Assessment Comments

Assessment is based on: (1) the results of IDNR/UHL ambient monthly monitoring during the 2004-2006 assessment period at STORET station 10630001 (formerly station 100818) approximately 3 miles southwest of Knoxville and (2) the results of biological monitoring conducted by the IDNR Fisheries Bureau in 1999.

Basis for Assessment

[Note:  Prior to the current (2008) Section 305(b) cycle, this stream 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 due to the completion of a Use Attainability Analysis, 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 (monitored) as "fully supported / threatened" with a declining water quality trend (=impaired) based primarily on results of biological monitoring in 1999.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.   The sources of data for this assessment are (1) the results of IDNR/UHL ambient monthly monitoring during the 2004-2006 assessment period at STORET station 10630001 (formerly station 100818) approximately 3 miles southwest of Knoxville and (2) the results of biological monitoring conducted by the INDR Fisheries Bureau in 1999.  

EXPLANATION:  The Class A1 uses are assessed (monitored) 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 (219 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Twelve of the 24 samples (50%) exceed 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).  

The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported / threatened" with a potentially declining water quality trend.   This assessment was partially based on data collected in 1999 as part of a DNR Fisheries Bureau stream sampling project: Manchester research station.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the Fisheries sampling data.   The biological metrics are based on the numbers and types of 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).   The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 1999 evaluated Fish IBI was 22 (poor).   The aquatic life use support was assessed (evaluated) as Not Supporting (=NS), based on a comparison of the F-IBI score with biological assessment criteria established for previous Section 305(b) reports.   The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.

In contrast to results of biological monitoring which suggest a threat to full support of the aquatic life uses, results of ambient chemical/physical water quality suggest “full support” of the aquatic life uses.   None of the 36 samples collected during the 2004-2006 assessment period at the IDNR monthly station violated Class B(WW1) water quality criteria for pH or ammonia-nitrogen; no violations occurred in the approximately 10 samples analyzed for toxic metals or in the eight samples analyzed for pesticides.   One of the 36 samples analyzed for dissolved oxygen violated the Class B(WW1) criterion of 5.0 mg/l (this sample contained a dissolved concentration of 4.2 mg/l).   According to U.S.  EPA guidelines (U.S.  EPA 1997b, page 3-17), however, a violation frequency of less than 10% for conventional parameters such as dissolved oxygen nonetheless suggest "full support" of aquatic life uses.   Thus, the percentage of violations of the dissolved oxygen criterion at this station (3%) does not suggest an impairment of aquatic life uses in this stream segment.  

Based, however, on the 2004 assessment, the aquatic life uses of this stream segment will remain assessed as “fully supported/threatened” with a declining trend (=impaired).   In the 2004 assessment, two of the 36 samples (6%) collected at IDNR/UHL station 10630001 from 2000 through 2002 violated the Class B(WW1) criterion for dissolved oxygen:  the sample collected on August 1, 2001 contained only 0.7 mg/l, and the sample collected on September 4, 2001, contained only 1.6 mg/l of dissolved oxygen.   Even though U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17) allow for up to 10% of samples to violate criteria for conventional parameters (such as dissolved oxygen), the August and September 2001 readings of dissolved oxygen were atypically low for Iowa streams, and the potential exists for a significant water quality impact, especially given the occurrence of consecutive monthly levels of dissolved oxygen far below the state water quality criterion.   The only violation documented since September 2001 was the level of 4.2 mg/l on September 6, 2005.   Also, the results of biological monitoring conducted in 1999 by the IDNR Fisheries Bureau suggested aquatic life conditions well-below those expected.   Follow-up monitoring should be conducted to better characterize the status of aquatic life of this stream segment.   While the recent (September 2005) violation is relatively minor, and while recent ambient monitoring suggests an improvement in levels of dissolved oxygen in this stream segment, additional biological monitoring is needed to determine whether biotic integrity of this segment meets regional expectations.  

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