Institute for Environmental Risk Management

Institute for Urban Environmental
Risk Management

WATER-QUALITY SIMULATION IN SUPPORT OF THE DEVELOPMENT OF AN INTEGRATED STRATEGY TO MEET DISSOLVED OXYGEN STANDARDS FOR THE CHICAGO AREA WATERWAYS

Primary Investigator: Dr. Charles S. Melching

Sponsor: Metropolitan Water Reclamation District of Greater Chicago

Duration: December 2007 – December 2009

Funding Level: $224,606

In early 2003, the Illinois Environmental Protection Agency (IEPA) initiated an Use Attainability Analysis (UAA) for the Chicago Area Waterways (CAWs) with Camp, Dresser & McKee (CDM) as the lead consultant and the Metropolitan Water Reclamation District of Greater Chicago (District) promising to provide data and modeling support for the UAA process. As a result of the UAA process a number of water-quality problems were identified in the CAWs. Through March 2004, the UAA had done an evaluation of water-quality problems and potential use classifications in the Upper North Shore Channel (UNSC), Lower North Shore Channel, Upper North Branch Chicago River (UNBCR), Lower North Branch Chicago River (LNBCR), Chicago River mainstem, and South Branch Chicago River (SBCR). The evaluation determined that fecal coliforms and dissolved oxygen (DO) are concerns at several locations in these reaches. For mitigation of DO problems the IEPA requested that the District evaluate flow augmentation alternatives for the UNSC; aeration alternatives for the UNSC, UNBCR, LNBCR, and SBCR; and combined sewer overflow (CSO) treatment alternatives for all reaches.

Simulations done by the Institute (TR#18) and by the District Monitoring and Research (M & R) Department and subsequent preliminary design and cost analysis done by AECOM-CTE indicated the following results.

1) Treatment of gravity CSOs would result in little water quality benefit at a large cost, and, thus, such treatment was eliminated as a potential approach to improve DO concentrations in the CAWs.

2) Transfer of aerated (to saturation) effluent from the North Side Water Reclamation Plant (WRP) to the upstream end of the NSC could substantially improve DO oxygen concentrations in the UNSC at a feasible cost, and, thus this is a possible component of an integrated plan to improve DO in the CAWs.

3) Transfer of unaerated flow from the SBCR to the upstream end of the South Fork of the South Branch Chicago River (commonly known as Bubbly Creek) and supplemental aeration of Bubbly Creek could substantially improve DO in Bubbly Creek at a feasible cost, and, thus, this is a possible component of an integrated plan to improve DO in the CAWs.

4) Addition of supplemental aeration along the NBCR, SBCR, and Chicago Sanitary and Ship Canal (CSSC) could substantially improve DO throughout the CAWs at a feasible cost, and, thus, this is a possible component of an integrated plan to improve DO in the CAWs.

After reviewing these results and seeing the potential benefits of flow augmentation and supplemental aeration, the IEPA has requested that the District evaluate integrated strategies to meet DO standards for the CAWs that combine flow augmentation, supplemental aeration, and, perhaps other strategies for DO improvement.

With the exception of the analysis of Bubbly Creek each of the simulation and design and cost analyses were done focusing on only one water-quality management technology—flow augmentation, supplemental aeration, or CSO treatment. However, the simulation results indicated that application of these management technologies can be mutually beneficial. TR#19 found that aeration of the flow transferred to the upstream end of the NSC would increase DO concentrations all the way down to Jackson Boulevard on the SBCR. Thus, the oxygen load required from supplemental aeration on the NBCR and SBCR might be reduced in a joint application of flow augmentation and supplemental aeration relative to the application of supplemental aeration alone. Similarly, TR#19 noted that the DO concentration in Bubbly Creek during dry weather flow was dominated by DO concentrations in the nearby SBCR and CSSC. Thus, if DO concentrations in the SBCR and CSSC were increased, the amount of supplemental aeration in Bubbly Creek may also be reduced. AECOM-CTE suggested that water quality management options to improve DO concentrations in the SBCR may eliminate the need for an aeration station near the mouth of Bubbly Creek. These results indicate the potential for cost savings and system optimization by the integration of water-quality management strategies.

The objective of this study is to provide modeling support to the District and AECOM-CTE in the development of integrated strategies to meet DO standards for the CAWs. In order to achieve this objective, a hydrologic analysis of the CAWs needs to be done to determine representative “wet” and “dry” years for evaluation of the effectiveness of the proposed water quality management strategies. Also a number of other improvements are needed for the model and its input in order to obtain the most reliable evaluation of the proposed water quality management strategies. Finally, sensitivity analysis should be applied to potentially improve the model and provide additional information regarding the performance of the proposed water quality management strategies.

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