5— MODELING APPROACH AND ASSUMPTIONS
There are two East Branch hydraulic structures. The upstream structure is located at the
Crescent Boulevard bridge (River mile 19.4) and maintains the pool of water in the lake in
Churchill Woods Forest Preserve. The downstream dam is located at the Seven Bridges Golf
Course upstream of Prentiss Creek confluence with East Branch (river mile 9.5).
Seven wastewater treatment plants discharge to East Branch. Bloomingdale and Glendale
Heights STPs are located upstream of the lake at Churchill Woods Forest Preserve. Glenbard
STP at Glenbard is located downstream of the lake and upstream of the USGS flow gauge
near Downers Grove (05540160). Downers Grove SD and Woodridge STPs discharge
between the USGS flow gauges near Downers Grove and Bolingbrook (05540250).
Bolingbrook #1 STP and Citizen #2 STP discharge downstream of the Bolingbrook gauge.
Woodridge, Bolingbrook, and Citizen #2 STPs all discharge to Segment GBL 02 which is not
listed for DO impairment. Current permit limits of all wastewater treatment plants for
CBOD5 and ammonia are listed in Table 5-6.
Current CBOD5 and Ammonia-N Permit Limits of the Wastewater Treatment Plants
Bloomingdale-Reeves WRF 20 10 3.0 1.5
Glenbard WW Auth-Glenbard 20 10 3.0 1.5
Downers Grove SD WTC 20 10 3.0 1.5
Glendale Heights STP 20 10 3.0 1.5
DuPage County Woodridge STP 20 10 3.0 1.5
Bolingbrook STP #1 40 20 3.0 1.5
Citizens Utility Company #2 STP 40 20 3.0 1.5
The modeling for TMDL development involved a two-step process. First, the model was set
up and calibrated using June 24–25, 1997 diel survey data. Second, the calibrated model was
used to develop TMDL allocation scenarios.
QUAL2E was set up to simulate flow, CBOD5, ammonia nitrogen, nitrite nitrogen, nitrate
nitrogen, and DO. The stream cross-section was assumed to be trapezoidal, and hydraulic
input data were estimated based on Reach File version 1 data in BASINS, field
reconnaissance, and drainage areas. The slope of each reach was estimated using contour
lines in USGS 7.5-min quadrangle maps. Literature values (Chow, 1959) and other studies in
the surrounding areas (e.g., USGS, 1996) were used to estimate Manning’s roughness
coefficients. Monthly average discharges of point sources were obtained from June 1997
DMR data and incorporated in the model. Incremental flows were estimated using observed
flow data at the gauges and discharge monitoring data (DMR) for point sources. Model and
observed flows at USGS gauges are shown in Figure 5-3.
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