Assessment Comments

Assessment is based on results of (1) IDNR/UHL ambient monthly water quality monitoring from 2002-04 and (2) U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 1994.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported".   The Class C (drinking water) uses are also assessed (monitored) as "fully supported”.  Fish consumption uses remain assessed (evaluated) as “fully supported” based on results of fish contaminant monitoring in 1994.   This assessment is based on (1) results of IDNR/UHL monthly ambient monitoring conducted during the 2002-2004 assessment period at the County Road J-53 bridge near Shambaugh (STORET station 10730001 (formerly station 787044)) and (2) results of U.S.  EPA / IDNR fish contaminant (RAFT) monitoring in 1994.  

EXPLANATION:  Results of ambient monitoring at the IDNR/UHL station near Shambaugh showed no violations of Class B(WW) water quality criteria during the 2002-2004 assessment period for dissolved oxygen (minimum value = 6.2 mg/l), pH (range = 7.6 to 8.9 units), or ammonia-nitrogen (maximum value = 0.62 mg/l) in the 36 samples collected.  Levels of pesticides in the seven samples analyzed, and levels of toxic metals in the ten samples analyzed, were all below the respective Class B(WW) criteria.   These results suggest "full support" of the Class B(WW) aquatic life uses.  

The Class C (drinking water) uses were also assessed as "fully supported".   Levels of atrazine exceeded the Class C criterion of 3 ppb (=EPA’s MCL) in two of the 36 samples (6%) analyzed (maximum value = 18 ppb).   The mean (0.85 ppb) and median (0.08 ppb) values of atrazine during the 2002-2004 period, however, were well-below the Class C criterion.   Also, the level of nitrate exceeded the Class C criterion of 10 mg/l (=EPA’s MCL) in one of 36 samples (3%) analyzed (maximum value = 11 ppm).   The mean (2.8 ppm) and median (2.0 ppm) values of nitrate during the 2002-2004 period, however, were well-below the Class C criterion.   According to IDNR guidelines for Section 305(b) assessments, these results do not suggest an impairment of drinking water uses for this assessment segment.  

Fish consumption uses remain assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Shambaugh in 1994.   Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).   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 1994 RAFT sampling conducted in this assessment segment:  levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.