Assessment Comments
Assessment remains based on results of IDNR/UHL routine ambient monitoring conducted downstream from Shenandoah during the 2004-2006 assessment period (STORET station 10360002): monitoring at this station was discontinued in November 2006.
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 remain assessed (evaluted) as "not supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW1) aquatic life uses remain assessed (evaluated) as "fully supported" based on results of chemical/physical water quality monitoring. Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river reach. This assessment is based on results of IDNR/UHL routine ambient monitoring conducted downstream from Shenandoah during the 2004-2006 assessment period (STORET station 10360002). Note: IDNR/UHL routine ambient monitoring at station 10360002 was discontinued in November 2006; thus, this assessment is the same as that developed for the previous assessment/listing cycles. Due to the age of the data upon which this assessment is based (greater than five years), the assessment type is changed from "monitored" (i.e., a higher confidence assessment) to "evaluated" (a lower confidence assessment).
EXPLANATION: The Class A1 uses remain assessed (evaluted) 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 24 samples collected at the IDNR/UHL ambient monitoring station downstream from Shenandoah during summer recreational seasons of 2004-2006 (272 orgs/100ml) exceeded the Iowa Class A1 water quality criterion of 126 orgs/100ml. Fifteen of the 24 samples (62%) exceeded 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 assessment of the Class B(WW1) aquatic life uses remains based on results of monitoring for conventional and toxic parameters conducted at the IDNR/UHL ambient monitoring station downstream from Shenandoah from 2004-2006. Results of ambient monitoring at the IDNR/UHL station showed no violations of Class B(WW1) water quality criteria during the 2004-2006 assessment period for ammonia-nitrogen (maximum value = 0.64 mg/l) in the 35 samples collected. One of the 35 samples (3%) analyzed for dissolved oxygen did violate the Iowa Water Quality criterion to protect Class B(WW1) uses: the sample collected on February 3, 2004 contained 3.8 mg/l of dissolved oxygen, thus violating the Iowa criterion of 5.0 mg/l. In addition, two of 35 samples (6%) analyzed for pH violated the Class B(WW1) upper criterion (9.0 pH units): the samples collected on October 3, 2005 and August 1, 2006, contained pH levels of 9.2 and 9.4 units, respectively. 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 and pH continues to suggest "full support" of aquatic life uses. Thus, the percentages of violations of criteria for dissolved oxygen (3%) and pH (6%) at this station do not suggest an impairment of the Class B(WW1) aquatic life uses. Levels of pesticides in the eight samples analyzed, and levels of toxic metals in the ten samples analyzed, were all below the respective Class B(WW1) criteria. Based on these data, the Class B(WW1) aquatic life uses are assessed (monitored) as “fully supported.”
Fish consumption uses remain “not assessed due to the lack of fish contaminant monitoring in this river reach.
