Assessment Comments
Assessment is based on results of (1) IDNR/UHL biological (biocriteria) monitoring in 2001: Fish IBI= 65(good), 46(fair); BM-IBI= 36(fair),30(poor) and (2) results of IDNR/UHL ambient water quality monitoring conducted in 2001 in support of TMDL development.
Basis for Assessment
[Note: Although originally placed in Category 3b of Iowa's 2004 Integrated Report by Iowa DNR, U.S. EPA Region VII, in their May 23, 2006 transmittal of Iowa's final approved 2004 Section 303(d) list, added this waterbody segment to Iowa's 2004 Section 303(d) list (IR Category 5a). Originally, Iowa DNR maintained that addition of this assessment segment to Iowa’s 2004 Section 303(d) list was inappropriate due to the difficulty of assessing general use waters using biological assessment protocols calibrated to reference conditions in designated use (Class B(LR) and wadeable Class B(WW)) streams. In their review of Iowa’s 2004 Section 303(d) list, U.S. EPA Region VII, however, maintained that Iowa DNR had improperly excluded existing and readily available data in the assessment of this assessment segment. That is, EPA maintained that Iowa DNR’s stressor identification document for this assessment segment demonstrated clear evidence of water quality impairment, and that IDNR had not demonstrated “good cause” for not including this segment on the state’s Section 303(d) list. EPA further stated that the IDNR stressor identification document clearly identified water quality impairments consistent with Iowa’s General Water Quality Criteria (e.g., nuisance algal blooms, depressed dissolved oxygen concentrations, and aesthetically objectionable conditions) generally attributable to elevated nutrient concentrations. EPA stated that they received comments and photographs during the public comment period that corroborated their determination. Thus, EPA added-back this assessment segment to Iowa's 2004 final approved Section 303(d) list (Category 5a). Contrary to EPA's contention in their May 23, 2006 transmittal letter, IDNR staff feel that the Stressor Identification (SI) analyses of these segments do not reveal evidence of impairment to narrative water quality standards that are applicable to these general use segments (personal communication from IDNR staff that authored the SI documents). In the case of Milford Creek, the SI found evidence of several factors contributing to biological impairment in the adjacent downstream segment (IA 06-LSR-0300-0) that is designated for aquatic life uses. A TMDL is being prepared for this segment, and it includes a consideration of pollutant loadings from the entire watershed, including the general use segment. With respect to the Middle Fork South Beaver Creek segment, the SI also found evidence of stressor levels that are consistent with a reduction in stream biological condition. However, the stressor evidence did not exceed acutely toxic levels and were not manifested as violations of narrative water quality standards for general use waters. Therefore, IDNR feels that the original placment of these stream segments in Category 3b was appropriate along with other general use waters for which there is only “evaluated” evidence of biological impairment." Iowa DNR’s original assessment for the 2004 Section 305(b) assessment cycle is included below.]
SUMMARY: The general (aquatic life) uses continued to be assessed (evaluated) as "partially supporting (=PS)" based on results of biological monitoring in 2001. Results ambient water quality monitoring suggest good water quality but suggest the potential for continued water quality problems. The sources of data for this assessment are results of (1) biological sampling data collected in 2001 as part of the DNR/UHL stream biocriteria and TMDL development projects and (2) IDNR/UHL monthly ambient water quality monitoring conducted in from March to November 2001 in support of TMDL development (STORET station 11380003; Site 45). The previous assessment of support for the general beneficial uses of this stream ("partially supported") was based on the occurrence of repeated fish kills from 1991 to 1997 (see assessment developed for the 1998 report). This assessment was the basis for adding this stream segment to Iowa's Section 303(d) list of impaired waters. The most recent kill occurred in September 1997. According to DNR's assessment methodology for Section 305(b) reporting, the lack of fish kills during the most recent three-year period suggest that the stream has fully recovered from fish kill-related impacts.
EXPLANATION: 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 (F-IBI) and a benthic macroinvertebrate index (BM-IBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2001 Fish IBI scores were 65 (good) and 46 (fair); the BM-IBI scores were 36 (fair) and 30 (poor). The aquatic life use support 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 2002 Section 305(b) report. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.
The results of monthly water quality monitoriong conducted in 2001 by IDNR/UHL at one location approximately 4 miles NW of Wellsburg show the potential for water quality impacts. Because the stream segment is classified only for general uses, and because general uses are not supported by numeric water quality criteria for conventional or toxic pollutants, Class B(LR) aquatic life criteria were used to estimate any potential water quality impairments for this stream reach. Results of this monitoring suggest the potential for water quality impacts to the general aquatic life uses. One of the nine samples (11%) violated the Class B(LR) chronic water quality criterion for ammonia nitrogen. According to U.S. EPA guidelines for Section 305(b) reporting, if, for a dataset where at least 10 samples have been collected over a three-year period, more than 10% of the samples exceed state criteria for toxics (including ammonia-nitrogen), the aquatic life uses are "not supported" (see pg 3-18 of U.S. EPA 1997b). However, because less than 10 samples were available for this assessment, the assessment type is considered "evaluated"; and the degree of support of the aquatic life uses was considered "fully supported/threatened." According to IDNR assessment guidelines, "evaluated" assessments are not of sufficient quality to support a Section 303(d) listing.
This assessment 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 a 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”.
