 

Additionally, Horsley pointed out that while some people have Title 5 septic systems in place, which were meant to have a lower environmental impact than regular septic systems, an enhanced I/A system will further decrease the output of nitrogen loads. Depending on the type of enhanced I/A system, it can reduce 28 percent to 81 percent of the loads if it replaces a Title 5 system. Horsley said the I/A systems being proposed for the plan would decrease nitrogen loads by around 70 percent. Upgrading to an I/A system can cost around $45,000 or more. 

Horsley said implementing these plans can reduce a total of 3,587 kilograms of nitrogen a year. Using the same strategy but at an increased rate, the strategy could reduce a total of 4,361 kilograms of nitrogen a year by 2043. 

If the board approved the plan, Horsley said, a finalized version could be sent to the state, and the town could proceed to try acquiring funding for things like upgrades. 

“Ultimately, the town gets what’s called a watershed permit,” he said. Watershed permits allow municipalities to design ways to improve and restore waterways. The state Department of Environmental Protection recently announced regulations meant to reduce nitrogen levels in Cape Cod watersheds, including the usage of watershed permits, although the Island was not included in these regulations. 

“There’s only been one watershed permit that has been issued, and that’s for Pleasant Bay in Cape Cod, to relieve some of the surrounding towns,” Horsley continued. 

Horsley said the presented plan is similar to a watershed management plan he worked on for Wellfleet, which is waiting for state approval.

The board took some time to ask some clarifying questions before giving its approval. 

4 COMMENTS

  1. What is funny and sad is we keep spending money on the same thing. A report from 1980 stated how to solve the nitrogen problem. 40 years later? We love to make reports. Shelfware. Waste of time and resources. And the costs have increased exponentially.

  2. So you mean to tell me that since we have already banned nice middle class families from from anchoring in Tashmoo to enjoy their boats, the majority of which are just for the day, during 8 weekends a year, all under the guise of “protecting the watershed”, we now have it revealed that data from as far back as 2010, that the board has had all this time, actually shows that the true threat to the waters are home owners on land and their own feces? Say it ain’t so!
    ‘Ban the anchoring ban’ is what I say. Bring back the so called falmouth navy and all the people who just wanted a small slice of a vineyard experience without taking the steamship to our island.

    Furthermore, start limiting the over fertilization of all the green lawns that surround the lake. You know the ones that belong to the ultra-rich-summer-only people that couldn’t handle seeing the plebeians with their fiberglass toy yachts come to visit for a few days. I’d be remiss if I didn’t point out that these ultra rich waterfront owners don’t even spend the whole summer in their homes nor rent them out to many visitors.

    And from now on when someone in power says they are “protecting the lake” by pushing around boaters, know that they are just straight lying. They are most likely pushing the agenda and doing the bidding of the ultra wealthy that don’t want to be named by using the guise of “environmental protection”.

    I also want to point out that the most politically liberal of the towns on the island is disproportionately effecting the watershed with their less stringent sceptic system requirements. Way to go West Tis “environmentalists”.

    I also appreciate that the article actually mentions Mink Meadows. Probably the largest single contributor of nitrogen to the Lake and a non environmentally friendly form of seasonal recreation that is no where near as damaging as the boaters who anchor or any other form of recreation for that matter.

    • Right On Bill Simpson!!!
      Foolishness happening on the Tashmoo Pond.
      I’d like to point out not everyone on Tashmoo is ultra wealthy but for sure many are.
      The Tisbury Selectmen were hoodwinked into believing the nitrogen issues with Tashmoo are somehow correlated to the boats anchoring and eel grass. As suggested in this article they were given the wrong information. The water is public and folks do not own their view. Kids and families frolicking’s on sunny weekend days should make folks smile and not want to Ban them. It’s called sharing. I might add has anyone seen how many geese paddle and poop their way around Tashmoo daily. Now there is a load (no pun intended) of nitrogen dropping directly into our Tashmoo. How about we mitigate that and bring back the boats and families.

  3. Decades ago my neighbors and I scuttled the building on the current Montessori School site, at Main and Tashmoo, in V.H., of proposed condominiums. Our environmental concerns back then, were of the unwanted potential impact of such a sizable septic system overflow or leaching downward via Owen Little Way, to our town beach and VHYC bathing waters.

    Now with the looming prospect of the doubling of current Montessori school population on that same site, and two new proposed buildings there, we fear again the possibility of toxic nitrogen run-off onto our too close by, town and VHYC bathing beaches. The current plight of our island ponds and Lake Tashmoo, serve as a precautionary and sadly repetitive tale.

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