Cedar River IA 02-CED-462

[Note: A TMDL for indicator bacteria impairments in eight segments of Cedar River was prepared and approved by EPA in February 2010. Because this segment (IA 02-CED-0040_2) was not included in this TMDL, the segment's bacterial impairment is considered appropriate for Category 5a of Iowa's Integrated Report.]

The Class A1 (primary contact recreation) uses are assessed as "partially supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2012 through 2014 at station 10070006 downstream from Waterloo were as follows: the 2012 geometric mean was 97 orgs/100 ml, the 2013 geometric mean was 165 orgs/100 ml and the 2014 geometric mean was 172 orgs/100 ml. The 2013 and 2014 geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml; the 2012 geometric mean was below this criterion. Six of the 22 samples (27%) exceeded the Class A1 single-sample maximum criterion of 235 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 Class A1 uses, these uses are assessed as “impaired.”

The Class B(WW1) aquatic life uses are assessed (evaluated) as "partially supported" based on results of DNR/SHL biological sampling in 2006, 2012-2014. Results of chemical/physical water quality monitoring from the DNR/SHL ambient station at Gilbertville from 2012 through 2014, however, suggest "full support" of these uses. Monitoring at this station showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, ammonia-nitrogen, chloride, or sulfate in the 33 samples analyzed during the 2012-2014 assessment period.

The results from DNR/SHL stream biological sampling in 2006, 2012-2014 suggest that the Class B(WW1) aquatic life uses should be assessed as "partially supporting." This evaluated biological assessment was based on data collected in 2006, 2012-2014 as part of the DNR/SHL stream sampling projects. A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2006 FIBI score was 58 (good). The 2012-2014 BMIBI scores were56, 57 (both good) and 43, 50, 51, 55 (all fair). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The non-riffle habitat FIBI BIC for this ecoregion is 44, the natural substrate BMIBI BIC for this ecoregion is 70 and the artificial substrate BIC is 52. This assessment is considered evaluated because the drainage areas (4766 and 5234 mi2) above the sampling sites were greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site passed the FIBI BIC and failed to meet the BMIBI BIC (passed 1/6), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the sites used for the assessmentdon’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 the 2008 EPA/DNR fish tissue (RAFT) sampling on the Cedar River near Gilbertville. 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 composite sample of common carp fillets in 2008 had low levels of the primary contaminants (total PCBs, and technical chlordane) that were all below levels of concern. The results from the 2008 sampling show low levels of primary contaminants in the composite sample of common carp fillets (technical chlordane: <0.03 ppm, PCBs: 0.132 ppm) and in the composite sample of walleye fillets (mercury: 0.212 ppm). Thus, results from the 2008 sampling show that the level of total PCBs in the composite sample of common carp fillets (0.132 ppm) is considerably lower than the elevated level of PCBs (0.38 ppm) found in the composite sample of whole-fish common carp collected for the 1997 RAFT. The level of PCBs in 2008 samples are also well below the DNR/IDPH trigger level of 0.2 ppm for a one meal/week advisory. This result was not unexpected: levels of PCBs in Iowa fish and fish nationwide have declined over the last 30 years following the banning of PCB production in the United States in the 1970s. Also, levels of PCBs tend to be higher in whole-fish samples than in fillet samples. Because levels of all these contaminants from the 2008 RAFT monitoring are below advisory trigger levels, the fish consumption uses in this segment of the Cedar River are assessed as “fully supported.”