Casey Springs IA 01-UIA-275

Assessment Comments

Assessment is based on results of monitoring for indicator bacteria and water quality conducted at Site 11 of the Upper Iowa River Watershed (UIRW) project from April 2010 through October 2012 and a 2012 summary of trout reproduction in Iowa streams.

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” (IR 5p) based on results of bacteria monitoring from 2010-2012.   The presumptive Class A2 (secondary contact recreation) uses are assessed (monitored) as “fully supported” (IR 2a).   The Class B(CW1) coldwater aquatic life uses are assessed as “fully supporting” (IR 2a), and the fish consumption uses remain “not assessed” (IR 3a) due to the lack of information upon which to base an assessment.   The sources of data for this assessment include the (1) results of monitoring for indicator bacteria conducted at Site 11 of the Upper Iowa River Watershed (UIRW) project (STORET No.   NEIARCD 191910005) from April 2010 through October 2012 and (2) a 2012 IDNR summary of trout reproduction in Iowa streams.  

EXPLANATION:  The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “partially 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 20 samples collected during the recreational seasons of 2010 through 2012 at UIRW Site 11 were as follows:  the 2010 geometric mean was 119 orgs/100 ml, the 2011 geometric mean was 96 orgs/100 ml and the 2012 geometric mean was 127 orgs/100 ml.   One of the three geometric means (127 orgs/100 ml in 2012) very slightly exceed the Class A1 criterion of 126 orgs/100 ml; the 2010 and 2011 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.   Five of the 20 samples (25%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml; none of the 20 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, or if significantly greater than 10% of the samples exceed the respective (Class A1 or A2) single sample maximum criterion, the contact recreation uses should be assessed as “impaired”  (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, the presumptive Class A1 uses are assessed as “partially supported” based on significantly greater that 10% of the samples exceeding the Class A1 single-sample maximum criterion.   Although assessed as "impaired", this stream has exceptionally low levels of indicator bacteria relative to other Iowa streams, and thus this impairment should be considered very slight and not justifying preparation of a TMDL for bacteria.

The Class B(CW1) coldwater aquatic life uses and fish consumption uses are assessed as “fully supporting” based on limited monitoring data at Upper Iowa River Watershed Site 11 and on a summary of trout reproduction.   Monitoring from 2010 to 2012 at Upper Iowa River Watershed Site 11 included analysis for ammonia and temperature.   All of the 20 samples analyzed for ammonia contained less than the limit of detection (0.05 mg/l).   In 2010 and 2011, water temperature was measured during 11 samplings; none of the nine samples exceeded the Class B(CW1) criterion for temperature.   These results do not suggest impairment of the Class B(CW1) aquatic life uses.

In addition, a summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2012, suggests that the Class B(CW1) uses of this stream should be assessed as "fully supported".   According to the updated summary, Casey Springs is in the group of Iowa coldwater streams that supports natural reproduction of trout.   Based on results of surveys by the IDNR Fisheries Bureau, this stream is placed in the category of Iowa trout streams that exhibit recent, but inconsistent reproductive success and that are generally not capable of maintaining a viable population for the resident trout species at this time (Category II stream).   This assessment is consistent with previous assessments of the ability of this stream to support natural reproduction of trout.  

The Class HH (human health/fish consumption) uses remain “not assessed” due to lack of fish contaminant monitoring in this assessment segment.