Ten Mile Creek IA 01-UIA-274

The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as “partially supported” based on levels of indicator bacteria that exceeded state water quality criteria while the presumptive Class A2 (secondary contact recreation) uses are assessed as "fully supported". The geometric means of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2012 through 2014 at UIRW Site 12 were as follows: the 2012 geometric mean was 110 orgs/100 ml, the 2013 geometric mean was 315 orgs/100 ml and the 2014 geometric mean was 506 orgs/100 ml. Two of the three geometric means (2013 and 2014) slightly exceed the Class A1 criterion of 126 orgs/100 ml; the 2012 geometric mean is below the Class A1 criterion of 126 orgs/100 ml. All three geometric means are well below the Class A2 geometric mean criterion of 630 orgs/100 ml. Twelve of the 21 samples (57%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml; three of the 21 samples (14%) 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 (primary contact recreation) uses are assessed as “impaired". Also, according to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if significantly greater than 10% of sample exceed the single-sample maximum criterion, the contact recreation uses should be assessed as “impaired”. According to Iowa DNR’s assessment methodology, however, the percentage of samples that exceeded this criterion during the 2012-2014 assessment period at Site 12 was not significantly greater than 10%. Thus, the Class A2 uses are assessed as “fully supporting".

The Class B(CW1) aquatic life uses areassessed (monitored) as "partially supported" based on biological data collected in 2011, 2013 and 2014 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 50, the 2013 CBI score was 66 and the 2014 CBI score was 56. The aquatic life use support was assessed (monitored) as partially supporting (=PS), 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 1/3 times. This aquatic life assessment is now considered "monitored" based on a change in the 2010 DNR assessment methodology. DNR now requires a segment have two or more biological samples collected from the segment in multiple years over a five-year period to be considered “monitored”. This segment had a multiple samples collected in a five-year period (2012-2016).

Monitoring from 2010 to 2012 at Upper Iowa River Watershed Site 12 included analysis for ammonia, pH, and temperature. Of the 14 samples analyzed for ammonia, 13 samples contained less than the limit of detection (0.05 mg/l); the one detected sample contained 0.18 mg/l of ammonia. This level is well below any Class B(CW1) aquatic life criterion for ammonia. None of the 14 samples measured for water temperature exceeded the Class B(CW1) criterion for temperature. Two of the 13 samples analyzed for pH exceeded the Class B(CW1) criterion of 9.0 units. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as pH, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). According to DNR’s assessment/listing methodology, however, the results from UIRW Site 12, however, do not indicate that significantly greater than 10% of the samples exceed the Class B(CW1) criterion for pH. Based on the DNR assessment/listing methodology, these results do not suggest impairment of the Class B(CW1) aquatic life uses.

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