Assessment Comments

Assessment is based on results of IDNR/UHL monthly ambient monitoring conducted during the 2004-2006 assessment period NE of Smithland (STORET station 10970001 (formerly station 911078)) and 2006 IDNR/UHL stream REMAP biological sampling near Rodney.

Basis for Assessment

[Note:  Prior to the current (2008) Section 305(b) cycle, this river segment was designated only for Class B(WW1) 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 the results of an 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 "fully supported" based on results of ambient chemical/physical water quality monitoring from 2004 through 2006 and are assessed as "partially supported" (evaluated) based on 2006 IDNR/UHL stream REMAP biological sampling near Rodney.   Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.   This assessment is based on results of IDNR/UHL monthly ambient monitoring conducted during the 2004-2006 assessment period NE of Smithland (STORET station 10970001 (formerly station 911078)) and 2006 IDNR/UHL stream REMAP biological sampling near Rodney.  

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 at the IDNR/UHL ambient monitoring station northeast of Smithland during summer recreational seasons of 2004-2006 (458 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Fifteen of the 24 samples (62%) 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).  

Regarding support of the Class B(WW1) aquatic life uses, monitoring at the IDNR/UHL ambient station northeast of Smithland showed no violations of Class B(WW1) water quality criteria for pH, dissolved oxygen (minimum value = 6.4 mg/l) or ammonia nitrogen (maximum value = 0.91 mg/l) in the approximately 35 samples analyzed during the 2004-2006 period.   In addition, levels of pesticides in the eight samples analyzed, and levels of toxic metals in the ten samples analyzed, were all below their respective Class B(WW1) criteria.   Similar to the previous assessment periods, these results suggest "full support" of the Class B(WW1) aquatic life uses.

However, the results of the 2006 IDNR/UHL stream REMAP biological sampling near Rodney suggest only "partial support" of the Class B(WW1) aquatic life uses.   This evaluated biological assessment was based on data collected in 2006 as part of the DNR/UHL stream REMAP project.   A series of biological metrics that 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 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 2006 FIBI score was 12 (poor) and the BMIBI score was 62 (good).  The aquatic life use support was assessed (evaluated) 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 43 and the BMIBI BIC for this ecoregion is 54.   This assessment is considered evaluated because the drainage area (2703 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 failed to meet the FIBI BIC and 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.  

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