Assessment Comments
Assessment remains based on results of monitoring from 2007 through 2008 by the National Laboratory for Agriculture and the Environment (NLAE), Ames, IA.)
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated 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, this segment is now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" (IR 5p) due to levels of indicator bacteria that violate state water quality criteria. The source of data for this assessment is the results of monitoring from April 2007 through October 2008 conducted by the National Laboratory for Agriculture and the Environment (NLAE), Ames, IA, at station TC313 approximately 3 miles SW of Buckeye in Hardin County. The Class B(WW2) aquatic life uses are considered “not assessed” (IR 3a) due to the age of the biological data (>10 years) that were previously used to assess the aquatic life uses of this stream segment.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric mean of E. coli in the 15 samples collected at station TC313 (445 orgs/100 ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Ten of the 15 samples (67%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).
For previous assessments, results of biological sampling conducted in 1999 as part of the IDNR/SHL stream biocriteria project were used to assess the aquatic life uses of this stream as “fully supported”. As both chemical and biological water quality data age, however, they are less able to represent current water quality conditions. As data age beyond ten years, their ability to represent current water quality conditions is increasing suspect. Thus, because the biological data collected in 1999 are well over 10 years old, these data are not being used for the current assessment, and thus the Class B(WW2) aquatic life uses are now considered “not assessed”. Additional monitoring is needed in this assessment segment to update status of its aquatic communities.
