Muddy Creek IA 02-IOW-2043

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 in 2005, the general uses were assessed (monitored) as "not supported" (IR 5a) due to water quality impacts from poorly-treated domestic sewage being discharged to Muddy Creek.  This impairment was added to Iowa’s 2008 Section 303(d) list.  With the addition of the presumptive Class A1 and Class B(WW1) uses to Muddy Creek in 2008, the impairment of Muddy Creek due to discharge of poorly-treated wastewater was added to the presumptive Class A1 and Class B(WW1) uses.

Based on updated (2012) information from the volunteer (IOWATER) monitor (D. Ratliff) who described the original wastewater-related impairments to Muddy Creek in 2006, these wastewater-related impacts to the general use, Class A1 uses, and Class B(WW1) uses are proposed for de-listing.  A March 2012 letter from D. Ratliff to Iowa DNR staff suggests that the wastewater-related impairments to Muddy Creek have been corrected due to improvements in wastewater treatment at North Liberty.  The following is an excerpt from that letter:

North Liberty hired new staff for the NLWWTP [North Liberty Wastewater Treatment Plant] and installed a new state of the art Membrane Reactor (MBR) to augment the Sequential Batch Reactor (SBR).  Because of the reduction, or lack of the Total Suspended Solids (TSS) and improvements in bacteria reduction from the plant, Muddy Creek began to improve.

I have walked Muddy Creek several times, not from the bank but in the water, and have seen how the creek has changed.  Long gone are the pools of black sludge feed by the NLWWTP.  The hydraulics of the creek have changed since the implementation of the MBR, which now is a continuous discharge.  Three years ago small fish were observed at the Muddy Creek test site MC03 and two years ago JAICWC volunteers observed some fish at a tributary about halfway between MC02 and the NLWWTP.

The presumptive Class A1 (primary contact recreation) uses of Muddy Creek however, remain 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 22 samples collected during the recreational seasons of 2012 and 2013 at the four stations monitored are summarized in the following table:

From 90 to 100% of the 20 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 "impaired".  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 is 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 nine 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 2012 to August 2013 at the four monitoring stations (16520003, 16520004, 1552003, and 15520002) showed no violations of Class B(WW1) criteria for pH, temperature, or chloride in the approximately 22 samples collected at each station (combined total of 87 samples).  Samples were not analyzed for ammonia-nitrogen.  The two sites upstream from the North Liberty wastewater treatment plant showed violations of the Class B(WW1) criteria for dissolved oxygen.  Six of 22 samples (27%) violated the Class B(WW1) criterion for dissolved oxygen of 5.0 mg/l at both station MCR1 (STORET station16520003) and at station MCB (STORET station 15520002 in the extreme upper reaches of Muddy Creek in the city of North Liberty.  The minimum dissolved oxygen concentration at Station 16520003 was 3.7 mg/l; the minimum concentration at station 15520002 was 3.95 mg/l.  Nearly 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 22 samples from each of the two stations downstream from the wastewater treatment plant (MCR2 (STORET station 16520004) and MC3 (STORET station 15520003).  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 (12 of 87 samples or 14 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 and 2013 do not suggest impairment of the presumptive Class B(WW1) aquatic life uses.  According to the Iowa DNR assessment methodology, however, the percentage of dissolved oxygen violations is only one violation away from being significantly greater than 10% and a Section 303(d) impairment. 

CONCLUSIONS:  Based on updated information on improvements of wastewater treatment and on improvements in the general condition of Muddy Creek—and based on the recent lack of violations Class B(WW1) water quality criteria for conventional parameters downstream from the North Liberty wastewater treatment plant--the wastewater-related impairments of the general uses and of the Class A1 and Class B(WW1) uses are proposed for de-listing.  Results of bacteria monitoring, however, suggest that the presumptive Class A1 (primary contact recreation) uses should remain impaired (“not supported”) due to violations of Class A1 water quality criteria for indicator bacteria (E. coli).  Additional biological monitoring is needed to better determine the status of the fish and aquatic macroinvertebrate communities of Muddy Creek.