Protecting groundwater in a karst landscape takes education and prevention
There are many factors that can make a city interesting and unique. For Bowling Green, Ky., one unique feature is its topography. The city lies on top of a karst system, which means there is soluble rock, commonly limestone, lying beneath the ground’s surface. As the limestone dissolves away it creates connected features underground like caves, sinkholes, springs, underground rivers and aquifers.
However, while it can be beautiful, there are also unique challenges that come along with living on and managing a karst landscape. This includes the fact that, although it may seem like a built-in sewer system for the city, it’s actually quite different from the average underground sewage system. Since it is all natural, it is difficult to know how large it is, what kind of shape it is in or its carrying capacity.
Leslie North, Western Kentucky University assistant professor, explained that Bowling Green has “the potential for cave and sinkhole development, along with many underground rivers that are integrated into the stormwater system. This is done through the use of hundreds of injection wells that drain rainwater into the subsurface. These can sometimes allow pollutants to enter the groundwater system.” Suspended solids can be one of the most widespread pollutants affecting the sewer system as well, normally coming from construction and post-construction sites.
The landscape itself is particularly susceptible to degradation from human activity. “These landscapes have a lot of connectivity between the surface and subsurface. Thus, any pollution that occurs on the surface, like polluted stormwater, can very quickly make its way to groundwater flows underground with little to no natural filtration,” North said. With the underground rivers, these pollutants can be carried long distances and eventually resurface miles away.
How can they manage a karst system?
According to Matt Powell, city of Bowling Green environmental manager, any developments the city makes are determined by topography. A primary focus is building retention and detention basins as well as drilling underground injection stormwater wells.
Using receptors and injection wells, the city attempts to map parts of the karst system to attempt to decipher how they are connected to springs and the strength of their connection. However, since they are limited in their ability to map the karst system, they rely primarily on prevention. Powell added, “Once something’s in there, there’s almost no getting it out.”
Since being issued a municipal separate storm sewer system permit, they are required to conform to certain rules and regulations set forth by the Environmental Protection Agency, which include a minimum of six control issues. These issues are public education; public involvement; monitoring for illicit discharges; strict procedures for construction sites; creating a manual of best management practices to be followed for post-construction; and utilizing proper inhouse practices in their own city projects.
With construction sites being a large conveyor of pollutants, they are inspected regularly. The city will also review permit applications and require an erosion protection and sediment control contractor.
Bowling Green is also classified as groundwater under direct influence — meaning that preparing groundwater for human consumption has higher standards since the groundwater can be the same as the surface water. This requires programs and reviews of systems, extra processes to keep water safe and strengthened filtration requirements.
The city also works closely with Bowling Green municipal utilities to coordinate water quality improvement. This ensures communication at all levels to protect water from surface stormwater pollution as well as potential threats from industrial and construction sites. In order to detect any problems, the city voluntarily performs quarterly sampling at a variety of surface water and groundwater sites.
Quarterly “grab sampling” began in 2004, which involves spot-checking groundwater and surface streams, mostly downstream. At one station they have started continuous monitoring since 2014. These stations are maintained by the students at Western Kentucky University who help record the information so that it will show trends over time.
Monetary fines are levied for those who are not in compliance with rules and regulations. The city will issue notices and warnings first on top of going out to the site and showing them what they need to do and how to improve. Powell believes in treating everyone as if they want to be a part of his team and said that tends to get good results. Regarding negligence or failure to follow the proper BMPs during construction and post-construction, the first fine is $500. For an illicit discharge or damage to city infrastructure, such as a drain, the first fine is $1,000. The fines double for any subsequent compliance issues.
Education and prevention
One of their six control issues was public education, and according to North, “the partnership was serendipitous.” A student intern at the city enhanced the ability of the city of Bowling Green and Western Kentucky University to integrate collaborative research. Since the city has a mandate to educate about stormwater in the region, the school teamed up with them to share their expertise with scientific monitoring and education related to karsts and stormwater.
North and her colleague, Jason Polk, were specifi cally asked to assist in a water education campaign since they had created a similar campaign in Florida. They helped the city create a website — Under Bowling Green — since there was a lack of information publicly available. This website is important because it allows residents and visitorsto get information specific to living in harmony with their natural landscape.
North said, “The project is geared at providing data and educational material that is easily accessible to the public while helping them connect things together. For example, the website features a calendar of events related to water and pollution in the region. They can learn about karst areas and stormwater management in Bowling Green, take a pledge for the behaviors they are willing to change to decrease instances of degradation and download resources for use in classrooms or other personal activities.”
Another benefit of the website is that it allows people to see all the work that is being done by both the city and Western Kentucky University in relation to groundwater and stormwater. Since many individuals do not truly understand or appreciate the sensitivity of the land, North believes the website creates “an avenue through which people can learn about the needs and challenges of protecting groundwater and surface water supplies in karst areas.”
The city staff also conducts presentations on water quality and the impact of contaminants in multiple ways. Two of these are the streamside field days where students learn how to determine stream health and city waste day events, which help to ensure everything above ground is clean.
Preventing and monitoring pollution is crucial for Bowling Green because it is an integral part of keeping its water clean. Partnerships with Western Kentucky University and municipal utilities help not only raise awareness, but also teach preventative measures.
• Spotlight on Bowling Green: Stormwater Management City of Bowling Green, Ky. — Official Municipal Government
• Under Bowling Green www.underbgky.org
Since anything buried in the earth potentially affects the groundwater, use only native earth materials or concrete for the fill. Broken limestone rip-rap or a concrete plug in the bottom of the sinkhole often helps create a stable foundation for the fill. Above that, add clayey sand to form a barrier that will help prevent water from seeping downward through the hole and enlarging it further. Lastly, add sand and top soil, and landscape to surrounding conditions. Additional fill may be necessary over time, but most holes eventually stabilize.