GLUMAC - Engineers for a sustainable future

Geoff Winslow, P.E., Portland Senior Associate

Glumac has designed numerous rainwater harvesting/reuse systems, but none as ambitious as the system currently in design for the 14^th and Everett Project in Portland, Oregon. The five-story full block Meier and Frank warehouse is being renovated to provide Class A office space with many green features. Working with GBD Architects, the project is on track to achieve LEED Platinum Certification. The large footprint and relatively small building size make this an ideal project to provide 100% of irrigation and flush water needs for the estimated 500 occupants.

History

Rainwater collection for re-use has been around for centuries and remnants of this ancient Roman and Turkish collection and storage system are still visible today. In the early 1990s, the Texas Development Board published "The Texas Manual on Rainwater Harvesting." This manual is a comprehensive design guide of rainwater harvesting systems in rural areas. The recent green movement has added emphasis to water conservation, increasing interest in rainwater catchment systems and significant progress has been made over the last five years.

Components

Rainwater is collected off of the eco and built up roofs using conventional roof drains and piping. Thirty percent of the total area is routed into a rainwater display in the lobby featuring a rock lined flow-through basin. Water from the basin and the other rain drains is then routed through storm filter located in the building. From there it goes into a 135,000 gallon cistern located under the building. The cistern is larger than the 90,000 gallons calculated to accommodate dry years. Sixty-one percent of all rainfall is collected and reused; leaving 358,600 gallons draining to Portland€™s overtaxed combined sewer system. Over 450,000 gallons a year are diverted from the municipal systems.

A duplex submersible pump controlled by a float switch pumps the recovered rainwater into the day/treatment tank. By utilizing low flow fixtures and drought resistant plants, a 1,600 gallon tank was selected.

Ultra violet light and chlorine injection were both explored for treating the water prior to distribution. A chemical system was ultimately selected for its ability to reduce odors and its lower cost. The system uses a probe to determine the chemical level in the tank and using a side stream approach injects the required amount of chlorine into the tank. Oregon recently added rainwater systems to the plumbing code, allowing the systems to be permitted without filing an appeal as had been required previously.

The day tank also employs several float switches controlling, low and high level alarms, cistern pump operation and make up water for extended droughts. With the over sizing of the cistern, adding domestic water make up is expected to be an extremely rare event.

A duplex booster pump is next in line drawing water from the day tank and routing it through a duplex bag filter. Bag filters were chosen for their large capacity and lower cost. Cartridge filters are a good choice if skilled maintenance people are not available. Recovered rainwater is supplied to the water closets and urinals in conventional copper piping with purple labeling. Irrigation water is separated via a double check valve and routed in purple PVC piping to planters and eco roofs.

Economics

Rainwater systems of this type will need further development before they will be cost effective. The expected installed cost of $100,000 includes the additional costs for the parallel water systems. The annual savings in sewer and water fees amounts to $4,500. Although the system drains to the sewer system, Portland uses the water meter to determine water and sewage fees. The real savings is in reducing the system development costs the City charges for connection to the municipal systems. This can often exceed the cost of the installation, making the system cost effective.

Conclusions

Re-using rainwater can go a long way to reducing overall flow into impacted combined sanitary sewer/storm drain systems. This can help cities such as Portland where sewage is diverted into the river during heavy rainstorms.

The system to be installed in the 14^th and Everett project with its open rainwater run off in the lobby and signage in the restrooms indicating its re-use tells a story and celebrates rainfall. Something we get to do 200 times a year here in the Northwest.