Assessment Comments

Assessment is based on: (1) the results of monthly monitoring from 2004 through 2006 at the IDNR/UHL ambient city monitoring station located upstream from Ames at the Sleepy Hollow canoe access (station 10850003), (2) results of IDNR/UHL biological monitoring in 2003; and (3) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2004.

Basis for Assessment

SUMMARY:  The Class A1 uses are assessed (monitored) as “not supported” due to high levels of indicator bacteria that violate state water quality criteria.   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of (1) biological monitoring in 2003 by IDNR/UHL and (2) ambient chemical/physical monitoring by IDNR/UHL from 2004-2006.   Fish consumption uses remain assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 2004.   The sources of data for this assessment include (1) the results of monthly monitoring from 2004 through 2006 at the IDNR/UHL ambient city monitoring station located upstream from Ames at the Sleepy Hollow canoe access (station 10850003), (2) results of IDNR/UHL biological monitoring in 2003; and (3) results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring in 2004.  

EXPLANATION:  The Class A1 uses are assessed as "not supported" based on results of monitoring for indicator bacteria (E.  coli) during recreational seasons of 2004 through 2006.   Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed.   Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses:  the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff."  Due to a change in the Standards in July 2003, E.  coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E.  coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.”  Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E.  coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of Section 305(b) assessments and Section 303(d) listings.  

The geometric mean level of indicator bacteria (E.  coli) in the 24 samples collected (162 orgs/100ml) slightly exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Nine of the 24 samples (38%) exceeded Iowa’s single-sample maximum value 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).   Monitoring results for indicator bacteria during the 2004-2006 assessment period are consistent with the generally low levels of indicator bacteria at the IDNR/UHL monitoring station during recent biennial periods.   For example, for the 2004 through 2008 assessment cycles, geometric mean values have either been below or slightly above the Class A1 criterion, and approximately one-third of the samples have exceeded the single-sample maximum value.   Relative to other river reaches in Iowa, these results suggest low levels of indicator bacteria in this segment of the South Skunk River.  

The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of both chemical/physical and biological monitoring.   Results of chemical/physical water quality monitoring during the 2004-06 period at the IDNR ambient station upstream from Ames showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the 36 samples collected, for toxic metals in the 14 samples collected, or for pesticides and other toxic organic compounds in the approximately 10 samples analyzed.   These results suggest “full support” of the Class B(WW1) aquatic life uses.    

Results of biological monitoring also suggest “full support” of the aquatic life uses of this river segment.   This assessment is partially based on results of IDNR/UHL biological monitoring in 2003.   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 fish species and benthic macroinvertebrate taxa 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 community index of biotic integrity (BMIBI).   The indices rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2003 FIBI scores were 54 (good), 44 (fair) and the FIBI average was 49.   The 2003 BMIBI scores were 76 (excellent), 65 (good) and the BMIBI average was 70.5.   The aquatic life use support was assessed as Fully Supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports.   The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62.   The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.

Fish consumption remain assessed (monitored) as "fully supported" based on results of U.S.  EPA/IDNR fish tissue (RAFT) monitoring conducted in 2004 near Story City.   The composite samples of fillets from common carp and smallmouth bass had low levels of contaminants.   Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.069 ppm; total PCBs: 0.09 ppm; and technical chlordane: 0.031 ppm.   Levels of primary contaminants in the composite sample of smallmouth bass fillets were as follows:  mercury: 0.109 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.   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 2004 RAFT 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.