Assessment Comments
Assessment is based on results of ambient water quality monitoring conducted at STORET station 15570005 at Donnelly Park from May 2010 to July 2011.
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 uses are assessed (monitored) as “not supported” (IR 5p) due to high levels of indicator bacteria. This impairment continues the Class A1 impairment identified for the 2008 Integrated Reporting cycle based on overwhelming evidence of impairment. The Class B(WW2) aquatic life uses are assessed (monitored) as “fully supporting” (IR 2a) based on ambient monitoring in 2010 and 2011. The source of data for this assessment is the results of ambient water quality monitoring conducted at station 15570005 at Donnelly Park from May 2010 to July 2011.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) 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 11 samples collected at station 15570005 during the recreational season of 2010 (1,121 orgs/100 ml), and the geometric mean of the 11 samples collected during the recreation season of 2011 (1,170 orgs/100 ml) both far exceeded the Class A1 criterion of 126 orgs/100 ml. Twenty of the combined 22 samples (91%) 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 dissolved oxygen, pH, or temperature occurred in the 22 samples collected at Station 15570005 and analyzed from May 2010 to July 2011.
