Assessment Comments
Assessment is based on results of monitoring for indicator bacteria conducted at Site 28 of the Upper Iowa River Watershed (UIRW) project from April 2010 through October 2012.
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” (IR 5p) due to levels of indicator bacteria that exceed state water quality criteria. The Class B(CW1) coldwater aquatic life uses remain “not assessed” due to the lack of water quality information upon which to base an assessment. Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this assessment segment. The source of data for this assessment is the results of monitoring for indicator bacteria conducted at Site 28 of the Upper Iowa River Watershed (UIRW) project (STORET No. NEIARCD 190050006) from April 2010 through October 2012.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses and the presumptive 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 mean of indicator bacteria (E. coli) in the 20 samples collected during the recreational seasons of 2010 through 2012 at UIRW station 28 were as follows: the 2010 geometric mean was 1,838 orgs/100 ml, the 2011 geometric mean was 3,742 orgs/100 ml and the 2012 geometric mean was 1,498 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml, and all three geometric means also exceed the Class A2 geometric mean criterion of 630 orgs/100 ml. Eighteen of the 20 samples (90%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml; six of the 20 samples (30%) 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 remain “not assessed” due to the lack of water quality information upon which to base an assessment. Monitoring from 2010 to 2012 at Upper Iowa River Watershed Site 30 included analysis for ammonia. None of the 20 samples collected appear to violate the respective ph/temperature-dependent aquatic life criteria for ammonia with ammonia levels 18 of the 20 samples being reported as less than the analytical level of detection (0.05 mg/l). The samples with the two detected levels of ammonia (0.18 mg/l on July 6, 2010 and 0.45 mg/l on July 2, 2012) do not have the accompanying data for pH and water temperature needed to calculate the respective Class B(CW1) criteria; however, these detected levels are well below criteria based on typical water quality conditions. These results suggest “full support” of the Class B(CW1) aquatic life uses.
