21-0915 Excess Non-potable to Sewer

QUESTION:

The project is pursuing full LBC certification however, there are no exemptions under LBC 3.1 that fully address our current situation.

The project includes:

  • Potable Water Demand - 100% supplied from harvested rain (cistern is ~60,000 gallons).
  • Non-Potable Water Demand - 100% supplied from captured and treated wastewater.

It is expected that the project will have more Non-Potable Supply than Non-Potable Demand.

Typically, excess Potable Supply (rain) and Non-Potable Supply (treated wastewater) would be infiltrated onsite. However, shallow groundwater and site-specific soils eliminate the potential for infiltration and groundwater recharge. As such, the project has focused on minimizing excess by:

  • robust cistern storage to reduce frequency of rain overflow
  • maximizing non-potable demand by working with regulators to allow:
    • non-potable supply maintenance spigots on each floor of the building for use of hand watering potted and interior landscapesmaking a pressurized non-potable supply available to neighbors

Stormwater and treated wastewater, that would have been ideally infiltrated, will be metered to the city sewer. Based on these strategies, and the fact that our project is essentially a zero lot-line building on a previously disturbed site in a dense urban city center (confirmed with LFI to be in an L5 transect), our project would qualify I05-E4 4/2010 Transects L5 and L6 - Municipal Stormwater Connection. However, we do not qualify for the I05-E6 3/2015 Municipal Sewage Connection, since the municipal wastewater system does not provide a non-potable supply. The site is only serviced by a combined sewer that sends all effluent to the city wastewater treatment plant ~ 5.6 miles from the site. The city installed infrastructure in 2011 to reduce combined sewer overflow by 94% (https://www.portlandoregon.gov/bes/31030).

Our project does manage and treat all human waste generated onsite with composting toilets. Urine is diverted through waterless fixtures in order to manufacture two types of retail grade fertilizer (registered with the State of Oregon Department of Agriculture), with a small amount of sterile filtrate (essentially water with some minerals) left over. The PAE building is the first office building in the world to turn high strength wastewater into a retail grade fertilizer onsite. Normally, again, the treated graywater and sterile filtrate could be infiltrated, but this is impossible on our site.

The project team would like to advocate for an exemption that allows our project to connect to city sewer infrastructure based on specific urban site conditions and inclusion of exemplary water and waste infrastructure.

In summary, the project:

  • is designed to use water within its rain/reuse carrying capacity for 100% of its water needs,
  • maximizes water conservation with use of composting toilets,
  • maximizes water reuse to meet all non-potable demand,
  • makes non-potable supply available to neighboring properties, and
  • produces retail grade fertilizer, and- measures all discharges (treated wastewater or cistern overflow) to city infrastructure.

Supplemental Information from the Team

In regard to this dialogue post response, there are only two releases to the municipal system, let us know if this does not answer:

  1. This excess sterile filtrate from the urine to fertilizer processing, which will occur on a monthly basis
  2. (infrequent) overflows from our rainwater collection system, per the stormwater exception, the lot line development, and lack of percolation in the soils beneath

The overall amount of sterile filtrate (essentially water with some minerals) from the urine nitrogen recovery is small compared to any stormwater overflow, estimated at 1 gpm over a predicted duration of 24 hours that would occur once a month (the actual frequency and duration will be dependent on the production of urine to the system), resulting in an overall estimated amount of 1440 gallons released to the combined sewer system (again, over 24 hours, and once a month).

The amount of any stormwater released to the combined sewer will be highly dependent on specific circumstances. The system has been designed not only to achieve net zero water, but also included additional tank capacity to handle the ten year storm, worst case, to the pre-development condition. 

ANSWER:

Regarding excess infiltrate, the system as described is deemed to meet the intent of the Imperative and the excess filtrate may be disposed of through the municipal sewer for the following reasons:

  1. the onsite sewage system is designed to minimize water consumption and beneficial use is being made of all of the components that can be beneficially used,
  2. site soils prohibit infiltration of the remainder, and
  3. the timing of the release of anticipated excess would normally not coincide with a combined sewer overflow event and even if it did, the quantity and rate of release would make a negligible contribution

Regarding connection to the municipal stormwater system, the site conditions and measures proposed to minimize overflow events meet the requirements of I05-E4 4/2010 Transects L5 and L6 - Municipal Stormwater Connection.

As indicated in the Dialogue post, discharges to the sewer will need to be metered and documented for the certification audit.

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