Assessment Comments
Assessment is based on: (1) results of IDNR/UHL ambient monthly water quality monitoring conducted on the English River near Riverside during the 2004-2006 assessment period (station 10920001) and (2) results of IDNR/UHL biological monitoring conducted from 1999-2002.
Basis for Assessment
[Note: Prior to the current (2008) Section 305(b) cycle, this river segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf) and results of an Use Attainability Analysis completed in 2007, this segment is also now designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supporting" based on results of biological monitoring from 1999-2002. 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 on (1) results of IDNR/UHL ambient monthly water quality monitoring conducted on the English River near Riverside during the 2004-2006 assessment period (station 10920001) and (2) results of IDNR/UHL biological monitoring conducted from 1999-2002.
EXPLANATION: The Class A1 uses are assessed as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses: the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff." Due to a change in the Standards in July 2003, E. coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E. coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.” Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E. coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of Section 305(b) assessments and Section 303(d) listings.
The geometric mean level of indicator bacteria (E. coli) in the 24 samples collected (754 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Seventeen of the 24 samples (71%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).
Results of biological monitoring suggest that the Class B(WW1) 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).
Despite the impairment of the Class B(WW1) uses suggested by results of biological monitoring, the results of IDNR/UHL ambient chemical/physical monitoring at the Riverside station from 2004-2006 do not suggest water quality problems. None of the approximately 36 samples collected during the 2004-2006 assessment period violated Class B(WW1) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen. None of the 10 samples analyzed for toxic metals, and none of the seven samples analyzed for chlorpyrifos during the 2004-2006 period, violated the respective Class B(WW1) criteria.
The fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river segment.
