Muddy Creek IA 02-IOW-2043

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 21 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 21 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 DNR’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”.

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 DNR/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 11 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. DNR’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 station 16520003) 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 DNR 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.