Assessment Comments

Assessment is based on results of (1) IDNR/UHL biological (REMAP) sampling in 2002, (2) IDNR/UHL biological (biocriteria) sampling in 2004, (3) IDNR/UHL biological (benthic macroinvertebrate) sampling in 2001, and (4) results of IDNR/UHL monthly ambient water quality monitoring SE of Norwalk from 2002-04.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed (monitored) as "partially supported” based on results of biological monitoring in 2004.   Fish consumption uses are "not assessed" due to the lack of fish contaminant monitoring in this river segment.   The sources of data for this assessment include (1) results of IDNR/UHL biological (REMAP) monitoring in 2002, (2) IDNR/UHL biological (Biocriteria) monitoring in 2004, (3) IDNR/UHL biological (benthic macroinvertebrate) sampling in 2001, and (4) results of IDNR/UHL ambient monthly water quality monitoring during the 2002-2004 assessment period at STORET station 10910002 (formerly station 426058) at the County Road R27 bridge SE of Norwalk.  

EXPLANATION:  The Class B(WW) aquatic life uses were assessed (monitored) as “partially supported” based on results of biological monitoring conducted in 2001, 2002 and 2004 as part of DNR/UHL biocriteria/REMAP/ambient site benthic macroinvertebrate monitoring.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2001 BMIBI score was 26 (poor).   The 2002 REMAP FIBI score was 29 (fair) and the BMIBI score was 56 (good).   The 2004 biocriteria FIBI score was 24 (poor) and the BMIBI score was 65 (good).   The FIBI average (n=2) was 26.5 and the BMIBI average (n=3) was 49.   The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports.  The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51.   It is important to note that the 2001 BMIBI score and site are really not representative (bridge location/slack water) of the reach in general.   However, the FIBI scores were from sites that were representative of the reach.   Thus, this stream segment continues to exhibit movement into, and out of, the range of impairment of aquatic life uses especially the FIBI scores.  

Despite the results of biological monitoring that show aquatic life uses to be only "partially supported," results of chemical/physical monitoring in this river segment continue to show relatively good water quality.   None of the approximately 70 samples collected during the 2000-2002 and the 2002-2004 assessment periods at the IDNR monthly ambient station violated Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen.   Also, no violations occurred in the approximately 20 samples analyzed for toxic metals, pesticides and other toxic organic compounds over the 2000-2004 period.    

Fish consumption uses are "not assessed" due to the lack of fish contaminant monitoring in this stream segment.