Stormwater runoff is a quiet polluter. Rain seems far less menacing than vehicle exhaust, power plant emissions, or improperly managed solid waste. Runoff is also most often dropped into pipes and whisked away to the nearest lake or stream- out of sight, out of mind. However, stormwater runoff brings a suite of pollutants to receiving waters, including phosphorous, which cases algae blooms that disrupt the natural balance, and solids like dirt which are vehicles for heavy metals and oils (those are called “total suspended solids” or TSS).
LHB Civil Engineers are engaged in Next Generation stormwater management practices. Stormwater management is a key component of sustainability efforts; endeavoring to restore our water cycle to pre-settlement conditions. Restoring the water cycle reduces the energy and costs associated with cleaning and delivering drinking water. Minneapolis and St. Paul infrastructure currently send stormwater into the Mississippi River, away from our watershed. Managing and infiltrating stormwater where it falls on site helps recharge our aquifers, and protects the quantity and quality of our drinking water. It also works towards mitigating problems of water pollution, erosion and flooding. For more information about the general importance of managing stormwater check out these websites: Capital Region Watershed District, Environmental Protection Agency, and Metropolitan Council.
Jay Bergman is a long-time leader at LHB and a Professional Engineer with over 30 years of experience in design construction and management of civil engineering projects. In this interview, Jay shares some of his process and specifics on a current LHB stormwater engineering project.
What is your personal approach to stormwater?
My approach is typically designing the most cost effective stormwater conveyance and treatment system that will meet the Minnesota Pollution Control Agency (MPCA) and Watershed’s requirements.
How did you get involved in the Midway Project?
I was first involved with the St. Paul Port Authority (SPPA), the stormwater system client for Midway, through Rick Carter in 1998 on the Maxson Steel project. LHB has been doing the civil engineering on SPPA’s Brown Field projects ever since.
What’s different with this project, what makes it unique/innovative?
This is a brown field site and the client strongly supported cutting edge, high-performance design with a special focus on Next Generation Storm Sewer Treatment. With the client’s collaboration we utilized recycled tire chips to create the underground stormwater retention volume. Typically, underground stormwater retention volume is created by using a combination of large pipes and rock. Tire chips allow for a much larger void space and cost significantly less. Our design utilized the 50% void ratio of the tire chips for the entire retention volume. Our system is designed to retain and infiltrate the 100-year stormwater event, this far exceeds the minimum retention requirements, and this site may never discharge into the St. Paul Stormwater System.
How did you come to the final storm water solution? What other options were considered?
We first evaluated locating the Stormwater Treatment Facility in the lowest area of the site where typically you would place it. This area of the site has contamination soils and would require the bottom of the stormwater facility to be lined so water dose not infiltrate through the contaminates. Instead, we proposed locating the stormwater treatment facility in the highest area of the site where we had clean native granular soils allowing us to infiltrate the stormwater. This final design solution increased the cost of the conveyance pipe and excavation but was more than offset by reducing the volume of the contaminated soils being disposed offsite and utilizing the clean granular soil excavate on site the instead of bringing the granular soil from off site.
What is the importance of continued monitoring and metrics of stormwater management?
The monitoring will allow us to check the water quality of the influent from the site, the effluent after passing through the tire shreds, and the treated effluent after being infiltrated. In addition, we will be able to compare rain events to the depth of the stormwater in the treatment facility. This will allow us compare the infiltration design rates to actual infiltration rates over time.
Above (the pervious pavement) is the Midway Project stormwater management system installed and ready for use. Few who pass by may know what innovation lies below.
Authored by Lindsey Kieffaber, November 1, 2016