Assessment Comments

Assessment is based on: (1) results of IDNR/UHL monthly ambient water quality monitoring conducted during the 2008-2010 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 1998 & 2004.

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), 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 are assessed (evaluated) as "partially supported" based on results of biological monitoring in 1998 and 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 2008-2010 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 1998 and 2004.  

EXPLANATION:  The presumptive Class A1 (primary contact recreation) are assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria.   The geometric means of indicator bacteria (E.  coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at the East Nodaway River near Clarinda were as follows:  the 2008 geometric mean was 998 orgs/100 ml, the 2009 geometric mean was 490 orgs/100 ml and the 2010 geometric mean was 261 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Nine of the 21 samples (43%) 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.”  

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 2008-2010 assessment period for dissolved oxygen (minimum value = 6.0 mg/l), pH (range = 7.2 to 8.5 units), or ammonia-nitrogen (maximum value = 0.96 mg/l) in the 31 samples analyzed.  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 "partially supported" based on IDNR/UHL biocriteria monitoring in 1998 and 2004.   The 1998 FIBI score was  28 (fair) and the BMIBI score was 59 (good).   The 2004 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 segment passed the FIBI BIC 0/2 times and passed the BMIBI BIC 1/2 times in the last 13 years.   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.

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 2006 and 2010 to be considered “monitored”.   This segment had multiple samples collected in the previous 13 years (1998-2010); however, the multiple samples were not collected during 2006-2010.   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).   However, despite this change in assessment methodology and type, this waterbody remains in IR Category 5p based on the bacteria data.

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