Bigalks Creek IA 01-UIA-284

Assessment Comments

Assessment remains based on: (1) the results of monitoring for indicator bacteria conducted at Site 7 of the Upper Iowa River Watershed (UIRW) project from April 2004 through October 2006 and (2) the May 2006 summary of trout reproduction in Iowa streams as prepared by the IDNR Fisheries Bureau.

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 “not supported” due to levels of indicator bacteria that exceed state water quality criteria.   The presumptive Class A2 (secondary contact recreation) uses, however, remain assessed (monitored) as “fully supported.”  The Class B(CW1) coldwater aquatic life uses remain assessed (monitored) as "fully supported" based on the May 2006 summary of trout reproduction in Iowa streams as prepared by the IDNR Fisheries Bureau.   Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this stream segment.   The sources of data for this assessment include (1) the results of monitoring for indicator bacteria conducted at Site 7 of the Upper Iowa River Watershed (UIRW) project (STORET No.  NEIARCD 191910001) from April 2004 through October 2006 and (2) the May 2006 summary of trout reproduction in Iowa streams as prepared by the IDNR Fisheries Bureau.  

EXPLANATION:  The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as impaired due to violations of Iowa’s water quality criteria for indicator bacteria.   The presumptive Class A2 (secondary contact recreation) uses, however, remain assessed (monitored) as “fully supported.”  The geometric mean of E.   coli in the 19 samples collected at UIRW site 7 during the recreational seasons of 2004 through 2006 was 436 orgs/100 ml.   This geometric mean far exceeds the Class A1 criterion of 126 orgs/100 ml but is below the Class A2 criterion of 630 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 applicable state criterion, the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S.   EPA 1997b).   Thus, the results from UIRW site 7 suggest that the Class A1 uses should be assessed as “not supported.”  In terms of Class A2 criteria, however, the geometric mean meets the Class A2 criteria thus suggesting that the Class A2 uses should be assessed as “fully supported.”  

The Class B(CW1) coldwater aquatic life uses remain assessed as “fully supported” based on an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in May 2006.   According to the updated summary, Bigalk Creek 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.   This assessment is consistent with previous assessments of the ability of this stream to support natural reproduction of trout.  

Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this stream segment.