Assessment Comments

Assessment is based on results of monthly monitoring from January 2008 through August 2010 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 2008-2010.   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 2008 through December 2010 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.  

The geometric means of indicator bacteria (E.  coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at IDNR station 10420001 were as follows:  the 2008 geometric mean was 151 orgs/100 ml, the 2009 geometric mean was 316 orgs/100 ml and the 2010 geometric mean was 292 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Ten of the 21 samples (48%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”  

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 2008 through 2010.   Monitoring at this station showed no violations of Class B(WW1) water quality criteria in the 29 samples analyzed for dissolved oxygen, pH, or ammonia.   These results suggest that the Class B(WW1)  uses should be assessed (monitored) as “fully supporting.”  

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