Coldwater Creek IA 01-UIA-280

The presumptive Class A1 (primary contact recreation) uses and Class A2 (secondary contact recreation uses remain assessed (monitored) as impaired (partially supporting) due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric means of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2012 through 2014 at UIRW Site 9 were as follows: the 2012 geometric mean was 131 orgs/100 ml, the 2013 geometric mean was 188 orgs/100 ml, and the 2014 geometric mean was 1,231 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml, and the 2014 geometric mean exceeds the Class A2 geometric mean criterion of 630 orgs/100 ml. Nine of the 21 samples (43%) 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, the presumptive Class A1 and Class A2 uses are assessed (monitored) as impaired.

The assessment of the Class B(CW1) aquatic life uses remains, in part, based on data collected in 2011 and 2016 as part of the DNR/SHL coldwater stream sampling project. A series of biological metrics which reflect coldwater stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa that were collected in the stream sampling reach. The biological metrics were combined to make a coldwater benthic index (CBI). The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2011 CBI score was 81 and the 2016 CBI scores were 61 and 67. The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the CBI scores with biological impairment criteria (BIC) established for the 2012 Section 305(b) report. The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011. The CW BIC is 60 and this segment passed the CW BIC 3/3 times in a recent six-year period (2011-2016).

An updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in January 2019 also suggests that theClass B(CW1) uses should beassessed as "fully supported". According to the updated summary, (Unnamed) Cold Water 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 category (I) of Iowa trout streams that exhibit fairly consistent natural reproduction and maintain a viable population of Brown Trout and in the category II of 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 for Rainbow Trout.

In addition, the Class B(CW1) coldwater aquatic life uses are assessed as “fully supported” based on results of water quality monitoring from 2012 to 2014. Thirteen of the 14 samples analyzed for ammonia from April 2012 to October 2014 contained less than the limit of detection (0.05 mg/l); the one detected level (0.08 mg/l) is well below Class B(CW1) criteria. None of the 14 samples violated the Class B(CW1) criteria for temperature. Two of the 13 samples (15%) analyzed for pH exceeded the Class B(CW1) criterion of 9.0 pH units. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if significantly greater than 10% of samples exceed criteria for conventional parameters such as pH, the assessed uses should be assessed as “impaired”. According to Iowa DNR’s assessment methodology, however, the percentage of samples that exceeded the Class B(CW1) pH criterion of 9.0 units during the 2012-2014 assessment period at Site 9 was not significantly greater than 10%. Thus, these results do not suggest impairment of the Class B(CW1) aquatic life uses.

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