Prairie Creek Treatment Train

Grand Lake St. Marys, Ohio

KCI provided concept development, 319 grant application development and administration, environmental documentation, ecological restoration design, engineering studies/ design, construction oversight, and system commissioning and monitoring for the Prairie Creek Treatment Train, an engineered ecosystem which addresses water quality degradation in Grand Lake St. Marys (GLSM), through removal of dissolved and particulate nutrients via a series of linked engineered, biotechnical and natural treatment systems. The firm also assisted with land acquisition support and community relations.

The Prairie Creek Treatment Train (PCTT) addresses nutrient loading into the lake through removal of bed load, and treatment of base flow and storm water discharges. The Prairie Creek watershed drains 2,310 acres of which 95% is in agricultural production. In-situ loading studies from adjacent drainages indicated a total phosphorus loading between 0.32 and 0.63ppm. The PCTT treats flows from the drainage via a series of interlinked treatment systems before discharge into GLSM.

The PCTT consists of a series of four in-line components that jointly result in significant improvements to the quality of water flowing through the system. The innovative application stems from the integration of engineered (MAID), bio-technical (constructed wetlands), and natural systems (riparian wetlands and littoral embayment) as an ‘engineered ecosystem’ to address anthropogenically-induced degradation of a natural system as part of an overall Adaptive Management Framework (Strategic Plan).

The system functions by conveying raw water via an intake, lift station and force main at a maximum rate of 1.3 million gallons per day to the treatment system. The intake is located at the intersection of the free flow of Prairie Creek and the backwater of GLSM. This positioning enables collection of base flow and storm flows from the watershed via Prairie Creek, or the treatment of lake water in the event drought conditions decrease the base flows below the treatment capacity of the system, allowing for full utilization of the treatment capacity of the system.

The treatment systems originate with a Mobile Alum Injection Device (MAID), which regulates the flow of water through the system and integrates the injection of alum or other treatment chemicals to remove particulate and dissolved constituents in advance of the wetlands to maximize the efficiency. Chemical injection and inflow is regulated by a software control system and variable frequency drive pumps. The software is web-enabled, allowing all aspects of the system to be monitored and controlled remotely from any location. Precipitates are collected in two stilling basins for removal and disposal, prior to the water entering the constructed wetlands.

“The elements have been tested in literature and some components have already been put to use in the lake. The unique feature of the treatment train is that these elements have been used in sequence to polish water quality prior to discharge into the main body of the lake.”

Joseph J. Pfeiffer Jr., SPWSVice President, Regional Practice Leader

Joseph J. Pfeiffer Jr., SPWS

An eight-acre constructed wetlands accepts flows from the stilling basins and utilizes a series of seven cells comprised of shallow water and deep water planted with persistent vegetation to biologically process and assimilate phosphorus loadings and allow de-nitrification. The water from the constructed wetland flows into a four-acre riparian wetland that was restored through removal of fill prior to entering an existing three-acre riparian forested wetland along the periphery of the lake. Treated water from the constructed, restored and existing wetland areas then enters a 30-acre embayment area of GLSM that was created by establishing shallow berms, which subrogate the embayment from the main body of the lake allowing natural regeneration of submerged aquatic vegetation, which is the historic condition of the lake. The shallow berms were designed to interact with GLSM; however, the interaction is significantly reduced from its current condition to maintain conditions favorable to initiate and sustain natural ecosystem function. Water returns to the lake through the berms.

The PCTT sets a new standard in the industry by demonstrating how engineered systems can be married with the natural environment to create a cost-effective and sustainable solution that could address a region-wide ecological crisis. It has become the poster child for the restoration of GLSM, providing an example how proper planning, design and execution can be integrated with natural systems to produce recognizable results.

Once the system was commissioned and placed into operation, water quality monitoring of the system documented an average removal efficiency of 31% and 71% for nitrogen and phosphorus respectively, resulting in a complete shift in water quality and trophic state in the embayment and resurgence of naturally generating aquatic vegetation. Scientists regularly observe localized improvements in clarity and aquatic plant growth near restoration areas.