Final Approved TMDL: Skillet Fork Watershed
Final Report Page 40 August 2007
number 31616) shall not exceed a geometric mean of 200 per 100ml, nor shall
more than 10% of the samples during any 30 day period exceed 400 per 100
ml in protected waters. Protected waters are defined as waters which, due to
natural characteristics, aesthetic value or environmental significance are
deserving of protection from pathogenic organisms. Protected waters will
meet one or both of the following conditions:
1. Presently support or have the physical characteristics to support primary
contact;
2. Flow through or adjacent to parks or residential areas.
The IEPA guidelines (IEPA, 2006) for identifying fecal coliform as a cause of
impairment in streams state that fecal coliform is a potential cause of impairment of the
primary contact use if the geometric mean of all samples collected during May through
October (minimum five samples) is greater than 200 cfu/100 mL, or if greater than 10%
of all samples exceed 400 cfu/100 mL. The available data support the listing of fecal
coliform as a cause of impairment in Skillet Fork (IL_CA-05, IL_CA-06).
4.2.2 Manganese
The water quality standard for total manganese in Illinois waters designated as public and
food processing water supplies (35 IAC 302.304) states that manganese (total) shall not
exceed 0.15 mg/L. The public and food processing water supply guideline for streams
indicates impairment if more than 10% of the observations measured since 2001 exceed
0.15 mg/L.
The water quality standard for total manganese in Illinois waters designated for aquatic
life (35 IAC 302.208) states that concentrations of manganese (total) shall not exceed 1.0
mg/l except in waters for which mixing is allowed pursuant to Section 302.102. The
aquatic life guideline for streams indicates impairment if more than 10% of the
observations measured in the last five years exceed 1.0 mg/L. The available data confirm
the listing of Skillet Fork (IL_CA-03, IL_CA-06), Brush Creek (IL_CAR-01) and Horse
Creek (IL_CAN-01) for total manganese is appropriate based on IEPA’s guidelines for
the aquatic life use. The data also confirm the listing of Skillet Fork (IL_CA-05) based
on the public and food processing water supply use.
4.2.3 Dissolved oxygen
The water quality standard for dissolved oxygen in Illinois waters designated for aquatic
life (35 IAC 302.206) is that dissolved oxygen 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.
The aquatic life guideline for streams indicates impairment if more than 10% of the
observations measured in the last five years are below 5 mg/L. The available data
confirm the listing of Skillet Fork (IL_CA-03, IL_CA-05, IL_CA-06, IL_CA-09), Brush
Creek (IL_CAR-01), Dums Creek (IL_CAW-04) and Horse Creek (IL_CAN-01) for
dissolved oxygen is appropriate based on IEPA’s guidelines.
