There are many layers to the Water Works project, most evident in the historic remnants that feature in the park and pavilion design. Less evident, but no less important, is an innovative rainwater reuse system being put in place to provide up to one million gallons of rainwater for the site’s irrigation and toilet flushing each year.
This month, I spoke with Jennifer Koehler, Senior Water Resource Engineer for Barr Engineering, a Minneapolis-based firm specializing civil and environmental engineering, water resources engineering, and geotechnical services. The occasion that prompted our call was the installation of a skid inside the future pavilion that includes the equipment that will treat water for toilet flushing. This is only one high-tech component of a much larger system that runs beneath the entire site and connects with adjacent properties, which was made possible through a generous grant from the Mississippi Watershed Management Organization.
The rainwater reuse system is the result of public-private partnerships that provides multiple benefits, including redirecting rainwater from two downtown rooftops that was otherwise being discharged, untreated, directly into the Mississippi River below the falls. Rainwater will also be collected from the new pavilion rooftop and a fourth adjacent property that will allow for disconnection of this rooftop from the City’s combine sewer system. In addition to environmental benefits, this system reduces the demand on the potable water system as this system is expected to provide about 30-40% of the water needed for irrigation and toilets at the site.
“The primary goal of a system like this is to help a site meet its runoff requirements and reduce demand on potable water, but there’s a greater good in that it also offers an opportunity to educate the community about where our water comes from, and that potable water isn’t limitless,” says Jennifer.
In the case of the Water Works system, rainwater will be collected from about 1.85 total acres of rooftop and directed to storage tanks under the park’s Mezzanine lawn. The capacity of these storage tanks is approximately 67,800 gallons, a size that was optimized considering the constraints on the site, the runoff area, and the estimated water demand. There, it undergoes pretreatment, allowing larger debris to settle out before it gets to the reuse system.
From the tanks, there’s a two-pump system – one for landscape irrigation and a second that’s directed inside the pavilion for flushing, where it passes through the treatment skid. Because this water is being used inside – even if only for toilet flushing, and not sinks or drinking fountains – the water is then further treated to meet the plumbing code requirements for reuse projects. These methods include 5-micron filter that removes small particles, as well as a UV (ultraviolet) filter for disinfection. Two additional treatment processes are also available, if needed: Granular activated carbon to remove minute colors and odors, and a 1-micron bag filter system to make sure the system can meet water clarity requirements.
This level of treatment is not expected to be necessary. “There are more and more of these reuse systems that are being implemented, but they’re still fairly new and we’re learning a lot from existing systems – what works well or possibly not so well,” says Jennifer. “At Water Works, we built in these treatment measures to meet code requirements and ensure the public’s safety and comfort with the water on site. We’ll also be studying the system and its outcomes to help inform future reuse projects.”
The site is continuing to take shape above ground, as well. Take a look at a few more pictures of the park and pavilion in progress this month.