Assessment Comments
Assessment remains based on (1) 2006 REMAP data: FIBI = 13 (poor) and 19 (poor); BMIBI = 50 (fair), 16 (poor). FIBI BIC = 43; BMIBI BIC = 54; and (2) results of an IDNR fish kill investigation in 2007.
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.gov/Portals/idnr/uploads/water/standards/files/swcdoc2.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 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" (IR 3a) due to a lack of water quality information upon which to base an assessment. The Class B(WW2) aquatic life uses remain assessed (monitored) as "partially supported" based on results of biological sampling (REMAP) in 2006, and a fish kill investigation in August 2007.
EXPLANATION: This aquatic life assessment was based on data collected in 2006 as part of the IDNR/SHL stream REMAP project. 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 2006 FIBI scores were 13 (poor) and 19 (poor); the 2006 BMIBI scores were 50 (fair) and 16 (poor). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The FIBI BIC for this ecoregion is 43 and the BMIBI BIC for this ecoregion is 54. This segment passed the FIBI and BMIBI BICs 0/2 times in 2006. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.
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 recent five-year period to be considered “monitored”. This segment had multiple samples collected in 2006; however, the multiple samples were not collected in multiple years. Also, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation). Despite this change in assessment methodology and type, this waterbody was previously on Iowa’s Section 303(d) list and thus remains on Iowa’s Section 303(d) list of impaired waters (IR Category 5b-t).
Sampling staff also indicated that there was evidence of a recent fishkill in the segment that may have contributed to the aquatic life impairment.
Results of a fish kill investigation also suggest "partial support" of the aquatic life uses. A fish kill occurred on or before August 17, 2007 and was attributed to runoff from a dairy farm after a heavy rainfall event. It was noted that the kill likely occurred a few days before it was reported. The kill affected approximately 10.9 miles of the stream from 100th Street bridge at Sioux/Plymouth Co Line to L12 Bridge, Remsen. The value of the fish was estimated to be $345.50. The party responsible for the kill was identified, and restitution was sought.
According to IDNR'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). However, due to results from the IDNR/SHL stream REMAP project that also suggest impairment this assessment segment will remain in Category 5b-t of Iowa's Integrated Report.
