Assessment Comments

Assessment is based on results of (1) IDNR/UHL monthly ambient monitoring conducted during the 2004-2006 assessment period at the County Road J-53 bridge near Shambaugh (STORET station 10730001 (formerly station 787044)) and (2) IDNR/UHL stream REMAP biological sampling in 2006.

Basis for Assessment

[Note:  Prior to the current (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 not assessed due to the lack of recent fish contaminant monitoring in this assessment segment.   This assessment is based on results of IDNR/UHL monthly ambient monitoring conducted during the 2004-2006 assessment period at the County Road J-53 bridge near Shambaugh (STORET station 10730001 (formerly station 787044)) and 2006 IDNR/UHL stream REMAP biological monitoring.  

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 near Shambaugh during summer recreational seasons of 2004-2006 (336 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Twelve of the 24 samples (50%) 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 ambient monitoring at the IDNR/UHL station near Shambaugh showed no violations of Class B(WW1) water quality criteria during the 2004-2006 assessment period for dissolved oxygen (minimum value = 7.7 mg/l) or ammonia-nitrogen (maximum value = 0.37 mg/l) in the 36 samples collected.   Levels of pesticides and toxic metals in the approximately ten samples analyzed were all below the respective Class B(WW1) criteria.   One of the 36 samples (3%) exceeded the upper pH criterion of 9.0 units.   The sample collected on November 1, 2005, contained a pH level of 9.1 pH units, thus slightly exceeding the water quality criterion of 9.0 pH units.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), the percentage of violations for pH at this station (3%) does not suggest a water quality impairment:  the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated.   These results suggest "full support" of the Class B(WW1) aquatic life uses.  

However, the 2006 biological sampling suggest "evaluated partial support" of the Class B(WW1) aquatic life uses.   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 as "fully supported."  Levels of atrazine exceeded the Class C criterion of 3 ppb (=EPA’s MCL) in one of the 36 samples (3%) analyzed (maximum value = 13 ppb).   The mean (0.57 ppb) and median (0.07 ppb) values of atrazine during the 2004-2006 period, however, are well-below the Class C criterion.   Also, the level of nitrate exceeded the Class C criterion of 10 mg/l (=EPA’s MCL) in two of 36 samples (6%) analyzed (maximum value = 11 ppm).   The mean (3.3 ppm) and median (2.9 ppm) values of nitrate during the 2004-2006 period, however, are well-below the Class C criterion, and the percentage of violations (6%) is below the IDNR impairment trigger level of a 10% violation frequency.   According to IDNR guidelines for Section 305(b) assessments, these results do not suggest an impairment of drinking water uses for this assessment segment.  

Fish consumption uses are not assessed due to the lack of recent fish contaminant monitoring in this assessment segment.   The most recent monitoring was conducted as part of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Shambaugh in 1994.   Because these data are now considered too old (greater than ten years) to accurately characterize current water quality conditions, the fish consumption uses are considered “not assessed.”  Note:  fish contaminant monitoring was conducted in 2007 as part of the RAFT program; these data will be used to assess fish consumption uses for the 2010 assessment/listing cycle.