Assessment Comments

Assessment is based on results of (1) USGS/NAWQA monitoring (fish tissue and water) at August from 1995 to 1998 and (2) fish tissue (RAFT) monitoring in 1999 & 2001.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses remain assessed as "partially supported;" the fish consumption uses are assessed as "fully supported."  EXPLANATION:  The assessment of support of the Class B(WW) uses remains based on results of monitoring conducted on the Skunk River 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 above).   No additional water quality monitoring was conducted in this river segment during the 2000-2001 biennial period.   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 Sepember 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 of 0.0014 ppb (the human health criteria for dieldrin were not affected by the October 2000 revisions of the Iowa Water Quality Standards).   Fish consumption uses are assessed as "fully supported" based on results of EPA/DNR fish tissue monitoring near Wever in 2001 that showed levels of all contaminants in the composite samples of whole-fish carp were less than ½ of the respective FDA action levels and DNR levels of concern.   The level of lead in the 1999 sample of whole-fish carp from this station (2.10 mg/kg), however, was twice the DNR level of concern of 1.0 mg/kg and resulted in an assessment of "fully supported / threatened" for fish consumption uses in the 2000 report (see above).   The level of lead in the 2001 whole-fish carp was less than the level of detection (<0.17 ppm); thus, the assessment of fish consumption uses was changed to "fully supported" for this report.   This site will again be monitored in 2003 as part of the U.S.  EPA/IDNR RAFT monitoring program.