Casey Springs IA 01-UIA-275

Assessment Comments

Assessment is based on results of monitoring for indicator bacteria conducted at Site 11 of the Upper Iowa River Watershed (UIRW) project from April 2008 through October 2010.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) 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 also now presumptively designated for Class A1 (primary contact recreation) and Class A2 (secondary contact recreation) uses.   This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) 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 “not supported” based on results of bacteria monitoring from 2008-10.   The presumptive Class A2 (secondary contact recreation) uses remain assessed (monitored) as “fully supported.”  The Class B(CW1) coldwater aquatic life uses and fish consumption uses remain “not assessed” due to the lack of information upon which to base an assessments.   The source of data for this assessment is the results of monitoring for indicator bacteria conducted at Site 11 of the Upper Iowa River Watershed (UIRW) project (STORET No.   NEIARCD 191910005) from April 2008 through October 2010.  

EXPLANATION:  The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported.”  The presumptive Class A2 (secondary contact recreation) uses are assessed (monitored) as “fully supported.”  The geometric means of indicator bacteria (E.  coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at UIRW Site 11 were as follows:  the 2008 geometric mean was 203 orgs/100 ml, the 2009 geometric mean was 79 orgs/100 ml and the 2010 geometric mean was 119 orgs/100 ml.   One of the three geometric means (2008) slightly exceed the Class A1 criterion of 126 orgs/100 ml; the 2009 and 2010 geometric means, however, are below the Class A1 criterion of 126 orgs/100 ml.   All three geometric means are well below the Class A2 geometric mean criterion of 630 orgs/100 ml.   Seven of the 21 samples (33%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml; none of the 21 samples exceeded the Class A2 single-sample maximum criterion of 2,880 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, the presumptive Class A1 uses are not supported.  

The Class B(CW1) coldwater aquatic life uses and fish consumption uses remain “not assessed” due to the lack of information upon which to base assessments.