Assessment Comments
Assessment is based on (1) observations and photo documentation by IDNR staff in 2005, (2) results of twice-monthly monitoring conducted from May through November 2012, and (3) IDNR/SHL biological sampling conducted in 2006, 2009 and 2010.
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, 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 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" (IR 5a) due to a history of impacts of poorly-treated wastewater discharged to the stream. In addition, the presumptive Class A1 (primary contact recreation) uses remain assessed as "not supported" (IR 5p) based on violations of Iowa's narrative water quality criteria due to discharge of poorly-treated wastewater to this stream segment. Also, monitoring conducted in 2012 continued to show that levels of indicator bacteria (E. coli) exceed Iowa’s criteria to protect the presumptive Class A1 (primary contact recreation) uses of this stream. The presumptive Class B(WW1) aquatic life uses of this stream remain assessed (monitored) (IR 5p) as "not supported" due to (1) impacts of poorly-treated wastewater discharged to the headwaters of this stream and (2) results of IDNR/SHL biological sampling conducted in 2006, 2009 and 2010.
The sources of data for this assessment include (1) results of observations and photo documentation by IDNR staff in 2005 and (2) results of chemical and bacteria monitoring conducted from May to November of 2012 at four locations from North Liberty downstream to First Avenue [Site MCR1 (STORET station 15620003), Site MCR2 (STORET station 16520004), Site MC3 at 1st Avenue (STORET station 15520003), and Site MCB at Golf View Drive (STORET station 15520002)], (3) IDNR/SHL biological sampling at three locations in the segment in 2006 and one location in 2009 and 2010.
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 showed 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 violated 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 were 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 (Category 5 of the Integrated Report).
The presumptive Class A1 (primary contact recreation) uses of Muddy Creek are assessed (monitored) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric means of indicator bacteria (E. coli) in the 15 samples collected during the recreational seasons of 2012 at the four stations monitored were as follows:
1. Muddy Creek at Golf View Dr. (MCB), STORET station 15520002: 1,126 orgs/100 ml;
2. Muddy Creek at 1st Avenue (MC3); STORET station 15520003: 896 orgs/100 ml;
3. Muddy Creek station MCR1; STORET station 16520003: 724 orgs/100 ml;
4. Muddy Creek station MCR2, STORET station 16520004: 949 orgs/100 ml.
From 85 to 100% of the 15 bacteria samples collected at each of these monitoring sites exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported". Thus, these results suggest that the presumptive Class A1 uses should be assessed as “not supporting” (IR Category 5a).
The assessment of the presumptive Class B(WW1) aquatic life uses was based in part on data collected in 2006, 2009 and 2010 as part of a IDNR/SHL stream biological sampling 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 (poor), 27 (fair) and 42 (fair). The 2006 BMIBI scores were 35, 52 (fair). The 2009 FIBI score was 13 (poor) and the BMIBI score was 54 (fair). The 2010 FIBI score was 30 (fair) and the BMIBI score was unavailable. 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 1994-2008. The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51. This segment passed the FIBI BIC 1/5 times and passed the BMIBI BIC 2/3 times in the last seven years. Even though this segment failed the FIBI BIC and passed the BMIBI BIC, 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.
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.
Results of chemical/physical water quality monitoring conducted from May to November 2012 at the four monitoring stations (16520003, 16520004, 1552003, and 15520002) showed no violations of Class B(WW1) criteria for pH or temperature in the 15 samples collected at each station (combined total of 60 samples). Samples were not analyzed for ammonia-nitrogen. The two upstream sites showed violations of the Class B(WW1) criteria for dissolved oxygen. Four of 15 samples (27%) violated the Class B(WW1) criterion for dissolved oxygen of 5.0 mg/l at both station 16520003 (Site MCR1, upstream from the wastewater treatment plant) and at station 15520002 (Site MCB) in the upper reaches of Muddy Creek in the city of North Liberty. The minimum dissolved oxygen concentration at Station 16520003 was 4.2 mg/l; the minimum concentration at station 15520002 was 4.1 mg/l. All samples at all stations were collected relatively early in the morning (between 0745 and 0830 hours). No violations of dissolved oxygen criterion occurred in the 15 samples from the two downstream stations (16520004 (MCR2) and 15520003 (MC3)). Considered separately, the percentage of violations at the two headwater station on Muddy Creek are significantly greater than 10% and, according to the IDNR assessment methodology, would suggest impairment of the Class B(WW1) aquatic life uses. If all samples are combined, however, the percentage violation (8 of 60 samples or 13 percent) is not significantly greater than 10% and thus does not suggest impairment of these uses. Thus, when considered on an assessment segment basis, the results of chemical/physical monitoring during 2012 do not suggest impairment of the presumptive Class B(WW1) aquatic life uses.
CONCLUSIONS: Based on the historical documentation of the impacts of poorly-treated wastewater in Muddy Creek, the general uses of this stream, as well as the presumptive Class B(WW1) aquatic life uses and the presumptive Class A1 primary contact recreation uses of this segment, remain assessed as impaired. The presumptive Class A1 (primary contact recreation) uses are also impaired due to violations of Class A1 water quality criteria for indicator bacteria (E. coli). Recent (2011) observations by volunteer monitors suggest improved water quality in Muddy Creek (D. Ratliff, personal communication). Upgrades to the wastewater treatment facility at North Liberty have eliminated the accumulations of sludge in pools of Muddy Creek. Based on these observations, additional biological monitoring and reporting of visual assessments are needed to determine whether the impairments of general uses and aquatic life uses can be removed. Despite potential improvements in the water quality conditions of this stream, this impairment remains on Iowa's impaired waters list.
