Assessment Comments

Assessment is based on results of (1) USGS/NAWQA monitoring (fish tissue and water) from 1995 to 1998 and again in 2004 and (2) U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2003.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses remain assessed (monitored) as "partially supported" based on results of USGS ambient water quality monitoring from March 1996 through September 1998 due to violations of human health criteria for dieldrin in 1996 and 1998.   Fish consumption uses remain assessed (monitored) as "fully supported."  The sources of data for this assessment include (1) USGS NAWQA monitoring from 1996-1998 and again in 2004 and (2) U.S.  EPA/IDNR fish contaminant (RAFT) monitoring in 2003.

EXPLANATION:  The assessment of the Class B(WW) uses of this segment of the Skunk River as “partially supported” remains 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) (see assessment for the 2002 report).   USGS monitoring from 1996-1998 showed two violations of the Class B(WW) chronic water quality criterion for dieldrin, and, according to U.S.  EPA's Section 305(b) assessment guidelines, these results indicate 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(WW) criterion was changed from 0.0019 ppb to 0.056 ppb.   Although all levels of dieldrin detected in USGS monitoring at the Wever station from March 1996 through September 1998 meet this revised criterion, the relatively high levels detected in samples from June 12, 1996 and May 26, 1998, continue to exceed the current Class B(WW) 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).   Results of USGS monitoring at this station from March to September 2004, however, show no violations of either (1) conventional parameters in the 10 samples analyzed for dissolved oxygen, pH, and ammonia or (2) toxic parameters in the seven samples analyzed for DDE, dieldrin, and chlorpyrifos.   The USGS detection level for dieldrin (0.009 ppb), however, is greater than Iowa’s human health criterion of 0.0014 ppb.   For this reason—and even though the data have aged beyond five years, the dieldrin impairment previously identified for this segment will remain.   USGS also conducted monitoring at this station from May 2002 through September 2004.   None of the 10 samples analyzed for conventional parameters from May 2002 through September 2004, and none of the seven samples analyzed for toxic parameters from March to September 2004, exceeded the respective Class B(WW) criteria.

Fish consumption uses are assessed (monitored) as "fully supported" based on the 2003 EPA/IDNR fish tissue (RAFT) sampling on the Skunk River NE 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.   The results from the 2003 sampling show that levels of the primary contaminants (chlordane, PCBs and mercury) are well below levels of concern.   The composite whole-fish samples of common carp had low levels of the primary contaminants:  mercury: 0.102 ppm; total PCBs: 0.09 ppm; and technical chlordane: 0.11 ppm.   The results from the 2001 sampling also show levels of the primary contaminants (chlordane, PCBs and mercury) well below levels of concern.   The 2001 composite whole-fish samples of common carp had  0.077 ppm of mercury, 0.189 ppm of total PCBs, and 0.12 ppm of technical chlordane.  

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 2003 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.