Assessment Comments
Assessment remains based on results of an IDNR investigation of a fish kill in May 2004.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general 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 and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters. Thus, for the current (2010) assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment. The presumptive Class B(WW1) aquatic life uses of this stream remain assessed (monitored) as “partially supported” due to a fish kill in May 2004. The kill was caused by a fertilizer spill. The party responsible for the kill was identified, and IDNR has sought restitution for the value of the fish killed and the costs incurred by IDNR during investigation of the kill. This impairment is appropriate for Category 4d of Iowa’s Integrated Report.
EXPLANATION: This kill occurred on or before May 2, 2004. The cause of the kill was identified as a fertilizer spill. An estimated 16,341 fish were killed with an estimated value of $1,942. All fish killed were non-game species including minnows (14,534), suckers (91), stonerollers (222), and darters (1,494). Approximately 1.25 miles of stream was affected. The kill occurred in Section 28 of T96N, R8W, Winneshiek County. According to the IDNR investigation of the kill, the spill sent approximately 1,250 gallons of fertilizer into Dry Branch Creek. According to the IDNR investigation, a farmer traveling downhill on a gravel road lost control of a trailer with a fertilizer nurse tank; the tank burst as a result of the accident. A mixture of approximately 1,000 gallons of 32 percent nitrogen fertilizer, and 250 gallons of thiosulfate, a chemical enhancement for fertilizer, spilled into the creek.
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 (2004-2007) 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. If, however, a consent order has been issued to the party responsible for the kill and monetary restitution has been sought for the fish killed, the affected waterbody will be placed in IR Category 4d (impaired but TMDL not required). Thus, this assessment segment was placed in Category 4d of Iowa’s 2006 Integrated Report. IDNR considers IR 4d fish kill waters with no subsequent kills in at least the five years subsequent to the kill as appropriate for movement to IR categories 2b or 3b (i.e., Iowa’s list of waters in need of further investigation). Because, however, this fish kill occurred within the most recent five years, this assessment segment will remain in Category 4d of Iowa’s 2010 Integrated Report.
