Assessment Comments
Insufficient information available to develop an assessment. Previous assessment was based the results of an IDNR investigation of a fish kill in July 1999.
Basis for Assessment
SUMMARY: The Class B(LR) aquatic life uses are assessed (evaluated) as "partially supported" for the 2006 assessment cycles due to occurrence of a fish kill in 1999. Due to the absence of kills in at least three years following this kill, this assessment segment will be considered “evaluated.” Due to EPA uncertainty regarding the full recovery of the aquatic life in this stream subsequent to the kill, this stream segment will remain on Iowa’s 2006 Section 303(d) list (IR Category 5b). Thus, the Class B(LR) uses of this stream segment are assessed (evaluated) as "partially supported” for the 2006 cycle.
EXPLANATION: The previous (2000, 2002 and 2004) assessments of the support of the Class B(LR) 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 as found during the investigation.
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 (2002-2005) 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 its draft 2006 assessment, IDNR considered this stream segment to be “not assessed” (IR Category 3a). According to IDNR’s assessment/listing methodology, if the most recent pollution-caused fish kill occurred on this stream segment more than six years ago (i.e., before the 2000-2005 period), any toxic impacts associated with the kill are assumed to have dissipated, and the assessment would thus not be included in the 2006 assessment/listing process. Due, however, to EPA uncertainty regarding the full recovery of the aquatic life in this stream subsequent to the kill, this stream segment will remain on Iowa’s 2006 Section 303(d) list (IR Category 5b).
