ADBNet

[Note:  A TMDL for indicator bacteria in this segment of Cedar River was prepared and approved by EPA in February 2010.  The approval of this TMDL moved the bacterial impairment for this segment from Iowa's list of Section 303(d) waters (Category 5a of the Integrated Report) to IR Category 4a (impaired; TMDL not required).]

The Class A1 uses are assessed as "partially supported" based on results of monitoring for indicator bacteria (E. coli).  The geometric mean level of indicator bacteria (E. coli) in the 23 samples collected during the recreation seasons of 2012 through 2014 are as follow:  the 2012 geometric mean was 56 orgs/100 ml, the 2013 geometric mean was 48 orgs/100 ml, and the 2014 geometric mean was 131 orgs/100 ml.  Only the 2014 geometric mean exceeded—and then only very slightly—the Class A1 geometric mean criterion of 126 orgs/100 ml.  Three of the 23 samples (13%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.  Only the 2014 geometric mean suggests impairment of the Class A1 uses.  These monitoring results indicate exceptionally low levels of indicator bacteria in this segment of the Cedar River.  According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35of U.S. EPA 1997b).  Thus, the Class A1 uses are assessed as “partially supported”.   Despite the ongoing impairment of the Class A1 uses in this river segment, levels of indicator bacteria are very low. 

Results of monitoring from the IDNR/SHL ambient station downstream from Cedar Rapids from 2012 through 2014 suggest "full support" of the Class B(WW1) aquatic life uses.  Monitoring at this station showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, ammonia-nitrogen, or chloride/sulfate in the approximately 35 samples collected.  During the assessment period, one of 34 samples (3%) contained a level of pH that violated the Class B(WW1) criterion of 9.0 pH units:  According to U.S. EPA assessment guidelines, if less than 10% of samples exceed state criteria for pH, the primary contact (Class A) and aquatic life (Class B) uses should be assessed as fully supported (see pgs 3-17 of U.S. EPA 1997b).  Violations of pH in ambient waters tend to reflect high levels of primary productivity and do not typically reflect the addition of pollutants to surface waters.    

However, the results IDNR/SHL stream REMAP biological sampling in 2005 indicate that the Class B(WW1) aquatic life uses should be assessed as "partially supporting".  The evaluated biological assessment was based on data collected in 2005 as part of the IDNR/SHL stream REMAP project.  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 2005 FIBI scores were 49, 46 (fair) and the BMIBI scores were 19 (poor) and 47 (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 FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51.  This segment passed the FIBI BIC 2/2 times and passed the BMIBI BIC 0/2 times in the last 10 years.  This assessment is considered evaluated because the drainage area (6829 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 passed the FIBI BIC and failed to meet 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 assessment doesn’t fall in the calibrated watershed size. 

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology.  IDNR 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 multiple samples collected in 2005; however, the samples were not collected in multiple years nor in the last five years.  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 results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Cedar Rapids in 2006.  The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes.  The composite samples of fillets from channel catfish and freshwater drum had low levels of contaminants.  Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.0803 ppm; total PCBs: 0.091 ppm; and technical chlordane: 0.03 ppm.  Levels of primary contaminants in the composite sample of freshwater drum fillets were as follows: mercury: 0.104 ppm; total PCBs: 0.09 ppm; and technical chlordane: 0.03 ppm.  All levels of these contaminants from this monitoring are below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses in this segment of the Cedar River.