Assessment Comments

Assessment is based on: (1) results of IDNR/UHL monthly ambient water quality monitoring conducted during the 2006-2008 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 2006-2008 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 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 21 samples collected at the IDNR/UHL ambient monitoring station east of Clarinda during summer recreational seasons of 2006-2008 (810 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Thirteen of the 21 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).   Note:  The February 2010 version of the Iowa surface water classification shows at least portions of this river segment designated for Class A2 (secondary contact recreation) uses.   This state-level designation, however, has not yet been approved by U.S.  EPA.   The geometric mean of the 31 E.  coli samples collected during calendar years 2006-2006 in this river segment (359 orgs/100 ml) would meet Iowa’s Class A2 geometric mean criterion of 630 orgs/100 ml, thus indicating “full support” of the Class A2 uses.  

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 2006-2008 assessment period for dissolved oxygen (minimum value = 6.0 mg/l), pH (range = 7.2 to 8.6 units), or ammonia-nitrogen (maximum value = 0.96 mg/l) in the 32 samples analyzed.   In addition, levels of toxic metals in the two 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 "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 11 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 2004 and 2008 to be considered “monitored”.   This segment had multiple samples collected in the previous 11 years (1998-2008); however, the multiple samples were not collected during 2004-2008 and/or were not collected in multiple years.   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.