Assessment Comments
Assessment is based on results of IDNR/UHL biological (biocriteria) monitoring in 1995: Fish IBI=30 (fair), BM-IBI= 39(fair).
Basis for Assessment
[NOTE: Following their review of Iowa's 2004 Section 303(d) list, EPA--in their November 2005 decision document--proposed adding-back this segment of West Tarkio Creek based on impairment of aquatic life uses suggested by the 1995 biological data. Although IDNR considered the 1995 as too old to justify addition to the 2004 Section 303(d) list, IDNR informed EPA--in our December 19, 2005 letter--that additional biological monitoring had, in fact, been conducted on this stream segment in 2004, and that this monitoring suggested current impairment of the aquatic life uses. Despite the fact that the 2004 data were well beyond the data cutoff deadline for the 2004 listing cycle of December 2002, IDNR agreed with EPA that the segment remains impaired and is thus a candidate for Iowa’s 2004 Section 303(d) list. Thus, the assessment type was changed from "evaluated" to "monitored," and the IR category was changed from 3b (water in need of further investigation) to 5b (=impaired and on Iowa's Section 303(d) list). Iowa DNR’s original assessment for the 2004 Section 305(b) assessment cycle is included below.]
SUMMARY: The Class B(LR) aquatic life uses remain assessed as "partially supported" based on results of biological monitoring and habitat assessment conducted as part of the IDNR/UHL stream biocriteria project. Due to the age of the data, the assessment category is changed from "monitored" (higher-confidence assessment) to "evaluated" (lower confidence assessment).
EXPLANATION: Continue to use the assessment developed for the 1998 and 2000 reporting cycles that was based on results of the 1995 IDNR biocriteria assessment. As stated in the assessment developed for the 1998 report: the F-IBI score was 30 (fair) and the BM-IBI score was 39 (fair), and the aquatic life use support was assessed as partially supported (=PS), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria. Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is changed from "monitored" (indicating an assessment with relatively high confidence) to "evaluated" (indicating an assessment with relatively low confidence).
