Assessment Comments

Assessment is based on: (1) the results of IDNR/UHL ambient monthly monitoring during the 2006-2008 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 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 are assessed (monitored) as "partially supported" 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 2006-2008 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).   The geometric mean level of indicator bacteria (E.   coli) in the 23 samples collected (279 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Twelve of the 23 samples (52%) 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 "partially supported" based on data collected in 1999 as part of an IDNR 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 (FIBI).   The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 1999 evaluated FIBI was 22 (poor).   The aquatic life use support was assessed (evaluated) as not supporting (=NS), based on a comparison of the FIBI 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 1994-2004.   This FIBI BIC for this ecoregion is 32 and this segment passed the FIBI BIC 0/1 times in 1999.  

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 between 2004 and 2008 to be considered “monitored”.   This segment had a single sample collected in 1999.   Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).    According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus 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).

In contrast to results of biological monitoring which suggest "not supporting" of the aquatic life uses, results of ambient chemical/physical water quality suggest “full support” of the aquatic life uses.   None of the 33 samples collected during the 2006-2008 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 33 samples analyzed for dissolved oxygen violated the Class B(WW1) criterion of 5.0 mg/l (this sample was collected on August 1, 2007 and contained a dissolved concentration of 4.7 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 results of the 1999 biological assessment and on occasional episodes of low levels of dissolved oxygen, the aquatic life uses of this stream segment will remain assessed as “partially supported.”  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 violations documented since September 2001 are the level of 4.2 mg/l on September 6, 2005 and the level of 4.7 mg/l on August 1, 2007.   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 (post-2001) dissolved oxygen violations have been infrequent and 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.