Assessment Comments

Assessment is based on (1) IDNR/UHL ambient monitoring downstream from Charles City from 2002-04, (2) 2002 evaluated biocriteria data: BM-IBI = 51 (fair), and (3) EPA/IDNR fish tissue (RAFT) monitoring in 2003.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed (evaluated) as "partially supporting" based on results of biological monitoring in 2002.   The fish consumption uses are 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 2002 through 2004, (2) results of IDNR/UHL biological (REMAP) monitoring in 2002, and (3) results of U.S.  EPA/IDNR fish tissue (RAFT) monitoring 4 miles southeast of Charles City in 2003.  

EXPLANATION:  The Class B(WW) aquatic life uses were assessed (evaluated) as "partially supporting" due to results of biological monitoring in 2002 conducted as part of the DNR/UHL stream biocriteria project.   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 (F-IBI) and a benthic macroinvertebrate index (BM-IBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2002 BM-IBI score was 51 (fair).   The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BM-IBI 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 1994-2001.   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 (approximately 1,000 mi2) exceeds the maximum drainage area cutoff (500 mi2) that IDNR has established for use of BMIBI and FIBI data.   Therefore, IDNR considers the aquatic life use impairments indicated by these data as “evaluated” assessments that are 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 2002-2004 suggest "full support" of the Class B(WW) aquatic life uses due to the lack of violations of water quality criteria in (1) the 36 samples analyzed for conventional and toxic parameters (dissolved oxygen, pH, and ammonia-nitrogen) and (2) the approximately 10 samples analyzed for pesticides at the IDNR monthly monitoring station during the 2002-2004 assessment period.   These results suggest full support of the Class B(WW) uses.   This station was monitored for toxic organic compounds and pesticides from March 1996 to September 1998 as part of the USGS National Water Quality Assessment (NAWQA) program in the eastern Iowa river basins study unit (see assessment for the 2000 report).   Results of this monitoring showed that one of 27 samples violated the Class B(WW) chronic water quality criterion for DDE.   IDNR monitoring during the 2000-2002 and the 2002-2004 assessment periods, however, have shown no violations of the Class B(WW) water quality criterion for DDE in the samples analyzed.  

Fish consumption uses were 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.

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.   Prior to 2006, IDNR used action levels published by the U.S Food and Drug Administration to determine whether consumption advisories should be issued for fish caught as part of recreational fishing in Iowa.   In an effort to make Iowa’s consumption more compatible with the various protocols used by adjacent states, the Iowa Department of Public Health, in cooperation with Iowa DNR, developed a risk-based advisory protocol.   This protocol went into effect in January 2006 (see http://www.iowadnr.gov/fish/news/consump.html for more information on Iowa’s revised fish consumption advisory protocol).   Because the revised (2006) protocol is more restrictive than the previous protocol based on FDA action levels; fish contaminant data that previously suggested “full support” may now suggest either a threat to, or impairment of, fish consumption uses.   This scenario, however, does not apply to the fish contaminant data generated from the 2003 RAFT sampling conducted in this assessment segment:  levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.