Assessment Comments

Assessment is based on results of (1) IDNR/UHL monthly ambient monitoring conducted during the 2008-2010 assessment period at the County Road J-53 bridge near Shambaugh (STORET station 10730001 (formerly station 787044)), (2) IDNR/UHL stream REMAP biological sampling in 2006, and (3) fish tissue (RAFT) monitoring in 2007.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this river segment was designated for Class B(WW) aquatic life uses, including fish consumption uses and for Class C (drinking water) 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), for fish consumption uses (now termed Class HH (human health/fish consumption uses), and for Class C (drinking water) uses.]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to high levels of indicator bacteria (E.  coli).   The results of the water quality sampling indicate that the Class B(WW1) aquatic life uses should be assessed (monitored) as "fully supported"; however, the 2006 biological sampling data indicate the Class B(WW1) aquatic life uses should be assessed (evaluated) as "partially supporting."  The Class C (drinking water) uses are also assessed (monitored) as "fully supported.”  Fish consumption uses are assessed (monitored) as “fully supported” based on fish contaminant monitoring in 2007.   This assessment is based on (1) results IDNR/UHL monthly ambient monitoring conducted during the 2008-2010 assessment period at the County Road J-53 bridge near Shambaugh (STORET station 10730001 (formerly station 787044)), (2) IDNR/UHL stream REMAP biological monitoring in 2006, and (3) results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring in 2007 south of Shambaugh.  

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 21 samples collected during the recreational seasons of 2008 through 2010 at the West Nodaway River near Shambaugh were as follows:  the 2008 geometric mean was 1512 orgs/100 ml, the 2009 geometric mean was 1053 orgs/100 ml and the 2010 geometric mean was 1007 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Twenty of the 21 samples (95%) 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.”  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.  

Regarding support of the Class B(WW1) aquatic life uses, results of ambient monitoring at the IDNR/UHL station near Shambaugh showed no violations of Class B(WW1) water quality criteria during the 2008-2010 assessment period for dissolved oxygen (minimum value = 7.7 mg/l), pH (range:  7.5-8.6 units), or ammonia-nitrogen (maximum value = 1.2 mg/l) in the 31 samples collected.   These results suggest "full support" of the Class B(WW1) aquatic life uses.  

However, the 2006 biological sampling suggest that the Class B(WW1) aquatic life uses should be assessed (evaluated) as “partially supported.”  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 34 (fair) and the BMIBI score was 25 (poor).   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 36 and the BMIBI BIC for this ecoregion is 51.   This assessment is considered evaluated because the drainage area (779 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 passed the FIBI BIC and failed to meet 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.  

The Class C (drinking water) uses are also assessed (monitored) as "fully supported."  Atrazine was not monitored at this site during the 2008-2010 assessment period.   However, levels of atrazine exceeded the Class C criterion of 3 ppb (=EPA’s MCL) in one of the 11 samples (9%) analyzed during the previous (2006-08) assessment period (maximum value = 13 ppb).   The mean (1.3 ppb) and median (0.07 ppb) values of atrazine during the 2006-2008 period, however, were well-below the Class C criterion.   The level of nitrate was below the Class C criterion of 10 mg/l (=EPA’s MCL) in all of the 29 samples collected during the 2008-2010 assessment period.   The mean (4.0 ppm) and median (4.0 ppm) values of nitrate during the 2008-2010 period are also well-below the Class C criterion.   According to IDNR guidelines for Section 305(b) assessments, these results suggest "full support" of drinking water uses for this assessment segment.  

Fish consumption uses are assessed (monitored) as “fully supported” based on results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring at the Nodaway River south of Shambaugh in 2007.   The composite samples of fillets from channel catfish had low levels of contaminants.   Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.087 ppm; total PCBs: <0.09 ppm; and technical chlordane: 0.068 ppm.   The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses.   The fish contaminant data generated from the 2007 RAFT sampling conducted at this river segment show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.