Assessment Comments
Assessment remains based on results of an IDNR investigation of a fish kill in June 2005.
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, 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 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" (IR 3a) due to the lack of information upon which to base an assessment. The presumptive Class B(WW1) aquatic life uses of this stream are assessed (evaluated) as “partially supported” (IR 3b) due to a fish kill in June 2005. The kill was caused by a spill of ammonia fertilizer. 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. Thus, this impairment was appropriate for Category 4d of Iowa’s 2006 Integrated Report and remained in Category 4d of Iowa's 2008 and 2010 Integrated Reports. Because this kill occurred more than five years ago, the assessment type is changed from “monitored” (higher confidence assessment) to “evaluated” (lower confidence assessment), and the Integrated Report category is changed to 3b (potentially impaired).
EXPLANATION: This kill occurred north of Chapin, IA, on or before June 18, 2005, and was attributed to fertilizer. A tank of anhydrous ammonia fertilizer being pulled by a tractor spilled. Despite attempts to control the discharge of the fertilizer, most of the 850 gallons of fertilizer vented to the atmosphere. The hovering of the vapor cloud near the ground, and the dissolving of the ammonia into the water of the unnamed tributary, is believed to be the cause of the kill. An estimated 2,072 non-game fish were killed (minnows, stonerollers, and darters). The estimated value of the fish killed was $201. Approximately 5.25 miles of stream were affected by the kill. The party responsible for the kill was identified.
According to DNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill during an assessment period indicates "partial support" of the aquatic life uses. 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 should be placed in IR Category 4d (impaired but TMDL not required). Thus, this assessment segment was placed in Category 4d of Iowa’s 2006 through 2010 Integrated Reports. 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). Thus, this fish kill impairment was moved from Category 4d to Category 3b of Iowa’s 2012 Integrated Report and will be included on Iowa’s list of waters in need of further investigation.
