Assessment Comments
Assessment remains 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. Assessment is also based on results of USGS monitoring near Jefferson from May to September of 2009.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses remain assessed (evaluated) as "not supported" (IR 4a) due to high levels of indicator bacteria (E. coli). The Class B(WW1) aquatic life uses remain assessed (monitored) as "fully supported" (IR 2a) based on results of ambient chemical/physical water quality monitoring. The assessment of the Class A1 uses is now considered of lower confidence (“evaluated”) and opposed to higher confidence (“monitored”) due to age of the data (greater than five years). As water quality data age beyond five years, they are less able to accurately describe current water quality conditions. Support of fish consumption uses remains "not assessed" due to the lack of fish contaminant monitoring in this river segment. The sources of data for this assessment include (1) 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 and (2) results of USGS monitoring from May to September 2009 at station 05482500 near Jefferson.
Note 1: IDNR/UHL routine ambient water quality monitoring at the ambient station near Jefferson was terminated in November 2006. Also, USGS has not conducted additional monitoring in this assessment segment. Thus, this is the same assessment as that developed for previous Integrated Reporting cycles.
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 cycle.
EXPLANATION: The Class A1 uses remain assessed (evaluated) 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."
USGS conducted water quality monitoring in this assessment segment at station 05482500 near Jefferson from May to September of 2009. No violations of Class B(WW1) criteria for ammonia, dissolved oxygen, or pH occurred in the seven samples collected. This results are consistent with the assessment of Class B(WW1) uses as “fully supported.”
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.
