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 2008-10, 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 remain assessed (monitored) as “not supported” based on results of monitoring for indicator bacteria. The Class B(WW1) aquatic life uses are assessed (monitored) as “partially supported” due to violations of water quality criteria for dissolved oxygen. This is a new impairment for this assessment segment. Fish consumption uses remain 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 (MNPCA station S000-084) near Gordonsville, MN, from August 28, 2008 to November 15, 2010, and (3) results of U.S. EPA/IDNR fish contaminant monitoring near Northwood in 2005.
EXPLANATION: Although recreation season geometric means for 2009 and 2010 were very low and easily met the Class A1 geometric mean criterion, the Class A1 uses of this segment remain assessed as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli) from 2006-2008. 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) exceeded the Iowa Class A1 water quality criterion of 126 orgs/100ml. According to IDNR’s methodology for de-listing impairments, geometric mean levels of bacteria must meet state standards over two consecutive assessment/listing cycles in order for the impairment to be removed. Because the geometric mean criterion was exceeded during the previous (2010) listing cycle, this impairment will remain for the current (2012) cycle. If geometric mean levels are again below state standards during the next (2014) assessment listing cycle, this impairment can be de-listed.
The geometric means of indicator bacteria (E. coli) in the 15 samples collected during the recreational seasons of 2009 and 2010 at MPCA station S000-084 near Gordonsville, MN, were as follows: the 2009 geometric mean was 78 orgs/100 ml and the 2010 geometric mean was 84 orgs/100 ml. Both geometric means were below and met the Class A1 criterion of 126 orgs/100 ml. Two of the 15 samples (13%) 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 means are below the water quality criterion, and the percentage of samples exceeding the state’s single-sample maximum criterion is not significantly greater than 10%, then the primary contact recreation uses should be assessed as “fully supporting.” According to Iowa’s assessment/listing methodology, the percentage of samples exceeding the single-sample maximum criterion is not significantly greater than 10%.
Results of ambient chemical/physical monitoring from MPCA suggest that the Class B(WW1) aquatic life uses should be assessed (monitored) as “partially supported.” Of the 114 samples analyzed for dissolved oxygen during the 2008-2010 period, 21 samples (18%) violated the Class B(WW1) aquatic life criterion of 5.0 mg/l. All violations occurred in the summer and early fall of 2010; violations ranged from 0.3 to .4.78 mg/l. None of the approximately 34 samples collected from 2008-10 at MPCA station S000-084 violated state water quality criteria for ammonia. Although five of the 134 samples analyzed for pH violated the Class B(WW1) criterion of 9.0 pH units, the percentage of sample violating this criterion (4%) is below the 10% threshold used to identify impairments for this parameter.
Consistent with the results of dissolved oxygen monitoring from 2008-10, results of IDNR/UHL biological monitoring in 2002 suggest that the aquatic life 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 high-water/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 over a five-year period. 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.”
