Green infrastructure: the next chapter in water quality

Evan Pratt Washtenaw County Drain Commissioner

Evan Pratt
Washtenaw County Drain Commissioner

When water pollution control began in the 1970’s, the first target was industry – stopping discharges of chemicals into the waterways.  This was followed by addressing wastewater treatment, then mitigating the impacts of combined sewer overflow (CSO).  Most recently, pollution in stormwater has been targeted, with federal regulations for urbanized areas coming on line in the late 1990s.

People had realized that hard surface development led to flooding, and some of the first steps to regulate runoff also started in the 1970s.  First, management of stormwater addressed runoff rates, through means such as detention ponds, with the goal of maintaining pre-development conditions and preventing flooding.  This philosophy, however, often falls short.  Addressing only the runoff rate does not address total runoff volumes, which also can cause downstream damage.  Further, studies found that detention basins usually did not address runoff water quality.

As a result of the 40 years of work noted above, stormwater runoff from roads is now thought to be the biggest source of pollutants today.  While agriculture is in the news for phosphorous loads, roads bring us urban phosphorous from lawns along with over a dozen other common human toxins such as lead, cadmium, copper, iron, and nickel.  Research shows that if you can handle the first inch of rain running off of roadways, you can manage most of this pollutant load.  This philosophy is one of the key drivers behind Washtenaw County’s Stormwater Design Standards, which focus not only on controlling the rate of runoff, but also the quantity and quality of that runoff.

The goal of the program is to allow stormwater to soak into the ground to the extent possible.  This approach provides many benefits:

  • the developer often can reduce the land required for detention ponds and meet landscape requirements at the same time by using raingardens, bio-swales, and other green infrastructure
  • downstream streams experience less scouring, stream bank damage, and other water quality impacts,
  • cost savings result from the use of green infrastructure to handle stormwater instead of investing money in systems to convey or detain the runoff, and
  • natural environmental systems are used to the largest extent possible to do what they were created to do, such as routing rain into the groundwater table to cool it off and slow it down.

Data from the National Oceanic and Atmospheric Administration (NOAA) indicate that Michigan is experiencing heavier rains than in previously recorded times; rainfall totals and peak intensities are 10+% and 15+% respectively over the past 30 years, even greater over the past 55 years. More rain is falling because more falls when it rains, but the dry periods are longer too.  The use of green infrastructure such as rain gardens, bioswales, and infiltration beds help to absorb this additional rain with moderate investment.  Infiltration under roadways has also proven promising, especially where there is native sand or sand backfill for a utility.

To address these issues, the Washtenaw County Water Resources Commissioner started a robust public comment period in late 2013 prior to implementing the current Stormwater Design Standards in August of 2014 and will soon embark on a follow up opportunity to receive additional feedback on the program to help guide the future.   The Commission is bringing in a stakeholder group in the next couple of weeks to get input on modifications to what was adopted in 2014.  That has been a part of the overall plan all along – to implement based on a stakeholder group that included development consultants, developers, municipal consultants, and municipal officials, then to assume there would be a need for minor tweaks after a year or so of use.   The Commission is working with a user group from the applicant side and the municipal agency side, as the standards are adopted by most of the developing communities in Washtenaw County.

I have been very impressed by the reaction of the development community and the ability of the geotechnical engineering community to implement these design regulations.  Partnership from the geotechnical profession has been the critical foundation allowing  implementation to go as smoothly as possible – we couldn’t do this without firms like G2 offering value and turnkey consulting on infiltration feasibility.  Prudent developers have always performed soils investigations early in the project; now data from these inexpensive investigations deliver information to determine how the site can implement needed infiltration – a real benefit since sites are now required to provide 20 percent more detention if they do not infiltrate the first one inch.  At the end of the day, the sooner the owner knows about the soils on the site, the fewer surprises they will experience.  Most have learned to get soil samples before site purchase.

Other communities will be moving in this direction in the near future as well.  The Environmental Protection Agency (EPA) has provided guidance on requiring infiltration in the context of stream channel protection.  In turn the Michigan Department of Environmental Quality (MDEQ) is requiring infiltration for all urbanized areas through their Municipal Separate Storm Sewer System (MS4) permit program which is on a 5-year renewal cycle – Washtenaw was on year 2 of that cycle in 2014-15.  All urban counties and communities – including Kent, Macomb, Livingston, Calhoun, Oakland and Wayne – are already working on revisions to address this approach in their  permitting cycle.

In closing, I see the use of green infrastructure expanding in its role to reduce stormwater runoff.  In fact, we are very encouraged by research documenting the ability of vegetation to transform heavy clay into medium grade soils with absorptive abilities.  The County currently is providing technical support to over 300 rain gardens.  I am planning to take this program to the next step, working with developers to use green infrastructure in place of ponds (as long as it performs) to handle stormwater.  We are currently developing the science to back this approach.

Thoughts? Comments?  Questions?  Check our our website or shoot me an email.

 

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