Assessment Comments
Assessment based on (1) 2008 & 2011 IDNR/SHL biological sampling data: FIBI = 61 (good), BMIBI = 46, 48 (both fair). FIBI BIC = 43; BMIBI BIC = 54 and (2) a fish kill in April 2011.
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 the lack of information upon which to base an assessment. The Class B(WW2) aquatic life uses are assessed as "partially supporting (IR 5b-v) based on results of biological monitoring in 2008 and 2011 and (2) are assessed as "partially supporting" (IR 4d) based on results of an IDNR fish kill investigation in April 2011.
EXPLANATION: The Class B(WW2) aquatic life uses are assessed (monitored) as “partially supporting" (IR 5b-v) based on biological data collected in 2008 and 2011 as part of the IDNR/SHL stream biocriteria 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 2008 BMIBI score was 46 and the FIBI was unavailable. The 2011 FIBI score was 61 (good) and the BMIBI score was 48 (fair). The aquatic life use support was assessed (monitored) 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 BIC 1/1 times and passed the BMIBI BIC 0/2 times in the last five years. 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 "monitored" 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 BMIBI samples collected from 2008-2012.
The fish kill occurred on April 1, 2011 and was attributed to the release of liquid nitrogen from an above ground storage tank. The kill affected 0.8 miles of Rio Grande Creek in the town of George and also affected this segment of the Little Rock River. Approximately 1,370 fish were killed. No information on the species of fish killed was provided. The value of these fish was estimated to be $404.88. IDNR sought an received restitution from the party responsible for this kill.
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). IDNR feels that (1) TMDLs should not be required for kills caused by a one-time illegal or unauthorized release of manure or other toxic substance where enforcement actions were taken and (2) enforcement action is more appropriate, efficient, and effective for addressing a spill-related impairment than is the TMDL process. Thus, this assessment segment is placed in Category 4d of Iowa’s Integrated Report.
