Bigalks Creek IA 01-UIA-284

The presumptive Class A1 (primary contact recreation) uses and the presumptive Class A2 (secondary contact recreation) uses remain 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 21 samples collected during the recreational seasons of 2012 through 2014 at UIRW Site 7 were as follows: the 2012 geometric mean was 156 orgs/100 ml, the 2013 geometric mean was 940 orgs/100 ml, and the 2014 geometric mean was 1,064 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml; the 2013 and 2014 geometric means exceed the Class A2 geometric mean criterion of 630 orgs/100 ml. Fifteen of the 21 samples (71%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml; four of the 21 samples (19%) 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 DNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as ”impaired" (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 Section 303(d) impaired.

Despite the lack of violations of the Class B(CW) criterion for temperature during the 2012-2014 assessment period, the Class B(CW1) coldwater aquatic life uses remain assessed as “partially supported” due to violations of the Class B(CW1) criterion for temperature during the previous (2010-2012) assessment period. 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 DNR’s assessment methodology, the results from Upper Iowa River Watershed Site 7 during the 2010-2012 period suggested that the violation frequency for temperature was significantly greater than 10% and thus suggested impairment of Class B(CW1) uses of this assessment segment. According to Iowa’s assessment/listing methodology, removal of an existing impairment due to violation of Iowa’s numeric water quality criteria requires that monitoring data show full support of the previously impaired beneficial use for two consecutive Integrated Report cycles. Although results of monitoring for the current (2016) IR cycle do not suggest an impairment of the Class B(CW1) uses due to temperature, this impairment will remain in effect. If monitoring results for the next (2018) IR cycle also show non-impairment levels of temperature, then this impairment can be removed.

Monitoring from 2012 to 2014 at Upper Iowa River Watershed Site 7 also included analysis for ammonia and pH. Ten of the 14 samples analyzed for ammonia contained less than the limit of detection (0.05 mg/l); the levels of ammonia in the four samples with detected levels are well below Class B(CW1) criteria and do not suggest impairment of the Class B(CW1) uses. One of the 13 samples (8%) measured for pH violated the Class B(CW1) criterion of 9.0 pH units. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), however, a violation frequency of less than 10% for conventional parameters such as pH does not suggest impairment of aquatic life uses.

The assessment of the Class B(CW1) uses was also partially based on an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in January 2019. 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 DNR 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 Rainbow Trout 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.

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