Des Moines River IA 04-LDM-1011

Assessment Comments

Assessment is based on (1) results from the IDNR ambient city station upstream from Ottumwa in 2000 & 2001 and (2) information from DNR Water Quality Bureau / Water Supply Section.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses were assessed (evaluated) as "fully supported," and the Class B(WW) aquatic life uses were assessed (monitored) as "fully supported."  The Class C (drinking water) uses were assessed (monitored) as "fully supported."  Fish consumption uses were not assessed.   The sources of data for this assessment include (1) the results of monthly monitoring from May 2000 through September 2001 at the IDNR ambient city monitoring station located upstream from Ottumwa at the County Road T67 bridge at Chillicothe and (2) the results of compliance monitoring required by the IDNR Water Supply Section.   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."  Seven of the 9 samples collected from the Chillicothe 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 seven  non-runoff-affected samples (62 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).   Because less than 10 non-flow affected samples were available for this assessment, the assessment type is considered "evaluated"; thus, this assessment is not of sufficient quality to support a Section 303(d) listing or de-listing.   The Class B(WW) aquatic life uses were assessed as "fully supported" based on results of monitoring from the IDNR ambient station at Chillicothe in 2000 and 2001.   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 14 samples analyzed or for pesticides and other toxic organic compounds in the 6 samples analyzed, during this biennial period.   The Class C (drinking water) uses were assessed as "fully supported."  Results of IDNR ambient monthly monitoring at the Chillicothe station show no violations of the nitrate MCL in the 14 samples collected during the 2000-2001 biennial period (mean=5.0 mg/l; maximum=10.0 mg/l).   In addition, compliance sampling conducted for the IDNR Water Supply Section as part of requirements of the federal Safe Drinking Water Act show no violations of the MCL for nitrate in finished water during the 2000-2001 biennial period.   Thus, support of the drinking water uses for the 1998-1999 biennial period ("partially supported") was upgraded to "fully supported."  See assessment developed for the 2000 report for more information on the assessment of drinking water uses for the 1998-1999 biennial period.   Fish consumption uses were not assessed due to lack of recent fish tissue monitoring in this river segment.