Assessment Comments
Assessment is based on results of monitoring from May 2011 to November 2012 as part of Turkey River watershed/RC&D monitoring at station DBR30 (Dry Branch at 110th St) (STORET station 15960015). Aquatic life uses remain 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, 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 (2014) 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 are assessed (monitored) as “not supported” due to violations of Iowa water quality criteria for indicator bacteria (IR 5p). This is a new impairment for this assessment segment. Results of chemical/physical water quality monitoring in 2011 and 2012 do not show water quality problems in this stream; thus, aquatic life uses are assessed as "fully supporting" (IR 2a). Prior to the current IR cycle, the presumptive Class B(WW1) aquatic life uses of this stream were assessed (evaluated) as “partially supported” due to a fish kill in May 2004 (IR 3b). The kill was caused by a fertilizer spill. The party responsible for the kill was identified, and IDNR sought restitution for the value of the fish killed and the costs incurred by IDNR during investigation of the kill. This impairment had been in Category 4d of Iowa’s Integrated Report. Because no subsequent kills have been reported in over five years, this 4d impairment was moved to Category 3b of Iowa’s Integrated Report. Because no fish kills have occurred in 10 years since the 2004 kill, this assessment is moved to IR Category 3a (not assessed) for the 2014 IR cycle. The source of data for this assessment is the results of monitoring from May 2011 to November 2012 as part of Turkey River watershed/RC&D monitoring at station DBR30 (Dry Branch at 110th St) (STORET station 15960015).
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the seven monthly samples collected during the recreational season of 2011 (455 orgs/100 ml), and the geometric mean of the eight samples collected during 2012 (1,700 orgs/100 ml) both exceeded the Class A1 criterion of 126 orgs/100 ml. Twelve of the combined 15 samples (80%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
Results of water quality monitoring from May 2011 to November 2012 do not suggest impairment of the presumptive Class B(WW1) aquatic life uses. No violations of Class B(WW1) water quality criteria for ammonia, dissolved oxygen, pH, or temperature occurred in the approximately 15 samples analyzed from May 2011 to November 2012.
A fish kill occurred in this stream 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 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 this fish kill occurred more than five years ago and no subsequent kills have been reported, this assessment segment will was moved to Category 3b of Iowa’s 2012 Integrated Report. Because no fish kills have occurred in this stream segment for over 10 years, this assessment is moved to IR Category 3a (not assessed) for the 2014 IR cycle.
