Des Moines River IA 04-LDM-1003

Assessment Comments

Assessment is based on results of (1) IDNR/UHL ambient monthly monitoring near Keokuk from 2002-04 and (2) U.S. EPA/IDNR fish contaminant monitoring in 1999 near Croton.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses were assessed (monitored) as "fully supported" based on results of monitoring for indicator bacteria (E.  coli) from 2002-04, and the Class B(WW) aquatic life uses were assessed (monitored) as "fully supported" based on results of ambient chemcial/physical water quality monitoring from 2002-04.   Fish consumption remain assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 1999.   The sources of data for this assessment include results of (1) monthly monitoring from January 2002 through December 2004 at the IDNR/UHL ambient station located at the Highway 61 bridge south of Keokuk (STORET station 10560001; formerly station 410085) and (2) results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring in 1999 near Croton.  

EXPLANATION:  The Class A uses were assessed (monitored) as "fully supported" based on results of ambient monitoring for indicator bacteria (E.  coli).   Due to recent changes in Iowa’s Water Quality Standards, Iowa’s 2006 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 the 2006 Section 305(b) assessments and Section 303(d) listings.

The geometric mean level of indicator bacteria (E.  coli) in the 24 samples collected during the recreational seasons of 2002 through 2004 (43 orgs/100ml) is well below the Iowa Class A water quality criterion of 126 orgs/100ml, thus suggesting relatively low levels of bacteria in this river segment.   Four of the 24 samples exceeded Iowa’s single-sample maximum value of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if levels of E.  coli exceed the single-sample maximum value in more than 10% of the samples, the primary contact recreation uses should be assessed as “partially supported” (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   According to IDNR’s assessment/listing methodology, however, these results do not suggest that the violation frequency of Iowa’s single-sample maximum criterion is significantly greater than 10%, and thus these results do not suggest impairment of the Class A uses of this river segment.  

Results of ambient chemical/physical water quality suggest that the Class B(WW) aquatic life uses should be assessed (monitored) as "fully supported".   Results of monitoring from the IDNR ambient station at Highway 61 near Keokuk from 2002 through 2004 showed no violations of Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 36 samples collected or for pesticides in the nine sampled analyzed.   As has been typical of monitoring results from this station, however, levels of pH occasionally violate the Class B(WW) criterion of 9.0 pH units.   Four of the 36 samples (11%) had pH values greater than 9.0 units, with a maximum value of 9.3 units.   Violations of the high-pH criterion tend to occur on days when dissolved oxygen levels were at or above 100% saturation; these conditions suggest that high levels of primary productivity may have resulted in the high levels of pH observed.   According to U.S.  EPA guidelines for Section 305(b) reporting (U.S.  EPA 1997b:  page 3-17), a violation frequency for conventional parameters (including pH) of 10% or more suggests an impairment of aquatic life uses.   Based on IDNR’s assessment methodology, however, these results do not suggest that significantly more than 10 percent of the samples exceed Iowa’s pH criteria and thus do not suggest an impairment of the Class A or Class B(WW) uses of this river segment.  

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Croton in 1999.   The composite samples of fillets from common carp and freshwater drum had low levels of contaminants.   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 1999 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.