Assessment Comments

Assessment is based on: (1) IDNR/UHL monthly ambient monitoring conducted during the 2006-2008 assessment period at the County Road F-58 bridge NE of Missouri Valley (STORET station 10430001 (formerly station 822304)) and (2) USGS chemical/physical water quality monitoring at Logan, IA, from January 2006 through December 2008.

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" due to levels of indicator bacteria that violate state water quality criteria.   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of chemical/physical water quality monitoring conducted from 2006 through 2008.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment.   This assessment is based on results of (1) IDNR/UHL monthly ambient monitoring conducted during the 2006-2008 assessment period at the County Road F-58 bridge NE of Missouri Valley (STORET station 10430001 (formerly station 822304)) and (2) USGS chemical/physical water quality monitoring at Logan, IA, from January 2006 through December 2008.  

EXPLANATION:  The 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 21 samples collected at the IDNR/UHL ambient monitoring station NE of Missouri Valley during summer recreational seasons of 2006-2008 (1,326 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Sixteen of the 21 samples (76%) 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).   The USGS monitoring conducted near Logan, IA, did not include analysis for indicator bacteria.

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 = 7.6 to 8.7), or ammonia (maximum = 1.7 mg/L) in the approximately 33 samples analyzed during the 2006-2008 period.  There was one violation of the Class B(WW1) criteria for dissolved oxygen in 33 samples (3%).   The violation (dissolved oxygen = 4.7 mg/L) occurred on August 7, 2007.   According to U.S.  EPA guidelines (U.S.   EPA 1997b, page 3-17), however, a violation frequency of less than 10% for conventional parameters such as dissolved oxygen continues to suggest "full support" of aquatic life uses.   Thus, the percentage of violations of criteria for dissolved oxygen (3%) at this station do not suggest an impairment of the Class B(WW1) aquatic life uses.   There was also one violation of the Class B(WW1) chronic criterion for lead out of two samples.   Because of the low number of samples collected during the 2006-2008 period these results are not sufficient to accurately characterize lead concentrations in this segment.   Data from 1999 through 2006 show no other violations of the Class B(WW1) chronic lead criterion at this site.   Also, total suspended solids concentrations on April 4, 2006, when the lead violation occurred were very high (1,590 mg/L) indicating that there was large amounts of sediment that were likely influencing the water sample.   Therefore the Class B(WW1) aquatic life uses remain assessed as "fully supported."      

The results of USGS monitoring near Logan, IA, showed no violations of Class B(WW1) criteria for dissolved oxygen (minimum = 7.4 mg/L), pH (range = 6.6 to 8.7) or ammonia (maximum = 0.9 mg/L) in the 34 samples collected or for the pesticides dieldrin and DDE in the 34 samples collected.   There was, however, one violation of the Class B(WW1) criterion for chlorpyrifos in 34 samples.   Based on IDNR's assessment methodology this one violation is not significantly greater than 10% of the samples and therefore does not suggest impairment of the Class B(WW1) uses.   Thus, the results from both the IDNR and USGS monitoring stations suggest "full support" of the Class B(WW1) aquatic life uses.  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment.