Assessment Comments
Assessment is based on (1) results of IDNR/UHL biological (biocriteria) monitoring conducted as part of a watershed bioassessment study in 1997: upstream/downstream Fish IBI= 25(poor)/35(fair), BM-IBI= 58(good)/44(fair) and (2) results of an IDNR investigation of a fish kill in August 2001.
Basis for Assessment
SUMMARY: The general aquatic life uses remain assessed (evaluated) as "partially supported" based on (1) results of IDNR/UHL biological (biocriteria) monitoring in 1997 and (2) the occurrence of a fish kill in August 2001. This is the same basic assessment as that developed for the 2002 report. This waterbody segment was included on Iowa's 2002 Section 303(d) list. Due to a change in IDNR's assessment methodology, however, this general use-only reach of Bear Creek will be moved off the Section 303(d) list and placed in Category 3b of the 2004 Integrated Report.
EXPLANATION: Results of IDNR/UHL biological monitoring near the Roland wastewater treatment plant in 1997 suggested only "partial support" of the general aquatic life uses. The F-IBI score upstream/downstream of the Roland wastewater treatment plant was 25(poor)/35(fair), and the BM-IBI score was 58(good)/44(fair). The aquatic life use support status was assessed as partially supporting (=PS), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established specifically for the 2000 Section 305b report (IDNR 2000). The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-1998. These data are less than five years old and are thus useful for characterizing current water quality conditions.
This assessment of Bear Creek is considered “evaluated” (of lower confidence) due to the lack of a biological assessment protocol for general use-only streams. IDNR’s existing protocol has been calibrated to aquatic life reference conditions in wadeable Class B(LR) and Class B(WW) streams. The aquatic environment of most general use streams is one of extremes in water quality. Consequently, general use-only streams tend to have biological diversity that is low relative to more stable aquatic environments of Class B(LR) and Class B(WW) streams. Thus, the use of biological assessment methods developed for the ecologically more stable and diverse Class B(LR) streams to assess general use reaches will likely overstate the existence of impairment. For these reasons, general use-only stream reaches that show impairment based on a comparison of monitoring data to Class B(LR) water quality criteria, or that show failure to meet regional expectations for aquatic biota (fish or aquatic macroinvertebrates) of Class B(LR) streams, will not be added to Iowa’s Section 303(d) list of impaired waters (Category 5 of the Integrated Report). The assessment type for these waters will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to “monitored" (indicating an assessment with relatively high confidence). Such waters will be placed in either Category 2b or 3b of the IR and thus will be added to the state’s list of “waters in need of further investigation”.
In addition, a fish kill occurred on this stream segment on August 27, 2001. The kill affected 0.3 miles of Bear Creek in Sections 24 and 25 of T86N, R23W, Hamilton County approximately four miles north of Roland. The kill was caused by release of manure from a swine production facility. An estimated 2,400 fish were killed. The party responsible for the kill was identified, and restitution was sought. According to DNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill during the most recent three-year period indicates "partial support" of the aquatic life uses. Thus, the general aquatic life uses of this stream were assessed as "partially supported." Also, according to DNR's assessment methodology, TMDLs will not be developed for kills caused by a one-time illegal or unauthorized release of manure or other toxic substance where enforcement actions were taken: no allocation process is possible with a pollutant that is discharged at irregular intervals. Such waterbodies will be placed into Integrated Report subcategory 4d. In this way, the impairment status of the affected waterbody remains highlighted.
