Assessment Comments

Assessment is based on: (1) the results of U.S. Geological Survey chemical/physical water quality monitoring at Keosauqua from 2008 through 2010, (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 are assessed (monitored) as “not supported” due to high levels of indicator bacteria (E.  coli); this is a new impairment for this assessment segment.   The Class B(WW1) aquatic life uses remain assessed (monitored) as “partially supporting” (IR Category 5b) 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 2008-2010, 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 February 2008 through December 2010, (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.   This is the same assessment as that developed for the adjacent upriver segment of the Des Moines River (IA 04-LDM-0010_4).

EXPLANATION:  The Class A1 uses are assessed (monitored) as “not supported” due to violations of Iowa’s water quality criteria for indicator bacteria (E.  coli).   The geometric means of indicator bacteria (E.  coli) in the 18 samples collected during the recreational seasons of 2008 through 2010 at USGS station 05490500 at Keosauqua were as follows:  the 2008 geometric mean was 13,416 orgs/100 ml, the 2009 geometric mean was 305 orgs/100 ml and the 2010 geometric mean was 226 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml; the 2008 geometric mean was exceptionally high; the 2009 and 2010 geometric means only slightly exceeded the criterion of 126 orgs/100 ml.   Ten of the 18 samples (56%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”  

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 (Scaphirhynchus 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.   Note:  According to the local IDNR Fisheries biologist, a severe fish kill was reported on the lower Des Moines River on July 7, 2012, from approximately Eldon (downriver from Ottumwa) to Farmington in Van Buren County.   An estimated 57,000 fish were killed including at least 35,000 shovelnose sturgeon.   No specific cause of the kill was identified, but low flow conditions, flow alterations, and very high water temperatures (95+F) are believed to have contributed to the kill.  

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).   This assessment is also applied to upriver segments (e.g., IA 04-LDM-0010_4).    

Results of water quality monitoring by the U.S.  Geological Survey near Keosauqua from 2008 through 2010, however, suggest "full support" of the Class B(WW1) uses.   No violations of Class B(WW1) water quality criteria occurred in the approximately 40 samples analyzed for dissolved oxygen, pH, ammonia, DDE, dieldrin, and chlorpyrifos.    These results suggest “full support” of the Class B(WW1) 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 42 samples analyzed for dieldrin at USGS station 05490500 during the 2008-2010 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 41 samples collected during the 2008-10 period were all reported as less than the level of detection of 0.009 ppb.   According to IDNR’s assessment/listing methodology, and according to U.S.  EPA assessment guidance, more than one violation of a toxic contaminant in a three-year period suggests impairment of the aquatic life use.   Thus, the single violation of the Human Health/fish criterion for dieldrin during the 2008-10 assessment period does not indicated impairment.   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.