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 2008-2010 assessment period (station 10920001) and (2) results of IDNR/UHL biological monitoring conducted in 1999-2002 and 2008.
Basis for Assessment
[Note: Prior to the 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 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 "fully supporting" based on results of biological monitoring from 1999-2002 and 2008. 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 2008-2010 assessment period (station 10920001) and (2) results of IDNR/UHL biological monitoring conducted in 1999-2002 and 2008.
EXPLANATION: The Class A1 uses are assessed as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2008 through 2010 at IDNR station 10920001 at Riverside were as follows: the 2008 geometric mean was 1,691 orgs/100 ml, the 2009 geometric mean was 864 orgs/100 ml and the 2010 geometric mean was 622 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Twenty-one of the 22 samples (95%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.” Levels of indicator bacteria in this assessment segment are moderately high thus suggesting sources of bacteria beyond that contributing to background levels.
Results of biological monitoring suggest that the Class B(WW1) uses should be assessed as “fully supported.” Biological data were collected in 1999-2002 and 2008 as part of the ambient monitoring project and the IDNR/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 34 (fair). The 1999-2002 BMIBI scores were 45, 51, 53, and 54 (all fair) respectively. The 2008 BMIBI score was 62 (good). The aquatic life use support was assessed as fully supporting (=FS), 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 segment passed the FIBI BIC (using the uncertainty adjustment value (UAV) of 7 points) 1/1 time in 2004 and passed the BMIBI BIC 4/5 times in the last 12 years. This assessment is considered evaluated because the drainage area (627 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 also passed 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.
This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology. IDNR now requires a segment have two or more biological samples collected from the segment in multiple years over a five-year period to be considered “monitored”. This segment had multiple samples collected in the previous 12 years (1999-2010); however, the samples were not collected during a five-year period.
In support of the biological assessment, the results of IDNR/UHL ambient chemical/physical monitoring at the Riverside station from 2008-2010 also do not suggest water quality problems. None of the approximately 33 samples collected during the 2008-2010 assessment period violated Class B(WW1) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen.
The fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river segment.
