Des Moines River IA 04-LDM-1002

Assessment Comments

Assessment is based on results of (1) IDNR ambient monthly monitoring near Keokuk in 2000 & 2001 and (2) EPA/IDNR fish tissue monitoring in 1999 near Croton.

Basis for Assessment

[Note:  For the 2002 report, the previous waterbody segment for the Des Moines River (IA 04-LDM-0010-0), which extended 76 miles from its mouth to the confluence with Soap Creek near Eldon (Wapello Co.), was split into four subsegments:  (1) mouth (Lee Co.) to the Sugar Creek Keokuk (IA 04-LDM-0010-1), (2) Sugar Creek to Indian Creek near Farmington, Van Buren Co.  (IA 04-LDM-0010-2), (3) Indian Creek to Chequest Creek near Keosauqua, Van Buren Co.  (IA 04-LDM-0010-3), and (4) Chequest Creek to Soap Creek near Eldon in Wapello Co.  (IA 04-LDM-0010-4).   See assessment documentation for segment IA 04-LDM-0010-2 for previous Section 305(b) assessments for the original 76-mile river reach.]

SUMMARY:  The Class A (primary contact recreation) uses were assessed (monitored) as "fully supported," and the Class B(WW) aquatic life uses were assessed (monitored) as "fully supported."  Fish consumption are assessed as "fully supported."  The sources of data for this assessment include (1) results of monthly monitoring from October 1999 through September 2001 at the IDNR ambient station located at the Highway 61 bridge south of Keokuk (station 10560001; formerly station 410085) and (2) results of U.S.  EPA/IDNR fish tissue monitoring in 1999 near Croton.   EXPLANATION:  The Class A uses were assessed as "fully supported."  For purposes of Section 305(b) assessments, DNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff.   According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff."  Thirteen of the 15 samples collected from the Highway 61 station during the 2000 and 2001 recreational seasons were collected at flows not materially affected by surface runoff.   The geometric mean level of indicator bacteria (fecal coliforms) in these 13 non-runoff-affected samples (40 orgs/100ml) is well below the Iowa Class A water quality criterion of 200 orgs/100ml.   Only one of the 13 samples (8%) exceeded the U.S.  EPA-recommended single-sample maximum value of 400 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if no more than 10% of the samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are "fully supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   The Class B(WW) aquatic life uses were assessed as "fully supported" based on results of monitoring from the IDNR ambient station at Highway 61 near Keokuk in 2000 and 2001.   Monitoring at this station showed no violations of Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 24 samples collected, for toxic metals in the four samples analyzed, or for pesticides and other toxic organic compounds in the six samples analyzed during this biennial period.   Levels of pH, however, occasionally violated the Class B(WW) criterion of 9.0 pH units.   Two of the 24 samples (8.3%) had pH values greater than 9.0 units, with a maximum value of 9.2 units.   All violations occurred on days when dissolved oxygen levels were at or above 100% saturation:  March 6, 2000 (pH=9.2; % DO saturation=120%) and November 6, 2000 (pH=9.2; DO saturation=100%).   These conditions suggest that high levels of primary productivity may have resulted in the high levels of pH observed.   Because these violations are likely more related to natural conditions than to pollution, the occurrence of high levels of pH in this river segment is not seen as a water quality impairment.   In addition, 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 less does not suggest an impairment of aquatic life uses.   Fish consumption uses are assessed as "fully supported" based on results of U.S.  EPA/IDNR fish tissue (RAFT) monitoring in 1999 near Croton.   This monitoring showed that levels of all contaminants in composite fillet samples from common carp and freshwater drum collected from the Des Moines River near Croton were well below ½ of the respective FDA action levels as well as DNR levels of concern (see also assessment for the 2000 report).