Assessment Comments

Assessment based on: (1) IDNR/SHL monthly ambient monitoring conducted during the 2010-2012 assessment period at the County Road F-58 bridge NE of Missouri Valley (STORET station 10430001 (formerly station 822304)), (2) USGS chemical/physical water quality monitoring at Logan, IA, from 2010-2012, and (3) IDNR/SHL biological sampling conducted in 2012.

Basis for Assessment

[Note:  Prior to the 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 due to the results of an Use Attainability Analysis in 2006, 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" (IR 5a) due to levels of indicator bacteria that violate state water quality criteria.   Although results of chemcial/physical water quality montioring at this station continue to suggest good water quality conditions and full support of aquatic life uses, the Class B(WW1) aquatic life uses are assessed (evaluated) as "not supported" (IR 3b-u) based on results of IDNR/SHL biological sampling conducted in 2012.   Fish consumption uses remain "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this river segment.   This assessment is based on results of (1) IDNR/SHL monthly ambient monitoring conducted during the 2010-2012 assessment period at the County Road F-58 bridge NE of Missouri Valley (STORET station 10430001 (formerly station 822304)), (2) USGS chemical/physical water quality monitoring at Logan, IA, during the 2010-2012 period, and (3) IDNR/SHL biological sampling conducted in 2012.  

EXPLANATION:  The 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 25 samples collected during the recreational seasons of 2010 through 2012 at the Boyer River at Logan by USGS were as follows: the 2010 geometric mean was 2,835 orgs/100 ml, the 2011 geometric mean was 677 orgs/100 ml, and the 2012 geometric mean was 298 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Fourteen of the 25 samples (56%) 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.”  

Similarly, results of bacterial monitoring by Iowa DNR also suggest that the Class A1 uses should be assessed as impaired.   The geometric means of indicator bacteria (E.  coli) in the 24 samples collected during the recreational seasons of 2010 through 2012 at the Boyer River near Missouri Valley through the IDNR/UHL ambient stream monitoring program were as follows: the 2010 geometric mean was 759 orgs/100 ml, the 2011 geometric mean was 146 orgs/100ml, and the 2012 geometric mean was 125 orgs/100 ml.   Two of the three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Eleven of the 24 samples (46%) 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, monitoring at the IDNR/UHL station NE of Missouri Valley showed no violations of Class B(WW1) water quality criteria for pH (range = 7.8 to 8.9), dissolved oxygen (minimum = 7.2 mg/L), or ammonia (maximum = 0.24 mg/L) in the 36 samples analyzed during the 2010-2012 period.  Also, none of the 36 samples analyzed for chloride or sulfate violated their respective Class B(WW1) criteria.   These results suggest "full support" of the Class B(LW) uses in this segment of the Boyer River.      

Similarly, the results of USGS monitoring near Logan, IA, showed no violations of Class B(WW1) criteria for dissolved oxygen (minimum = 6.5 mg/L), pH (range = 7.5 to 8.8) or ammonia (maximum = 0.9 mg/L) in the 35 samples collected or for the pesticides chlorpyrifos, dieldrin, or DDE in the 34 samples collected.   Thus, the results from both the IDNR and USGS monitoring stations suggest that the Class B(WW1) aquatic life uses should be assessed as "fully supporting".  

In contrast to the water quality aquatic life assessment, the aquatic life assessment based on biological sampling suggests the aquatic life uses are "not supporting".   This evaluated biological assessment was based on data collected in 2012 as part of the IDNR/SHL large river sampling project.   A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biological sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa collected in the stream sampling reach.   The biological metrics were combined a benthic macroinvertebrate index (BMIBI).   The index rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2012 BMIBI score was 23 (poor).  The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008.   The BMIBI BIC for this ecoregion is 54.   This assessment is considered evaluated because the drainage area (928 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 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.   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).  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment.   Results of USGS monitoring near Logan, IA, from 2010-2012 show no violations of the human health/fish criteria for DDE or dieldrin in the 34 samples analyzed.