Assessment Comments

Assessment is based on results of monthly monitoring from January 2004 through December 2006 at the IDNR ambient monthly monitoring station located at Hardin County Road D53 approximately 1.8 miles northeast of Gifford (STORET station 10420001).

Basis for Assessment

NOTE:  The placement of recent water quality assessments for this segment and the downriver segment (IA 02-IOW-0070-2) have been confused.   Segment IA 02-IOW-0070_2 extends from the Hardin/Marshall county line upriver to the South Fork Iowa River; segment IA 02-IOW-0070-3 (this segment) extends from the South Fork Iowa River upriver to Pine Creek near Eldora.   Because IDNR/UHL ambient monitoring station 10420001 is upstream from the confluence with the South Fork Iowa River--and is thus in this segment (i.e., IA 02-IOW-0070-3)--any assessments based on monitoring data from this station should have been applied to this segment.   Thus, any assessments based on data from this station and erroneously placed in the downriver segment (IA 02-IOW-0070-2) were restored to this segment (IA 02-IOW-0070-3) as part of the 2006 Section 305(b) assessment cycle.   Also, recent assessments for the downriver segment (IA 02-IOW-0070-2) are now correctly considered "not assessed" due to the lack of monitoring information upon which to base an assessment.  

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to high levels of indicator bacteria.   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring from 2004-2006.   Fish consumption uses remain not assessed due to the lack of fish contaminant monitoring in this river reach.   The source of data for this assessment is the results of monthly monitoring from January 2004 through December 2006 at the IDNR ambient monthly monitoring station located at Hardin County Road D53 approximately 1.8 miles northeast of Gifford (STORET station 10420001).  

EXPLANATION:  The Class A1 uses are assessed (monitored) as "not supported" due to levels of indicator bacteria (E.  coli) that exceed state criteria.   Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed.   Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses:  the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff."  Due to a change in the Standards in July 2003, E.  coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E.  coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.”  Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E.  coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of Section 305(b) assessments and Section 303(d) listings.    

The geometric mean level of indicator bacteria (E.  coli) in the 24 samples collected during the recreational seasons of 2004-2006 (145 orgs/100ml) is slightly above the Iowa Class A water quality criterion of 126 orgs/100ml.   Seven of the 24 samples (29%) contained a level of E.  coli bacteria that exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, and according to IDNR’s assessment/listing methodology, if the geometric mean level of E.  coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   Also according to U.S.  EPA guidelines for Section 305(b) reporting, if more than 10% of the samples exceed the single-sample maximum criterion, the primary contact recreation uses should be assessed as "partially supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   According to IDNR’s assessment/listing methodology, the monitoring results from the IDNR/UHL station northeast of Gifford suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum criterion.   Thus, even though the geometric mean level of bacteria for the 2004-06 period was only slightly greater than the Class A1 criterion of 126 orgs/100 ml, the percentage of samples exceeding the single sample maximum criterion of 235 orgs/100 ml also suggests impairment.  

The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of monitoring from the IDNR/UHL ambient station near Gifford from 2004 through 2006.   Monitoring at this station showed no violations of Class B(WW1) water quality criteria in the 36 samples analyzed for dissolved oxygen or ammonia; in the 10 samples analyzed for toxic metals, or in the approximately seven samples analyzed for pesticides.   One of the 36 samples (3%) had a pH value greater than the Class B(WW1) criterion of 9.0 units (9.4 pH units).   Because this violation is more related to natural conditions (i.e., high levels of primary productivity) than to a pollutant, the occurrence of high levels of pH in this river segment is not seen as a water quality impairment.   Also, according to U.S.  EPA guidelines (U.S.  EPA 1997b, page 3-17), a violation frequency of less than 10 % for conventional parameters such as dissolved oxygen and pH suggest "full support" of aquatic life uses.   Thus, the percentage of violations of the pH criterion at this station (3%) does not suggest an impairment of aquatic life uses in this stream segment.

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