East Branch Iowa River IA 02-IOW-771

Assessment Comments

Assessment is based on results of monitoring conducted as part of a Clean Water Act Section 319 water quality project from June 2009 through October 2010.

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, and due to the completion of a Use Attainability Analysis in 2007, this segment is now 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” (IR Category 5p) 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 remain “not assessed” due to the lack of water quality information upon which to base an assessment.   The source of data for this assessment is the results of monitoring at three sites (EBIR-6, EBIR-7, and EBIR-2) conducted as part of a Clean Water Act Section 319 water quality project from June 2009 through October 2010.  

EXPLANATION:  The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria.   The geometric means of indicator bacteria (E.  coli) in the approximately 20 samples collected during the recreational seasons of 2009 and 2010, respectively, at each of the three Section 319 monitoring stations in this assessment segment were as follows:

1.   EBIR-6 geometric means were 1,064 and 794 orgs/100 ml;
2.   EBIR-7 geometric means were 843 and 483 orgs/100 ml;
3.   EBIR-2 geometric means were 579 and 534 orgs/100 ml.

From 80 to 90% of the samples at each of the Section 319 sites 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 the geometric mean 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).