Iowa River IA 02-IOW-627

The Class A1 (primary contact recreation) uses remain assessed (monitored) as "partially supported" based on results of monitoring for indicator bacteria (E. coli) during the previous (2010-2012) monitoring period. Results of monitoring during the current monitoring period (2012-2014), however, suggest "full support" of these uses. The geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2012 through 2014 at DNR station 10520003 were as follows: the 2012 geometric mean was 75 orgs/100 ml, the 2013 geometric mean was 63 orgs/100 ml, and the 2014 geometric mean was 94 orgs/100 ml. All three geometric means were below (and met) the Class A1 criterion of 126 orgs/100 ml. Four of the 22 samples (18%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to DNR's assessment/listing methodology, this violation frequency is not significantly greater than 10%. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if all recreation season geometric means meet the respective water quality criterion, and if the violation frequency of the single-sample maximum criterion is not significantly greater than 10%, then the contact recreation uses should be assessed as “fully supported". Because, however, DNR’s assessment/listing methodology requires that standards be met for two consecutive assessment cycles (total of five years) before an impairment can be removed, the impairment of the Class A1 uses will remain and will be based on the 2011 recreation season geometric mean of 132 orgs/100 ml which very slightly exceeded the Class A1 criterion of 126 orgs/100 ml.

Assessments developed for this segment for recent Section 305(b) cycles demonstrate that levels of bacteria in this segment of the Iowa River are low relative to other Iowa rivers. Although bacterial impairments have been identified for this segment in past Section 305(b) cycles based on either the percentage of samples exceeding single sample maximum criteria or a slight violation of the geometric mean criterion, recreation season geometric mean levels of indicator bacteria have typically been below the applicable Class A1 criterion since routine ambient monitoring began in this segment in 2000. As noted in the assessment narrative for this river segment developed for the 2008 cycle, additional changes from “full support” to “impaired” (and back again) can be expected in future assessment/listing cycles.

Results of monitoring from the DNR ambient station downstream from Iowa City from 2012 through 2014 continue to suggest full support of the Class B(WW1) uses: none of the 33 samples analyzed for dissolved oxygen, temperature, pH, or ammonia-nitrogen, chloride, or sulfate showed violations of the respective Class B(WW1) criteria.

The aquatic life assessment based on 2012 and 2013 biological sampling, however, suggests the aquatic life uses should be assessed as "partially supporting". This evaluated biological assessment was based on data collected in 2012 as part of the DNR/SHL stream nutrient sampling project. A series of biological metrics that reflect 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 collected in the stream sampling reach. The biological metrics were combined a benthic macroinvertebrate index (BMIBI). The index rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2012 BMIBI score was 30 (poor) and the 2013 BMIBI score was 15 (poor). The aquatic life use support was assessed (evaluated) as partiallysupporting (=PS), based on a comparison of the BMIBI score with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008. The BMIBI BIC for this ecoregion is 51. This assessment is considered evaluated because the drainage area (3323 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site failed the BMIBI BIC (0/2), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the site used for the assessment doesn’t fall in the calibrated watershed size. According to DNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). DNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).

Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S. EPA/DNR fish contaminant (RAFT) monitoring at the Iowa River in 2007 and 2008. The composite samples of fillets from channel catfish from the 2007 sampling had low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.058 ppm; total PCBs: 0.125 ppm; and technical chlordane: 0.045 ppm. The composite samples of fillets from common carp and white bass from the 2008 sampling had low levels of contaminants. Levels of primary contaminants in the composite sample of common carp fillets were as follows: total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of white bass fillets were as follows: mercury: 0.218 ppm. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The fish contaminant data generated from the 2007 and 2008 RAFT sampling conducted at this river segment show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.