Mud Creek IA 06-BSR-1546

The Class A1 uses remain assessed as "not supported" based on results of ambient monitoring for indicator bacteria (E.coli). The geometric mean levels of indicator bacteria (E.coli) at both of the DNR/SHL TMDL stations during the 2002 and 2003 recreational seasons suggest impairment of the Class A1 uses. The geometric mean level of indicator bacteria (E.coli) in the 20 samples collected at the DNR/SHL TMDL station near Doon (839 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Fourteen of the 20 samples (70%) exceed Iowa’s single-sample maximum criterion of 235 orgs/100 ml. The geometric mean level of indicator bacteria (E.coli) in the 18 samples collected at the DNR/SHL TMDL station near the Iowa/Minnesota border (328 orgs/100ml) also exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Eleven of the 18 samples (61%) exceed Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S.EPA guidelines for Section 305(b) reporting and according to DNR’s assessment/listing methodology, if the geometric mean level 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" (see pgs 3-33 to 3-35 of U.S.EPA 1997b).

Results of chemical/physical water quality monitoring conducted by DNR/SHL from March 2002 through December 2003 in support of TMDL development suggest relatively good water quality in this stream and "full support" of the Class B(WW2) aquatic life uses. None of the combined 44 samples collected from these two stations had levels of dissolved oxygen or ammonia-nitrogen that violated state water quality standards (these samples were not analyzed for toxic metals or pesticides). Monitoring results for pH, however, showed that one of the combined 44 samples analyzed (3%) violated the Class B(WW2) water quality criterion for dissolved oxygen: the level of pH in the sample collected on May 20, 2003 at TMDL station 5 (STORET No. 11600004) (10.3 pH units) violated the Class B(WW2) criterion of 9.0 units. According to U.S.EPA guidelines for Section 305(b) water quality assessments (U.S.EPA 1997b, page 3-17), however, if 10% or less of samples exceed criteria for conventional parameters (e.g., dissolved oxygen and pH), aquatic life uses should be assessed as “fully supported”. These results, although somewhat limited in terms of parameter coverage, suggest "full support" of the Class B(WW2) aquatic life uses.

Despite results of ambient water quality monitoring that suggest “full support” of the Class B(WW-2) uses, the results of the 2004 & 2005 biological sampling in this river segment suggests that these uses should be assessed (evaluated) as only “partially supported”. The aquatic life assessment was based on data collected in 2004 & 2005 as part of the DNR/SHL stream REMAP project. A series of biological metrics which 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 2004 FIBI score was 20 (poor) and the 2004 BMIBI score was 58 (good). The 2005 FIBI score was 13 (poor) and the 2005 BMIBI score was 26 (poor). The FIBI BIC for this ecoregion is 43 and the BMIBI BIC for this ecoregion is 54. This segment passed the FIBI BIC 0/2 times and passed the BMIBI BIC 1/2 times in the last 13 years. The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.

This assessment is now considered "evaluated" because there were not two or more samples collected in multiple years during a recent five year period (2012-2016). Also, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). According to DNR’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). DNR 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). However, despite this change in assessment methodology and type, this waterbody remains on Iowa’s Section 303(d) list of impaired waters.

In addition, a fish kill in this river segment in September 2003 also suggests that these uses should be assessed (evaluated) as only “partially supported”. This kill occurred on or before September 10, 2003. The cause of the kill was attributed to low levels of dissolved oxygen, potentially related to a rainfall event and high levels of turbidity that resulted. An estimated 130 fish were killed, including common carp (20), channel catfish (10), and “minnows” (100). No estimate of the length of this stream affected by the kill was provided. No responsible party was identified. The location point for this kill is the SW ¼ of the SE ¼ of Section 15, T98N, R46W, Sioux County. According to the DNR investigation, the kill occurred at a road construction site at the county road A42 bridge. Due to the construction the water was diverted through a culvert which caused the stream to form a pool; the kill took place in the pooled area. The pooled water became very turbid following the heavy rains, thus potentially killing the fish.

This is the same fish-kill assessment as that developed for the 2006 through 2016 assessment/listing cycles. The occurrence of the fish kill in 2003 suggests continuance of the IR Category 5b listing is based on DNR's assessment methodology that states the following the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.”If a cause of the kill is identified, and the cause is either known, or suspected, to be a “pollutant”, the assessment type is considered “monitored” and the affected waterbody is a candidate for Section 303(d) listing. Fish kills attributed to a pollutant, but where a source of the pollutant was not identified and/or where enforcement actions were not taken against the responsible party, will be placed into Integrated Report subcategory 5b. The intent of placing these waterbodies into Category 5 is not to necessarily require a TMDL but to keep the impairment highlighted due to the potential for similar future kills from the unaddressed causes and/or sources.Any existing fish kill (5b) impairment will remain in IR Category 5b until more recent monitoring has shown recovery of the aquatic communities affected by the kill. Thus, this assessment segment will remain in Category 5b of Iowa’s Integrated Report.