Assessment Comments
Assessment remains based on (1) observations and photo documentation by IDNR staff in 2005, (2) results of weekly chemical monitoring conducted by IDNR staff from May 2005 through July 2006, and (3) IDNR/UHL biological monitoring at three sites in the segment in 2006.
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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters. Thus, for the current (2010) assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]
SUMMARY: The general uses of this stream remain assessed (monitored) as "not supported" due to impacts of poorly-treated wastewater discharged to the stream. In addition, the presumptive Class A1 (primary contact recreation) uses remain assessed as "not supported" based on violations of Iowa's narrative water quality criteria due to discharge of poorly-treated wastewater to this stream segment. The presumptive Class B(WW1) aquatic life uses of this stream also remain assessed (monitored) as "not supported" due to impacts of poorly-treated wastewater discharged to the headwaters of this stream.
This assessment remains based on results of observations and water quality monitoring conducted by IDNR staff in 2005 and 2006. IDNR has documented accumulations of sewage sludge in the channel of this stream; these conditions are a violation of the narrative criteria in the Iowa Water Quality Standards that protect against accumulations of sewage sludge in Iowa streams. In addition, IDNR and UHL conducted biological monitoring in 2006 and the data suggest that this segment is "partially supporting" the aquatic life/overall uses of the stream based on an evaluated assessment. The sources of data for this assessment include (1) results of observations and photo documentation by IDNR staff in 2005 and (2) results of weekly chemical monitoring conducted by IDNR staff from May 2005 through July 2006 at three locations from North Liberty downstream to First Avenue in Coralville, IA and (3) IDNR/UHL biological monitoring at three locations in the segment in 2006. This stream was not assessed for purposes of Section 305(b) assessment or Section 303(d) listing prior to the 2006 assessment/listing cycle.
EXPLANATION: A survey conducted in October 2005 by IDNR staff documented accumulations of sewage sludge in Muddy Creek downstream from the North Liberty wastewater treatment facility. Accumulations of sludge were up to 12 inches deep and occurred up to one-half mile downstream from the wastewater treatment facility. In addition, results of water quality monitoring from May 2005 through July 2006 show acutely toxic levels of ammonia occurring on December 5, 2005. The accumulations of sewage sludge and poor water quality conditions observed and reported by IDNR staff potentially violate 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):
--such waters shall be free from substances from point source dischargers that will settle to form sludge deposits;
--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;
--such waters shall be free from materials from wastewater discharges or agricultural practices producing objectionable color, odor, or other aesthetically objectionable conditions;
--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.
Based on the information received by IDNR on this stream, the general uses are assessed (monitored) as "not supported" due to water quality impacts from poorly-treated domestic sewage being discharged to Muddy Creek. Waters assessed as “monitored/not supported” are considered appropriate for addition to Iowa’s Section 303(d) list of impaired waters.
In addition, this assessment remains based on data collected in 2006 as part of a IDNR/UHL stream biological monitoring project. A series of biological metrics that 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 collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2006 FIBI scores were 2, 24 (poor) and 42 (fair). The 2006 BMIBI scores were 35, 50 (fair). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51. This segment passed the FIBI BIC 1/3 times and passed the BMIBI BIC 0/2 times in the last five years. Even though this segment failed both the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small general use stream and doesn’t fall in the calibrated watershed size.
This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology. IDNR now requires a segment have two or more biological samples collected from the segment in multiple years between 2004 and 2008 to be considered “monitored”. This segment had multiple samples collected in the previous five years (1999-2008); however, were not collected in multiple years. According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).
Prior to the changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this stream was classified only for general uses due to the inability of the stream to support a viable aquatic community at low-flow conditions. IDNR’s existing biological assessment protocol, however, was calibrated to aquatic life reference conditions in larger wadeable streams with perennial flow. The aquatic environment of most headwater streams is one of extremes in water quality. Consequently, intermittent headwater streams tend to have biological diversity that is low relative to more stable aquatic environments of larger streams with perennial flow. Thus, the use of biological assessment methods developed for the ecologically more stable and diverse streams will likely overstate the existence of impairment in headwater streams.
CONCLUSION: Based on the documentation of the impacts of poorly-treated wastewater in Muddy Creek, the general uses of this stream, as well as the presumptive aquatic life uses and the presumptive primary contact recreation uses of this segment, are assessed as impaired. This waterbody was assessed as impaired for general aquatic life and was added to Iowa’s 2006 list of impaired waters as required by Section 303(d) of the federal Clean Water Act. This impairment remains on Iowa's 2010 list. Due to the February 2008 EPA approval of changes to Iowa Water Quality Standards, this segment is now also impaired for the presumptive Class A1 (primary contact recreation) and Class B(WW1) aquatic life uses.
