Assessment Comments
Assessment based on results of (1) IDNR/UHL ambient monthly water quality monitoring near Riverside from 2002-04 and (2) IDNR/UHL biological monitoring from 2000-2002.
Basis for Assessment
SUMMARY: The Class B(WW) aquatic life uses are assessed (evaluated) as "partially supporting " based on results of both chemical/physical monitoring and biological monitoring. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment. The assessments of support of beneficial uses are based (1) on results of IDNR/UHL ambient monthly-plus water quality monitoring conducted on the English River near Riverside during the 2002-2004 assessment period (station 10920001) and (2) results of IDNR/UHL biological monitoring conducted from 1999-2002.
EXPLANATION: None of the approximately 40 samples collected during the 2002-2004 assessment period violated Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen. Although single violations of Class B(WW) criteria for lead and the pesticide chlorpyrifos occurred during the 2000-2002 assessment period (see assessment developed for the 2004 reporting cycle), none of the 11 samples analyzed for toxic metals, and none of the 18 samples analyzed for chlorpyrifos during the 2002-2004 period violated these Class B(WW) criteria. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-18), one violation of a water quality criterion for a toxic pollutant in an abundant data set (at least 10 samples over at three-year period) does not indicate an impairment of aquatic life uses. Thus, the single violations of Class B(WW) criteria for lead and chlorpyrifos in the previous (2004) assessment cycle do not indicate an impairment of aquatic life uses in this river segment.
Results of biological monitoring suggest that the Class B(WW) uses should be assessed as “partially supported”. Biological data were collected in 2000, 2001, and 2002 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 (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 FIBI score was 33 (fair). The 2000, 2001, and 2002 BMIBI scores were 50 (fair), 53 (fair), 51 (fair), and 42 (fair) respectively. The BMIBI average was 48. 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 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. This assessment is considered evaluated because the drainage area (626 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site passed the FIBI BIC (using the UAV +7) and failed the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size. Therefore, IDNR considers the aquatic life use impairments indicated by these data as “evaluated” assessments that are not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).
The fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river segment.
