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Assessment Comments

Assessment is based on results of results of IDNR/UHL chemical/physical/bacterial water quality monitoring conducted from January 2008 through September 2009 at the IDNR/UHL station near county road X26 (STORET station 15030006) as part of the Yellow River Watershed Project. The impairment of the Class A2 uses is a new Section 303(d) listing.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) aquatic life uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008, this segment is also now presumptively designated for Class A1 (primary contact recreation) and Class A2 (secondary contact recreation) uses.   This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption) uses.]

SUMMARY:  The presumptive Class A1 (primary contact recreation) and Class A2 (secondary contact recreation) uses are both assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed state water quality criteria.   The impairment of the Class A2 uses represents a new Section 303(d) listing for this assessment segment.   The Class B(CW1) aquatic life uses remain assessed (monitored) as "not supported" based on the historical impairment due to dissolved oxygen levels.   Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this stream segment.   The source of data for this assessment is the results of IDNR/UHL chemical/physical water quality monitoring conducted from January 2008 through September 2009 at the IDNR/UHL station near county road X26 (STORET station 15030006) as part of the Yellow River Watershed Project.

Note: A TMDL for the bacterial impairment for streams in the Yellow River basin was prepared by Iowa DNR in 2012 and was approved by U.S.  EPA in February 2013 (see http://www.iowadnr.gov/Environment/WaterQuality/WatershedImprovement/WatershedResearchData/WaterImprovementPlans/PublicMeetingsPlans.aspx).  Due to completion of the TMDL, the Integrated Report categories for the Class A1 and Class A2 recreational uses are changed from 5p (impaired; TMDL needed) to 4a (impaired; TMDL approved).  Because not all impairments identified for this assessment segment are covered by the TMDL (aquatic life impairment due to low dissolved oxygen), this segment remains in Category 5a of Iowa's 2012 Integrated Report (impaired and TMDL required).  

EXPLANATION:  The presumptive Class A1 (primary contact recreation) and A2 (secondary contact recreation) uses are assessed (monitored) as impaired due to violations of Iowa’s water quality criteria for indicator bacteria.   The geometric means of indicator bacteria (E.  coli) in the 20 samples collected during the recreational seasons of 2008 and 2009 at station 15030006 were as follows:  the 2008 geometric mean was 218 orgs/100 ml and the 2009 geometric mean was 874 orgs/100 ml.   Both geometric means exceed the Class A1 criterion of 126 orgs/100 ml, and the 2009 geometric means exceed the Class A2 geometric mean criterion of 630 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 both the presumptive Class A1 and A2 uses, these uses are assessed as “impaired.”  

The results of the IDNR/UHL water quality monitoring in 2009 show no violations of the Class B(CW1) criteria for dissolved oxygen (7.0 mg/l) in the 12 samples collected from May through September.   The minimum level of dissolved oxygen was 8.3 mg/l.   In addition, there were no violations of pH in the 12 samples collected in 2009 or were there violations of ammonia in the 25 samples collected in 2008 and 2009.   These result suggest full support of the Class B(CW1) uses.   These results are in contrast to the 2004-06 period when 42 of 80 samples violated the Class B(CW1) criterion for dissolved oxygen of 7.0 mg/l.   Based on IDNR's assessment methodology, however, two consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the standard are necessary to suggest de-listing of an impairment due to low dissolved oxygen.    Therefore, the impairment for dissolved oxygen will remain for the 2012 assessment/listing cycle.  

Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this stream segment.