Assessment Comments

Assessment is based on results of IDNR/UHL ambient monthly monitoring at Shell Rock, Butler Co., from 2000-02.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses were assessed (monitored) as "fully supported" based on results of IDNR/UHL ambient water quality monitoring.   [This river segment is not designated for Class A (primary contact recreation) uses.]  Fish consumption remain “not assessed” due to the lack of fish contaminant monitoring in this river segment.   The source of data for this assessment is the results of monthly-plus monitoring from January 2000 through December 2002 at the IDNR/UHL ambient station located at the County Road C45 bridge at Shell Rock, Butler Co.  (STORET station 10120001).  

EXPLANATION:  Monitoring at this station from 2000 through 2002 showed no violations of Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 42 samples collected for pesticides in the 9 samples analyzed during this assessment period.   One of the 24 samples, however, had a pH value greater than 9.0 units:  the sample collected on April 12, 2000, had a pH of 9.1 units.   This violation occurred on a day when the level of dissolved oxygen (15.3 mg/l) was relatively high and the percent DO saturation was approximately 120%.   These conditions suggest that the high level of primary productivity resulted in the high level of pH.   Because these violations are more related to natural conditions than to pollution, the occurrence of high levels of pH in this river segment is not seen as a water quality impairment.   Fish consumption uses remain “not assessed” due to lack of recent fish tissue monitoring in this river segment.