First tenant of the Kentucky Transpark incorporates storm water treatment systems to comply with strict local requirements
At its inception, proponents of the Kentucky TriModal Transpark proclaimed the business park to be a new economic engine for south-central Kentucky. The planned high-tech commerce and business park would offer railway, highway and someday airport access to tenant companies. By making it easier and less expensive to build and ship their products, it would be an attractive draw for manufacturing companies.
The proposed location, off U.S. 31-W and U.S. 68/KY 80 on the north side of Bowling Green, would be perfect—it is within 600 miles of 43% of the country’s population and less than 1 mile from I-65, the busiest north-south corridor. Conservative projections anticipated the 1,500-acre Transpark would bring over 2,500 jobs to the area.
The proposed site also had its drawbacks. It was located on karst terrain, which is made up of soluble bedrock such as limestone and dolomite. Very prevalent in the region, karst formed the Mammoth Cave National Park several miles north of the project site. This unique environment creates multiple surface water pathways directly to groundwater aquifers. Because the clay residual soils are relatively impermeable, natural filtration of runoff is very limited.
Uncontrolled and contaminated storm water flows are capable of eroding the cave’s structural integrity and polluting the community’s groundwater aquifers.
The storm water factor
To gain local support, a major focus of the Transpark’s development became environmental protection, with particular attention paid to the storm water treatment plan. Multiple studies were completed, and standards were set in place by the city-county planning commission and the Intermodal Transportation Authority. The standards exceeded the current local and national regulations. In the end, 22 counties and municipalities supported the development, making it one of the best examples of regional cooperation in the state of Kentucky.
In December 2003, the first tenant of the park was announced. The Cosma International Group of Magna International Inc., a global supplier of technologically advanced automotive systems, components and complete modules, would build its new facility, now known as Bowling Green Metalforming.
This huge industrial project, the largest in the U.S. at the time of construction, included building a 1 million-sq-ft structure on a 150-acre parcel, creating over 80 acres of impervious surface.
The project presented a number of unique storm water-related challenges. Not only is karst terrain prone to sinkholes, flash flooding and unusual hydraulic grades, but the requirements set forth in the design binding elements for tenants of the Transpark were strict.
Civil engineer of record on the project, Richard Tutt, P.E., of American Engineers Inc., was well aware of these challenges as he began to conceptualize and design the site’s storm water quantity and quality plan.
“In this type of environment, it is of utmost importance to capture surface water efficiently, use water-tight systems and discharge to a feature that has the capacity to handle the storm volume,” said Tutt. “If it’s allowed to go where you don’t want it to go, you could face the possibility of multiple dropouts across the site, which can have serious structural and ecological consequences.”
Requirements stated that all storm water runoff from the site had to be treated, with at least 80% of the total suspended solids load removed.
In addition, all storm water needed to be contained onsite and recirculated for landscaping purposes during dry weather with a separate connection to the domestic water system, as needed during extended dry periods.
Storm water solution
Tutt’s research for a suitable storm water treatment system led him to the Vortechs System, a hydrodynamic separator manufactured by Vortechnics Inc., with an extensive third-party testing history. While comparing the Vortechs System with others on the market, he realized its unique characteristics made it the best choice for this site.
First of all, the system was a single structure with a low profile. Separated systems would be more susceptible to differential settlement, so the potential for future connection failures and leakage were a concern for Tutt.
In addition, the expansive site, coupled with only two receiving basins at opposite corners of the development, required minimal storm sewer grade, so the low profile of the units was a benefit.
Tutt then discovered that the system had been installed on similar sites in the region. A recent expansion project at nearby Western Kentucky University used the system to treat runoff before discharging into the Lost River Cave system. Those involved in the project were very pleased with the outcome and highly recommended the system.
“If it was good enough for the Park Service at Mammoth Cave, I felt very comfortable using the same technology on our project,” said Tutt.
Eventually, 10 of the storm water treatment systems were installed on the site. The systems treat the first 11?2 in. of rainfall, with flows through the systems ranging from 5 cfs to 39 cfs. An efficient combination of swirl-concentrator and flow-control technology eliminates turbulence within the system, ensuring proper physical separation and capture of sediment and oils throughout the entire range of flows. Treated storm water discharges from the units into one of two drainage basins located at opposite corners of the site. One basin is approximately 10 acre-ft in size, and the other approximately 26 acre-ft. Both basins were lined with a fusion welded 40-mil HDPE liner and covered with a clay membrane to ensure the water is retained. The basins are fitted with a pump house and intake design, so that the collected water could be recirculated and used as irrigation for the extensive landscaping required in the development.
“This was a very successful project,” said Tutt. “We were able to blend what was required with what was best for the environment. Our design should protect our water resources while at the same time hold up under scrutiny.” Completion of the Magna facility is only the first step in the Transpark’s development. The Technical Training Center recently broke ground, which will house classrooms and labs that will train workers throughout the region as well as the Transpark’s tenants. According to Sandy Jones, Bowling Green’s mayor during the key project stages, “Our design and engineering focus for this industrial park proves that industrial development, good jobs and environmentally prudent practices can coexist and work together well. The Kentucky Trimodal Transpark will become the success we envision.”