Assessment Comments
Assessment is based on: (1) results of biological monitoring by the IDNR Fisheries Bureau from 1999-2002, and (2)results of water quality monitoring conducted from 2006-2008 on the South Fork Chariton River near Cambria (station RA-35) 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.
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 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 (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 2006-2008 on the South Fork Chariton River near Cambria (station RA-35) 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). The geometric mean level of indicator bacteria (E. coli) in the 23 samples collected at station RA-35 during recreational seasons of 2006 through 2008 (624 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Sixteen of the 23 samples (70%) 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 Class B(WW2) aquatic life uses are assessed (evaluated) as “partially supporting“ based on biological data collected in 1999-2002 as part of an IDNR 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 (FIBI). 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 FIBI scores were 3, 12, 24 (all poor) and 36 (fair). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI scores 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 1994-2004. This FIBI BIC for this ecoregion is 33. This segment passed the FIBI BIC 1/4 times in the last 10 years.
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. Additionally, 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 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 5b and remains on Iowa’s 2010 Section 303(d) list of impaired waters.
Because the biological impairment of the Class B(WW2) uses is based on an “evaluated” (lower confidence) 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 physical/chemical water quality monitoring during the 2006-2008 period do not suggest water quality problems in this assessment segment. None of the 22 samples violated Class B(WW2) criteria for dissolved oxygen and none of the 23 samples violated the Class B(WW-2) criteria for pH during the 2006-2008 assessment period. In addition, none of the 20 samples analyzed for ammonia from 2006-08 violated Class B(WW2) criteria. These results suggest improving water quality conditions in this segment of the South Fork Chariton River. That is, previous assessment cycles have shown impairments related to low levels of dissolved oxygen (see assessments developed for the 2002 and 2004 assessment cycles). Although this stream segment has a history of potential problems with low levels of dissolved oxygen, levels of dissolved oxygen over the last ten years of monitoring appear to have improved.
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 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 this segment of 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. For example, the mean level of atrazine in the 9 samples collected in 2004 at Station RA-35 (1.2 ug/l) is below the atrazine MCL of 3 ug/l; the maximum level of 4.6 ug/l of atrazine occurred in the sample collected on May 26, 2004. Atrazine was not monitored at Station RA-35 during the 2006-08 period.
