Assessment Comments

Assessment is based on: (1) results of IDNR ambient monthly monitoring approximately 4 miles southeast of Charles City (STORET station 10340001) from 2008 through 2010, (2) results of IDNR/UHL biological monitoring in 2000, 2001, 2002, and 2008, and (3) results of U.S. EPA/IDNR fish tissue (RAFT) monitoring 4 miles southeast of Charles City in 2003.

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 due to the completion of a Use Attainability Analysis, 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 "not supported" based on results of ambient monitoring for indicator bacteria during recreational seasons of 2008 through 2010.   The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supporting" based on results of biological monitoring in 2002.   The fish consumption uses remain assessed (monitored) as "fully supporting" based on results of fish contaminant monitoring in 2003.   The primary sources of data for this assessment are (1) results of IDNR ambient monthly monitoring approximately 4 miles southeast of Charles City (STORET station 10340001) from 2008 through 2010, (2) results of IDNR/UHL benthic macroinvertebrate monitoring in 2000, 2001, 2002, and 2008 and (3) results of U.S.  EPA/IDNR fish tissue (RAFT) monitoring 4 miles southeast of Charles City in 2003.  

Note:  A TMDL for indicator bacteria impairments in eight segments of Cedar River was prepared and approved by EPA in February 2010.   Because the bacterial impairment in this segment (IA 02-CED-0110_1) was not included in the EPA TMDL, this impairment is considered appropriate for Category 5a of Iowa's 2010 Integrated Report.  

EXPLANATION:  The Class A1 uses are assessed as "not supported" based on results of monitoring for indicator bacteria (E.  coli).   The geometric means of indicator bacteria (E.  coli) in the 22 samples collected during the recreational seasons of 2008 through 2010 at IDNR station 10340001 near Charles City were as follows:  the 2008 geometric mean was 204 orgs/100 ml, the 2009 geometric mean was 85 orgs/100 ml and the 2010 geometric mean was 163 orgs/100 ml.   The geometric means for 2008 and 2010 slightly exceed the Class A1 criterion of 126 orgs/100 ml.   Five of the 22 samples (23%) 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 are "not supported" (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 remain assessed (evaluated) as "partially supporting" due to results of IDNR/UHL biological monitoring in 2000, 2001, 2002 and 2008.   A series of biological metrics which 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 that were 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 BMIBI scores were 35, 42, 52 (all fair) and 63 (good).   The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BMIBI scores with biological assessment criteria established for previous Section 305(b) reports.   The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The BMIBI BIC for this ecoregion is 52 or 70 depending on sampling gear used to collect the sample.   This segment passed the BMIBI BIC 0/4 times in the last 10 years.   The assessment type is considered “evaluated” (of lower confidence) because the size of the segment’s watershed exceeds the range of reference condition watershed sizes used to calibrate the benthic macroinvertebrate and fish bioassessment indexes.   For this assessment, the drainage area for the segment (1,095 mi2) exceeds the maximum drainage area cutoff (500 mi2) that IDNR has established for use of BMIBI and FIBI data.  

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 the previous 11 years (2000-2010); however, the samples were not collected during a five-year period.   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).  

Despite results of biological monitoring that suggest impairment of aquatic life uses, results of ambient water quality monitoring from this segment continue to show no violations of Class B(WW1) water quality criteria and thus suggest good water quality conditions.   Similar to previous Section 305(b) assessment periods, results of IDNR/UHL ambient monitoring SE of Charles City from 2008-2010 show no violations of water quality criteria in the 32 samples analyzed for dissolved oxygen, pH, and ammonia-nitrogen.  

Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Midway in 2003.   The composite samples of fillets from channel catfish and smallmouth bass had low levels of contaminants.   Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.107 ppm; total PCBs: 0.119 ppm; and technical chlordane: < 0.03 ppm.   Levels of primary contaminants in the composite sample of smallmouth bass fillets were as follows: mercury: 0.124 ppm; total PCBs: 0.09 ppm; and technical chlordane: < 0.03 ppm.   Thus, levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.