Assessment Comments
Assessment is based on the results of monitoring from March to July 2010 at IDNR TMDL station LTR2 near Colesburg, IA.
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, 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 (2012) 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” due to violations of Iowa water quality criteria for indicator bacteria. This is a new impairment for this previously unassessed segment. The Class B(WW1) aquatic life uses are assessed (monitored) as “fully supported.” The source of data for this assessment is the results of monitoring from March to July 2010 at IDNR TMDL station LTR2 near Colesburg, IA (STORET station 11280003).
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 eight samples collected monthly during the recreational season of 2010 at Site LTR2 (914 orgs/100 ml) exceeded the Iowa water quality criterion to protect primary contact recreation uses (126 orgs/100 ml). Seven of the eight samples (88%) 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).
The Class B(WW2) aquatic life uses are assessed (monitored) as “fully supported.” No violations of Class B(WW2) water quality criteria for ammonia, dissolved oxygen, pH, or chloride occurred in the nine samples analyzed from March to July 2012.
