Des Moines River IA 04-LDM-1011

Assessment Comments

Assessment is based on results of (1) IDNR/UHL monthly ambient city monitoring upstream from Ottumwa from 2000-02 and (2) information from DNR Water Quality Bureau / Water Supply Section.

Basis for Assessment

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"; both assessments are based on results of IDNR/UHL ambient water quality monitoring upstream from Ottumwa.   The Class C (drinking water) uses were assessed (monitored) as "fully supported" based on results of the IDNR/UHL ambient monitoring.  Compliance monitoring required by the IDNR Water Supply Section did not show violations of the nitrate MCL in finished water at the Cargill, Inc.  facility during the 2000-02 period.   Fish consumption uses were not assessed due to the lack of fish contaminant monitoring in this river reach.   The sources of data for this assessment include (1) the results of monthly monitoring from May 2000 through December 2002 at the IDNR ambient city monitoring station located upstream from Ottumwa at the County Road T67 bridge at Chillicothe (STORET station 10900003) and (2) the results of compliance monitoring required by the IDNR Water Supply Section as reported in annual compliance reports for the years 2000 through 2002 (these reports are available at the following location at the Iowa DNR’s home page:  http://www.state.ia.us/epd/wtrsuply/report/report.htm).    

EXPLANATION:  The Class A uses were assessed as "fully supported" based on results of ambient monitoring for indicator bacteria.   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."  Fourteen of the 16 samples collected from the Chillicothe station during the 2000, 2001, and 2002 recreational seasons were collected at flows not materially affected by surface runoff.   The geometric mean level of indicator bacteria (fecal coliforms) in these 14 non-runoff-affected samples (76 orgs/100ml) is well below the Iowa Class A water quality criterion of 200 orgs/100ml.   In addition, none of the seven samples contained a level of fecal coliform bacteria that 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 the geometric mean is less than 200 orgs/100ml, and less than 10% or less 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 3-35 of 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 Chillicothe from 2000 through 2002.   Monitoring at this station showed no violations of Class B(WW) water quality criteria for dissolved oxygen, pH, ammonia-nitrogen or toxic metals in the 28 samples analyzed or for pesticides and other toxic organic compounds in the nine samples analyzed, during this assessment period.  

The Class C (drinking water) uses are also assessed as "fully supported."  Results of IDNR ambient monthly monitoring at the Chillicothe station show no violations of the nitrate MCL in the 28 samples collected during the 2000-2002 assessment period (mean=5.1 mg/l; maximum=10.0 mg/l).   2000-2002 assessment.   A previous (2000) assessment of drinking water uses for this segment (“partially supported”) was based on the issuance by Cargill Inc.  (Eddyville) of a notice of an MCL violation for nitrate on June 11, 1998 (see the assessment for the 2000 report).   Since that violation, however, compliance sampling conducted for the IDNR Water Supply Section as part of requirements of the federal Safe Drinking Water Act have shown no violations of the MCL for nitrate in finished water at this facility.

Fish consumption uses were not assessed due to lack of recent fish tissue monitoring in this river segment.