Assessment Comments
Assessment is based on: (1) results of water quality monitoring conducted from 2004-2006 on the South Fork Chariton River near Promise City (station RA-12) 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, and (2) results of biological monitoring by the IDNR Fisheries Bureau from 1999-2002.
Basis for Assessment
[Note: Prior to the current (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 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 (2008) 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 remain assessed (evaluated) as "partially supported" based on (1) results of biological monitoring by the IDNR Fisheries Bureau from 1999-2002 that suggest impairment of these uses and (2) information in U.S. EPA's May 23, 2006 letter transmitting Iowa's final 2004 Section 303(d) list. This assessment is also based on results of water quality monitoring conducted from 2004-2006 on the South Fork Chariton River near Promise City (station RA-12) 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.
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses: the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff." Due to a change in the Standards in July 2003, E. coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E. coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.” Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E. coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of Section 305(b) assessments and Section 303(d) listings.
The geometric mean level of indicator bacteria (E. coli) in the 30 samples collected at station RA-12 during recreational seasons of 2004 through 2006 (394 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Twenty of the 30 samples (67%) 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 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).
The assessment of the Class B(WW2) aquatic life uses (partially supporting) remains based on biological data collected in 1999-2002 as part of a DNR Fisheries stream sampling project: Chariton research station. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the Fisheries sampling data. The biological metrics are based on the numbers and types of fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (F-IBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 1999-2002 evaluated Fish IBI average score (n=13) was 25 (poor). The aquatic life use support was assessed (evaluated) as Not Supporting (=NS), based on a comparison of the F-IBI score with biological assessment criteria established for previous Section 305(b) reports. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.
Based on the results of biological monitoring by the IDNR Fisheries Bureau, the Class B(WW2) aquatic life uses remain assessed (evaluated) as impaired. Because the previous impairment due to violations of Class B(WW2) criteria for dissolved oxygen no longer exists, and because the current impairment of the Class B(WW2) uses is based on an “evaluated” assessment, the IDNR assessment/listing methodology indicates that this assessment segment should be placed into IR Category 3b (potentially impaired; in need of further investigation). In their May 23, 2006 transmittal letter for Iowa’s 2004 Section 303(d) list, however, U.S. EPA Region 7 informed IDNR that biological impairments based on bioassessment data from the IDNR Fisheries Bureau, even though IDNR/UHL bioassessment protocols were not strictly followed, should nonetheless be placed into IR Category 5. Thus, this waterbody was placed into Category 5b of Iowa’s 2006 Integrated Report and will remain on Iowa’s future Section 303(d) lists.
Results of ambient chemical/physical water quality monitoring do not suggest impairments of the Class B(WW2) aquatic life uses of this stream segment. Results of monitoring during the 2004-2006 assessment period showed that none of the 35 samples violated Class B(WW2) criteria for pH, and none of the 10 samples collected in 2004 violated Class B(WW2) criteria for ammonia-nitrogen (maximum level = 3.1 mg/l). Monitoring results for dissolved oxygen showed that only one of 34 samples (3%) violated the Class B(WW2) water quality criterion for dissolved oxygen; this violation (4.3 mg/l) occurred on July 27, 2006. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), if 10% or less of samples exceed criteria for conventional parameters (e.g., dissolved oxygen and pH), uses should be assessed as “fully supported.” Although this stream segment has a history of potential problems with low levels of dissolved oxygen, levels of dissolved oxygen over the last eight years of monitoring appear to have improved. Based on results of recent monitoring, this stream segment does not currently show a dissolved oxygen-related impairment of its Class B(WW2) aquatic life uses.
Although this river reach is not designated for Class C drinking water uses, the South Fork Chariton River does flow into Rathbun Reservoir which is used as a source of drinking water for a public water supply. Thus, the seasonal elevation of pesticide levels in this stream and other tributaries of Rathbun Reservoir presents a continuing concern for the 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 the South Fork Chariton River during the 2004-06 period do not suggest a serious threat to support of drinking water uses in Rathbun Reservoir. The mean level of atrazine in the 11 samples collected in 2004 at Station RA-12 (1.1 ug/l) was approximately one-third of the MCL for atrazine of 3 ug/l. The maximum levels of 5.6 ug/l of atrazine occurred in the sample collected on May 26, 2004.
