Carol L. Hufnagel, P.E., Senior Project Manager

McNamee, Porter and Seeley, 220 Bagley, Suite 710, Detroit, MI 48226

Phone: (313) 964-0790; Fax: (313) 964-6957; E-mail: Hufncaro@mcnamee.com

Vyto P. Kaunelis, P.E., Director of Public Works

Department of the Environment, Wayne County, Michigan

The Rouge National Wet Weather Demonstration Project was initiated in 1992 to identify and implement measures to improve water quality in the Rouge River. The watershed approach included the construction of 10 CSO retention treatment basins to control a portion of the CSO discharges. An evaluation of the effectiveness of these facilities will assist in determining the design criteria for future CSO control projects. The evaluation will help to identify the relative impacts of CSO versus stormwater discharges, to further facilitate evaluation of various projects on a financial basis. Six CSO facilities are currently in operation as of April, 1998, and the remainder will be operational in late 1998. This paper is intended to describe the basin and supporting river monitoring studies and intended outcomes of the evaluation study.

The Rouge River watershed is located in southeast Michigan within Wayne, Oakland and Washtenaw Counties. The City of Detroit and 47 other communities are located wholly or partially within the watershed. Combined sewer systems are prevalent in much of the tributary area. Prior to implementation of the Rouge Project there were approximately 59,300 acres of CSO service area, with 157 outfalls. The initial series of basin and separation projects will control or partially control approximately one half of the service area and 83 of the outfalls.

The Michigan Department of Environmental Quality (MDEQ) established a definition of "adequate treatment" for CSOs as part of the National Pollutant Discharge Elimination System (NPDES) permitting program. Under this definition, CSOs must be eliminated through sewer separation or the construction of basins capable of completely capturing the 1-year/1-hour storm and detaining the 10-year/1-hour storm for 30 minutes. Among CSO communities, the level of required control was a major issue since the estimated costs ranged from roughly $1 billion to $3 billion. Believing that a smaller level of control would meet water quality objectives, the CSO communities contested the resultant proposed NPDES permits.

Negotiations were conducted by a U.S. District Court-appointed monitor in an attempt to identify a less costly first round CSO control program and avoid lengthy litigation over the permit requirements. The negotiations led to a settlement document that was incorporated as a formal modification to the disputed NPDES permits. The revised permits required each permittee, at selected CSOs, to construct and evaluate varying sizes of CSO demonstration basins. A two-year time period was allotted to evaluate the performance of these Phase I CSO control basins. Evaluation findings will establish the level of control needed for the remaining CSOs. These controls will be implemented as Phase II of the project prior to 2005.

It is recognized that other sources are contributing to water quality problems in the river. Even with control basins in place for all CSO outfalls, the Rouge River still will not meet all water quality standards. Pollution sources include stormwater, septic systems, sediment, air deposition and others which need to be controlled to attain desired uses in the river. Thus, evaluation efforts will also need to improve the understanding of relative impacts caused by CSO versus other sources and what water quality can be expected following implementation of CSO control projects.

Primary CSO objectives of the Rouge Project include control of Phase I CSO outfalls and the determination of the level of control for remaining outfalls. A listing of these objectives follows:

The location of CSO projects implemented in Phase I is shown in Figure 1. The Rouge River divides into four branches, including the Lower, Middle, Upper and Main. Following the completion of Phase I facilities, all CSOs on the Upper Main and a section of the Upper Rouge will be controlled. Other segments of the river will be partially controlled.

Design criteria for CSO basin projects are identified in Table 1. A range in sizing criteria was established as part of the permit negotiations. The range of sizing criteria results in basin sizing from 0.06² to 0.29² (in inches over the tributary area). Facilities also incorporate a variety of additional features or variations in compartment sizing and sequencing in an effort to improve their effectiveness.

The primary goal for the basin evaluation study is to identify the level of control required for future control projects. A series of objectives were developed to address this goal. These objectives are identified in Table 2, along with an indication of an initial hypothesis to be tested, and the data which will be collected for addressing the objective.

The data collected as part of the basin monitoring efforts are summarized in Table 3.

River monitoring is intended to address issues regarding the impact of CSO capture and treated basin discharge. It will also show the stormwater impact on sections of the river upstream of the CSO areas. As part of the river monitoring program, weekly monitoring of dissolved oxygen and bacteria in areas where CSO controls are being implemented is being conducted. During CSO discharge events, and during events where CSO basins fill but do not discharge, river monitoring will be conducted to provide a picture of the river response to stormwater-only discharges, and stormwater/treated CSO discharges. Samples will be collected upstream and downstream of the CSO facilities before, during and after the events. Additional efforts will include identification of the total residual chlorine (TRC) plume at instream sites during and following basin discharge.

River monitoring locations are identified in Figure 2. A summary of river sampling and monitoring activities is provided in Table 4.

As part of the basin evaluation study, a peer review committee assembled by the Water Environment Research Foundation (WERF) is participating in a review of the project. The peer review committee is to review the monitoring and study plan for completeness, evaluate its suitability to achieve goals, and to maximize transferability between this project and other CSO control efforts. The peer review committee met initially to review the study plan and again in October, 1997 to review the preliminary data set.

Five CSO basins were placed into operation in 1997 and an additional basin was placed in operation in 1998. The Inkster, Redford, Dearborn Heights and Acacia Park basins have been collecting data. The Bloomfield Village and the Birmingham basins have been addressing various start up issues with respect to accuracy and operation of metering and sampling equipment. Table 5 shows the operational and evaluation status of these basins.

Routine river monitoring has been conducted since May 1, 1997. Significant wet weather events occurred on July 2 - 4 and on September 9 - 11, 1997. Basin and river monitoring was performed for the Inkster and Redford CSO facilities.

Data sets are being compiled for the Inkster, Redford, Dearborn Heights and Acacia Park CSO Basins. The Bloomfield Village and Birmingham basins are operational and are resolving some metering issues.

Samples have been collected for a number of events since the beginning of the monitoring period. The total number of events which have been sampled are provided in Table 6.

Limited data from the evaluation basin monitoring and river monitoring are now available. These data are primarily from the Inkster, Redford and Acacia Park facilities. In addition, river monitoring was conducted during some of the basin overflow events. The river monitoring data from the July and September events are also available.

Sharp transitory DO drops at the start of wet weather events caused by high initial CBOD concentrations in uncontrolled CSOs were not observed downstream of the Redford or Inkster basins discharge points for the July 2, 1997 or the September 10,1997 events. The CBOD concentrations in the basin overflow are now in the range of 5 to 30 mg/L, instead of up to several hundred mg/L previously, and overflows are delayed until more instream flow is available for dilution. Figures 3 and 4 indicate that annual CBOD contributions (lbs/acre) from the untreated Redford CSOs were nearly triple that of upstream stormwater runoff, while the treated Redford CSO basin effluent now contributes about half as much as upstream stormwater runoff.

Gradual sags in DO during wet weather due to the combined effects of low pre-event DO and BOD contributions from stormwater runoff were observed in the vicinity of the Redford basin for the July 2, 1997 event. At the first monitoring location downstream of the basin the DO dropped below 5 mg/L for several hours during the event. However, the DO impairment occurred hours after the treated basin effluent would have passed that monitoring location, so it appears that upstream stormwater inputs were the primary cause of the DO sag. To be certain, continuous DO data downstream of the basin would be need to be monitored.

Dry weather DO impairments in CSO controlled areas are expected to improve over a period of years, but some degree of dry weather impairment is expected to remain. These dry weather impairments in the CSO impacted areas are primarily caused by high sediment oxygen demand (SOD) and low reaeration due to naturally flat river bed slopes. The primary contribution to the SOD problem is the discharge of oxygen-demanding, settleable solids by uncontrolled CSOs; but decaying plant material, stormwater runoff and other unidentified sources also contribute. Results to date have shown a significant reduction in the settleable solids discharged.

The dry weather DO impairments upstream of the CSO impacted areas are expected to continue. However, these impairments are typically less severe than in the CSO impacted areas.

The summer of 1998 will be a primary time frame for evaluating the impacts of CSO basin discharges on instream water quality. During this period, CSO controls will have been completed on localized reaches of the river. Extensive dissolved oxygen and water chemistry monitoring will be performed during the warmer weather months of May through October.

Table 7 summarizes the yearly influent flow and effluent flow frequency, volume and duration for the Inkster, Redford and Acacia Park basins. The monitoring period for the Dearborn Heights Basin began in September of 1997; therefore, the table reflects only seven months of data at the Dearborn Heights Basin. As can be seen in the table where CSO basins are in place most rain events have no discharge to the river.

Samples collected during the evaluation monitoring provide information regarding the range in concentrations. These data provide some insight into the concentrations observed at the influent and effluent of the CSO basins. These data are summarized in Table 8.

Table 9 presents the pollutant load removals at the Inkster, Redford, Dearborn Heights and Acacia Park basins. CSO basins are effectively removing the majority of pollutants which were previously reaching the river.

Bacteria contributions from CSOs to the receiving water have been completely eliminated for many of the wet weather events, because the CSO basins do not overflow for the many smaller events. When CSO basins do overflow, public health is protected by the disinfection that occurs in the basins. In 1997 the bacteria levels in the effluent of the Inkster, Redford and Acacia Park Basins have been controlled. That is, the event geometric mean concentrations have consistently fallen below the Michigan Department of Environmental Quality permit limits of 400 colony forming units (cfu) per 100 milliliters. Limit is defined as the numerical value established in the NPDES permit that must be met before there is a violation. There were no effluent events at the Dearborn Heights basin in 1997.

Data are currently being compiled to identify the level of control required for future facilities. Included within this data set are event volume, frequency and duration and pollutant concentrations. Data are also being collected at the facilities to compare the efficiency of varying operational modes, to evaluate dewatering and decanting capabilities and to evaluate the effectiveness of disinfection and the presence of residual chlorine.

Routine river monitoring includes continuous DO and temperature measurements and periodic sampling for bacteria. Monitoring for wet weather events includes DO, temperature, and bacteria as well as additional parameters. In addition, during overflow events the river is monitored for total residual chlorine.

Limited data are available through March, 1998. As additional data are collected, they will be evaluated relative to the basin monitoring objectives.

Table 5. Rouge River CSO Detention Projects Operational

Table 8. Quality Concentration Data