Assessment Comments
Assessment based on results of (1) IDNR/UHL biological sampling in 2008: FIBI = 43, 52 (fair) and 65 (good); BMIBI = 62, 66, 68 (all good). FIBI BIC = 52, BMIBI BIC = 61; and (2) an IDNR investigation of a fish kill in August 2005.
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 (2010) 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 are assessed as "fully supported" based on results of IDNR/UHL biological sampling in 2008. Occurrence of a fish kill in August 2005 due to hog manure suggests impairment of the Class B(WW2) uses of this stream. The party responsible for this kill was identified, and IDNR has sought restitution for the value of the fish killed and the costs incurred by IDNR during investigation of the kill. This fish kill-related impairment would be appropriate for Category 4d of Iowa’s Integrated Report.
EXPLANATION: The assessment of the Class B(WW2) aquatic life uses was based on data collected in 2008 as part of the IDNR/UHL stream biological monitoring projects. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were 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 FIBI scores were 43, 52 (fair) and 65 (good) and the BMIBI scores were 62, 66, 68 (all 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 biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61. This segment passed the FIBI BIC 2/3 times and passed the BMIBI BIC 3/3 times in 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 between 2004 and 2008 to be considered “monitored”. This segment had multiple samples collected in 2008; however, the samples were not collected in multiple years. Despite this change in assessment methodology and type, this waterbody will remain in IR Category 5b.
A fish kill occurred in this stream segment on or before August 1, 2005 and was caused by a release of hog manure from an over-full storage pit. According to the IDNR investigation, an outdoor storage pit lacked sufficient capacity to handle the amount of manure delivered to it from an indoor storage pit; thus, an overflow occurred. Approximately 2.25 miles of Roberts Creek were affected by the resulting kill. The kill began in an unnamed tributary to Roberts Creek (waterbody IA 01-TRK-0361-0) in Section 8 of T95N, R6W, Clayton County, and proceeded downstream through Section 9, 15, and 15 of T95N, R6W. An estimated 8,000 fish were killed. Based on IDNR records, the value of the fish killed was estimated at $4,893. Other than a notation that the kill affected “mostly non-game species", no detailed information on species killed is available. The party responsible for the kill was identified. IDNR has sought restitution for the value of the fish killed and the costs incurred by IDNR during investigation of the kill.
According to DNR'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). Thus, this impairment was appropriate for Category 4d of Iowa’s 2008 Integrated Report. IDNR considers IR 4d fish kill waters with no subsequent kills in at least the five years subsequent to the kill as appropriate for movement to IR categories 2b or 3b (i.e., Iowa’s list of waters in need of further investigation). Because, however, this fish kill occurred within the most recent five years, this impairment remains appropriate for Category 4d of Iowa’s 2010 Integrated Report.
