Assessment Comments
Assessment remains based on the results of monitoring in 2010 at Stations WQ-02, WQ-03, and WQ-04 of the Catfish Creek Watershed Project.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, and due to a UAA, this segment is now designated for Class A2 (secondary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2014) assessment, the available water quality monitoring data will be compared to the applicable Class A2 and Class B(WW2) water quality criteria.]
SUMMARY: The Class A2 (secondary contact recreation) uses remain assessed (monitored) as “not supported” due to violations of Iowa water quality criteria for indicator bacteria. The Class B(WW2) aquatic life uses remain “not assessed” due to the lack of water quality information upon which to base an assessment. The source of data for this assessment is the results of monitoring in 2010 at Stations WQ-02, WQ-03, and WQ-04 of the Catfish Creek Watershed Project (quality assurance/project plan available upon request)
EXPLANATION: The Class A2 (secondary contact recreation) uses are 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 eight samples collected approximately every two weeks during the recreational season of 2010 at Site WQ-03 of the Catfish Creek Watershed Project (1,263 orgs/100 ml) exceeded the Iowa water quality criterion to protect secondary contact recreation uses (630 orgs/100 ml); two of the eight samples (25%) exceeded Iowa’s single-sample maximum criterion of 2,880 orgs/100 ml for secondary contact uses. Similarly, at Station WQ-04, the geometric mean of E. coli in the 10 samples collected (1,430 orgs/100 ml) also exceeded the Class A2 geometric mean criterion. Three of the 10 samples exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. The geometric mean of the 11 samples collected at Site WQ-02 during 2010 (627 orgs/100 ml), however, was slightly below the Class A2 geometric mean criterion with only two of the 11 samples (18%) exceeding the Class A2 single-sample maximum criterion. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean is greater than 630 orgs/100 ml., the secondary contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
