Casey Springs IA 01-UIA-275

Assessment Comments

Assessment remains based on results of monitoring for indicator bacteria conducted at Site 11 of the Upper Iowa River Watershed (UIRW) project from April 2004 through October 2006.

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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), 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 remain assessed (monitored) as “partially supported” based on results of bacteria monitoring from 2004-06.   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 2004 through October 2006.  

EXPLANATION:  The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as “partially supported.”  The presumptive Class A2 (secondary contact recreation) uses remain assessed (monitored) as “fully supported.”  The geometric mean of E.   coli in the 22 samples collected at UIRW site 11 during the recreational seasons of 2004 through 2006 was 124 orgs/100 ml.   This geometric mean is slightly below the Class A1 criterion of 126 orgs/100 ml and is far below the Class A2 criterion of 630 orgs/100 ml.   Seven of the 22 samples (32%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml.; only 1 of the 22 samples (5%) exceeded Iowa’s Class A2 single-sample maximum criterion (2,880 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 less than the applicable state criterion, the contact recreation uses should be assessed as "fully supported" (see pgs 3-33 to 3-35of U.S.   EPA 1997b).   However, according to these U.S.   EPA guidelines, if more than 10% of samples exceed the single-sample maximum criterion, the primary contact recreation uses should be assessed as "partially supported" (see pgs 3-33 to 3-35of U.S.   EPA 1997b).    According to IDNR’s assessment/listing methodology, the results from UIRW site 11 suggest that significantly more than 10% of the 22 samples collected exceed the Class A1 single-sample maximum criterion of 235 org/100 ml.    Thus, the Class A1 uses should be assessed as “partially supported.”  In terms of Class A2 criteria, however, both the geometric mean (124 orgs/100 ml) and the percentage of samples exceeding the Class A2 single-sample maximum criterion (5%) meet the Class A2 criteria; thus, these results suggest that the Class A2 uses should be assessed 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 assessments.