Assessment Comments

Assessment is based on: (1) USGS NAWQA monitoring from 2010 through 2012 at station 05474000 near Augusta, (2) IDNR ambient monitoring from October 2010 to June 2012, (3) U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2006, 2007, and 2010, (4) fish contaminant monitoring conducted as part of the IDNR/SHL REMAP biological monitoring project in 2006 (REMAP Site 194), and (5) IDNR/SHL biological sampling in 2006 near Burlington and in 2012 near Augusta.

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 5a) due to levels of indicator bacteria that slightly exceed state criteria.   The Class B(WW1) aquatic life uses are assessed (evaluated) as "partially supported" (IR 3b-u) based on results of USGS and IDNR ambient water quality monitoring from 2010-12 and IDNR/SHL stream REMAP biological sampling in 2006 near Burlington and stream nutrient sampling in 2012 near Augusta.   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 occasionally exceed Iowa’s Human-Health/fish criterion and indicate that these uses should be assessed (evaluated) as “partially supporting” (IR 3b).   The sources of data for this assessment include (1) USGS NAWQA monitoring from February 2010 through December 2012 at station 05474000 near Augusta, (2) Iowa DNR ambient monitoring from October 2010 to June 2012 at station 10560002, (3) U.S.  EPA/IDNR fish contaminant (RAFT) monitoring in 2006, 2007, and 2010, (4) fish contaminant monitoring conducted as part of the IDNR/SHL REMAP biological monitoring project in 2006 (REMAP Site 194), and (5) IDNR/SHL biological sampling in 2006 near Burlington and in 2012 near Augusta.

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 23 samples collected during the recreational seasons of 2010 through 2012 at USGS station 05474000 at Augusta, IA, were as follows:  the 2010 geometric mean was 651 orgs/100 ml, the 2011 geometric mean was 213 orgs/100 ml, and the 2012 geometric mean was 43 orgs/100 ml.   The 2010 and 2011 geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Nine of the 23 samples (39%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.  

At IDNR ambient station 10560002, too few bacteria samples were collected during the recreation seasons of 2010 (2 samples) and 2012 (3 samples) to calculate meaningful geometric means.   During the 2011 recreation season, however, 8 samples were collected, and the geometric mean was 73 orgs/100ml.   If all 13 recreation samples collected from 2010 to 2012 are combined, two of the 13 samples (15%) 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.”  

The Class B(WW1) aquatic life uses are assessed (evaluated) as “partially supported” based on results of USGS and IDNR monitoring from 2010 through 2012 and based on results of IDNR/SHL biological sampling in 2006 and 2012.   Results of USGS and IDNR monitoring at this station from February 2010 through December 2012 show no violations of Class B(WW1) criteria for dissolved oxygen, pH, or ammonia in the combined 54 samples analyzed at these stations.   None of the 21 samples analyzed for chloride and sulfate at the IDNR monitoring station exceeded their respective Class B(WW) criteria.   In addition, none of the 32 samples analyzed for the chlorphyrifos, DDE, or dieldrin exceeded their respective Class B(WW1) aquatic life criteria.   Twenty-two of the 1,061 readings of water temperature (2%) exceeded the Class B(WW1) criterion of temperature of 32C.   According to EPA assessment guidelines and IDNR’s assessment methodology, a violation frequency of less than 10% for conventional parameters such as water temperature does not indicate impairment of aquatic life uses.   Thus, these results suggest “full support” of the Class B(WW1) aquatic life uses.

In contrast to the USGS WQ monitoring, the results of IDNR/SHL stream biological sampling in 2006 and 2012 suggest "partial support" of the Class B(WW1) aquatic life uses.   This evaluated biological assessment was based on data collected in 2006 and 2012 as part of the IDNR/SHL stream REMAP and stream nutrient sampling projects.   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 41 (fair) and the BMIBI score was 45 (fair).   The 2012 BMIBI scores were 29 (poor) and 45 (fair).   The aquatic life use support was assessed (evaluated) as partially supporting (=PS), 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 1994-2008.   The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51 (2006 sample).   The BMIBI BIC for this ecoregion is 51 (2012 samples).   This assessment is considered evaluated because the drainage areas (4342 and 4303 mi2) above the sampling sites were far greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   Even though this site passed the FIBI BIC and failed the BMIBI BIC (1/3), 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.   According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus 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).    

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 2010-2012.   Six of 32 samples from USGS station 05474000 analyzed for dieldrin during the 2010-2012 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 (six:  two detected values (0.003 & 0.005 ug/l) and four values estimated at 0.002 ug/l), and the method detection level (0.008 ug/l) was too high (~15 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 (note:  RAFT trend samples were not collected in 2012 due to low water conditions).   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.