Assessment Comments

Assessment is based on: (1) USGS NAWQA monitoring from 2008 through 2010 at station 05474000 near Augusta, (2) U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2006, 2007, and 2010, (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 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 assessed (monitored) as “not supporting” (IR Category 5a) due to levels of indicator bacteria that exceed state criteria.   This is a new impairment for this assessment segment.   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of USGS ambient water quality monitoring from February 2008 through December 2010 and IDNR/UHL stream REMAP biological monitoring in 2006 near Burlington.   Although results of fish contaminant monitoring in 2005, 2006, and 2010 suggest “full support” of fish consumption uses, results of USGS monitoring show that levels of dieldrin exceed Iowa’s Human-Health/fish criterion and indicate that these uses should be assessed (evaluated) as “partially supporting” (IR Category 3b).   The sources of data for this assessment include (1) USGS NAWQA monitoring from 2008 through 2010 at station 05474000 near Augusta, (2) U.S.  EPA/IDNR fish contaminant (RAFT) monitoring in 2006, 2007, and 2010, (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) are assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria.   The geometric means of indicator bacteria (E.  coli) in the 14 samples collected during the recreational seasons of 2008 through 2010 at USGS station 05474000 at Augusta, IA, were as follows:  the 2008 geometric mean was 100 orgs/100 ml, the 2009 geometric mean was 1,799 orgs/100 ml and the 2010 geometric mean was 651 orgs/100 ml.   The 2009 and 2010 geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Nine of the 14 samples (64%) 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.”  This is a new impairment for this assessment segment.

The Class B(WW1) aquatic life uses are assessed (monitored) as “fully supported” based on results of USGS monitoring from 2008 through 2010 and based on results of IDNR/UHL biological monitoring in 2006.   Results of USGS monitoring at this station from February 2008 through December 2010 show no violations of Class B(WW1) criteria for dissolved oxygen, pH, ammonia, or pesticides in the approximately 30 samples analyzed.  

The 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 2010.   None of the approximately 70 samples analyzed over that time contained a detectable level of dieldrin.   Thus, in spite of the issues with detection levels, these additional data continue to suggest good cause for delisting the dieldrin impairment of the Class B(WW1) aquatic life uses that was first identified for the 2002 listing cycle and that was de-listed for the 2008 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 of aquatic life uses 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 (4342 mi2) above this sampling site was far 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.  

The Human Health designated use (including the fish consumption use) is assessed (evaluated) as “partially supporting” (IR Category 3b-potentially impaired) based on USGS monitoring from 2008-2010.   Five of 30 samples from USGS station 05474000 analyzed for dieldrin during the 2008-2010 period exceeded the Iowa human health-fish (HH-fish) criterion of 0.00054 ppb (=54 parts per trillion).   According to IDNR’s assessment/listing methodology, if the mean level of a toxic metal or pesticide is greater than its respective human health criterion, impairment ("nonsupport") of the Human Health use is indicated.   However, the samples with detectable levels of dieldrin were too few (five) and the method detection level (0.009 ug/l) were too high (16 times the HH criterion for dieldrin) to allow calculation of a meaningful summary statistic (e.g., mean) for dieldrin at USGS station 05474000.  

Despite the violations of Iowa’s human-health/fish criterion for dieldrin, results of recent fish contaminant sampling in this river segment conducted as part of the U.S.  EPA/IDNR RAFT program show low levels of dieldrin in Skunk River fish.   This monitoring showed 15 ppb of dieldrin in the composite sample of common carp fillets analyzed for the 2007 RAFT, 10 ppb of dieldrin in the composite sample of common carp fillets analyzed for the 2007 RAFT, and 44 ppb in the composite sample of whole-fish common carp analyzed for the 2010 RAFT.   Although Iowa does not have an advisory trigger level for dieldrin, the levels seen in the 2005, 2007 and 2010 whole-fish composite samples from August are well below the Iowa’s previous advisory trigger of 300 ppb of dieldrin (i.e., the U.S.   FDA action level for dieldrin).   Levels of dieldrin in Iowa fish have declined significantly since the early and mid-1980s when levels of 300 ppb were not uncommon (see ftp://ftp.igsb.uiowa.edu/igspubs/pdf/WFS-2006-05.pdf).   Samples from this station in the early and mid-1980s averaged over 150 ppm of dieldrin.  

Fish contaminant monitoring for toxic parameters other than dieldrin (e.g., mercury, PCBs, and chlordane) suggest “full support” of fish consumption uses.   This site has been sampled for whole-fish common carp since 1995 on an every-other-year basis as part of RAFT trend monitoring.   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.   The 2007 composite samples of common carp fillets had low levels of the primary contaminants:  mercury: 0.208 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.   The composite samples of white bass fillets also had low levels of mercury (0.152 ppm).   The 2010 composite samples of whole fish samples of common carp had low levels of primary contaminants: mercury: 0.117 ppm; total PCBs: 0.162 ppm; and technical chlordane: 0.092 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 the degree to which Iowa’s lakes and rivers support their fish consumption uses.   The fish contaminant data generated from the 2006, 2007, and 2010 RAFT sampling and the fish tissue data collected as part of the IDNR/UHL REMAP project conducted at this river show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.   Due, however, to the low frequency with which violations of the human health (fish + water) dieldrin criterion occurs, the assessment of the HH-fish consumption uses in this river segment is considered appropriate for Iowa’s IR Category 3b (potential impairment).   IR Category 3b waters will be added to Iowa’s list of waters in need of further investigation.