Assessment Comments
Assessment is based on: (1) results of chemical/physical water quality monitoring conducted from 2006 through 2008 on Wolf Creek near Chariton (station RA-41; lower segment) and near Humeston (station RA-44; upper segment) by Iowa State University under contract with the U.S. Army Corps of Engineers-Kansas City District as part of the Rathbun Water Quality Project, (2) results of IDNR/UHL biocriteria and REMAP monitoring in 1999 and 2005, and (3) results of biological monitoring by the IDNR Fisheries Bureau in 2002.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2010) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW2) aquatic life uses are assessed (monitored) as "partially supported" based on results of chemical/physical water quality monitoring and on results of biological monitoring. The sources of data for this assessment include (1) results of chemical/physical water quality monitoring conducted from 2006 through 2008 on Wolf Creek near Chariton (station RA-41; lower segment) and near Humeston (station RA-44; upper segment) by Iowa State University under contract with the U.S. Army Corps of Engineers-Kansas City District as part of the Rathbun Water Quality Project, (2) results of IDNR/UHL biocriteria and REMAP monitoring in 1999 and 2005, and (3) results of biological monitoring by the IDNR Fisheries Bureau in 2002.
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric mean level of indicator bacteria (E. coli) in the approximately 25 samples collected at both the lower (RA-41) monitoring station (309 orgs/100 ml) and upper (RA-44) monitoring station (260 orgs/100 ml) on Wolf Creek during recreational seasons of 2006 through 2008 exceeded the Iowa Class A1 water quality criterion of 126 orgs/100ml. Fifteen of 25 samples (60%) at the lower station, and 13 of 24 samples (54%) at the upper station, exceeded 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 IDNR’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 3-35of U.S. EPA 1997b).
Regarding support of the Class B(WW2) aquatic life uses, none of the 20 samples collected from 2006-08 at (downstream) station RA-41 violated Class B(WW2) criteria for ammonia-nitrogen (maximum level = 0.5 mg/l). Similarly, none of the 19 samples collected from 2006-08 from the upstream station (RA-44) violated ammonia criteria (maximum level = 1.0mg/l). Three of the 24 samples (13%) collected at station RA-41, and 3 of 22 samples (14%) collected (at station RA-44 during the 2004 through 2006 assessment period violated the Class B(WW2) water quality criterion for dissolved oxygen. Minimum dissolved oxygen values were 3.1 mg/l at the downstream station and 1.9 mg/l at the upstream station. The violations occurred on the sample three sampling dates at both stations: June 7, 2006, September 27, 2007, and October 4, 2007. Stream discharges were low on these three dates with the maximum flow at either site equal to 0.02 cfs. None of the combined 48 samples collected from both stations during the 2006-2008 period violated the Class B(WW2) criteria for pH. The violations of the criteria for dissolved oxygen that occurred during the 2006-2008 period do not suggest an impairment: according to U.S. EPA assessment guidelines, if 10% or less of the samples exceed state criteria for conventional parameters such as dissolved oxygen and pH, the aquatic life uses should be assessed as "fully supported" (see pgs 3-17 of U.S. EPA 1997b). And, according to IDNR’s assessment/listing methodology, these results do not suggest that significantly greater than 10% of the samples violated the dissolved oxygen criterion, thus suggesting that the Class B(WW2) aquatic life uses should be assessed as “fully supported.” Water quality conditions in Wolf Creek, as in other tributaries in the Rathbun watershed, is strongly and adversely influenced by low flow periods when levels of dissolved oxygen are most likely to violate criteria designed to protect aquatic life.
Results of biological monitoring from IDNR/UHL biocriteria and REMAP sampling and from IDNR Fisheries monitoring suggest that the Class B(WW2) uses should be assessed (monitored) as "partially supported." This biological assessment was based on data collected in 1999 and 2005 as part of the IDNR/UHL stream biocriteria and REMAP projects and 2002 Fisheries bureau data. 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 1999 FIBI score was 33 (fair) and the BMIBI score was 41 (fair). The 2005 IDNR/UHL biocriteria FIBI scores were 18, 18 (poor) and the single biocriteria BMIBI score was 31 (fair). The evaluated Fisheries FIBI scores were 23, 23, 17 (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 1/6 times and passed the BMIBI BIC 1/2 times in the last 10 years. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.
This aquatic life assessment is now considered "evaluated" 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 between 2004 and 2008 to be considered “monitored”. This segment had multiple samples collected in the previous 10 years (1999-2008); however, the multiple samples were not collected during 2004-2008 and were not collected in multiple years (2005 data). According to IDNR’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). IDNR 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 in IR Category 5p based on the bacteria data.
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. Fortunately, however, the levels of atrazine in Wolf Creek during the 2004-2006 period do not suggest a serious threat to support of drinking water uses in Rathbun Reservoir. For example, the mean level of atrazine in the 11 samples collected in 2004 at Station RA-41 (1.2 ug/l) is well-below the atrazine MCL of 3 ug/l. Similarly, at station RA-44, the mean level of atrazine in the 11 samples collected in 2004 (1.3 ug/l) was well-below the atrazine MCL of 3 ug/l. Atrazine was not monitored at either station RA-41 or RA-44 during the 2006-08 period.
