Assessment Comments
Assessment is based on: (1) the results of monitoring for indicator bacteria conducted at Site 23 of the Upper Iowa River Watershed (UIRW) project from April 2008 through October 2010 and (2) results of a fish kill investigation near Highlandville in 1999.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this segment is also now presumptively designated for Class A1 (primary contact recreation) and Class A2 (secondary contact recreation) uses. This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses and the presumptive Class A2 (secondary contact recreation) uses are assessed (monitored) as “fully supported.” The Class B(CW1) coldwater aquatic life uses remain assessed (evaluated) as "partially supported” due to a fish kill in 1999. Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this stream segment. The sources of data for this assessment are (1) the results of monitoring for indicator bacteria conducted at Site 23 of the Upper Iowa River Watershed (UIRW) project (STORET No. NEIARCD 191910014) from April 2008 through October 2010 and (2) results of the fish kill investigation near Highlandville in 1999.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses and the presumptive Class A2 (secondary contact recreation) uses are both assessed (monitored) as “fully supported.” The Class A1 (primary contact recreation) uses and the Class A2 (secondary contact recreation) uses are both assessed as "fully supported" based on levels of indicator bacteria that are below state water quality criteria. The geometric mean of indicator bacteria (E. coli) in the 20 samples collected during the recreational seasons of 2008 through 2010 at UIRW Site 23 were as follows: the 2008 geometric mean was 114 orgs/100 ml, the 2009 geometric mean was 78 orgs/100 ml and the 2010 geometric mean was 70 orgs/100 ml. All three geometric means meet both the Class A1 criterion of 126 orgs/100 ml and the Class A2 geometric mean criterion of 630 orgs/100 ml. Four of the 20 samples (20%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. Based on the IDNR assessment methodology, the number of single-sample violation is not significantly greater than the 10% impairment threshold and thus does not indicate impairment. Only two of the 20 samples (10%) exceeded the Class A2 single-sample maximum criterion of 2,880 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if all recreation season geometric means meet the respective water quality criterion, the contact recreation uses are "fully supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The Class B(CW) coldwater aquatic life uses remain assessed (evaluated) as "partially supported.” These uses were assessed as "partially supported" for the 2000 through 2004 assessment cycles due to occurrence of a fish kill on August 5, 1999 northwest of Highlandville in Winneshiek County. As stated in the assessment developed for the 2000 report, the kill followed a 2-3 inch rainfall event; no other water quality problems were observed. An estimated 3,200 fish were killed. No responsible party for the kill was identified. 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 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) and proposed this impairment for removal from Iowa’s 2006 Section 303(d) list. According to IDNR’s assessment/listing methodology at that time, 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 affected water would be considered “not assessed.” Due, however, to EPA uncertainty regarding the full recovery of the aquatic life in this stream subsequent to the kill, this stream segment remained on Iowa’s 2006 Section 303(d) list (IR Category 5b) and will remain on subsequent lists until biological monitoring is conducted to demonstrate recovery of the aquatic community.
Fish consumption uses are not assessed due to the lack of fish contaminant monitoring in this stream reach.
