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Wolfeboro prepares to renew permit for effluent disposal site

WOLFEBORO PUBLIC WORKS DIRECTOR DAVE FORD began his tour of the Rapid Infiltration Basin operations on Tuesday morning, Dec. 6, with an informational session on the history, workings and unintended issues that are involved with Wolfeboro’s yearly production of 140 million gallons of treated wastewater. A report on the tour will follow next week. (Elissa Paquette photo) (click for larger version)
December 08, 2011
WOLFEBORO — The Town of Wolfeboro received its five-year state permit to dispose of its treated effluent into Rapid Infiltration Basins in 2007, and that permit is coming up for renewal in 2012.

In preparation for that renewal Public Works Director Dave Ford has been reviewing both data and analyses of the problems encountered at the Rapid Infilatration Basin (RIB) site, including a hydrogeological and geotechnical study of the site just received from S.W. Cole Engineers dated Nov. 30, 2011. On Friday, Dec. 2, he sat down with this reporter and with Allen Kasiewicz, who requested an information briefing on the RIBs, and on Tuesday, Dec. 6 he gave a tour of the RIB site to two Department of Environmental Services (DES) officials, selectmen and Conservation Commission members from both Wolfeboro and Tuftonboro, and interested individuals.

Ford's goal in both presentations was to present clearly the issues that have arisen with the RIBs, what steps the town and its engineers are taking to identify and deal with these issues, and to outline future options. He also wanted to make clear that the town is not violating its current DES permit and has more than adequate capacity to dispose of the town's wastewater safely for the foreseeable future.

For many years the town was storing the treated effluent from its wastewater treatment plant in a lagoon near the Abenaki Ski Area and disposing of it by spraying the water on five fields laid out over a large area. Because winter spraying is not effective, the level in the lagoon had to be lowered by heavy spraying during the other three seasons to make room for effluent collected during the winter. As the amount of effluent increased with town growth, the disposal system reached its capacity and instead of being absorbed into the ground after spraying, some effluent began to run off the saturated ground. This led to a sewer moratorium and pressure to come up with an alternate method of effluent disposal.

Since Wolfeboro lacks a river that would safely dilute the treated effluent, the best option came down to using RIBs, which are essentially huge pits filled with sand designed to disperse the fluid into the water table over a wide area on a suitable permeable site. Unfortunately there are very few suitable sites in Wolfeboro, and the site chosen near the Tuftonboro town line had the best soils available. Voters approved funds to construct three RIBs as well as the pipe connection needed to bring the effluent to the site from the existing lagoon.

The project was completed in March 2009 and, following engineers' recommendation, the RIBs were initially overcharged with 800,000 gallons per day – more than the 600,000 average planned – for 21 days and then cut back to 5,000 gallons per day to allow inspections. What Ford called "issues" began to appear not very long afterward. These issues included seepages higher up on the sloped site than expected, then outflows of sand. Clearly there was a problem and the amount of effluent disposed per day was cut back.

Although the site has a planned series of monitoring wells to keep track of the water table, issues appeared in areas not monitored, so additional wells were installed. Issues kept happening, including a sudden sand flow that threatened to clog 19 Mile Brook.

Eventually the town did two things: it added two smaller RIBs in a different area to spread out the fluid dispersion and commissioned a more thorough hydrogeological and geotechnical study of fluid flows on the site than the contract engineers had performed during the planning stage. What the fluid study found was that the existing water table and flows at the site had been underestimated, meaning that the true disposal capacity of the site was much less than the original estimate of up to 1 million gallons per day. Part of the problem was that there were also layers of silt that shifted water flows and led to the formation of underground streams instead of fluid dispersion, producing breakouts, slope failures and seepage in places.

The net result, Ford explained, is that the RIBs do not have the 600,000 gallons per day capacity they were supposed to have. The safe capacity recommended by the S.W. Çole study is an average of 340,000 gallons per day. This means that, for now, the site can still handle up to 124 million gallons per year of the 140 million gallons that the town needs to dispose.

To dispose of the remaining 16 to 20 million gallons a year the town received a permit to reactivate three of its five spray fields. The pipes for the other two spray fields, which had drained toward Mirror Lake, had already been removed. The amount to be sprayed is a fraction of what used to be sprayed before the RIBs.

In the meantime, the town has been working at reducing the amount of effluent to be disposed, Ford said. Over the past two years a series of projects have identified and eliminated areas in the sewer system where ground water infiltrates and adds to fluid flow going into the wastewater treatment plant. Ford said he plans to continue tracing and eliminating infiltrations and inflows of ground and surface water. Just this year it was discovered that the roof drains at Town Hall were tied into the sewer line rather than the storm drain system; that problem was corrected this summer.

Copies of the studies of the RIB site will be made available at the Wolfeboro Public Library and on the town Web site.

Klumb Environmenta;
Varney Smith
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