Assessment Comments
Assessment is based on results of IDNR/UHL ambient monthly monitoring from 2004-06 west of Jefferson: IDNR/UHL ambient monitoring in this river segment was terminated in 2006.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses remain assessed (monitored) as "not supported" due to high levels of indicator bacteria (E. coli). The Class B(WW1) aquatic life uses remain assessed (monitored) as "fully supported" based on results of ambient chemical/physical water quality monitoring. Support of fish consumption uses remains "not assessed" due to the lack of fish contaminant monitoring in this river segment. The source of data for this assessment is the results from IDNR/UHL ambient monthly monitoring at the station near Jefferson in Greene County (STORET station 10370001 (formerly station 700101)) during the period 2004 through 2006.
Note 1: IDNR/UHL routine ambient water quality monitoring at this station was terminated in November 2006. Thus, this is the same assessment as that developed for the previous (2008) Integrated Reporting cycle.
Note 2: A TMDL for pathogen indicator (E. coli) impairments in the Raccoon River basin was prepared by IDNR and approved by EPA in June 2008. Because this TMDL covers the primary Section 303(d) impairment identified for the 2006 assessment/listing cycle, this waterbody was moved from IR Category 5a from the 2006 assessment/listing cycle to IR Category 4a (impaired; TMDL approved) for the 2008 cycle. This waterbody remains in IR Category 4a for the current (2010) cycle.
EXPLANATION: The Class A1 uses remain assessed (monitored) as "not supported" due to levels of indicator bacteria (E. coli) that exceed Iowa water quality criteria. The geometric mean level of indicator bacteria (E. coli) in the 31 samples collected during recreational seasons of 2004, 2005, and 2006 (186 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml, and thus suggests an impairment of the Class A1 uses. In addition, eight of the 31 samples (26%) exceeded 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 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(WW1) uses remain assessed (monitored) as "fully supported." Results of IDNR/UHL ambient chemical/physical monitoring at the Jefferson station during the 2004-2006 assessment period show no violations of Class B(WW1) (aquatic life) water quality criteria in the approximately 40 samples analyzed for pH and ammonia, in the eight samples analyzed for pesticides, or in the 10 samples analyzed for toxic metals. One of the 42 samples analyzed for dissolved oxygen violated the Class B(WW1) criterion of 5.0 mg/l (this sample contained a dissolved concentration of 4.5 mg/l). According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), however, a violation frequency of less than 10% for conventional parameters such as dissolved oxygen nonetheless suggest "full support" of aquatic life uses. Thus, the percentage of violations of the dissolved oxygen criterion at this station (2%) does not suggest an impairment of aquatic life uses in this stream segment. These results suggest that the aquatic life uses of this river segment should be assessed as "fully supported."
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.
