Assessment Comments
Assessment remains based the results of an IDNR investigation of a fish kill in July 1999.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2010) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are "not assessed" due to the lack of information upon which to base an assessment. The Class B(WW2) aquatic life uses remain assessed (evaluated) as "partially supported" due to occurrence of a fish kill in 1999. Due to the absence of kills in the five years following this kill, this assessment segment is considered “evaluated.” Due to EPA uncertainty regarding the full recovery of the aquatic life in this stream subsequent to the kill, this stream segment was placed on Iowa’s 2006 and 2008 Section 303(d) lists (IR Category 5b) where it will remain for the 2010 assessment/listing cycle.
EXPLANATION: The previous (2000, 2002 and 2004) assessments of the support of the Class B(WW2) aquatic life uses were based on the occurrence of a fish kill in 1999 (see assessment for the 2000 report). This fish kill occurred on Walnut Creek near Olin in Jones County on July 26, 1999; approximately three miles of stream were affected; an estimated 120 fish were killed. This kill was attributed to runoff of animal waste from an open (cattle) feedlot. The person reporting the kill had noticed manure in South Fork Walnut Creek a week prior to the kill. Although no source of the animal waste was identified, a waterway containing manure leading from open cattle lots to the South Fork Walnut Creek was found during the investigation.
According to IDNR’s assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2007-2009) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill is identified, and the cause is either known, or suspected, to be a “pollutant”, the assessment type is considered “monitored” and the affected waterbody is a candidate for Section 303(d) listing. Fish kills attributed to a pollutant, but where a source of the pollutant was not identified and/or where enforcement actions were not taken against the responsible party, will be placed into Integrated Report subcategory 5b. The intent of placing these waterbodies into Category 5 is not to necessarily require a TMDL but to keep the impairment highlighted due to the potential for similar future kills from the unaddressed causes and/or sources. For previous assessment/listing cycles, IDNR had considered fish kill-impaired (IR 5b) waters with no subsequent kills in the three year subsequent to the kill as appropriate for de-listing and for movement to IR categories 2b or 3b (i.e., Iowa’s list of waters in need of further investigation). Due, however, to EPA uncertainty regarding the full recovery of the aquatic life following the kill, any existing fish kill (5b) impairment will remain in IR Category 5b until more recent monitoring has shown full recovery of the aquatic communities affected by the kill. Thus, this assessment segment will remain in Category 5b of Iowa’s 2010 Integrated Report.
