The constructed wetland at Desert Rain is nearly finished, full of filtration materials, and holding water. After many months of design, permits pending, frustrations, and perseverance (see July 25 blog, Leading the Way to Yes)– watching the water flow into the wetland is a welcome sight. Whole Water Systems president, Morgan Brown, and engineer, Patrick Fitzgerald were at Desert Rain last week to oversee the project. The Living Building Challenge requires that 100% of the water used on the site is produced and collected on site. In addition all wastewater must be processed on site and reused, recycled or evaporated. Patrick said, ‘ what sets this project apart from most others it that wastewater treatment of any kind has not been done within city limits where a public sewer system exists. The design of the system at Desert Rain is pretty much the same system used in other projects that Whole Water Systems has been doing for 20+ years.”
The wetland at Desert Rain will be used as a pre-treatment processor for all the graywater from the sinks, showers, tub, and washing machine. The water will drain to a primary treatment tank, then flow into the first of the two-chamber wetland. Water will spill over the 3′ dam into the second chamber where it will be retained in the wetland filtration process for approximately seven days to maximize the treatment of the water and generate appropriate flows. After treatment it will flow to a 1,000 gallon holding tank located below the wetland. From there is will be pumped to a 5,000 reclaimed water tank to be used for irrigation purposes and to fill an outdoor water feature. The water feature will help dispose of excess, treated graywater via evaporation, during the winter months when the water is not needed for irrigation.
The wetland has approximately 600 square feet of surface area, about 450 square feet is the working area. The system at Desert Rain was originally conceived for full wastewater treatment (blackwater and graywater), essentially for a multi-capacity, 3 home site. Including blackwater in the designs greatly impeded the permitting process. The decision was made to get the graywater approval first. The system design was more challenging due to the storage of the graywater. Storing graywater defines it as Class II with more stringent requirements for the permitting process. Class II Graywater also, cannot contain wastewater from a dishwasher due to organic food particles. Desert Rain is the first graywater system in Oregon to receive state and city approval for treatment and reuse for on-site irrigation.
The excavated, wetland surface area is covered with a geotextile fabric as a base for soil stabilization, filtration, and reinforcement. That layer is then covered with a product called Bentomat, a geosynthetic, clay liner. The Bentomat is woven and unwoven geotextile that encapsulates a layer of sodium bentonite between. The layers are then needle punched to reinforce the mat and minimize shift. When wet, the bentonite expands between the layers to ‘glue’ the fabric together and seal the seams. Patrick Fitzgerald applied loose bentonite between the seams on the dam for additional sealing protection.
The wetland then gets filled with gravel for filtering. Whole Water Systems uses a standard basalt gravel with larger fill on the bottom covered by a 6″ layer of pea gravel. Morgan and Patrick were interested in using local, red cinder for the Desert Rain project. The porous surface area would allow for more bacteria growth – possibly, 50% more. The bacteria is the active purifier in a constructed wetland. More bacteria on the rock surfaces would ultimately make the wetland more efficient. Morgan liked the idea of the red rock for aesthetic reasons also. Since it takes a couple of years for vegetation to cover the rock the cinder color would make a better blend with the environment at Desert Rain. There were some concerns about the possibility of ‘fines’ due to the brittleness of the cinder. Terry Mckernan, with McKernan Enterprises would haul the cinder and distribute the material with a conveyor belt instead of dumping to eliminate impact and dust. The choice was made to try the cinder.
The price of building on the cutting edge: in the end, the cinder rock generated more dust than expected and the material was not acceptable for use in the wetland. The rock was removed from the wetland with a powerful vacuum on a storm water maintenance truck. Trial and error provide good data for future projects. Options were discussed and the tried and true , gravel/pea gravel fill was used instead.
The surface will eventually be covered in vegetation. Rock surface bacteria and root mass on the plants work as filters and purifiers. Ironically’, Morgan said, ‘due to the maximized wicking capabilities, the constructed wetland may be the driest surface area on the property’. Whole Water Systems will work with local, plant expert, Rick Martinson of Wintercreek Restoration in Bend on plant material. Rick will also set up monitoring equipment to collect data on evaporation measurements and inlet/outlet flows. This will be a first data collection project for Whole Water Systems. Morgan was excited about having this information available for future reference. He said, ‘There has not been enough data collection and analysis done in the United States. Europe is more advanced in that regard. The information will help demonstrate how the wetland systems function, the limitations, and the numbers that will help make it easier to get approval for future projects.” With water in the wetland, Desert Rain, once again, is demonstrating the educational aspect of the Living Building Challenge and the process of building to extreme green.