South Fork Chariton River IA 05-CHA-1327

Assessment Comments

Assessment is based on results of monitoring conducted by ACOE.

Basis for Assessment

Had no new data from US ACOE.   Thus, used assessment of support of the Class B(LR) aquatic life uses developed for the 1994 report (=PS).  

For the 1998 report, changed the assessment of support of Class B(LR) uses from PS to "not assessed":  no biological information available.   Monitoring is needed to determine the status of aquatic communities and habitats.   Monitoring conducted by the U.S.  Army Corps of Engineers from April through September 1997 show no violations of Class B(LR) WQ criteria for DO (2 samples), pH (2 samples), or ammonia (10 samples).   This monitoring showed that 3 of 10 samples had levels of atrazine that exceeded the MCL of 3 ug/l, with two of the three samples collected in June 1997.   The average level of atrazine in the 10 samples was 5.8 ug/l; the median was 1.05 ug/l; levels of atrazine ranged from 0.12 to 30.2 ug/l.   All levels of alachlor were below the MCL of 2.0 ug/l.   Levels of cyanazine ranged from 0.04 to 8.3 ug/l, with an average of 1.56 ug/l.   Although the S.Fk.  Chariton River is not designated for Class C drinking water uses, the river is tributary to Rathbun Lake, a Class C waterbody.   A summary of the 1997 ACOE sampling is available.  

For the 2000 report:  SUMMARY:  The Class B(LR) aquatic life uses were assessed as "fully supported."  EXPLANATION:  The assessment of support of the Class B(LR) uses is based on results of water quality monitoring conducted on the South Fork Chariton River near Promise City (station RA-12) by the U.S.  Army Corps of Engineers-Kansas City District (1998) and by Iowa State University / Limnology under contract with the U.S.  Army Corps of Engineers (1999) as part of the Rathbun Water Quality Project.   The results of this monitoring are summarized in the "Rathbun Lake Water Quality Reports" for 1998 and 1999 (see ACOE 1999 and Kirsh and Leonard 2000).   Results of this monitoring show no violations of Iowa Class B(LR) water quality criteria for dissolved oxygen in the 9 samples analyzed in 1999, for pH in the 10 samples analyzed in 1999, or for ammonia-nitrogen in the 23 samples analyzed during 1998 and 1999.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), these results suggest "full support" of the Class B(LR) uses.   Additional monitoring is needed to better define the water quality conditions in this stream reach.   This additional monitoring is being conducted in 2000 as part of the ongoing Rathbun Water Quality Project.   Monitoring conducted during 1998 and 1999 showed high levels of both nutrient parameters (total nitrogen and total phosphorus) and pesticides at station RA-12 and at stations on other reservoir tributaries, with the highest levels often associated with storm runoff.   The Iowa Water Quality Standards does not currently have aquatic life criteria for these nutrient parameters or for other nonpoint source-related parameters (for example, total suspended solids).   Although this stream reach is not designated for Class C drinking water uses, the South Fork Chariton River does flow into Rathbun Reservoir which is designated for Class C uses.   The seasonal elevation of pesticides levels in the tributaries of the Rathbun watershed presents a continuing threat to full support of the Class C (drinking water) uses designated for Rathbun Reservoir.   For example, of the 23 samples collected at Station RA-12 in 1998 and 1999, the four samples that exceeded the atrazine MCL of 3.0 ug/l were collected in late May or June following application of herbicides to farm fields and during months with typically high levels of rainfall.   The mean levels of atrazine at Station RA-12 were 5.72 ug/l in 1998 (N=13; maximum of 48.70 ug/l) and 4.19 ug/l in 1999 (N=10; maximum of 25.7 ug/l).  

For the 2002 report:  SUMMARY:  The Class B(LR) aquatic life uses were assessed as "partially supported."  The assessment of support of the Class B(LR) uses is based on results of water quality monitoring conducted in 2000 and 2001 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.   The results of this monitoring are summarized in the "Rathbun Lake Water Quality Reports" for 2000 and 2001.   EXPLANATION:  Although none of the 20 samples violated Class B(LR) criteria for ammonia-nitrogen (maximum level = 0.45 mg/l) or for pH, monitoring results for dissolved oxygen suggest a potentially significant water quality problem.   Three of the 20 samples collected (15%) at station RA-12 in 2000 and 2001 violated the Class B(LR) water quality criterion for dissolved oxygen; all of these violations occurred in the relatively dry year of 2000 and are as follows:  4.6 mg/l on May 16, 2.8 mg/l on June 13, and 1.8 mg/l on June 27.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), if criteria for conventional parameters (e.g., pH, dissolved oxygen and temperature) are exceeded in from 11% to 25% of the samples "partial support" of beneficial uses is indicated.   Thus, the violation frequency of the Class B(LR) criterion for dissolved oxygen (15%) suggests "partial support" of the Class B(LR) aquatic life uses.   Similar to results of monitoring conducted in 1998 and 1999, results from the 2000-2001 period continued to show high levels of nutrient parameters.   While levels of total nitrogen in the South Fork Chariton River and other streams in the Rathbun watershed are relatively low for Iowa, levels of total phosphorus tend to be relatively high.   The 2000-2001 mean and median levels for total phosphorus at Station RA-12 were 0.24 mg/l and 0.21 mg/l, respectively (N=20); the mean and median levels of total nitrogen for this period were 1.5 mg/l and 1.1 mg/l, respectively.   The Iowa Water Quality Standards does not currently have aquatic life criteria for these nutrient parameters or for other nonpoint source-related parameters (for example, total suspended solids).   The Iowa DNR is, however, participating in a nationwide program, led by U.S.  EPA, for states to develop and adopt surface water criteria for total phosphorus, total nitrogen, chlorophyll, and some measure of turbidity.   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 designated for Class C uses.   Thus, the seasonal elevation of pesticides levels in this stream and other tributaries of Rathbun Reservoir presents a continuing threat to full support of the Class C (drinking water) uses designated for Rathbun Reservoir.   For example, the mean level of atrazine in the 20 samples collected at Station RA-12 in 2000 and 2001 (3.0 ug/l) equaled the atrazine MCL of 3.0 ug/l; the maximum levels of 23.8 ug/l of atrazine occurred in the sample collected on June 1, 2001.