Cedar River IA 02-CED-457

[Note: A TMDL for the bacteria impairments in the two downriver assessment segments of the Cedar River was prepared and approved by EPA in February 2010. This TMDL addressed bacteria impairments in Cedar River segments IA 02-CED-0030_1 and IA 02-CED-0030_2 but did not include this segment of the Cedar River (IA 02-CED-0030_3). The bacteria impairments in all three segments, however, were based on the same monitoring data from the same Iowa DNR ambient water quality monitoring station: Cedar River at County Road E36 east of Palo (STORET station 10570002)). As noted in comments from U.S. EPA in May 2011, however, the failure of the TMDL to include segment IA 02-CED-0030_3 required that this segment remain in IR Category 5a and be included on Iowa's Section 303(d) list.]

The 2012-2014 monitoring period continued to show exceptionally low levels of indicator bacteria (E. coli) in this assessment segment, and thus the IR 5a impairment of the Class A1 uses is proposed for de-listing. Similar to the previous monitoring periods, all geometric means for recreation seasons of 2012 through 2014 were below the Class A1 criterion of 126 orgs/100 ml at the DNR monitoring station. The geometric means of indicator bacteria (E. coli) in the 22 monthly samples collected during the recreational seasons of 2012 through 2014 at DNR station 10570002 upstream from Cedar Rapids were as follows: the 2012 geometric mean was 11 orgs/100 ml, the 2013 geometric mean was 53 orgs/100 ml and the 2014 geometric mean was 81 orgs/100 ml. Three of the 22 samples collected (14%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. The 2008 recreational season geometric mean of 202 orgs/100 ml is the only E. coli recreation season geometric mean to violate the Class A1 criterion in 12 years of routine monthly ambient water quality monitoring at this station.

Only seven samples were analyzed for indicator bacteria (E. coli) at USGS station 05464480 upstream from Cedar Rapids. Four samples were collected during the 2012 recreation season (geometric mean of 6 orgs/100 ml); two samples during the 2013 season (geometric mean of 747 orgs/100 ml), and only one sample (3 orgs/100 ml) during the 2014 season. Only one of the seven samples exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to Iowa’s assessment/listing methodology (Table 6), none of these recreation seasons has a sufficient number of data points (at least seven samples/season) for calculating a meaningful geometric mean that can be compared to Iowa’s Class A1 water quality criterion. Thus, the USGS data are not used for this assessment.

The results for both geometric means and for the percentage of samples that exceed Iowa’s single sample maximum criterion suggest that the Class A1 primary contact recreation uses should be assessed as “fully supporting”. This was the second consecutive Integrated Reporting cycle where (1) all geometric means were below the Class A1 criterion, and (2) according to DNR’s assessment/listing methodology, the percentages of samples greater than the single-sample maximum criterion were not significantly greater than 10%. Because, DNR’s assessment/listing methodology requires that standards be met for two consecutive assessment cycles (total of five years) before a Section 303(d) impairment can be removed, the bacteria impairment of the Class A1 uses will be de-listed for the current (2016) IR cycle.

The Class A1 (primary contact recreation) and Class B(WW1) aquatic life uses remain assessed (monitored) as "partially supported" due violations of criteria for pH during the previous (2010-2012) monitoring period when five of 36 samples (14%) analyzed for pH at DNR monitoring station 10570002 violated the pH criterion, and four of 18 samples (22%) analyzed at USGS station 05464480 at Edgewood Road violated this criterion. According to U.S. EPA guidelines for Section 305(b) reporting, if significantly greater than 10% of samples exceed state criteria for pH, the primary contact and aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). While the 2010-2012 results from the DNR station did not show impairment, the violation frequency at the USGS station was significantly greater than 10%. For the 2012-2014 monitoring period, however, levels of pH at both stations were below the impairment threshold. Four of 33 samples (12%) from the DNR station exceeded the pH criterion of 9.0 pH units, and two of 10 samples (20%) exceeded this criterion at the USGS station. Neither violation frequency is significantly greater than 10%, thus suggesting “full support” of the designated uses. Because, however, Iowa’s assessment/listing methodology requires that a standard be met for two consecutive IR cycles before an impairment can be de-listed, the pH impairment of the Class A1 and Class B(WW1) uses will remain in effect.

Results of water quality monitoring for other parameters during the 2012-2014 monitoring period at the DNR ambient station near Palo and at the USGS station at Edgewood Road, however, do not suggest impairment of the Class B(WW1) uses. Monitoring at these stations showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, ammonia-nitrogen, chloride, or sulfate in the 43 samples analyzed at the two monitoring stations from 2012 to 2014. In addition, levels of the pesticide carbofuran in the 26 samples analyzed at the USGS station were below the Class B(WW1) criteria.

In agreement with the water quality aquatic life assessment, the evaluated aquatic life assessment based on biological sampling suggests the aquatic life uses are "partially supporting". This evaluated biological assessment was based on data collected in 2011 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 2011 BMIBI score was 45 (good).The aquatic life use support was assessed (evaluated) as partially supporting (=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 natural substrate BMIBI BIC for this ecoregion is 70. This assessment is considered evaluated because the drainage area (6238 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, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the site used for the assessmentdoesn’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 “not assessed” due to lack of recent fish tissue monitoring in this river segment.