Assessment Comments
Assessment remains based on results of a use attainability analysis (UAA) conducted by IDNR staff in September 2005.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are presumptively designated as Class A1 and Class B(WW1) waters. Results of a use attainability analysis, however, suggest that this stream segment lacks the physical characteristics to support designated uses for either contact recreation or aquatic life and thus should remain a general use-only stream segment. Thus, for the current (2012) assessment cycle, this stream segment will be assessed as a “general use-only” segment.
SUMMARY: The general uses of this stream are assessed (evaluated) as "partially supported" based on results of an IDNR use attainability analysis (UAA) conducted in September 2005 that suggest potential impacts of inadequately-treated wastewater discharged to the stream. Waters assessed as “evaluated/partially supported” lack conclusive evidence of Section 303(d) impairment. Due to evidence of potential impairment, however, such waters are appropriate for addition to Iowa’s list of waters in need of further investigation (WINOFI). Thus, this assessment segment was placed in Category 3b of Iowa’s 2010 Integrated Report (i.e., insufficient data exist to determine whether any designated uses are met, but at least one use is assessed as potentially impaired based on an “evaluated” assessment). This assessment segment remains in Category 3b.
EXPLANATION: The assessment of support of the general uses of this stream segment is based on results of observations and biological monitoring conducted by IDNR staff on September 28, 2005, as part of a use attainability analysis for an Rhine Creek in Johnson County near the outfall of Oxford WWTP. The following comments from the UAA are relevant to this assessment (see http://programs.iowadnr.gov/uaa/search.aspx):
Aquatic Vegetation Comments: Rocks [sic] attached to algae on rocks. Comments: Water was green in color, muck/silt for the most part. (http://programs.iowadnr.gov/uaa/resources1/sites/2350/388-1%20Recreation%20Data.pdf)
These comments suggest potentially poor water quality conditions that may, upon further investigation, constitute violations of several of Iowa's narrative water quality standards (IAC 61.3(2)) designed to protect general uses of Iowa's surface waters (e.g., livestock and wildlife watering, aquatic life and non-contact recreation). Based on the information available, however, the UAA comment does not appear to suggest violation of any of the following narrative criteria (IDNR rationales are in parentheses):
--such waters shall be free from substances from point source dischargers that will settle to form sludge deposits. (No “sludge deposits” are mentioned in UAA recommendation documents, and “muck” (which was a commonly-used term for silt/mud substrate by one of the lead UAA field staff) does not indicate presence of “sludge”.)
--such waters shall be free from floating debris, oil, grease, scum and other materials from wastewater discharges or agricultural practices in amounts sufficient to create a nuisance. (Although water was noted as “green,” thus suggesting a high chlorophyll concentration, no “debris, oil, grease, scum, or other materials” are mentioned in UAA reports; thus the UAA comments do not suggest a violation of this narrative water quality criterion.)
--such waters shall be free from materials from wastewater discharges or agricultural practices producing objectionable color, odor, or other aesthetically objectionable conditions. (The only potential violation of this narrative criterion mentioned in the UAA was the “green” color of the water in Rhine Creek. While a potential violation is suggested, high levels of chlorophyll in Iowa streams are not atypical and may or may not be related to wastewater discharges.)
--such waters shall be free from substance attributable to wastewater discharges or agricultural practices in concentrations or combinations which are acutely toxic to human, animal, or plant life. [There is no suggestion of a “toxic condition” in the UAA recommendation documents or on the UAA field sheets.]
Based on the information from the September 2005 UAA, the general uses of this stream segment are assessed (evaluated) as "partially supported" due to the potential for water quality impacts from inadequately-treated domestic sewage. Such waters, although not appropriate for addition to Iowa’s Section 303(d) list of impaired waters, are appropriate for addition to Iowa’s list of waters in need of further investigation (WINOFI). Thus, this assessment segment was placed in Category 3b of Iowa’s 2010 Integrated Report and remains in this category.
