South Fork Chariton River IA 05-CHA-1328

The presumptive Class A1 (primary contact recreation) are assessed (evaluated) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 15 samples collected during the recreational seasons of 2010 through 2012 at the South Fork Chariton River near Cambria were as follows: the 2010 geometric mean was 679 orgs/100 ml, the 2011 geometric mean was 489 orgs/100 ml and the 2012 geometric mean was 208 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Ten of the 15 samples (67%) 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 should have been listed as (monitored) “partially 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 be listed as "partially supported" for the 2016 assessment/listing cycle. 

The Class B(WW2) aquatic life uses are assessed (evaluated) as “partially supporting“ based on biological data collected in 2012 as part of the IDNR/SHL stream nutrient and follow-up sampling projects and on data collected in 2000-2002 as part of an IDNR Fisheries stream sampling project: Chariton research station. A series of biological metrics that 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 collected in the stream sampling reach. The biological metrics were combined to make a benthic macroinvertebrate index (BMIBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2012 FIBI score was 28 (fair) and the BMIBI scores were 20 and 24 (both poor). The 2000-2002 evaluated FIBI scores were 12, 24 (both 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 1994-2008. This FIBI BIC for this ecoregion is 33. This segment passed the FIBI BIC 1/4 times in the last 15 years and passed the BMIBI BIC 0/2 times in 2012.

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 over a recent five-year period to be considered “monitored”. This segment had multiple FIBI samples collected in the previous 15 years (2000-2014) and had multiple BMIBI samples collected in a single year (2012). 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 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 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/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 Chariton River near Cambria suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW2) water quality criteria for 24 Ammonia samples (maximum = 0.8 mg/L), 38 Dissolved Oxygen samples (minimum = 5.2 mg/L), 38 pH samples (range = 6.9 to 8), 38 Temperature samples (maximum = 25.3° c) or 17 Chloride samples (maximum = 17 mg/L) occurred during monitoring from March 2012 to October 2014. 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. 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 12 years of monitoring appear to have improved.

The results of continuous dissolved oxygen (DO) and temperature monitoring in 2012 for the IDNR/SHL sampling project Class B(WW2) suggest impairment of aquatic life uses. The lowest DO concentration recorded in 70 days of continuous monitoring was 1.9 mg/L. The daily DO minimum concentration failed to meet the 24-hour DO criterion (4 mg/L) in 48 of 70 days and the 16-hour DO criterion (5 mg/L) in 30 of 70 days. The percentages exceeding the 24-hour and 16-hour DO criteria (68.6% and 42.9%, respectively) were greater than (failing) the 10% impairment threshold used to assess conventional water quality parameters. The associated statistical analysis confidence level was high (>90%). The maximum stream temperature recorded during the sensor deployment period was 35.7 degrees (C). The temperature criterion for warmwater interior streams (32 C) was exceeded in 24 of 70 days. The percentage exceeding (34.3%) 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.

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. The levels of atrazine in this segment of the South Fork Chariton River during the 2012-14 period, however, do not suggest a serious threat to support of drinking water uses in Rathbun Reservoir. For example, the mean level of atrazine in the 19 samples collected during 2012-14 at Station RA-35 (6.3 ug/l) is above the atrazine MCL of 3 ug/l, thus suggesting relatively moderate contributions of atrazine to Rathbun Reservoir; the maximum atrazine level during this period was 46.0 ug/l of atrazine.