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 2008 through October 2010.
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, 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 and the presumptive Class A2 (secondary contact recreation) uses are both assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed the respective state water quality criteria. The impairment of the presumptive Class A2 (secondary contact recreation) is a new impairment for this assessment segment. 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 2008 through October 2010.
EXPLANATION: The Class A1 (primary contact recreation) uses and the Class A2 (secondary contact recreation) uses are both assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at UIRW Site 21 were as follows: the 2008 geometric mean was 752 orgs/100 ml, the 2009 geometric mean was 471 orgs/100 ml and the 2010 geometric mean was 1,092 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml; the 2008 and 2010 geometric means exceed the Class A2 geometric mean criterion of 630 orgs/100 ml. Seventeen of the 21 samples (81%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml; five of the 21 samples (24%) exceeded the Class A2 single-sample maximum criterion of 2,880 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
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.
