Assessment Comments
Assessment is based on results of (1) IDNR/UHL ambient monthly monitoring near Knoxville from 2002-04 and (2) biological monitoring conducted by the IDNR Fisheries Bureau in 1999.
Basis for Assessment
SUMMARY: Based on results of routine ambient chemical/physical water quality monitoring and on results of biological monitoring in 1999 by the IDNR Fisheries Bureau, the Class B(WW) aquatic life uses remain assessed (monitored) as "fully supported / threatened" with a declining water quality trend (=impaired). Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment. The source of data for this assessment is the results of IDNR/UHL ambient monthly monitoring during the 2002-2004 assessment period at STORET station 10630001 (formerly station 100818) approximately 3 miles southwest of Knoxville.
EXPLANATION: The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported / threatened" with a potentially declining water quality trend. This assessment was partially based on data collected in 1999 as part of a DNR Fisheries Bureau stream sampling project: Manchester research station. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the Fisheries sampling data. The biological metrics are based on the numbers and types of fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (F-IBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 1999 evaluated Fish IBI was 22 (poor). The aquatic life use support was assessed (evaluated) as Not Supporting (=NS), based on a comparison of the F-IBI score with biological assessment criteria established for previous Section 305(b) reports. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.
In contrast to results of biological monitoring which suggest a threat to full support of the aquatic life uses, results of ambient chemical/physical water quality monitoring from 2002 through 2004 suggest “full support” of the aquatic life uses. None of the 36 samples collected during the 2002-2004 assessment period at the IDNR monthly station violated Class B(WW) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen; no violations occurred in the approximately 10 samples analyzed for pesticides and other toxic organic compounds. Based, however, on the previous (2004) assessment, the aquatic life uses of this stream segment will remain assessed as “fully supported/threatened” with a declining trend. In the 2004 assessment, two of the 36 samples (6%) collected at IDNR/UHL station 10630001 from 2000 through 2002 violated the Class B(WW) criterion for dissolved oxygen: the sample collected on August 1, 2001 contained only 0.7 mg/l, and the sample collected on September 4, 2001, contained only 1.6 mg/l of dissolved oxygen; no violations have been documented since September 2001. Even though U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), allow for up to 10% of sample to violate criteria for conventional parameters (such as dissolved oxygen), the August and September 2001 readings of dissolved oxygen were atypically low for Iowa streams, and the potential exists for a significant water quality impact, especially given the occurrence of consecutive monthly levels of dissolved oxygen far below the state water quality criterion. Also, the results of biological monitoring conducted in 1999 by the IDNR Fisheries Bureau suggested aquatic life conditions well-below those expected. Follow-up monitoring should be conducted to better characterize water quality conditions and status of aquatic life of this stream segment.
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this stream segment.
