Questions answered about workforce housing septic plans
October 22, 2009
WOLFEBORO — Critics of the sewer design planned for the Harriman Hill workforce housing development raised a number of concerns at the Oct. 6 planning board hearing about the septic plans for the site.
David Doane, manager of Birch Hill Estates, even went so far as to say that the proposed two-inch effluent line "doesn't even come close to making sense." Local landlord Tom Fergus also wondered if it would smell.
A subsequent conversation with Wolfeboro Public Works Director Dave Ford revealed that systems similar to that proposed for Harriman Hill are functioning already in Wolfeboro without problems. They have been constructed to handle the needs of Sewall Road, Christian Ridge, Fairway View Estates and the Kingswood Acres Condominums near the Kingswood Golf Course.
While people may be more familiar with the concept of a gravity fed system, with sewage traveling along a four-inch diameter pipe line into the municipal system, low pressure systems using two-inch diameter pipes, like the one designed by engineer Erin Reardon of Nobis Engineering, the company hired by the ELRHC for the Harriman Hill site, have been in use for 20 to 30 years, according to Ford.
The system, referred to as a STEP system – an acronym for Septic Tank Effluent Pump – is a pressurized system. Solids are pumped from the buildings into individual tanks. Ford explains that the solids settle out in the tank, and there is a filter at the end of the tank to keep solids out of the line, thus only effluent flows through the 2" pipe. There is no need for a leach field to absorb the effluent.
The pipe itself is built to withstand pressure. The joints are glued, and no water is allowed to get out. The individual pumps can handle up to 10 gallons a minute. If anything goes wrong with a unit's pump, an alarm goes off, alerting the occupant and the management, so concerns that the whole system would be affected are unfounded.
Solids are pumped out every two years or so. Ford describes it as " kind of a pretreatment system."
The design makes expansion of a sewer system more cost effective. In the case of the Harriman Hill site, it is a practical choice considering the amount of ledge under the surface. The low pressure system also avoids the problem of infiltration.
Ford says that he has reviewed Reardon's design and made comments and will send it along for further scrutiny by the Department of Environmental Services' waste water review design review group. Nobis Engineering will receive their additional comments and respond to recommendations as part of the approval process.
When asked if Wolfeboro's treatment facility and rapid infiltration basins (RIB) can handle the increased flow of effluent from the development, Ford responded that the Harriman Hill system is approved for up to 24,000 gallons a day, a figure which will apply when it reaches its "ultimate buildout" of 68 units, perhaps 10 years from now.
The town plant currently handles an average of about 400,000 gallons a day. Ford says the addition of the maximum flow allowed from the Harriman Hill neighborhood, bringing it to a "theoretical" 424,000 gallons a day, does not pose a problem.
His department has been finding and fixing leaks in pipes leading to the system to reduce the inflow of groundwater, in order to decrease the amount of water needing treatment, and they will continue to do so.
Ford says the department is in a good position to welcome increased sewer customers. They will increase revenue and share the costs with current users.