Assessment Comments
Assessment is based on results of monitoring conducted in 2011 and 2012 as part of the Turkey River Watershed project at station WON-10 at Main Street/W14 (STORET station 15960020).
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 (2014) 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 levels of indicator bacteria that exceed state water quality criteria (IR 5p). This is a new impairment for this previously unassessed stream segment. The Class B(WW2) aquatic life uses are assessed (monitored) as “fully supported” based on results of water quality monitoring from May 2011 to November 2012 (IR 2a). The data used for this assessment are from monitoring conducted from May 2011 to November 2012 as part of the Turkey River Watershed project at station WON-10 at Main Street/W14 (STORET station 15960020).
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 means of indicator bacteria (E. coli) in the 15 samples collected during the recreational seasons of 2011 and 2012 at monitoring station 15960020 were as follows: the 2011 geometric mean of seven samples was 435 orgs/100 ml and the 2012 geometric mean of eight samples was 976 orgs/100 ml. Both geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Twelve of the 15 samples (80%) exceeded the Class A1 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 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). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”
Results of chemical/physical water quality monitoring in 2011 and 2012 do not suggest impairment of the Class B(WW2) aquatic life uses. Monitoring at station WON-10 (STORET station 15960020) showed no violations of Class B(WW2) water quality criteria for dissolved oxygen, ammonia or pH in the 14 samples analyzed during 2011 and 2012. These results suggest “full support” of the Class B(WW2) aquatic life uses.
