Assessment Comments
Assessment is based on the results of monitoring in 2010 at Station WQ-15 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 general uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this segment is now presumptively designated for Class A1 (primary contact recreation) uses and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters. Thus, for the current (2012) assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to violations of Iowa water quality criteria for indicator bacteria. This is a new impairment for this previously unassessed segment. The presumptive Class B(WW1) aquatic life uses are “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 Station WQ-15 of the Catfish Creek Watershed Project (quality assurance/project plan available upon request)
EXPLANATION: The presumptive Class A1 (primary 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 11 samples collected approximately every two weeks during the recreational season of 2010 at Site WQ-15 of the Catfish Creek Watershed Project (1,494 orgs/100 ml) far exceeded the Iowa water quality criterion to protect primary contact recreation uses (126 orgs/100 ml). All 11 samples (100%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
