English River IA 02-IOW-671

Assessment Comments

Assessment is based on results from the IDNR ambient monthly water quality monitoring station near Riverside in 2000 and 2001.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses were assessed as "fully supporting / threatened."  Fish consumption uses remain "not assessed."  The assessments of support of beneficial uses are based on results of IDNR ambient monthly+ water quality monitoring conducted on the English River near Riverside during the 2000-2001 biennial period (station 10920001).   EXPLANATION:  None of the 30 samples collected during the 2000-2001 biennial period violated Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen.   Violations did occur, however, for Class B(WW) criteria for toxic metals and for pesticides.   One of the four samples analyzed for toxic metals exceeded the Class B(WW) chronic criterion for lead.   The sample collected on July 5, 2000, contained 50 ppb of lead, thus exceeding the Class B(WW) chronic criterion of 30 ppb.   Similarly, one of the 11 samples analyzed for pesticides exceeded Class B(WW) criteria.   The sample collected on June 15, 2001, contained 0.053 ppb of chlorpyrifos; this level exceeds the Class B(WW) chronic criterion of 0.041 ppb.   According to U.S.  EPA guidelines for Section 305(b) reporting (U.S.  EPA 1997b, page 3-18), these single violation of chronic criteria for lead and chlorpyrifos do not suggest an impairment of aquatic life uses.   Based on DNR's assessment methodology for Section 305(b) reporting, however, these violations suggest that the Class B(WW) aquatic life uses should be assessed as "fully supported/threatened."  The occurrence of a violation of the Class B(WW) chronic criterion for chlorpyrifos during the previous (1998-1999) biennial period (see assessment for the 2000 report above) suggests a potential impairment due to this pesticide.   Additional monitoring should be conducted to better characterize the levels of chlorpyrifos in this river segment and to better determine whether an impairment of aquatic life uses may exist.                                  
                                              
Biological data were collected in 1999, 2000, and 2001 as part of the ambient monitoring project and the DNR/UHL stream biocriteria project.   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 that were collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (F-IBI) and a benthic macroinvertebrate index (BM-IBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2001 Fish IBI score was 33 (fair).   The 1999, 2000, and 2001 BM-IBI scores were 54 (fair), 56 (good), and 51 (fair), respectively.  The aquatic life use support was assessed as fully supporting / threatened (=FST), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established specifically for the 2002 Section 305(b) report.  The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.