Assessment Comments

Assessment is based on: (1) USGS NAWQA monitoring from 2004 through 2006 at station 05474000 near Augusta, (2) U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2005 and 2006, (3) fish contaminant monitoring conducted as part of the IDNR/UHL REMAP biological monitoring project in 2006 (REMAP Site 194), and (4) IDNR/UHL stream REMAP biological monitoring in 2006 near Burlington.

Basis for Assessment

[Note:  Prior to the current (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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf) and due to the completion of a Use Attainability Analysis in 2007, 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 “not assessed” due to the lack of information upon which to base as assessment.   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of USGS ambient water quality monitoring from March 2004 through December 2006 and IDNR/UHL stream REMAP biological monitoring in 2006 near Burlington.   The previous impairment of the Class B(WW1) aquatic life uses due to dieldrin is de-listed for the 2008 Section 303(d) cycle.   Fish consumption uses remain assessed (monitored) as "fully supported."  The sources of data for this assessment include (1) USGS NAWQA monitoring from 2004 through 2006 at station 05474000 near Augusta, (2) U.S.  EPA/IDNR fish contaminant (RAFT) monitoring in 2005 and 2006, (3) fish contaminant monitoring conducted as part of the IDNR/UHL REMAP biological monitoring project in 2006 (REMAP Site 194), and (4) IDNR/UHL stream REMAP biological monitoring in 2006 near Burlington.

EXPLANATION:  The Class A1 (primary contact recreation) uses are “not assessed” due to the lack of information upon which to base as assessment:  the USGS monitoring conducted in this assessment segment did not include sampling for indicator bacteria.

The Class B(WW1) aquatic life uses are assessed (monitored) as “fully supported” based on results of USGS monitoring from 2004 through 2006.   Results of USGS monitoring at this station from March 2004 through December 2006 show no violations of Class B(WW1) criteria for dissolved oxygen or ammonia in the 34 samples analyzed, for toxic metals in the two samples analyzed, or for pesticides in the 34 samples analyzed.   One of the 34 samples analyzed for pH, however, exceeded the Class B(WW1) criterion of 9.0 pH units (this sample contained a pH of 10.3 pH units).   According to U.S.  EPA guidelines (U.S.  EPA 1997b, page 3-17), however, a violation frequency of less than 10% for conventional parameters such as pH nonetheless suggests "full support" of aquatic life uses.   Thus, the percentage of violations of the pH criterion at this station (3%) does not suggest an impairment of aquatic life uses in this stream segment.  

The previous (2006) assessment of the Class B(WW1) uses of this segment of the Skunk River was “partially supported.”  This assessment was based on results of monitoring conducted at Augusta from March 1996 to September 1998 by USGS as part of the National Water Quality Assessment Program (NAWQA) (eastern Iowa river basins study unit, station 05474000).   USGS monitoring from 1996-1998 showed two violations of the Class B(WW1) chronic water quality criterion for dieldrin, and, according to U.S.  EPA's Section 305(b) assessment guidelines, these results indicated only "partial support" of the aquatic life uses.   In October 2000, water quality criteria for dieldrin in the Iowa Water Quality Standards were revised.   As part of these revisions, the chronic Class B(WW1) criterion was changed from 0.0019 ppb to 0.056 ppb.   Although all levels of dieldrin detected in USGS monitoring at the USGS station from March 1996 through September 1998 met this revised criterion, the relatively high levels detected in samples from June 12, 1996 and May 26, 1998, continued to exceed the Class B(WW1) human health criterion (fish) of 0.0014 ppb (the human health criteria for dieldrin were not affected by the October 2000 revisions of the Iowa Water Quality Standards).   Because the USGS detection level for dieldrin (0.009 ppb) was greater than Iowa’s human health criterion of 0.0014 ppb, the dieldrin impairment was retained for Iowa’s 2006 Section 303(d) list.  

Monthly monitoring for dieldrin has been conducted at this station from 2004 through 2006.   None of the 34 samples analyzed have contained a detectable level of dieldrin.   Thus, in spite of the issues with detection levels, these additional data suggest good cause for delisting the dieldrin impairment first identified for the 2002 listing cycle.   Given the lack of detectable levels of dieldrin, and with a detection level of 0.009 ppb, there is no method of verifying whether levels of dieldrin remain above Iowa’s current human health criterion of 0.0054 ppb (note:  the IDNR/UHL detection level for dieldrin in water is 0.050 ppb).   The existing and readily available data, however, do not suggest any dieldrin-related impairment in this assessment segment.  

In addition to the USGS WQ monitoring, the results of the 2006 IDNR/UHL stream REMAP biological monitoring in 2006 near Burlington also suggest "full support" of the Class B(WW1) aquatic life uses.   This evaluated biological assessment was based on data collected in 2006 as part of the DNR/UHL 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 2006 FIBI score was 43 (fair) and the BMIBI score was 45 (fair).  The aquatic life use support was assessed (evaluated) as fully supporting (=FS), 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 1994-2004.   The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51.   This site met the BMIBI BIC with the aid of the BMIBI UAV of 8 points.    This assessment is considered evaluated because the drainage area (4344 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 both the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.

Fish consumption uses are assessed (monitored) as "fully supported" based on the 2005 and 2006 EPA/IDNR fish tissue (RAFT) samplings on the Skunk River northeast of Wever.   This site has been sampled for whole-fish common carp since 1995 on an every-other-year basis as part of RAFT trend monitoring.   Due to a change in the design of the RAFT program, this site was sampled in the consecutive years of 2005 and 2006.   The 2005 composite whole-fish samples of common carp had low levels of the primary contaminants:  mercury: 0.086 ppm; total PCBs: 0.188 ppm; and technical chlordane: 0.076 ppm.   The 2006 composite whole-fish samples of common carp had similar levels of these contaminants:  mercury: 0.191 ppm; total PCBs: 0.133 ppm; and technical chlordane: 0.046 ppm.   Results of fish contaminant monitoring conducted in this assessment segment in September 2006 as part of the IDNR/UHL REMAP project (Site 194) showed similar results in the composite samples of common carp fillets:  mercury: 0.218 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 2005 or 2005 RAFT sampling or the 2006 REMAP sampling conducted in this assessment segment:  the levels of contaminants do not exceed any of the new (2006) advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.