Assessment Comments
Assessment remains based on results of monitoring for indicator bacteria conducted at Site 21 of the Upper Iowa River Watershed (UIRW) project from April 2004 through October 2006.
Basis for Assessment
Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) aquatic life 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) and Class A2 (secondary contact recreation) uses. This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses)).]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed state water quality criteria. The presumptive Class A2 (secondary contact recreation) uses remain assessed (monitored) as “fully supported.” The Class B(CW1) coldwater aquatic life uses and the fish consumption uses both remain “not assessed” due to the lack of information upon which to base an assessment. The source of data for this assessment is the results of monitoring for indicator bacteria conducted at Site 21 of the Upper Iowa River Watershed (UIRW) project (STORET No. NEIARCD 19005004) from April 2004 through October 2006.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as impaired due to violations of Iowa’s water quality criteria for indicator bacteria. The presumptive Class A2 (secondary contact recreation) uses, however, are assessed (monitored) as “fully supported.” The geometric mean of E. coli in the 21 samples collected at UIRW site 21 during the recreational seasons of 2004 through 2006 was 418 orgs/100 ml. This geometric mean far exceeds the Class A1 criterion of 126 orgs/100 ml but is below the Class A2 criterion of 630 orgs/100 ml. Seventeen of the 21 samples (81%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml.; 2 of the 21 samples (10%) exceeded Iowa’s Class A2 single-sample maximum criterion (2,880 orgs/100 ml.). According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean of E. coli is greater than the applicable state criterion, the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, the results from UIRW site 21 suggest that the geometric mean exceeds the Class A1 criterion; thus, the Class A1 uses should be assessed as “not supported.” In terms of Class A2 criteria, however, the geometric mean meets the Class A2 criteria; thus, these results suggest that the Class A2 uses should be assessed as “fully supported.”
The Class B(CW1) coldwater aquatic life uses and the fish consumption uses both remain “not assessed” due to the lack of information upon which to base an assessment.
