Lary Lane Ground Water Treatment Plant

The Town of Exeter groundwater plant was completed in 2015.  Weston and Sampson designed the new pressure filtration facility featuring Greensand PlusTM filter media. The facility provides treatment for the Town of Exeter’s three existing groundwater production wells and one future well for removal of iron, manganese, and arsenic. The town received a $6.3 million loan from the Drinking Water State Revolving Fund administered by the New Hampshire Department of Environmental Services (NHDES) for construction of the plant and water main improvements. The project also includes reactivation of the existing Stadium and Gilman gravel packed water supply wells.  The town received 20% debt forgiveness on the SRF loan resulting in a total cost of $5.08 million dollars for plant design and construction, and well reactivation.

The Lary Lane Groundwater Treatment Plant can treat up to 1.56-million gallons per day (mgd) using three, nine-foot diameter greensand pressure filters. A fourth filter will be installed in the future to treat additional flow, and will raise the facility’s treatment flow rate to 2.06 mgd. The treatment process includes ferric chloride to promote co-precipitation of arsenic, sodium hydroxide for pH adjustment of the treated water and an ortho/polyphosphate blend as a corrosion inhibitor. Sodium hypochlorite is also added for disinfection and oxidation. The plant includes a backwash supply tank and two backwash water decant/recycle tanks in which residuals will be concentrated prior to ultimate disposal.

Additional features of the facility include a bathroom, laboratory area, fully automated SCADA system integrated with the existing surface water treatment plant, site piping, a paved driveway and gravel access road along the perimeter of an emergency residuals lagoon.

The existing Gilman Pump Station was refurbished and receive new exterior finishing to maintain the aesthetic of Gilman Park. The Lary Lane Pump Station was renovated to allow the station to operate more effectively and with newer equipment. A new precast concrete pump station was constructed at the Stadium Well site, including a backup generator, pump and motor, and electrical equipment. All pump stations are outfitted with new instrumentation and controls and integrated with the town’s SCADA system.

The raw water transmission main to the new plant was constructed based on the results of a routing study. The water main connects the Stadium, Gilman and Lary Lane well sites to the new groundwater treatment facility. The project includes installation of a water main via horizontal directional drill methods under the Exeter River and approximately 6,200 linear feet of new pipe.

The construction of the Lary Lane Groundwater Treatment Plant was completed and the went online in 2015.

This article was written by Jeffrey W. McClure, P.E. and Samuel H. Kenney, E.I.T. of Weston & Sampson Engineers, 100 International Drive, Suite 152, Portsmouth. They may be reached at 431-3937.