Assessment Comments
Assessment remains based on (1) 2007 IDNR biological monitoring data and (2) an IDNR investigation of a fish kill in August 2002.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life 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. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2012) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) 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 Class B(WW2) aquatic life uses remain assessed (evaluated) as “partially supporting” (IR Category 5b) due to a 2002 fish kill despite IDNR/UHL biological monitoring in 2007 that suggested that the aquatic life uses should be assessed as “fully supporting." The fish kill is believed to have been caused by animal waste.
EXPLANATION: The fish kill occurred on August 24, 2002, near the intersection of 255th Avenue and 310th Street; the kill was localized to an approximately 40-meter segment of stream; approximately 100 fish were killed. The kill was believed to be caused by manure.
The results of the IDNR/UHL follow-up biological monitoring in 2007 suggests that the Class B(WW2) aquatic life uses should be assessed (evaluated) as “fully supporting.” A series of biological metrics which 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 2007 FIBI score was 43 (fair) and the BMIBI scores were 65, 61 (good). The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62. This segment passed the FIBI BIC 1/1 times and passed the BMIBI BIC 2/2 times in 2007. One of the BMIBI samples (61) was an artificial substrate sample where the samples quality was poor due to exposed plates on the artificial substrates. Even though the BMIBI score of 61 is lower than the BMIBI BIC of 62, due to the actual score being 61.43 and sampling conditions, IDNR considers it a passing score. The biological impairment criteria were determined from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2004.
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 over a five-year period to be considered “monitored”. This segment had multiple BMIBI samples collected in 2007; however, the multiple samples were not collected in multiple years. Despite this change in assessment methodology and type, this waterbody will remain in IR Category 5b due to the lack of a follow-up biological assessment to confirm the “full support” of aquatic life uses.
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.
