Silver Creek IA 05-NSH-1454

The Class B(WW2) aquatic life uses remain assessed (evaluated) as "not supporting" based on biological data from the DNR Fisheries Bureau, Manchester research station, in 1998. Although originally placed in Category 3b of Iowa's 2004 Integrated Report by Iowa DNR, U.S. EPA Region VII, in their May 23, 2006 transmittal of Iowa's final approved 2004 Section 303(d) list, added this waterbody segment to Iowa's 2004 Section 303(d) list (IR Category 5b). Iowa DNR maintained that addition of this assessment segment to Iowa’s 2004 Section 303(d) list was inappropriate. That is, the bioassessment data generated by the DNR Fisheries Bureau for this assessment segment lacked the necessary documentation or metadata to determine whether the data meet quality and completeness criteria required of higher confidence (i.e., “monitored”) assessments that DNR considers appropriate for Section 303(d) listing. Thus, the assessment type was considered of lower confidence (i.e., "evaluated"), and thus this "partially supported" waterbody was considered not appropriate for Section 303(d) listing. U.S. EPA Region VII, however, based on their review of the DNR Fisheries bioassessment data for this assessment segment, concluded that these data are, in fact, scientifically adequate and representative of current water quality. Thus, EPA added-back this assessment segment to Iowa's 2004 final approved Section 303(d) list (Category 5b). This assessment segment remained in Category 5b of Iowa's 2006 Integrated Report and remains in Category 5b-t of the Iowa’s Integrated Reports. For additional detail on this impairment, please the 2010 assessment.

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 DNR assessment methodology. DNR now requires a segment have two or more biological samples collected from the segment in multiple years over a five-year period to be considered “monitored”. This segment had a single sample collected in 1998. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). According to DNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). DNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation). However, despite this change in assessment methodology and type, this waterbody was previously on Iowa’s Section 303(d) list and thus remains on Iowa’s Section 303(d) list of impaired waters (IR Category 5b-t).

In addition, the data upon which this biological assessment is based are now more than ten years old. As water quality data age, they are less able to represent current water quality conditions. As data age beyond ten years, their ability to represent current water quality conditions is increasingly suspect. Despite the age of these data, the aquatic life uses of this assessment segment will remain “partially supporting/evaluated” and will remain on Iowa’s Section 303(d) list of impaired waters (IR Category 5b-t). According to DNR’s assessment/listing methodology, age of data is not a sufficient justification for de-listing an existing impairment. Additional monitoring is needed in this assessment segment to update status of its aquatic communities.