Page 252

              FINAL APPROVED TMDL September 2006
North Fork Kaskaskia River Watershed
Limno-Tech, Inc. Page 17
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 the North Fork Kaskaskia River (IL_OKA-01 and Il_OKA-02) for dissolved
oxygen is appropriate based on IEPA’s guidelines.
4.2.2 pH
The water quality standard for pH in Illinois waters designated for aquatic life is greater
than or equal to 6.5 SU and less than or equal to 9.0 SU. The aquatic life guideline for
streams indicates impairment if more than 10% of the observations measured in the last
five years are greater than 9.0 SU or less than 6.5 SU. The available data confirm the
listing of the North Fork Kaskaskia River (IL_OKA-01 and Il_OKA-02) for pH is
appropriate based on IEPA’s guidelines.
4.2.3 Manganese
The water quality standard for total manganese in Illinois waters designated as public and
food processing water supplies is 150 ug/l. The public and food processing water supply
guideline for streams indicates impairment if more than 10% of the observations
measured since 2001 exceed 150 ug/L. The water quality standard for manganese in
Illinois waters designated for aquatic life is 1000 ug/l. The aquatic life guideline for
streams indicates impairment if more than 10% of the observations measured in the last
five years exceed 1,000 ug/l. The available data confirm the listing of the North Fork
Kaskaskia River (IL_OKA-01 and Il_OKA-02) for total manganese is appropriate based
on IEPA’s guidelines for the aquatic life use. The data also confirm the listing based on
the public and food processing water supply use; however, it should be noted that the sole
public water intake on the North Fork Kaskaskia River was discontinued July 31, 2006.
4.2.4 Iron
The water quality standard for dissolved iron in Illinois waters designated as public and
food processing water supplies is 300 ug/l. The public and food processing water supply
guideline for streams indicates impairment if more than 10% of the observations
measured since 2001 exceed 300 ug/L. The water quality standard for iron in Illinois
waters designated for aquatic life is 1000 ug/l. The aquatic life guideline for streams
indicates impairment if more than 10% of the observations measured in the last five years
exceed 1,000 ug/l. The available data confirm the listing of the North Fork Kaskaskia
River (IL_OKA-01 and Il_OKA-02) for dissolved iron is appropriate based on IEPA’s
guidelines for the aquatic life use. The data also confirm the listing based on the public
and food processing water supply use; however, it should be noted that the sole public
water intake on the North Fork Kaskaskia River was discontinued July 31, 2006.
4.2.5 Fecal Coliform
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