Assessment Comments
Assessment is based on: (1) results of IDNR/UHL biological (REMAP) monitoring in 2002, (2) results of ambient chemical/physical monitoring by the Minnesota Pollution Control Agency (MPCA) near Gordonsville, MN from 2006-08, and (3) results of U.S. EPA/IDNR fish contaminant monitoring near Northwood in 2005.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” based on results of monitoring for indicator bacteria. This assessment represents a new Section 303(d) listing for this assessment segment. The Class B(WW1) aquatic life uses are assessed (evaluated) as “partially supported” based on results of biological monitoring in 2002. Fish consumption uses are assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 2005. Sources of data for this assessment include (1) results of IDNR/UHL biological (REMAP) monitoring in 2002, (2) results of ambient chemical/physical monitoring by the Minnesota Pollution Control Agency (MNPCA1, station S000-084) near Gordonsville, MN from 2006-2008, and (3) results of U.S. EPA/IDNR fish contaminant monitoring near Northwood in 2005.
EXPLANATION: The Class A1 uses are assessed as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric mean level of indicator bacteria (E. coli) in the 12 independent samples collected by MPCA during the 2006 recreation season (198 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Six of the 12 samples (50%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. 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 "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).
Results of ambient chemical/physical monitoring from MPCA suggest that the Class B(WW1) aquatic life uses should be assessed (monitored) as “fully supported.” None of the approximately 20 samples collected in 2006 and 2008 at MPCA station S000-084 violated state water quality criteria for dissolved oxygen or pH. None of the 11 samples collected in 2006 and 2008 at this station violated Class B(WW1) criteria for ammonia nitrogen.
Results of IDNR/UHL biological monitoring, however, suggest that these uses should be assessed (evaluated) as “partially supported.” The biological assessment was based on data collected in 2002 as part of the IDNR/UHL REMAP project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological 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 2002 FIBI score was not available and the BMIBI score was 57 (good). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BMIBI score with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The natural substrate BMIBI BIC for this ecoregion is 70. This assessment is considered evaluated because of recent highwater/flood event directly preceding the sampling and the sampling conditions at the time of the sampling were unfavorable.
This aquatic life assessment is also considered "evaluated" because there were not two or more samples collected from this segment in multiple years from 2004-2008. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
Fish consumption uses remain assessed (monitored) as "fully supported " based on the 2005 EPA/IDNR fish tissue (RAFT) sampling on the Shell Rock River south of Northwood. The composite sample of common carp fillets had low levels of the primary contaminants (mercury, total PCBs, and technical chlordane) that were all below levels of concern. 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 results from the 2005 sampling show low levels of the primary contaminants (chlordane, PCBs and mercury) in the composite sample of common carp fillets: mercury: 0.181 ppm; total PCBs: 0.108 ppm; and technical chlordane: <0.03 ppm. Because levels of all these contaminants from the 2005 RAFT monitoring are below Iowa’s advisory trigger levels, the fish consumption uses in this segment of the Shell Rock River are assessed as “fully supported.”
