Assessment Comments

Assessment is based on: (1) the results of U.S. Geological Survey chemical/physical water quality monitoring at Keosauqua from 2006 through 2008, (2) results of U.S. EPA/IDNR fish contaminant monitoring in 2006 and 2008 at Keosauqua, and (3) results of a fish kill investigation in July 2006.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses remain "not assessed" due to the lack of water quality information upon which to base an assessment.   The Class B(WW1) aquatic life uses remain assessed (monitored) as “partially supporting” based on results of a fish kill investigation in July 2006 and a history of fish kills in, and upstream from, this assessment segment.   Results of chemical/physical monitoring from 2006-2008, however, suggest "full support" of the Class B(WW1) uses.   Fish consumption uses remain assessed (monitored) as "fully supported" based on fish contaminant monitoring in 2006 and 2008.   The sources of data for this assessment are (1) the results of U.S.  Geological Survey chemical/physical water quality monitoring from station 05490500 at Keosauqua from January 2006 through December 2008, (2) results of U.S.  EPA/IDNR fish contaminant monitoring in 2006 and 2008 at Keosauqua, (3) results of fish kill investigations in July 2002 and July 2006.  

EXPLANATION:  The Class A1 uses remain “not assessed” due to the lack of water quality monitoring and other water quality information for this river segment upon which to assess support of these uses (USGS monitoring in this river segment does not include analysis for indicator bacteria).   Prior to the 2002 report, these uses were assessed based on results of water quality monitoring conducted by IDNR/UHL near Keokuk (see assessments for the 1998 and 2000 reports).   This monitoring station, however, is more than 30 miles downriver from the current assessment segment (IA 04-LDM-0010-3), and previous assessment likely represent an excessive extrapolation of the monitoring results from the Keokuk station.  

The Class B(WW1) aquatic life uses remain assessed (monitored) as “partially supported” due to fish kills on July 31, 2002 and on July 10, 2006 on the reach of river between Eldon (Wapello Co.) and Douds (Van Buren Co.).    These kills are two in a series of kills that have occurred over the last ten years or so that appear to involve primarily shovelnose sturgeon (Schaphirynchus platorynchus).    Although the cause of the 2002 and 2006 kills and the previous kills remains unknown, the leading hypotheses are (1) that very high water temperatures, very low river flows, and elevated pH levels combine to make ambient levels of ammonia in the river toxic to the ammonia-intolerant shovelnose sturgeon and (2) that the kills are caused by a virus specific to shovelnose sturgeon.    

According to IDNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill within the most recent three-year period indicates that the aquatic life uses of a waterbody are only "partially supported."  Thus, the Class B(WW1) aquatic life uses of this river reach were assessed as "partially supported."  Also, according to IDNR’s assessment methodology, if a cause of a fishkill was not identified during the IDNR investigation (cause = "unknown"), or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.”  Such assessments, although suitable for Section 305(b) reporting, typically lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (Category 5 of the Integrated Report).    Waterbodies affected by such fish kills at usually placed in IR subcategories 2b or 3b and are added to the state’s list of “waters in need of further investigation”.    Due however to (1) the repeated occurrence of these kills over the last 10 years in Wapello and Van Buren counties, (2) the often large numbers of sturgeon killed (thousands), (3) the likelihood that these kills are caused by a pollutant and (4) the possibility that the kills have extended further downstream (possibly to Bonaparte), this impairment is added to Iowa’s Section 303(d) list (Category 5 of the Integrated Report).   Although applied to upriver segments (e.g., IA 04-LDM-0010_4) for the previous (2006) assessment/listing cycle, this (2008) is the first cycle in which this segment (IA 04-LDM-0010_3) has been considered fishkill-impaired.    

Results of water quality monitoring by the U.S.   Geological Survey near Keosauqua from 2006 through 2008, however, suggest "full support" of the Class B(WW1) uses.   No violations of Class B(WW1) water quality criteria occurred in the approximately 33 samples analyzed for dissolved oxygen, ammonia, DDE, and dieldrin.   Only one sample was analyzed for toxic metals during the 2006-2008 assessment period; no violations of Class B(WW1) criteria occurred in this sample.   The level of pH in one of the 33 samples analyzed (9.1 pH units) exceeded the Class B(WW1) pH criterion of 9.0 units (violation frequency of 3%).   According to U.S.  EPA guidelines for Section 305(b) reporting (U.S.  EPA 1997b:  page 3-17), however, a violation frequency for conventional parameters (including pH) of less than 10% does not suggest an impairment of aquatic life uses.  

Fish consumption uses are assessed (monitored) as "fully supported" based on the 2006 and 2008 EPA/IDNR fish tissue (RAFT) sampling on the Des Moines River NNW of Keosauqua.   This site has been sampled for whole-fish common carp since 1994 on an every-other-year basis as part of RAFT trend monitoring.   The 2006 and 2008 whole-fish samples of common carp had generally low levels of the primary contaminants.   The 2006 sample contained the following: mercury: 0.133 ppm; total PCBs: 0.164 ppm; and technical chlordane: 0.058 ppm.   The 2008 sample contained the following: mercury: 0.102 ppm; total PCBs: 0.187 ppm; and technical chlordane: 0.0833 ppm.   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.   The fish contaminant data generated from the 2006 and 2008 and previous RAFT sampling conducted at this river segment show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.

One of 33 samples analyzed for dieldrin at USGS station 05490500 during the 2006-2008 period exceeded the Iowa human health-fish (HH-fish) criterion of 0.00054 ppb.   The level of dieldrin in the sample collected on June 16, 2008 was a remarked data value estimated at 0.003 ppb.   Levels of dieldrin in the remaining 32 samples collected during the 2006-08 period were all reported as less than the level of detection of 0.009 ppb.   For purposes of Section 305(b) assessment, Iowa DNR views the Human Health criterion for dieldrin as analogous to a chronic criterion for a toxic parameter.   Thus, impairment of the HH use by dieldrin would be suggested if significantly more than 10% of the samples violated this criterion.   Because only 3% of the samples (1 of 33) violated this criterion, this violation does not indicate impairment of the HH-fish use.   Results of recent fish contaminant sampling in this river segment conducted as part of the U.S.  EPA/IDNR RAFT program showed 26 ppb of dieldrin in the composite sample of whole-fish common carp analyzed for the 2008 RAFT.   Although Iowa does not have an advisory trigger level for dieldrin, the levels seen in the 2007 and 2008 whole-fish composite samples from the Des Moines River near Keosauqua are well below the Iowa’s previous advisory trigger of 300 ppb of dieldrin (i.e., the U.S.  FDA action level for dieldrin).   In addition, levels of dieldrin in whole-fish samples tend to be higher than (i.e., overstate) levels of dieldrin in fillet samples.   Levels of dieldrin in Iowa fish have declined significantly since the early and mid-1980s when levels of 300 ppb to 500 ppb were not uncommon.