Effluent ponding and surfacing sewage from the Sherman Adams Building on Mount Washington, N.H., alerted the Mount Washington State Park staff to the failure of its conventional septic system with sand filter and drainfield.
Dennis Tupick, owner of White Mountain Communications Corp. in Randolph, N.H., won the bid and teamed with Bob Tsigonis, P.E., at Lifewater Engineering Co. in Fairbanks, Alaska, to find an answer. “We’re accustomed to manufacturing treatment plants for extreme climates and vastly different summer and winter loading conditions, but designing for winds exceeding 200 miles per hour made me nervous,” says Tsigonis.
Tsigonis visited the site to learn how air intakes and exhausts were handled and how the staff dealt with rime ice. His solution was a treatment plant using cross-flow tubular membranes and a bioreactor inside a 40-foot shipping container. Meanwhile, Tupick hired Mary Ellen Parker, P.E., of Stantec, an engineering company in Auburn, N.H., to draw the as-built plans and handle the permitting and plan review submittals.
Once installed, the system performed well, producing effluent meeting the state Department of Environmental Services requirements for surface discharge.
Site conditions
Mount Washington, at 6,288 feet, is the highest peak in the northeastern United States. Winds exceeding hurricane force occur 110 days per year, and blow two-thirds of the day from November to April. The second highest wind ever recorded on the surface of the earth — 231 mph — was recorded there. The sensitive environment is alpine, but the climate is subarctic, averaging 26 feet of snow per year and a temperature of 27 degrees Fahrenheit. Snowstorms happen every month.
System components
Tsigonis and lead mechanical engineer Jason Rowland designed the pre-engineered plant to handle 7,000 gpd. At its heart is an ExtremeSTP treatment plant from Lifewater Engineering. Its major components include:
• Rotating auger inlet screen, IPEC Consultants Ltd., Burnaby, British Columbia.
• Two-compartment welded plastic tank with 1,500-gallon bioreactor and 3,000-gallon surge tank.
• Four Norit X-Flow side-stream tubular membranes from X-Flow North America, Rock-ford, Ill.
• Two-compartment welded plastic tank with 700-gallon anoxic chamber and 600-gallon permeate chamber.
• Process monitoring sensors for pH, dissolved oxygen, and mixed liquor suspended solids, MJK North America Inc., Lake Bluff, Ill.
• UV disinfection unit, Trojan Technologies, London, Ontario.
Other elements of the treatment solution include HDPE pipe with 2-inch insulation from Tricon Piping, Canastota, N.Y., two existing 8,000-gallon concrete septic tanks for temporary storage of overflow and sludge, supervisory control and data acquisition (SCADA) system, and custom-built control panel.
System operation
The summit building houses a weather observatory, living facilities for the park and observatory staffs, visitors center with restrooms and cafeteria, two gift shops and a post office. Each summer, the center greets up to 4,000 tourists per day.
Sewage from the building runs 400 feet through a 4-inch arctic pipe that drops 75 feet to the treatment plant. Inside, a 22-foot-long tank holds the bioreactor and surge tank compartments. Stacked on top of it is a 17-foot-long tank with the anoxic chamber for denitrification and permeate compartment.
A rotating, shaftless auger screen with 1.5-mm openings filters solids from the influent before it is pumped to the anoxic tank. After the sewage mixes with returned mixed liquor from the membranes, the liquid flows to the bioreactor. Its 8-mm ultrafiltration high-flux membranes resemble straws packed inside 10-foot by 3-inch fiberglass pipes mounted in a horizontal loop. “They are called cross-flow membranes because the high velocity passing across their surfaces helps to clean them,” says Tupick.
As the mixed liquor is pumped through the modules, clean water draining from the membranes overflows into the permeate chamber. The suspended solids in the membranes flow into the surge tank. The closed-loop system returns the sludge to the bioreactor, but a sidestream goes to the anoxic tank to mix with the raw sewage.
The thick sludge in the bioreactor and surge tank remains in suspension and has an extended age. During winter, the sludge is stored in the two septic tanks. In summer, AAA Septic in Berlin, N.H., pumps the excess sludge from the bioreactor and septic tanks, which may also receive occasional high surge flows from the plant.
The clean water from the permeate compartment is used for flushing the membranes, mixing chemicals, controlling foam in the bioreactor and surge tank and flushing the inlet screen. Each time the system has a rest period, the computer activates an abbreviated automatic cleaning program. It flushes the membranes with permeate, then adds a little mild hypochlorite solution to the water and flushes again.
Extra permeate in the tank is surface discharged through a 4-inch arctic pipe. The system’s retention time in summer is about 24 hours, and flows average 5,000 gpd. In winter, flows often average 100 to 200 gpd.
Installation
The Lifewater team insulated the container with 4-inch foam sheets covered with plywood and fiberglass reinforced plastic for a white, durable, cleanable interior. The tanks, made of CNC router-cut thermoplastic sheets extrusion-welded together, were filled with water and the system tested. The crew then drained the membranes and winterized them with propylene glycol.
The men installed chemical tanks, a Web camera, pumps, and the control panel in the 15-foot-long equipment room. They added wood framing around the door so that park staff could attach a 4- by 8-foot arctic entry to improve access in winter. Framing around the windows enabled the staff to screw on plywood sheets in case flying ice or debris should break the glass.
To prevent rime ice from blocking the air intakes and exhausts, the men covered them with curved plastic shields. “Sometimes conditions are right for rime ice to grow three feet thick in one night,” says Tsigonis. “Just hitting the plastic with a fist knocks off the crystals, but hurricane force winds will vibrate the plastic and break off the crystals as they form.”
Before shipping the container 4,500 miles across the continent, the men painted the container to match the color of the summit rocks. They applied Loctite sealant, a division of Henkel, to the nuts and bolts and taped or zip-tied anything that could vibrate loose. The container then was loaded and welded to a gooseneck chassis. Only one pipe union came loose on the trip to Tupick’s yard.
Meanwhile, Tupick’s team built a retaining wall 75 feet below the summit building to conceal the container and its power transformer. All goods were transported up the mountain at night when there was no tourist traffic on the narrow road.
Trucks hauled gravel to the site before the men built the form for the 8.5- by 41- by 5-foot-thick concrete slab. “We welded 12 rectangular metal plates horizontally to the top of the rebar, six per side,” Tupick says. “They are embedded flush in the concrete and the container is welded to them so it won’t blow off in the wind.”
The concrete cured for two weeks. “The weather changes second by second, and a dense cloud rolled in just as the heavy crane arrived to set the container,” says Tupick. “We couldn’t see five feet in front of us as we tried to direct the operator. That was the trickiest part of the installation.”
Once the men connected the plug-and-play plant, AAA Septic hauled a load of seed sludge to start the system. The permeate is discharged in large enough doses to minimize ice accumulation. “The water usually runs away before it freezes,” says Tupick. “We also created a depression in the rocks to trap snow, which insulates the pipe and protects it from the wind.”
Maintenance
Lifewater trained the park service employees to operate and maintain the system. When severe weather prevents even the Tucker Sno-Cat from reaching the plant, the staff can operate it remotely using SCADA. The system even turns on a light and the Web camera. The state permit requires weekly sampling. AAA Septic pumps the bioreactor and surge tank as necessary.
