20-0605 v4.0 Project Use of Exception WT-009 Municipal Sewage Treatment for Affordable Housing

QUESTION

The Community Rebuilds Projects at Mill Creek is one of the pilot teams for LBC 4.0 and an Affordable Housing team. We are pursuing full Living Building Certification for this project of 4 single family homes. Our team would like to use Exception WT-009 Municipal Sewage Treatment for Affordable Housing in order to send the leachate from our composting toilets to the local wastewater treatment facility.
The original plan for this project's 'black water' has been to collect our excess leachate then circulate it back through the composing unit if the compost is dry or the leachate levels are too high. As the project progresses, the Community Rebuilds team has a lot of concerns about the time and cost burdens this part of the system places on our low income homeowners when the City of Moab has a brand new wastewater treatment facility that nearly fits ILFI's parameters as a "Sustainable Utility."
Our water model is based on AN SAC and the Bullitt Center's designs. The Bullitt Center sends their leachate to a wastewater treatment facility while AN SAC is able to evaporate all of theirs. While AN SAC and the Projects at Mill Creek use nearly identical equipment, the composting units on our project would be expected to evaporate more water than those at AN SAC. In addition, the manufacturer of the composting units explicitly states that leachate should not be sent back into the units as it can compromise the compost pile.
Both the Bullitt Center and AN SAC spent a lot of time troubleshooting to find a proper water balance with their composting units and leachate tanks. Since Community Rebuilds is not the final owner and operator of our LBC homes, we are uncomfortable with the idea of asking our low income homeowners to experiment this much with the capacity of their systems, especially when it looks like there will be way to much leachate for the composting units to handle.
Furthermore, this recirculating design adds two pumps to the water system in each home just to handle the leachate (one for material going from the composter into the tank and another to pump it back into the composter). We believe that these additional two pumps, on top of the two that are already part of our water system, pose a significant burden to our low income homeowners for little benefit because of their initial cost, ongoing maintenance, and eventual repair and replacement costs. The leachate would require a lot of monitoring and maintenance just to keep it out of the sewer with little direct benefit to the homeowners (unlike the composting toilets and greywater systems). We want our homeowners to feel comfortable with their water systems and continue using these systems for years to come and making it as simple as possible is the best way to promote this.
Finally, the composting units are already connected to the municipal sewer, as was required by code, and any leachate that enters the sewer would travel by gravity (no pumping) to the wastewater treatment plant, which is 2.25 miles from the project site. The brand new facility uses all biological treatment, no chlorine or other red list chemicals, and all of the treated water is either reused in the plant or put into the Colorado River. Water is taken out of the Colorado upstream and downstream of Moab and the low water levels of the river are almost always a concern, making The Colorado the part of our watershed in most need of this treated water. The plant monitors and captures nutrients (nitrogen, phosphorus, and biosolids included) and uses about 0.3 kW per 1000 gallons treated. As a comparison, the two pumps required to circulate the leachate on site would use around 2 kW per 1000 gallons. The wastewater plant is partially run on solar energy and the City of Moab has plans to increase the solar capacity of the facility.
As an affordable housing builder, being able to deliver a home that does not impose a burden on our homeowners is of the upmost importance to us. This project is already pushing regulatory barriers with greywater and composting toilets and we are excited for these components. However, considering how efficient and sustainable our local wastewater treatment plant is, expending additional time, money, and energy to keep out leachate out of the sewer, which may compromise the other equipment in our system, does not seem like the right option for our project. Would using the Exception WT-009 Municipal Sewage Treatment for Affordable Housing work for this situation?

ANSWER

Because the project is substantially treating its own wastewater and diverting all but the leachate from the municipal sewer system by use of composting toilets, and provided that the results of testing meet local health department standards, the project plans to use the compost as fertilizer on site, the project may send the wastewater treatment leachate to the municipal sewer. 

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