Wolf Creek IA 05-CHA-1339

The presumptive Class A1 (primary contact recreation) are assessed (evaluated) as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 19 samples collected during the recreational seasons of 2010 through 2012 at site RA-41 (downstream) were as follows: the 2010 geometric mean was 959 orgs/100 ml, the 2011 geometric mean was 185 orgs/100 ml, and the 2012 geometric mean was 2,469 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Fifteen of the 19 samples (79%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. The geometric means of indicator bacteria (E. coli) in the 15 samples collected during the recreational seasons of 2010 through 2012 at site RA-44 (upstream) were as follows: the 2010 geometric mean was 470 orgs/100 ml, the 2011 geometric mean was 138 orgs/100 ml, and the 2012 geometric mean was 632 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Eight of the 15 samples (53%) 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 a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). In the 2014 assessment/listing cycle, the presumptive Class A1 uses were listed as (monitored) "not supported" due to levels of indicator bacteria that exceeded state water quality criteria. Therefore, due to the lack of new data collected during the 2012 -2014 sampling seasons, the Class A1 uses will remain listed as "not supported" for the 2016 assessment/listing cycle.  

Results of chemical/physical water quality monitoring at site RA-41 (downstream) suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW2) water quality criteria for 28 Ammonia samples (maximum = 0.7 mg/L), 53 pH samples (range = 7 to 8), 53 Temperature samples (maximum = 27.5° c) or 34 Chloride samples (maximum = 14 mg/L) occurred during monitoring from March 2012 to October 2014. One of the 53 samples (2%) analyzed for Dissolved Oxygen (minimum = 3.2 mg/L) violated the Class B(WW2) criteria during the 2012-2014 monitoring period. Additionally results of chemical/physical water quality monitoring at site RA-44 (upstream) also suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW2) water quality criteria for 21 Ammonia samples (maximum = 0.7 mg/L), 35 pH samples (range = 7 to 7.9), 35 Temperature samples (maximum = 25.1° c) or 14 Chloride samples (maximum = 13 mg/L) occurred during monitoring from March 2012 to October 2014. One of the 35 samples (3%) analyzed for Dissolved Oxygen (minimum = 3.6 mg/L) violated the Class B(WW2) criteria during the 2012-2014 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as Dissolved Oxygen suggests impairment of aquatic life uses. Because the frequency of violations for this parameter is not greater than 10 percent, these results do not suggest impairment of the Class B(WW2) aquatic life uses.

However, the results of continuous dissolved oxygen (DO) and temperature monitoring in 2012 for the IDNR/SHL sampling project do suggest impairment of Class B(WW2) aquatic life uses. The lowest DO concentration recorded in 69 days of continuous monitoring was 2.1 mg/L. The daily DO minimum concentration failed to meet the 24-hour DO criterion (4 mg/L) in 29 of 69 days and the 16-hour DO criterion (5 mg/L) in 9 of 69 days. The percentages exceeding the 24-hour and 16-hour DO criteria (42.0% and 13.0%, respectively) were greater than (failing) the 10% impairment threshold used to assess conventional water quality parameters. The associated statistical analysis confidence level for the 24-hour analysis result was high (>90%), while the confidence level for the 16-hour analysis result was not high (<90%). The maximum stream temperature recorded during the sensor deployment period was 34.2 degrees (C). The temperature criterion for warmwater interior streams (32 C) was exceeded in 15 of 69 days. The percentage exceeding (21.7%) was greater than (failing) the 10% impairment threshold with high statistical confidence (>90%). Based on these data, the B(WW1) aquatic life use is assessed as impaired for DO and temperature. The assessment type is “evaluated” because it is based on data collected from a single year within the current data assessment period. In order to meet the requirements for a “monitored” assessment, the IDNR’s continuous monitoring assessment methodology requires monitoring data from two or more years within the assessment period.

Results of biological sampling from IDNR/SHL suggest that the Class B(WW2) uses should be assessed (monitored) as "partially supported." This biological assessment was based on data collected in 2011 and 2012 as part of the IDNR/SHL stream biocriteria and TMDL/SI sampling projects. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological 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 2011 FIBI scores were 24 (poor) and 34 (fair) and the BMIBI scores were 33 (fair) and 56 (good). The 2012 FIBI score was 23 (poor) and the BMIBI score was 27 (poor). 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 FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41. This segment passed the FIBI BIC 1/3 times and passed the BMIBI BIC 1/3 times in the last five years. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.

This aquatic life assessment is now considered "monitored" 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 over a recent five-year period to be considered “monitored”.

Although this stream reach is not designated for Class C drinking water uses, Wolf Creek does flow into Rathbun Reservoir which is used as a source of drinking water for a public water supply. The seasonal elevation of pesticide levels in the Chariton River and other tributaries of Rathbun Reservoir presents a continuing concern for full support of the Class C (drinking water) uses designated for the Chariton River immediately downriver from Rathbun Reservoir. The mean level of atrazine in the 19 samples collected from 2012-14 at Station RA-41 (5.4 ug/l) is above the atrazine MCL of 3 ug/l, thus suggesting relatively low contributions of atrazine to Rathbun Reservoir. Similarly, at station RA-44, the mean level of atrazine in the 17 samples collected from 2012-14 (9.2 ug/l) is above the atrazine MCL of 3 ug/l, thus suggesting relatively moderate contributions of atrazine to Rathbun Reservoir.