Bigalks Creek IA 01-UIA-284

Assessment Comments

Assessment is 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 current (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)).   This stream segment also remains identified as an “HQ” (high quality) water.]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses are 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 are assessed (monitored) as “fully supported.”  The Class B(CW1) coldwater aquatic life uses are 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 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 were 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, were assessed (monitored) as “fully supported.”  Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed.   Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A1 criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses:  the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff."  Due to a change in the Standards in July 2003, E.  coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E.  coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.”  Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E.  coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of Section 305(b) assessments and Section 303(d) listings.  

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.   Eleven of the 19 samples (58%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml.; 4 of the 19 samples (21%) 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 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).   Also, according to U.S.  EPA guidelines for Section 305(b) reporting, 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 3-35 of U.S.  EPA 1997b).   According to IDNR’s assessment/listing methodology, the results from UIRW site 7 suggest that the geometric mean exceeds the Class A1 criterion; thus, the Class A1 uses should be assessed as “not supported.”  In terms of Class A2 criteria, however, both the geometric mean and the number of samples exceeding the Class A2 single-sample maximum criterion meet the Class A2 criteria; thus, these results suggest that the Class A2 uses should be assessed as “fully supported.”  According to IDNR’s assessment/listing methodology, the results from UIRW site 7 do not indicate that significantly greater than 10% of the samples exceed the Class A2 single-sample maximum criterion.

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.