South Fork Chariton River IA 05-CHA-1327

The presumptive Class A1 (primary contact recreation) will remain 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 the South Fork of the Chariton River near Promise City were as follows: the 2010 geometric mean was 794 orgs/100 ml, the 2011 geometric mean was 1,368 orgs/100 ml, and the 2012 geometric mean was 576 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Thirteen of the 19 samples (68%) 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 DNR’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.

The Class B(WW2) aquatic life uses remain assessed as “partially supporting” based on biological data collected in 2000-2002 as part of an 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 (FIBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2000-2002 evaluated FIBI scores were 15, 21, 22, 22, 22, 24, 25 (all poor), 27, 28, 28, 33 and 35 (all 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 1994-2008. The FIBI BIC for this ecoregion is 33. This segment passed the FIBI BIC 2/13 times in the last 20 years.

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 DNR assessment methodology. DNR 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”. This segment had multiple samples collected in the previous 17 years (2000-2016); however, the multiple samples were not collected during a recent five-year period. 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 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 was previously on Iowa’s Section 303(d) list and thus remains on Iowa’s Section 303(d) list of impaired waters (IR Category 5b-t).

Because the biological impairment of the Class B(WW2) uses is based on an “evaluated” (lower confidence) assessment, the DNR 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 DNR that biological impairments based on bioassessment data from the DNR Fisheries Bureau, even though DNR/SHL 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 chemical/physical water quality monitoring at the South Fork of the Chariton River near Promise City suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW2) water quality criteria for 30 Ammonia samples (maximum = 1 mg/L), 59 Dissolved Oxygen samples (minimum = 6.2 mg/L), 59 pH samples (range = 6.7 to 8.4), 59 Temperature samples (maximum = 28.6° c) or 40 Chloride samples (maximum = 17 mg/L) occurred during monitoring from March 2012 to October 2014.Results of chemical/physical water quality monitoring at the South Fork of the Chariton River near Promise City (site RA-12) in 2015 also suggest “full support” of the aquatic life uses. Monitoring data from 2015 showedno violations of Class B(WW2) water quality criteria for 6 Ammonia samples (maximum = 0.6 mg/L), 5 Dissolved Oxygen samples (minimum = 7.5 mg/L), 6 pH samples (range = 7.2 to 7.9), or 6 Temperature samples (maximum = 23.5° c) occurred during monitoring from April 2015 to September 2015.

According to U.S.EPA guidelines for Section 305(b) water quality assessments (U.S.EPA 1997b, page 3-17), the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” of the 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 2012-14 period do not suggest a serious threat to support of drinking water uses in Rathbun Reservoir. The mean level of atrazine in the 18 samples collected during this period at Station RA-12 (3.8 ug/l) is slightly above the atrazine MCL of 3 ug/l, thus suggesting relatively low contributions of atrazine to Rathbun Reservoir. The maximum level of atrazine during this period was 21.0 ug/l.