Assessment is based on results of IDNR/UHL monthly ambient water quality monitoring conducted during the 2006-2008 assessment period east of Malvern (STORET station 10650001).
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), and due to the completion of a Use Attainability Analysis in 2007, 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 ambient chemical/physical water quality monitoring 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 IDNR/UHL monthly ambient water quality monitoring conducted during the 2004-2006 assessment period east of Malvern (STORET station 10650001 (formerly station 822310)).
EXPLANATION: The 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 Malvern during summer recreational seasons of 2006-2008 (917 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Eighteen of the 21 samples (86%) 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 Class B(WW1) aquatic life uses are assessed (monitored) as “fully supporting.” Results of routine ambient monitoring at the IDNR/UHL station near Malvern showed no violations of Class B(WW1) water quality criteria during the 2006-2008 assessment period for dissolved oxygen and ammonia-nitrogen in the 32 samples analyzed. One of the 32 samples violated the Class B(WW1) criterion for pH: the pH of the sample collected on August 1, 2006 was 9.1 units, thus violating the Class B(WW1) criterion of 9.0 pH units. Also, this sample had a water temperature of 33C, thus exceeding the water temperature criterion of 32C. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), the percentages of violations at this station during the 2004-2006 period for pH and water temperature (both 3%) do not suggest a water quality impairment. These guidelines allow up to 10% violations of conventional parameters such as dissolved oxygen, pH, and water temperature before impairment of water quality is indicated. The violations of the criteria for pH and water temperature are both likely related to naturally-occurring conditions (bright sunshine, warm air temperatures, and high levels of primary productivity) and do not reflect the influence of anthropogenic pollutants. In addition, levels of toxic metals in the two samples analyzed were below the respective Class B(WW1) criteria. These results suggest "full support" of the Class B(WW1) aquatic life uses.
Fish consumption uses remain "not assessed" due to the lack of fish tissue monitoring in this river segment.