| The Boy Scouts had a problem. They operate a primitive campground on Big Munson Island in the Florida Keys. In 2003, during a routine inspection, the Monroe County Health Department questioned what the campers were doing with the soapy water they used to wash dishes and pans.
"The policy of discharging soapy water into the vegetation that we had followed in the past was no longer in compliance," says Philip E. Davis, the camp's facilities director. "We were ordered to find a non-discharge system for our soapy water. A new system designed by a licensed engineer had to be installed by the end of 2004."
The compliance issue arose because Monroe County's comprehensive plan, adopted in 1986 and revised in 1995, imposes obligations on property owners to deal with nutrient loading in storm and wastewater. George Garrett, director of Marine Resources for Monroe County, explains that the comprehensive plan requires all Monroe County facilities—no matter how remote or how long out of compliance—to have an onsite septic system or wastewater treatment system by mid-2010.
The National Council of the Boys Scouts of America (BSA), which owns Big Munson Island, requested support from the property division of BSA, which recommended North American Wetland Engineering (NAWE) of Forest Lake, MN. NAWE had assisted the BSA in 2000 and 2001 on an equally sensitive environmental project at Northern Tier High Adventure Base in Ely, MN.
The national BSA hired NAWE to design a graywater system for Big Munson Island. Scott Wallace, P.E., NAWE's vice president and co-founder, and environmental engineer Kris Evans worked with Davis to create an innovative low-tech system that consists of an intermittent sand filter with subsurface flow wetlands.
Remote and Inaccessible
"The Big Munson Island project is on a remote barrier island with primitive zoning," says Wallace. "There is no road access, no electrical power, and no dock. Everything we used had to be carried from our boat to the island while wading through 3 feet of water. "In the construction world, contractors are accustomed to using power equipment, backhoes, concrete tanks, and other tools and equipment. None of this was an option on Big Munson Island. We knew going into this project that everything we did would require easily obtainable, very light-weight materials.
"Big Munson Island is part of a very sensitive environment," Wallace continues. "The coral reefs around the island are sensitive to runoff nutrients. Anything that gets into the seawater can affect the coral. As a result, the Florida Department of Health has special septic codes—some of the most stringent treatment standards in the US—that apply only to the Florida Keys. The state requires a very high level of treatment for organic matter, and for suspended solids and nitrogen and phosphates. We were charged with creating a design that could meet all of these standards."
System Constraints
Most of the developments in the Keys use chemicals and electrically operated mechanical treatment equipment. On Big Munson Island, because of its remote location and the stringent regulations governing it, such technology was not an option.
The Boy Scouts operate 11 different campsites on Big Munson Island, so a central treatment system wasn't feasible. "We could have built one," Wallace says, "but we couldn't dig in the limestone rock, with less than 3 feet of soil, to install connecting pipes without using heavy construction equipment, and we couldn't get such equipment onto the island. Another option would have been to require campers to carry 5-gallon containers of graywater about a mile to a central treatment facility. We decided that wasn't feasible, either."
Wallace and Evans chose instead to design a small, easily installed modular system for each campsite. They explored the island to identify the 11 best locations for these installations. The materials they specified could be bought off the shelf in a local hardware store. Davis found sources for everything either in the Keys or ordered through a Keys supplier. Crushed brick was the hardest item to find.
System Design
"Part of our original field work was to make a soil boring by hand at each potential site. We bored down to the bedrock," says Wallace. "Our infiltration design was driven by the fact that there had to be at least 2 feet of soil material above either the bedrock or the seasonal high-water mark."
Each installation consists of a four-layer constructed wetland
6 feet wide and 8 feet long. The top layer is 6 inches of
soil and growing plant material. Eight species of plants were
used. They will be monitored to determine which species the
Key deer like to eat and which they leave alone. Davis expects
to replant those that are eaten. Once established, the plants
will require little care.
The second layer is 5 inches of crushed brick, an approved phosphorus-absorbing medium.
The third layer is 1 inch of sand.
The bottom layer is a 30-mil plastic liner laid on the ground surface.
The wetland base is enclosed in a wooden frame of boards 2 inches thick and 8 feet long. The boards come in 12-foot lengths and are cut to an 8-foot length, with the remaining 4 feet used as diagonal reinforcements.
At one end of the wetland is a perforated collection pipe 1 inch in diameter and 4 feet long, with four rows of holes every 3 inches. At the other end of the wetland, a 5-gallon bucket and 55-gallon barrel are installed. Attached to the bucket is a PVC snap-in drain with a coffee filter that collects scraps. The filter must be changed after each use of the system; used filters are carried off the island with other trash.
The sand-filter barrel is divided into four sections. The first section is empty. The second section contains 6 inches of palm fronds. The third section contains 18 inches of sand. The bottom section contains 6 inches of locally collected oyster shells.
The graywater that campers pour into the bucket filters through
the sand-filter barrel into the wetland, where some of the
liquid evaporates. The plants consume the nutrients and most
of the remaining liquid. Any overflow from the wetland goes
into a discharge pipe that leads to a 20-foot-long drain field/infiltration
trench where a bundle of corrugated drainpipe or PVC pipe
distributes the water into the soil.
Depending on the terrain at each of the 11 sites, the trench may be standard (entirely below grade), mound (built entirely above grade within a mound of earth), or filled (partially above and partially below grade) to maintain the required 2-foot vertical separation.
The system functions in both dry and wet weather. Rainwater flows through the wetland and out through the drainfield.
Capacity Variance
"The system is designed to meet the treatment standards and yet be easily taken apart or replaced if it is blown away by a hurricane or swamped by a storm surge," Wallace says. "Our survey of the area included designing for the highest known tides from National Oceanic and Atmospheric Administration charts. We compared daily tides when we were on the island with the NOAA charts to help us relate our elevations to the highest known tides."
Florida regulations say that every wastewater system should
be designed for a minimum capacity of 1,000 gallons. Each
of the Big Munson Island installations is designed to handle
about 4 gallons of gray water per day.
"We did the math and found it would take 250 days to just fill the tank," Wallace says, "so we applied for a variance from the Florida Department of Health. We won the variance at a hearing in August of 2004. Our presentation to the state health department's engineers included the unique situation we faced and our theory behind the design. The state engineers issued us a variance, and told us they thought our system looked good and used appropriate technology for the remote wilderness environment."
A special permit had to be pulled for each of the 11 sites. Then a local contractor, Ryan Construction on Big Pine Key, was hired and a lot of "sweat equity" was used to create the 11 sites. The physical demands of carrying crushed brick, sand, and rocks to the island one bucket at a time prompted some of the construction workers to quit mid-job.
NAWE does not plan to copyright this system and plans to post design drawings and photographs of an operating installation on its Web site, www.nawe-pa.com .
ROSALIE E. LEPOSKY is a writer in Miami, FL, who specializes
in transportation, travel, and development issues.
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- September/October 2005
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