Assessment Comments

Assessment is based on results of IDNR/UHL ambient water quality monitoring NE of Gifford, IA, from 2002-04.

Basis for Assessment

[Note:  For the 2002 report, the previous waterbody segment IA 02-IOW-0070-2, which extended 43 miles from Hardin/Marshall line to the east corporate limit of Iowa Falls, was split into three subsegments:  (1) Hardin/Marshall county line to South Fork Iowa River (IA 02-IOW-0070-2), (2) South Fork Iowa River to Pine Creek near Eldora (IA 02-IOW-0070-3), (3) Pine Creek to bridge in S12, T88N, R20W, Hardin Co.  (IA 02-IOW-0070-4), and (4) Hardin Co.  bridge to east corporate limit of Iowa Falls (IA 02-IOW-0070-5).   As part of this splitting, the identification number for segment IA 02-IOW-0070-3 (east corporate limit of Iowa Falls to unnamed tributary 3 miles SE of Popejoy) was changed to IA 02-IOW-0070-6.   See assessment information for the original 43-mile segment under the documentation for segment IA 02-IOW-0070-2 for earlier Section 305(b) assessments for this river reach.]

NOTE:  The placement of recent water quality assessments for this segment and the downriver segment (IA 02-IOW-0070-2) have been confused.   Because IDNR/UHL ambient monitoring station 10420001 is upstream from the confluence with the South Fork Iowa River--and is thus in segment (IA 02-IOW-0070-3)--any assessments based on monitoring data from this station should have been applied to IA 02-IOW-0070-3.    Thus, any assessments  based on data from this station and erroneously placed in the downriver segment (IA 02-IOW-0070-2) have been restored to IA 02-IOW-0070-3.   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.   I apologize for this confusion.  

2006 ASSESSMENT:  SUMMARY:  The Class A (primary contact recreation) uses were assessed (monitored) as "partially supported" due to high levels of indicator bacteria.   The Class B(WW) aquatic life uses were assessed (monitored) as "fully supported" based on results of ambient water quality monitoring.   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 are (1) the results of monthly monitoring from January 2002 through December 2004 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 A uses were assessed as "partially 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 2006 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 the 2006 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 2002-2004 (97 orgs/100ml) is below (meets) the Iowa Class A water quality criterion of 126 orgs/100ml.   Five of the 24 samples (21%), however, 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, if the geometric mean is less than 126 orgs/100ml, but more than 10% of the samples exceed the single-sample maximum value, 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, these results suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum value, thus suggesting that the Class A uses should be assessed as “partially supported/impaired”.   This assessment is consistent with the previous (2004) assessment for this river segment.

The Class B(WW) aquatic life uses were assessed as "fully supported" based on results of monitoring from the IDNR/UHL ambient station near Gifford from 2002 through 2004.   Monitoring at this station showed no violations of Class B(WW) water quality criteria in the 36 samples analyzed for dissolved oxygen, pH, and ammonia; in the 10 samples analyzed for toxic metals, or in the approximately 7 samples analyzed for pesticides.  

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