The Class A1 (primary contact recreation) uses are assessed (monitored) 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 24 samples collected during the recreational seasons of 2014 through 2016 at the ambient monthly monitoring site on the Chariton River at 461st Street (STORET station 10040002) were as follows: the 2014 geometric mean was 31 orgs/100 ml, the 2015 geometric mean was 21 orgs/100 ml, and the 2016 geometric mean was 145 orgs/100 ml. One of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Four of the combined 24 samples (17%) exceeded Iowa’s 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 the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as "partially supported."

The Class B(WW1) aquatic life uses remain assessed as "fully supporting" based on results of DNR/SHL biological sampling conducted in 2012 and 2016 as part of the large river sampling project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach. The biological metrics were combined to make a benthic macroinvertebrate index (BMIBI) and fish index of biotic integrity (FIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2012 BMIBI score was 52 (fair) and the 2016 BMIBI score was 53 (fair). There were no FIBI/fish community samples collected in this reach in the previous five years. The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The BMIBI BIC for this ecoregion is 41. This segment passed the BMIBI BIC 2/2 times in the last five years. This assessment is considered evaluated because the drainage areas (641 and 550 mi2) above the sampling sites were greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site passed the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the sites used for the assessment don’t fall in the calibrated watershed size.

Results of chemical/physical water quality monitoring at the ambient monthly monitoring site on the Chariton River at 461st Street (STORET station 10040002) suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW1) water quality criteria for 35 Ammonia samples (maximum = 0.2 mg/L), 36 Dissolved Oxygen samples (minimum = 6.1 mg/L), 36 Temperature samples (maximum = 25° c), 36 Chloride samples (maximum = 33 mg/L), or 36 Sulfate samples (maximum = 22 mg/L) occurred during monitoring from January 2014 to December 2016. One of the 35 samples (3%) analyzed for pH (range = 6.1 to 8.5) violated the Class B(WW1) criteria during the 2014-2016 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17) and Iowa DNR's assessment/listing methodology, a violation frequency of significantly greater than 10% for conventional parameters such as pH suggests impairment of aquatic life uses. Because the frequency of violations for this parameter is not greater than 10 percent, these results do not suggest impairment of the Class B(WW1) aquatic life uses.

Results of chemical/physical water quality monitoring at Rathbun Watershed station RA-28 at the reservoir outlet also suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW1) water quality criteria for 7 Ammonia samples (maximum = 0.3 mg/L), 16 Dissolved Oxygen samples (minimum = 7 mg/L), 7 pH samples (range = 7.5 to 8.6), or 16 Temperature samples (maximum = 25.7° c) occurred during monitoring from May 2014 to September 2016. 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(WW1) aquatic life uses.

Results of Class C (drinking water) monitoring at the ambient monthly monitoring site on the Chariton River at 461st Street (STORET station 10040002) suggest “full support” of the Class C (drinking water)uses. Monitoring showed no violations of Class C (drinking water) criteria for 36 Chloride samples (maximum = 33 mg/L and average = 6.3 mg/L), 36 nitrate-nitrite samples (maximum = 0.83 ug/L and average = 0.45 ug/L), 14 Alachlor samples (maximum = 0.05 ug/L and average = 0.03 ug/L), 7 Atrazine samples (maximum = 0.9 ug/L and average = 0.44 ug/L), 7 Carbofuran samples (maximum = 0.05 ug/L and average = 0.05 ug/L), or 7 Cyanazine samples (maximum = 0.05 ug/L and average = 0.05 ug/L) occurred during monitoring from January 2014 to December 2016.

Results of Class C (drinking water) monitoring at Rathbun Watershed station RA-28 at the reservoir outlet also suggest “full support” of the Class C (drinking water)uses. Monitoring showed no violations of Class C (drinking water) criteria for 18 nitrate-nitrite samples (maximum = 0.83 mg/L and average = 0.48 mg/L), 7 Alachlor samples (maximum = 0.88 ug/L and average = 0.47 ug/L) or 6 Atrazine samples (maximum = 0.96 ug/L and average = 0.44 ug/L) occurred during monitoring from April 2014 to September 2016.

Fish consumption uses are assessed (monitored) as "fully supported" based on results of the U.S. EPA/DNR fish tissue (RAFT) monitoring north of Centerville in 2011 and 2013. The 2011 composite samples of fillets from channel catfish had very low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.197 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Levels of mercury in the 2011 tissue plug samples of white crappie, however, were above the one meal per week consumption advisory threshold. The average level of mercury in the tissue plugs from five white crappie was 0.316 ppm (SD=0.043 ppm; maximum=0.386; minimum=0.269). The average and maximum levels of mercury were well below Iowa’s “do not eat” advisory threshold of 1.0 ppm but were above Iowa’s threshold for issuance of a one meal per week fish consumption advisory. According to the DNR/DPH advisory protocol, two consecutive samplings showing that contaminant levels are above the advisory threshold level are needed to justify issuance of a consumption advisory. Additional monitoring of levels of mercury in white crappie was conducted in 2013. Results show that the average level of mercury in the five white crappie was 0.195 ppm (standard deviation = 0.079; maximum level = 0.286). This level is well below Iowa's threshold for a 1 meal/week consumption advisory.

The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The fish contaminant data generated for this segment of the Chariton River in 2011 and 2013 show that the levels of all contaminants are below the DPH/DNR advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory and "full support" of fish consumption uses.