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Environmental Challenges
Specific environmental challenges identified during the initial phases of the Bubbly Creek study include (1) stagnant flow conditions, (2) combined sewer overflows, (3) poor sediment quality, (4) poor water quality, and (5) severely degraded habitat and biological integrity. These challenges are described in greater detail below.
(1) Stagnant Flow Conditions — During dry weather, Bubbly Creek is stagnant, except for the occasional movement of water caused by a passing boat or a slight surge from the South Branch. Even after light to moderate rainstorms, flow in Bubbly Creek is not noticeably changed, since most rainfall runoff is captured in the combined sewer system, conveyed for treatment, and released downstream. Because of this short-circuiting effect on drainage, Bubbly Creek functions the majority of the time more like a lake system than a river system. During stagnant periods, severely degraded water quality in Bubbly Creek can be attributed to several factors, including the biochemical interaction between the sediment and the water column, residual water quality from combined sewer overflows, and photosynthetic activity. Levels of dissolved oxygen (DO), which are good indicators of water quality impairment, typically plummet during stagnant periods and often reach zero.
In 2002 and 2003, the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC), which operates RAPS, conducted a demonstration project. The project artificially introduced flows to Bubbly Creek during dry weather by opening a gate at RAPS to allow water to enter the interceptor sewers and be pumped for treatment, thereby establishing a reverse flow in the creek when otherwise it would have been stagnant. It was determined that creation of an artificial flow during dry weather can drastically improve water quality. However, the method used to create artificial flow used in this project cannot be viewed as a long-term solution for the water quality improvements in Bubbly Creek because allowing water to enter interceptor sewers at RAPS requires additional treatment capacity that may not be available in wet weather and entails significant additional operating costs.
(2) Combined Sewer Overflows — During excessively heavy rainfall events, the combined sewer system that drains surface water runoff and sanitary waste by gravity to RAPS can be overwhelmed. Pumps at RAPS are turned on to discharge combined sewer overflow to Bubbly Creek when the capacity of the sewer system is reached to prevent local flooding and basement backup within the sewershed. When this discharge occurs, the water level in the creek rises, forcing the combined sewer overflow to flow north toward the South Branch of the Chicago River. The water quality in the channel is severely degraded during overflow events as combined sewer overflow contains significant quantities of fresh sewage, street runoff solids, and some floatable materials, as shown in Figure 3. In addition to water quality degradation, riverine habitats are severely eroded by the high channel velocities caused by combined sewer overflow discharges.
The completion of the TARP, which encompasses a system of deep tunnels and reservoirs used to store overflows, will reduce the frequency of combined sewer overflows to Bubbly Creek. In the interim period before TARP is complete, the City of Chicago is implementing a plan to reduce the volume of storm water that enters the combined sewer system by using Best Management Practices (BMPs) citywide. Unfortunately, the TARP project will not eliminate all combined sewer overflows; therefore, pumping from RAPS will continue when intense storms with heavy rainfall hit Chicago.
(3) Sediment Quality — The sediments within the Bubbly Creek channel contain remnants of animal wastes such as carcasses, hair, and offal from the meat processing plants that previously lined its banks. Sediments also contain raw sewage once directly dumped into the channel and solids contained in combined sewer overflows still released by RAPS and other combined sewer overflow outfalls along the channel. The Illinois Environmental Protection Agency (IEPA), U.S. Environmental Protection Agency (USEPA), MWRDGC, and USACE have all collected sediment samples in the past, and results of bulk chemistry analyses are consistent among these sampling events. USACE collected most of the sediment information that is now available in the spring of 2004. Thirteen core samples and five grab samples along the entire length of Bubbly Creek were collected and analyzed. Sediment samples all showed elevated levels of polycyclic aromatic hydrocarbons (PAHs) and heavy metals. Other detected contaminants included semivolatile organic compounds (SVOCs), volatile organic compounds (VOCs), polychlorinated biphenyls (PCBs), oil and grease, and nutrients. Existing sediment quality will be closely examined during the feasibility study, as disposal locations and costs can significantly alter the feasibility of measures that address sediment quality.Additional sediment sampling may be needed, depending on measures considered during the feasibility study. Biochemical reactions within the sediment caused by anaerobic organic decomposition pr oduce methane and hydrogen sulfide bubbles that float to the surface, sometimes carrying clumps of sediment when made buoyant by entrapped gas bubbles, as shown in Figure 4. These clumps eventually sink when entrained gas vents to the atmosphere. Odors produced by the gases and the appearance of these clumps are aesthetically unpleasant.
Figure 4 - Clumps of sediments at water surface
(4) Water Quality — In general, the water quality in the Chicago Waterway system is marginal, but constantly improving. Bubbly Creek is classified for “secondary use” by the Illinois Pollution Control Board (IPCB), which indicates the water is suitable only for limited contact activities such as boating and fishing. IEPA also lists Bubbly Creek as an impaired stream according to Section 303(d) of the Clean Water Act. The listed causes of impairment include high pH, low dissolved oxygen, and high total phosphorus, with combined sewer overflows as the primary source of impairment. Stagnant flow and the biochemical interaction with contaminated sediments also contribute to water quality degradation. Water quality is critical to maintaining high-quality habitats needed to support diverse fish and wildlife populations. Poor water quality severely limits the aquatic habitat and communities within Bubbly Creek.
(5) Habitat and Biological Integrity — Currently, Bubbly Creek no longer maintains hydro-geomorphic function that historically supported a broad diversity of habitats. Thus, this system no longer supports healthy and rich plant and animal communities. The health of the Bubbly Creek ecosystem has severely declined in response to a loss of habitat to support various life stages of aquatic and terrestrial biota and a reduction in habitat quality caused by several factors. The lack of flow diversity caused stagnant water and high velocities from combined sewer overflows have resulted in severe habitat degradation. Poor sediment quality and the biochemical reactions from organic decomposition further degrade the aquatic habitat for fish and macroinvertebrates. Furthermore, poor water quality caused by combined sewer overflows, hydrologic alterations, and reactions with underlying sediments also contribute to habitat degradation. The channel is absent of any aquatic vegetation, natural physical structure, or lotic (or flowing-water) characteristics, which would provide the basis for healthy and diverse riverine communities.
An Index of Biotic Integrity (IBI) was used to assess the status and probable improvements to the riverine ecosystem of Bubbly Creek in lieu of ecological restoration. This IBI may be viewed as a quantitative empirical index for rating the health of a riverine ecosystem on a scale between 0 and 60. A spring fish survey was performed where six species were collected, all consisting of tolerant or non-native species. Based on structural, compositional, and functional components of the fish community surveyed, Bubbly Creek received an IBI score of 10. This score corresponds to a very poor rating and is characterized as an imperiled aquatic ecosystem where biotic integrity has been severely reduced.
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