4—ASSESSMENT OF WATER QUALITY DATA AND TMDL APPROACH
WDC023080001.ZIP/TAF 4-13
4.6 Dissolved Oxygen
4.6.1 Historic Data/Causes for Listing
Salt Creek segments (GL 03, GLB 01, GLBA, and GL 19) and Addison Creek segments
(GLA02 and GLA04) are listed for DO impairment. Long-term in-stream DO data are
available at the Addison Creek monitoring site (station 05532000) and the Salt Creek
monitoring site (station 05531500). These data are collected during daytime hours nine times
per year. Also, intensive sampling data for summer 1995 are available from USGS (Melching
and Chang, 1996). These data were collected at 28 sites within the Salt Creek Basin including
Salt Creek, Spring Brook, and Addison Creek. The data were collected monthly in April,
June, August, and October, and intensive diurnal data were collected in June and August.
Illinois WQS states that the DO (STORET number 00300) shall not be less than 6.0 mg/L
during at least 16 hours of any 24-hour period, nor less than 5.0 mg/L at any time. Two
STORET parameters (00300 and 00299) represent DO (mg/L). Parameter 00299 specifically
designates measurements of DO by probe in the field. Available data show that the number
of DO measurements by probe (parameter 00299) is significantly larger than the number of
DO measurements in the laboratory (parameter 00300). All IEPA data are currently collected
by probe, and data collected at the long-term ambient stations have been collected by probe
since 1981. All DO data, both parameters 00299 and 00300, were included in the analysis and
the TMDL development.
DO data collected at various locations in Salt Creek and Addison Creek can be divided into two
groups for a clear understanding of the problem. The first group includes samples collected at
regular intervals from the Addison Creek monitoring site (station 05532000, GLA-02) and the Salt
Creek monitoring site (station 05531500, GL-09). These data generally include nine samples per
year at each monitoring site. The second group includes data from two extensive diel data
collection efforts on June 27 and 28, 1995 and August 29 and 30, 1995. DO and other water quality
data were collected at 6-hour intervals from many sites along Salt and Addison Creeks, including
point source effluents. These data provide information on the extent of diurnal variation of DO
along the creeks.
Except for one sample at the Salt Creek station, long-term regular interval samples collected
between 1991 through 1998 (not including the diel samples collected in 1995) do not show any
excursion below the 5 mg/L standard. Long-term DO from the Salt Creek and Addison Creek
sites are presented in Figures 4-12 and 4-13, respectively. The DO data on December 5, 1995, at
the Salt Creek station (Figure 4-12) was potentially recorded erroneously as 3.5 mg/L. Data
collected between 1991 through 1998 show that DO consistently exceeded 10 mg/L from
December through February. Continuous monitoring data (30-min interval) at the Salt Creek
monitoring site at Western Springs (station 05531500), as shown in Figure 4-15, showed DO
was always above the WQS (6 mg/L) between November 01, 2001 and March 31, 2002. There
were two incidences of instrument malfunctioning (perhaps frozen probe) in November -
January. Correspondence with IEPA (Eicken, 2003) indicates that the data at this continuos
monitoring point may be suspect because the area sometimes is a backwater area filled with
debris. DO observations under these conditions should be low. Observed DO at the Addison
Creek site on December 9, 1995, was recorded as 13.75 mg/L. Except for two summer samples
at the Addison Creek site and one sample at the Salt Creek site, DO concentrations were
consistently above 6 mg/L at both Salt Creek and Addison Creek stations. DO concentrations
