Bigalks Creek IA 01-UIA-284

Assessment Comments

Assessment is based on: (1) the results of monitoring for indicator bacteria and water quality conducted at Site 7 of the Upper Iowa River Watershed (UIRW) project from April 2010 through October 2012 and (2) the February 2012 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, 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 and the presumptive Class A2 (secondary contact recreation) uses are both assessed (monitored) as “not supported” (IR 5p) due to levels of indicator bacteria that exceed state water quality criteria.   The Class B(CW1) coldwater aquatic life uses are assessed (monitored) as "partially  supported" (IR 5a) due to violations of the Class B(CW1) criterion for temperature.   This is a new impairment for this assessment segment.   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 2010 through October 2012 and (2) the February 2012 summary of trout reproduction in Iowa streams as prepared by the IDNR Fisheries Bureau.  

EXPLANATION:  The presumptive Class A1 (primary contact recreation) uses and the presumptive Class A2 (secondary contact recreation) uses are both assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria.   The geometric means of indicator bacteria (E.  coli) in the 19 samples collected during the recreational seasons of 2010 through 2012 at UIRW Site 7 were as follows:  the 2010 geometric mean was 474 orgs/100 ml, the 2011 geometric mean was 1,011 orgs/100 ml and the 2012 geometric mean was 156 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml; the 2011 geometric mean exceed the Class A2 geometric mean criterion of 630 orgs/100 ml.   Thirteen of the 19 samples (68%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml; three of the 19 samples (16%) 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, because at least one recreation season geometric mean exceeded criteria for both the presumptive Class A1 and A2 uses, these uses are assessed as “not supported” and Section 303(d) impaired.  

The Class B(CW1) coldwater aquatic life uses are assessed as “partially supported” due to violations of the Class B(CW1) criterion for temperature.   In 2010 and 2011, water temperature was measured during 12 samplings at UIRW Site 7 with four of the 12 samples exceeding the Class B(CW1) criterion of 20C:  June 1, 2010:  20.7C; June 7, 2011:  23.5C; July 5, 2011:  22.4C; and August 2, 2011:  29.0C.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), "partial support" of beneficial uses is indicated if criteria are exceeded in more than 10% of the samples for conventional parameters (e.g., pH, temperature, or dissolved oxygen).   Based on IDNR’s assessment methodology, the results from Upper Iowa River Watershed Site 7 suggest that the violation frequency for temperature is significantly greater than 10% and thus suggests impairment of Class B(CW1) uses of this assessment segment.   Monitoring from 2010 to 2012 at Upper Iowa River Watershed Site 7 also included analysis for ammonia.   Seventeen of the 19 samples analyzed for ammonia contained less than the limit of detection (0.05 mg/l); the levels of ammonia in the two samples with detected levels (0.05 and 0.17 mg/l) are well below Class B(CW1) criteria and to not suggest impairment of the Class B(CW1) uses.  

The assessment of the Class B(CW1) uses are also based on an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2012.   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.