Joining us are Ali Elhassan, manager of water supply planning, and Brian Davis, senior environmental scientist. Welcome to you both.
On the MPR News end are Michael Olson, who has been fielding questions from people in the “water network” that we’ve built around the series, and me. I direct Ground Level, MPR News’ project on community issues.
Other parts of the country, particularly the Southwest, have done a lot in the realm of using water differently and using it more than once. People are capturing rainwater from rooftops, retaining stormwater to use in irrigation and other ways, encouraging households to reuse gray water from the shower or the laundry and even reclaiming wastewater for use again.
Wichita Falls, Texas, for example, is about to become the first sizable city in the U.S. to run water directly from the wastewater treatment plant to the drinking water plant.
Hi everyone. Thanks for joining!
We have a lot of good question from the Public Insight Network, but everyone here should also feel free to pose a question by entering it in the comment field.
First question: In Minnesota, too, people are expressing increasing interest in the idea of using water more than once before we send it merrily down the Mississippi River. So far, this seems mostly to revolve around the idea of using stormwater instead of just letting it run off the land. As people in the Twin Cities think more and more about the availability of good water, how big is the potential impact of this idea?
There is potential. The volume of stormwater runoff from urban and suburban areas is significant. As the intensity of storms increases (more rainfall in less time), the amount of water that can infiltrate in a given storm is decreased, resulting in more runoff per storm event. So as the climate is changing, the opportunity for stormwater reuse is increasing as well.
What are the biggest stormwater re-use projects either functioning or on the drawing boards?
The Minnesota Twins have a stormwater reuse system at Target Field that captures stormwater from the playing field and lower grandstand, holds it in a 200,000 gallon cistern under the warning track, treats it and then uses the water for ballfield irrigation and washing down the lower grandstand seats. This system reduced city water use by 2 million gallons per year.
The City of Saint Anthony Village captures stormwater from city streets, treats it and then uses it for irrigating the city hall landscape and park, saving about 4.6 million gallons per year.
The City of Centerville captures stormwater from its downtown area in a pond and uses it to irrigate 11 acres of athletic fields, using 7 large irrigation spray guns.
The City of Cottage Grove collects rainwater from about 1 acre of the City Hall roof and uses it to irrigate planting beds throughout the 6.8 acre City Hall site. This has reduced the City’s water use by 570,000 gallons per year.
And the Met Council and the City of Saint Paul are working together on a rainwater harvesting project right in downtown Saint Paul, where we will be providing rainwater from the roof of our Green Line Maintenance Building to the adjacent Lowertown Ballpark for irrigation.
There are many more examples.
Are there incentives for communities to reuse stormwater and conserve water? – PIN member Mary Theresa Downing, Shorewood
Stormwater reuse can reduce potable (drinking) water use. One incentive is that stormwater reuse can help reduce future infrastructure costs. For example, irrigation does not require water treated to drinking water standards. Plants don’t need that. So if stormwater can be used for that purpose, perhaps fewer new wells may need to be drilled in the future as population increases. Some communities have cost-sharing programs for rain gardens and rebates for water efficient appliances, but these are actions at the municipal level--there is not statewide program for conservation and reuse.
When stormwater is collected for reuse, what treatment must be done to extract vehicle oil and antifreeze, and lawn chemicals? - Multiple PIN members, various locations around the state
If vehicle oil and antifreeze are in stormwater, then one should perhaps not reuse it. The cost of treatment may be high. Carbon adsorption might be the best treatment technology for those organic chemicals, and perhaps lawn chemicals as well. But it is not cheap. It comes down to the concentration of those contaminants in the stormwater--this is why it's a good idea to take samples of the water before designing the system. There are no State standards for stormwater treatment in a reuse system.
Some people distinguish between, on one hand, capturing and using rainwater, say, off roofs and, on the other hand, using stormwater that has been collected from city streets and treated. Is it useful to think of these as two separate activities? Are there different water quality concerns, for example?
Yes, there is difference between what are usually termed "rainwater harvesting" and "stormwater reuse." Rainwater harvesting is collecting rainwater from a roof before it touches the ground, and stormwater reuse is collecting stormwater from the ground surface.
Rainwater can contain trace amounts of many of the volatile chemicals that are emitted from internal combustion engines. And of course all water has dissolved carbon dioxide in it, which helps to keep the pH in a range where it is suitable for life. Treatment for bacteria from rooftop birds, squirrels, raccoons, and the like is the most likely concern, followed by zinc and lead from old gutters. Stormwater can have all of the components of rainwater, plus chemicals from automobiles, road salt, pesticides, fertilizers, and anything else that is found on the ground.
Is there any downside to homeowners collecting rainwater runoff from gutters in water barrels and using it in gardens? – PIN member, Minneapolis
There aren't many downsides as long as the use is outdoors, in a garden, from rainbarrels.
But here are some caveats, gained from our experience:
1. Provide an overflow and piping away from the house for when the barrel is filled and rain continues to fall. A 1” rainfall on a 40 ft by 40 ft roof generates almost 1,000 gallons of water, and a rainbarrel holds about 50 gallons.
2. Screen the inlet into the barrel so that mosquitoes cannot breed in the small amount of standing water at the bottom of the barrel.
3. Make sure that the barrel has a stable, strong set of footings. Water is heavy: 50 gallons weighs 415 lb.
In terms of larger projects, does it make sense to store stormwater in the ground for use later?
Yes, a cistern makes sense for larger projects. Underground tanks (cisterns) can hold hundreds or even thousands of gallons--the Target Field cistern (under the outfield warning track) holds 200,000 gallons of water. Above ground storage is an option too. Steel, concrete, plastic, or fiberglass can be used--depending on the site and budget.
Research has shown that urban storm water can contain fecal bacteria with counts up to 1.4 million per 100 ml sample which is much higher than raw sewage at 33,000 per 100 ml. Considering the potential of public health outbreak of disease how is this justified? Yet the Met Council refuses to reuse treated wastewater. Please explain. – PIN member Mark Hayes, Buffalo
You are correct—it is important to understand the source area for stormwater and, if required, treat the water using disinfection. Some reuse systems do this, some do not, and to my knowledge there are no Minnesota Rules regarding water quality for reuse. The Metropolitan Council is placing into operation the East Bethel Wastewater Treatment Plant, which will treat wastewater to even more stringent standards than required, and then infiltrate it below grade, with the idea of making it available for reuse prior to infiltration.
The water from the East Bethel facility could be reused on golf courses, for industrial purposes, or other purposes. The Metropolitan Council is currently studying the potential for treated wastewater reuse in the metro area.
One of the coolest new technologies is controlling the reuse system remotely, using moisture sensors, rain sensors, and water demand sensors to remotely control the system and make it "smart." This allows the efficiency to be maximized, and energy costs to be reduced.
Benefits of a smart system (source: Capitol Region Watershed District)
• Easily modified through programming
• Irrigation will only occur if sufficient rain is not predicted (connects to NOAA)
• Level sensor in cistern can reserve specific quantity for flushing
• System can detect leaks in irrigation or plumbing system (more water savings!)
• Smart system can detect malfunctions and notify via email, text etc.
• Data collection (gallons saved, current tank level etc.) is automated and can be displayed real-time on a “dashboard” at interactive kiosks and websites.
You mentioned that you're studying the potential for using treated wastewater in the Twin Cities. I'm guessing you're not talking about using it for drinking water, a la Wichita Falls, Texas, at least at this point, but what might that entail and when might you start to draw conclusions about what's feasible?
Our wastewater treatment specialists are currently studying the feasibility and potential to reuse treated wastewater for industrial and commercial purposes--at this point, not for drinking (potable) water. But those are good questions for our wastewater group.
Looks like we have time for one more question.
Have you heard of any examples of several neighbors join together and build a common underground plastic or fiber glass tank and reuse water later for lawns? Is this legal? – PIN member Frank Lorenz, Edina
I do not know of legal requirements regarding neighbors banding together for common reuse systems, but I would think it could be done. I like the idea, and significant economies of scale could be realized. In Santa Fe, New Mexico, for example some of the new developments have built-in cistern systems for irrigating common areas. There is a lot of potential for that here in Minnesota.
This was fun! Thanks for the opportunity.
Thank you so much for spending the time. This has been helpful in understanding a piece of the water question in Minnesota. Just as a reminder, the responses people have been seeing from Brian have been the joint efforts of him and Ali Elhassan, both at the Metropolitan Council.