Approaches to restoring urban watersheds
The Northeast Ohio Regional Sewer District recently completed a water-quality study to find a way to meet Clean Water Act (CWA) regulations governing Mill Creek’s drainage basin in Cleveland. In the process, the district discovered there are no simple answers. Rather, the study brought to light a regulatory dilemma, which stems from the need to meet CWA regulations, while balancing community expectations for money invested.
Performed over an 18-month period, the Mill Creek Watershed Study identified two specific uncertainties in the potential for watershed restoration in urban areas: 1) defining all factors that preclude attainment of water-quality standards and 2) understanding the possible level of restoration, given existing pollution. Based on the study, the district believes its non-attainment status is a result of the combined impact of urbanization and pollution sources. The Mill Creek watershed is 17,000 acres and contains an extremely complex sewer system that crosses the boundaries of 11 municipalities and comprises separate, common trench, and combined sewers. Combined sewer overflows, sanitary sewer overflows, residential and industrial stormwater and landfill leachate presently pollute the creek.
The district analyzed fish habitats and aquatic communities in the creek to identify key pollution sources and to help officials understand the status of the polluted creek.
As part of the study, the district:
* developed a hydraulic model of the entire watershed using record years of rainfall data;
* collected data through biological surveys, stream habitat evaluation, water analysis and source identification;
* selected sampling and flow measuring stations in the creek to determine the impacts on receiving water quality;
* produced a water-quality model to analyze the impact of the pollutants discharged into the creek from different sources; and
* developed and screened control alternatives to evaluate their costs and benefits.
While the study revealed biological degradation, it did not pinpoint how or when it occurred. It found peaking flows (20 times to 80 times the dry weather flow), large temperature variations during a 24-hour cycle and extreme siltation during storms that harm equatic wildlife. Water samples also show that over the long term, a combination of sometimes irreversible urbanization factors have resulted in pollution and low fish populations. The study raises concerns that biological standards set forth in regulations may be unrealistically high, and there may be no guaranteed solution to providing watershed restoration within urban environments like Mill Creek. Under current Ohio law, water quality goals are set by “use designations,” established for aquatic life, public water supply use and recreational use. For Mill Creek, the most significant use designations are “warm water habitat” for aquatic life and “primary contact” for recreational use.
Need for change
Based on this study, the district feels many agencies in heavily urbanized areas are asked, through CWA regulations, to spend a considerable amount of capital on storage/treatment facilities that provide uncertain outcomes. While there are good reasons for proceeding with projects to control pollutant sources, there is also a need for regulatory policies that recognize these uncertainties and provide protection to agencies.
The development of recreational criteria to better manage the problems of urban streams can be accomplished by minimizing the length of time bacteria levels are likely to be elevated; assuring bacteriological safety during periods of dry weather; promoting signage to identify high levels of contamination and discourage recreational use when these levels occur – usually after rain; and assessing the importance of land and water environmental factors for attaining biological criteria. Based on the experience in Mill Creek, the district is considering collection and treatment of stormwater in certain areas where recreational activities are common.