Assessment Comments
Assessment is based on results of monitoring from May 2011 to November 2012 at station ELK10 (at Colesburg Rd/X3c; STORET station 15220012).
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this river segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 and due to the completion of a Use Attainability Analysis, this segment is also now presumptively designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to violations of Iowa water quality criteria for indicator bacteria (IR 5p). This is a new impairment for this previously unassessed stream segment. The Class B(WW1) aquatic life uses are assessed (monitored) as “fully supported.” The Class HH (fish consumption) uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment. The source of data for this assessment is the results of monitoring from May 2011 to November 2012 at station ELK10 (at Colesburg Rd/X3c; STORET station 15220012).
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that slightly exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the seven monthly samples collected during the recreational season of 2011 (189 orgs/100 ml), and the geometric mean of the eight samples collected during 2012 (386 orgs/100 ml) both exceeded the Class A1 criterion of 126 orgs/100 ml. Five of the combined 15 samples (33 %) 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 should be asssessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The Class B(WW1) aquatic life uses remain assessed (monitored) as “fully supported.” No violations of Class B(WW1) water quality criteria for ammonia, dissolved oxygen, pH, or temperature occurred in the approximately 15 samples analyzed from May 2011 to November 2012.
The Class HH (fish consumption) uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.
