Background for Nov. 20, 2017 hearing on Nagog Pond

On Nov. 20, 2017, the Acton Board of Selectmen (BoS) will re-open the hearing for Concord’s proposed work to replace and upgrade their water pumping and treatment facility on Nagog Pond. Here’s a link to the hearing notice.

Green Acton’s position is to urge our Board of Selectmen to vote no on Concord’s application to expand their water treatment capacity at Nagog Pond. Here is a link to the complete position and rationale, agreed to with the unanimous consent of Green Acton’s directors.

This website post aims to document the rationale behind Green Acton’s position, and provide information with which you can inform your own position for your letter to the BoS, your individual statement at the hearing, or your vote on the matter if you are an Acton Selectman.

The document that will be discussed on November 20 is the Draft Modified Special Permit Decision

Acton’s water supply comes entirely from a network of shallow wells within the borders of the town, and delivered by the Acton Water District. (Interactive version of the map available here.)

The Town’s water supply is threatened by:

Nagog Pond could be a valuable additional source of water for Acton.

  • Nagog Pond sits on the border of Littleton and Acton, on the “upstream” edge of Acton:
  • Littleton, Acton, and Concord all have the rights to withdraw water from Nagog Pond: here’s a link to the legislative background
  • Only Concord has exercised that right to date, but Littleton and Acton have the right to do so in the future, should the need arise; here’s more:
  • history and analysis from Bob Sekular
  • The need for Acton to withdraw water from Nagog could arise due to any of the threats mentioned above.
  • The original Nagog Pond special use permit decision included language requiring the three towns to engage in regional planning for water, and work to clarify the legal rights under the law of 1884.
  • These terms and conditions aligned well with 2017 Acton Town meeting articles 27 and 28. Here’s a link to more information about the 2017 Acton Water articles
  • The regional planning section of the special use permit has been gutted in the modified version. 

The outflow from Nagog Pond flows across Acton, supporting wetlands and a cold water fishery, and replenishing the aquifer.

Stream flow across Acton

  • In the normal course of events, Nagog Pond flows into Nagog Brook, which joins Nashoba Brook. Nashoba Brook flows across the full width of Acton, joins the Assabet River in West Concord, and then flows toward the sea from there.
  • Nagog Brook is a cold water fishery, the only cold water fishery in Acton. Cold water fisheries are protected, as spelled out in this letter from OARS.
  • Would withdrawing additional water from Nagog Pond reduce the water availability in any of Acton’s wells?
    • There is a surface flow from Nagog Pond to Acton’s Conant I and II wells, which would certainly be diminished.
    • Because Nagog Pond lies uphill from the Conant wells, there might be groundwater flow as well, but the data in existence are not sufficient to test this possibility. Absence of evidence is not evidence of absence.
  • The original Nagog Pond special use permit included a monitoring program to understand better the hydrology of the region downstream from the pond, and to test for deterioration of Acton’s wells following the proposed increase in Concord’s Nagog Pond withdrawals.
  • The entire monitoring program has been deleted from the modified special use permit decision.

Monitoring DeletedConcord’s proposed water treatment plant is designed to treat up to 1.5 million gallons per day (mgd) of water. Is that a lot or a little?

Concord's historical withdrawal

Increased withdrawals could cause the reservoir to fail.

  • The US Geological Survey calculates that the the firm yield — the rate of water withdrawal beyond which the reservoir would fail in a drought — of Nagog Pond is only 0.86 mgd, much less than the design capacity of Concord’s proposed plant (1.5 mgd). Link to USGS Report. Link to Table Reporting Firm Yields.

Historic Water Graph

  • “Reservoir failure” means that the water level is drawn down to the level of the intake pipe. (Here’s a photo of a failed reservoir out west.)
  • The current intake pipe is 12 vertical feet below the spillway.
  • With a withdrawal of 1.5 mgd, Nagog would be the worst reservoir in the Commonwealth as far as ratio of withdrawal to firm yield.
  • At the request of an Acton resident, the lead author of the USGS report performed an additional modeling run in which all the Nagog parameters were kept as before, but the withdrawal rate was increased to 1.5 mgd. Under this set of conditions:
    • The reservoir failed 2,196 days out of the 44 year simulation, or 13.7% of the days.
    • In the simulation, the reservoir failed during the drought of the 1960s, the drought of the 1980s, and the drought of the early 2000s.

The replacement pipe would allow the pond to be drawn down even farther.

  • In addition to replacing the water treatment plant, Concord also plans to replace the aging pipe that carries water out of the pond into the treatment plant.
  • Rather than an exact replacement, the new pipe would extend much farther into the pond, reaching deeper water. (See pages 18 and 19 of Concord’s presentation from January 17, 2017 and the map below.)

Engineering Drawing - Map and Profile

  • According to the engineering drawing below, the longer pipe and new intake system would take water from 210.7 ft. elevation, or 15 ft. below the spillway — under normal conditions.
  • However, the engineering drawings also show that the system is designed to take water from even deeper in the pond. An annotation states that “IN THE EVENT OF A LOW WATER EVENT, SCREEN AND BLIND FLANGE WILL BE REMOVED AND LOCATION INTERCHANGED.” The “blind flange” is at 200.7 ft. elevation. Note the language: “will be removed.” They are planning and designing for an extreme “low water event.”

Engineering Drawing - intake

Sorry this is so blurry; download the original from the DocuShare and zoom in.

  • Here is what Nagog Pond would look like with the water drawn down to 200 ft. — a large puddle in the midst of its former self.

Credit: bathymetry from Appendix 2 of Levin et al. (2011)

Other things that you might not like in the Draft Modified Special Permit Decision:

  • Summary table of the entire set of changes
  • The safeguard that would allow Acton to revoke the permits in the event that Concord fails to adhere to the conditions has been removed (see p. 14, old section 3.3.2).
  • Acton archeology group (Friends of Pine Hawk) is cut out of the section on inspection of the pond floor for archeological features when the pond is dewatered (see p. 15, old section 3.3.4-5B).
  • Protection for nesting bald eagles is weak (see p. 21, new section 3.3.10-8).
  • The last paragraph of the document says that the BoS can undo anything in the agreement at will and without a public hearing (see p. 22, section 3.4.6).
  • The Citizen’s comments from before the hearing was closed may be helpful.

What can you do?

  • Write an email to the Acton Board of Selectmen. Urge them to vote “no” on the modified special use permit, and support your position with any of the points above, or with other issues close to your own heart.
  • Come, and bring your friends, to the hearing:
    7:00pm, Monday, November 20, 2017
    Room 204, Town Hall, 472 Main Street, Acton

Leave a Reply