Assessment Comments
Assessment based on: (1) 2009 IDNR/SHL biological sampling results and (2) results of an IDNR investigation of a fish kill in December 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 (2012) 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 remain assessed (monitored) as "partially supported" based on results of an IDNR investigation of a fish kill in December 2005 and 2009 IDNR/SHL biological monitoring.
[Note: For the 2006 cycle, a fish kill that occurred in May 2000 was identified as the most recent fish kill in this assessment segment. Because no additional kills had occurred since the May 2000 kill, this segment was placed into Category 3b of Iowa’s 2006 Integrated Report (i.e., insufficient information existed to determine whether the impairment was still occurring). Because, however, the December 2005 kill extended well into this segment, the kill should have been identified as a cause of impairment for the 2006 Section 303(d) listing cycle, and this segment should have been placed into Category 5b of Iowa’s 2006 Integrated Report (the December 2005 kill was correctly identified during the 2006 cycle as the cause of impairment for the adjacent downstream segment of Brushy Creek (IA 04-RAC-0251_0)). Thus, for the 2008 listing cycle, the December 2005 fish kill was identified as the cause of impairment to the presumptive aquatic life uses, and this segment was added to Category 5b of Iowa’s 2008 Integrated Report where it remains.
EXPLANATION: This fish kill occurred on or before December 19, 2005; the kill occurred near Dedham in Carroll County and was attributed to run-off from at least six identified open cattle lots as well as potentially from swine confinements. An estimated 100 fish were killed although field investigators were unable to accurately estimate the number of fish killed due to ice cover on the stream. The fish kill affected approximately 13 miles of Brushy Creek. DNR field staff observed dead fish as far upstream as Highway 71, and even further upstream, during tracking of significant manure discharges. Although the parties responsible for the kill were identified; and although this kill was referred to the IDNR legal bureau, restitution for the fish killed or costs of investigation have not been received by IDNR.
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. 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 previous assessment/listing cycles, IDNR had considered fish kill-impaired (IR 5b) waters with no subsequent kills in the three year subsequent to the kill as appropriate for de-listing and for movement to IR categories 2b or 3b (i.e., Iowa’s list of waters in need of further investigation). Due, however, to EPA uncertainty regarding the full recovery of the aquatic life following the kill, any existing fish kill (5b) impairment will remain in IR Category 5b until more recent monitoring has shown full recovery of the aquatic communities affected by the kill. Thus, this assessment segment will remain in Category 5b of Iowa’s Integrated Report.
In contrast to the 2005 fish kill data, biological sampling conducted in 2009 by DNR/SHL suggests "full support" of the aquatic life uses of this segment.
SUMMARY: This evaluated biological assessment was based on data collected in 2009 as part of the DNR/SHL headwater stream sampling project. A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2009 FIBI score was 28 (fair) and the BMIBI score was 48 (fair). The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008. The FIBI BIC for this ecoregion is 31 and the BMIBI BIC for this ecoregion is 54.
Even though this site passed both the FIBI and BMIBI BICs (using the FIBI UAV of 7 points and BMIBI UAV of 8 points), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small presumed B-WW1 (formally general use) stream and doesn’t fall in the calibrated watershed size. This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology. IDNR now requires a segment have two or more biological samples collected from the segment in multiple years between 2006 and 2010 to be considered “monitored”. This segment had a single sample collected in 2009.
