Assessment Comments
Assessment is based on: (1) the results of monthly monitoring from January 2010 through December 2012 at the IDNR ambient city monitoring station located downstream from Waterloo at County Road D38 bridge at Gilbertville (STORET station 10070006), (2) IDNR/SHL stream biological sampling near Waterloo in 2006, 2011 and 2012, and (3) the results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2006 and 2008.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this river segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 and the completion of a Use Attainability Analysis in 2007, this segment is also now designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" (IR 5a) due to levels of indicator bacteria that violate state water quality criteria. Although results of IDNR/SHL ambient water quality monitoring from 2010-2012 suggest "full support" of the Class B(WW1) aquatic life, these uses are assessed (evaluated) as "partially supporting" (IR 3b-u) based on IDNR/SHL stream biological monitoring in 2006, 2011 and 2012. Fish consumption uses remain assessed (monitored) as "fully supported" (IR 2a) based on results of fish contaminant monitoring in 2006 and 2008. The sources of data for this assessment are (1) the results of monthly monitoring from January 2010 through December 2012 at the IDNR ambient city monitoring station located downstream from Waterloo at County Road D38 bridge at Gilbertville (STORET station 10070006), (2) IDNR/SHL stream biological sampling near Waterloo in 2006, 2011 and 2012, and (3) the results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2006 and 2008. Note: USGS conducted monitoring at station 05463050 at Cedar Falls in October 2010. Too few data were produced from this monitoring during the 2010-2012 assessment period (one sample) to be of use for assessment for purposes of either Section 305(b) reporting or Section 303(d) listing.
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.
EXPLANATION: 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 24 samples collected during the recreational seasons of 2010 through 2012 at station 10070006 downstream from Waterloo were as follows: the 2010 geometric mean was 161 orgs/100 ml, the 2011 geometric mean was 159 orgs/100 ml and the 2012 geometric mean was 97 orgs/100 ml. The 2010 and 2011 geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml; the 2012 geometric mean was below this criterion. Six of the 24 samples (25%) 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 IDNR’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 IDNR/SHL biological sampling in 2006, 2011 and 2012. Results of chemical/physical water quality monitoring from the IDNR/UHL ambient station at Gilbertville from 2008 through 2010, 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 36 samples analyzed during the 2010-2012 assessment period.
The results from IDNR/SHL stream biological sampling in 2006, 2011 and 2012 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, 2011 and 2012 as part of the IDNR/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 2011 BMIBI scores was 60 (good) and the 2012 BMIBI scores were 43 and 50 (both 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 (4,766 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 1/3), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size. According to IDNR’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). IDNR 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 2006 and 2008 EPA/IDNR 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 2006 and 2008 had low levels of the primary contaminants (mercury, total PCBs, and technical chlordane) that were all below levels of concern. The results from the 2006 sampling show low levels of the primary contaminants (chlordane, PCBs and mercury) in the composite sample of common carp fillets: mercury: 0.166 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. 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 2006 and 2008 sampling show that the level of total PCBs in the composite sample of common carp fillets (0.09 ppm and 0.132 ppm, respectively) 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 the 2006 and 2008 samples are also well below the IDNR/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 2006 RAFT monitoring are below advisory trigger levels, the fish consumption uses in this segment of the Cedar River are assessed as “fully supported.”
