Monitoring for CSO Mitigation

Jan. 16, 2013
Storm water control solutions monitoring in Cincinnati

About the author: MaryLynn Lodor is environmental program manager for the Metropolitan Sewer District of Greater Cincinnati. Lodor can be reached at [email protected]. Laith Alfaqih, P.E., is project manager for CH2M HILL. Alfaqih can be reached at [email protected]. Sharon Jean-Baptiste, P.E., is project manager for CH2M HILL. Jean-Baptiste can be reached at [email protected].


The Metropolitan Sewer District of Greater Cincinnati (MSDGC) is among the top five combined sewer overflow (CSO) dischargers in the country, releasing approximately 14 billion gal of overflow during a typical year of rainfall. MSDGC is implementing an integrated, watershed-based approach to reducing CSO volume by evaluating solutions using direct and enabled impact approaches. Direct impact projects are planned, designed and implemented by MSDGC to reduce the storm water flow entering the wastewater system through strategic separation of storm water and natural drainage. 

Enabled Impact Program

Enabled impact projects are similar to direct impact; however, they differ in that they rely on partnerships with public and private entities to implement source control solutions that reduce storm water from entering the combined system. To date, MSDGC has partnered with a diverse group of public and private owners to install several enabled impact projects comprising sustainable infrastructure features such as bioinfiltration basins, bioswales and rain gardens. The estimated annual storm water capture volume of these installed source control solutions is approximately 86 million gal of storm water runoff (based on a typical year of rainfall).

Direct projects source control through strategic separation, detention, stream separation and other sustainable infrastructure techniques that play a lead role in a watershed-based approach. Through partnerships with both public and private entities, however, enabled impact projects can provide additional value and benefits that lead to greater understanding of sustainable infrastructure. This understanding can be leveraged and shared within local service area communities.

The Enabled Impact program is part of the larger MSDGC Project Groundwork effort to improve quality of life through cleaner streams, better protection of public health and enhancements to the communities where residents work, live and play. The program is designed to leverage complementary public or private investments in green infrastructure, either alone or integrated with traditional storm water mitigation approaches, to have more significant impact on the reduction of CSOs in the MSDGC service area, particularly in Lower Mill Creek. 

To date, MSDGC has entered into formal partnerships, through funding agreements or memoranda of understanding, with 13 public and private partners on 22 projects. The list of partners includes the American Red Cross; Christ Hospital; Cincinnati Department of Transportation and Engineering; Cincinnati Museum Center; Cincinnati Park Board; Cincinnati Public Schools; Cincinnati Recreation Commission; Cincinnati State Technical and Community College; Cincinnati Zoo and Botanical Garden; city of Wyoming (Ohio); Civic Garden Center of Greater Cincinnati; University of Cincinnati; and Wyoming School Board/Environmental Commission.

At present, MSDGC funding participation has resulted in approximately 290,000 sq ft of bioinfiltration practices; 168,000 sq ft of vegetative (green) roofs; 155,000 sq ft of porous/pervious paving; 125,000 gal of rainwater storage for reuse; 2,040 ln ft of storm sewer separation; and five large-capacity storm water dry wells. These source control solutions are currently monitored and the data is being analyzed to inform the future designs and operation and maintenance activities within MSDGC’s service area. 

Monitoring of Storm Water Controls

Performance assessment of the installed storm water controls is critical. The program’s monitoring approach encompasses a variety of objectives, including storm water runoff volume reduction, vegetative success, operational/functional issues, maintenance and long-term viability. These objectives lend themselves to both quantitative and qualitative monitoring approaches. 

An MSDGC partnership with the Cincinnati Civic Garden Center, U.S. Environmental Protection Agency (EPA), U.S. Geological Survey (USGS), University of Cincinnati and Cincinnati Parks has resulted in the installation of an elaborate monitoring network that is helping to assess the performance of various storm water controls to solve the CSO problem. 

In one particular installation, MSDGC sought partnership with USGS and EPA, and then utilized emerging sensor technology to monitor the storm water controls. These sensors, located throughout the site, continuously monitor site conditions. A sophisticated system of nodes/routers, servers and cloud-based analyses will deliver data to a Web-based interface. Users of the website will be able to view and download real-time data. 

The St. Francis Court Apartments project is an example of such monitoring. The project includes a two-stage rain garden that is located in MSD’s largest CSO watershed. The upper rain garden covers 3,816 cu ft and receives water from direct precipitation and a 12-in. pipe that drains a parking lot and some forested area, plus any overland flow that makes it down the hill. The lower rain garden covers 3,214 cu ft and receives water from direct precipitation, overland flow and any excess or overflow from the upper rain garden.

Onsite Studies

USGS and EPA are conducting multiple studies at the St. Francis site. One is a soil moisture study in the lower rain garden. This garden was chosen because it contained more engineered sand/soil mixture than the upper one. Additionally, the inflow to the lower garden is controlled by the upper garden, which makes it less “flashy.” USGS installed nine soil moisture nests. Each nest consists of three sensors (CWS655 moisture probes), positioned horizontally at about 0.5 ft, 1 ft and 2 ft below the surface (the deepest sensor is located about 0.2 ft above the geotextile liner). The wired sensors have the advantage of not needing a radio connection to send data, but the ancillary data are not part of this device. The data from each sensor are collected and stored each hour.

The lessons that can be learned from this study involve the efficiency of the soil mixture and grading throughout the garden. Additionally, it will assist in optimizing the location of the inflow pipe to assure even distribution of storm water flow in the garden.

Another monitoring method that MSDGC is conducting to evaluate storm water controls is direct measurement of potential reductions in runoff volume to the combined system. This monitoring evaluation is being conducted by in-system flow monitors placed in combined or storm sewers on or adjacent to several of the storm water control sites. These flow monitors were installed early in the program to provide pre-construction baseline flow data, and this data will be compared with the collected post-construction data. Flow monitors are currently in place at three locations surrounding the Cincinnati State facility: two locations at the Cincinnati Zoo and one location at the Clark Montessori High School site. 

Finally, MSDGC conducts, with assistance from Cincinnati Parks, periodic qualitative evaluations of the different storm water controls. The qualitative evaluation includes site visits, photo documentation, maintenance inspections, aesthetics, wet weather, seasonal and resident/owner issues. MSDGC developed a systematic approach and tool to document these qualitative evaluations for each site. The database is called “Green Storm Water Control Post-Construction Site Evaluation Database.”

A Continued Effort

MSDGC will continue to work with its partners to monitor and evaluate the performance of the implemented storm water controls. Additionally, MSDGC will report the monitoring results and evaluations to the storm water community to inform industry standards for design, construction, and operation and maintenance activities. Furthermore, this data and information will advocate for additional partners to implement such controls on other public or private property to gain the benefits of onsite storm water runoff management.  

This integrated approach of direct and enabled solutions not only yields benefits to reduce inflow into the combined system, but also provides ways to achieve additional community connectivity and site aesthetics. These benefits include preserving ecological systems, creating balance between built and natural environments, and reducing air temperature and energy usage costs. 

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