Assessment Comments

Assessment is based on: (1) results of IDNR/UHL monthly ambient water quality monitoring conducted during the 2004-2006 assessment period at the State Highway 2 bridge 2 miles east of Clarinda (STORET station 10730002 (formerly station 780809)) and (2) results of IDNR/UHL biocriteria monitoring in 2004.

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), this segment is also now presumptively 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 presumptive 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 supported" based on results of biological monitoring in 2004.   Fish consumption uses remain assessed "not assessed" due to the lack of fish contaminant monitoring in this river reach.   This assessment is based on (1) results of IDNR/UHL monthly ambient water quality monitoring conducted during the 2004-2006 assessment period at the State Highway 2 bridge 2 miles east of Clarinda (STORET station 10730002 (formerly station 780809)) and (2) results of IDNR/UHL biocriteria monitoring in 2004.  

EXPLANATION:  The presumptive 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 east of Clarinda during summer recreational seasons of 2004-2006 (429 orgs/100ml) 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, results of monitoring at the IDNR/UHL ambient monitoring station east of Clarinda showed no violations of Class B(WW1) water quality criteria during the 2004-2006 assessment period for dissolved oxygen (minimum value = 5.7 mg/l), pH (range = 7.2 to 8.6 units), or ammonia-nitrogen (maximum value = 0.5 mg/l) in the 36 samples analyzed.   In addition, levels of pesticides in the eight samples analyzed, and levels of toxic metals in the ten samples analyzed, were all below the respective Class B(WW1) criteria.   These results suggest "full support" of the Class B(WW1) aquatic life uses.  

Results of biological monitoring, however, suggest that the Class B(WW1) uses should be assessed (“evaluated”) as only "partially supported".   Based on IDNR/UHL biocriteria monitoring in 2004, the FIBI score was 23 (poor) and the BMIBI score was 46 (fair).   This suggests the aquatic life use support be assessed as partially supported (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports.   The biological impairment criteria were determined 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 biological assessment is considered “evaluated” (i.e., of lower confidence) because during the field fish collection, staff encountered equipment failure and, combined with the width and depth of the stream, the results are unreliable.   The aquatic life uses are considered "partially supporting" because the FIBI score (23 + UAV (7)) failed to meet the FIBI BIC (36).   This site will be assessed again in the near future.    

Fish consumption uses remain "not assessed" due to the lack of recent fish tissue monitoring in this river reach.