Assessment Comments

Assessment is based on results of (1) IDNR/UHL biological (REMAP) sampling in 2002, (2) IDNR/UHL biological (Biocriteria) sampling in 1998 & 2004, and (3) results of IDNR/UHL monthly ambient water quality monitoring SE of Norwalk from 2000-02.

Basis for Assessment

[NOTE:  During U.S.  EPA's review of Iowa's 2004 Section 303(d) list, EPA proposed adding-back this segment of North River based on impairment of aquatic life uses suggested by the 2002 biological data generated as part of  IDNR/UHL biological monitoring.   As suggested in Table 2 of their November 2005 decision document, EPA believes that IDNR’s qualitative characterization of the Fish-IBI for the 2002 biological data as “fair” for North River indicates impairment.   In IDNR’s December 19, 2005 response to EPA, an explanation was provided on the differences between IDNR’s qualitative biological condition ratings (e.g., “good”, “fair”, “poor”) and the numeric thresholds of biological impairment used to determine the appropriate use support category.   This explanation emphasized that a qualitative characterization of “fair” does not necessarily equate to an assessment of “impaired,” and that this case does apply to this segment of the North River.   Nonetheless, IDNR noted that more recent biological data generated as part of IDNR/UHL biological monitoring in 2004 do indicate marginal impairment of the biological community.   Thus, even though these data were generated well-beyond the data cutoff deadline for the 2004 cycle (December 2002), IDNR accepted EPA’s suggestion to add-back this reach of the North River (IR Category 5b) based on these more recent data.   Based on these developments, the 2004 assessment was updated in January 2006 as follows:]

SUMMARY:  The Class B(WW) aquatic life 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 1998 and 2004, and (3) results of IDNR/UHL ambient monthly water quality monitoring during the 2000-2002 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 2004 as part of DNR/UHL biological monitoring.   Results of chemical and biological monitoring conducted in 2002, however, suggested that the aquatic life uses were "fully supported/threatened."  The 2002 fish IBI score was 29 (fair) and the BM-IBI score was 56 (good).   Given these results, the aquatic life use support would be assessed as “fully supported / threatened” (=FST), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established for previous Section 305(b) reports.   The results of the 2004 biological assessment--although conducted beyond the data cutoff deadline for the 2004 reporting/listing cycle--however, do suggest slight impairment of the aquatic life uses.   The fish IBI score was 24 (poor) and the BM-IBI score was 65 (good).   Given the result for the FIBI (24=poor), the aquatic life use support would be assessed as “partially supported” (=PS).   The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.  

While results of REMAP sampling in 2002 suggest that the aquatic life uses were “fully supported/threatened,” results of the IDNR/UHL biocriteria sampling in 1998 and 2004 suggest only “partial support” of these uses (see also assessment for the 2002 report).   The 1998 Fish IBI score was 11 (poor) and the BM-IBI score was 60 (good); similarly, the 2004 Fish IBI score was 24 (poor) and the BM-IBI score was 65 (good).   Thus, this stream segment continues to exhibit movement into, and out of, the range of impairment of aquatic life uses.   For purposes of the 2004 305(b) assessment, the results from the 2004 IDNR/UHL biological assessment of this segment were used to assess the aquatic life uses as "partially supported."  

Despite the results of biological monitoring that show aquatic life uses to be only "partially supported," results of chemical monitoring in this river segment continue to show relatively good water quality.   None of the 36 samples collected during the 2000-2002 assessment period at the IDNR monthly ambient station violated Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen; no violations occurred in the nine samples analyzed for pesticides and other toxic organic compounds.  

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