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.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed as "partially supported;" the fish consumption uses are assessed as "fully supported / threatened."  EXPLANATION:  The assessment of support of the Class B(WW) uses is 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).   This monitoring showed (1) no violations of Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen in the 34 samples collected, (2) a single violation of the Class B(WW) chronic water quality criterion for chlorpyrifos in the 21 samples analyzed, and (3) two violations of the Class B(WW) chronic water quality criterion for dieldrin (0.0019 ug/l) in the 21 samples analyzed.   The violations of dieldrin occurred on June 12, 1996 (0.004 ug/l) and on May 26, 1998 (0.0058 ug/l).   Although the results for pH, dissolved oxygen, and ammonia-nitrogen suggest full support of the aquatic life uses, the results of pesticide monitoring (dieldrin) indicate only partial support of these uses.   According to U.S.  EPA guidelines for Section 305(b) reporting (U.S.  EPA 1997b, page 3-18), the one violation of the chronic criterion for chlorpyrifos does not suggest an impairment of the aquatic life uses.   The EPA guidelines, however, specify that more than one violation of a water quality criterion for a toxic contaminant within a three-year period indicates that the aquatic life uses are not fully supported.   Thus, according to the U.S.  EPA guidelines, the two violations of the chronic criterion for dieldrin (9.5 % violation) indicate "partial support" of the Class B(WW) uses.   Fish consumption uses remain assessed as "fully supported / threatened" based on results of (1) the USGS/NAWQA fish tissue monitoring in September 1995 that showed levels of organochlorine contaminants were less than ½ of the respective FDA action levels and DNR levels of concern (see assessment for the 1998 report above) and (2) EPA/DNR fish tissue monitoring near Wever in 1999 that showed levels of all contaminants in the composite samples of whole-fish carp were less than ½ of the respective FDA action levels.   The level of lead in this sample (2.10 mg/kg), however, is twice the DNR level of concern of 1.0 mg/kg and is well above typical lead concentrations in Iowa fish.   An FDA action level does not exist for lead, and U.S.  EPA does not include lead in its list of target analytes for screening studies in fish and shellfish (see page 4-2 of U.S.  EPA's "Guidance for Assessing Chemical Contaminant Data for Use in Fish Advisories," document EPA 823-R-93-002, August 1993).   Due to this unusually high level of lead, however, the fish consumption uses were assessed as "fully supporting / threatened."