Assessment Comments
Assessment is based on results of IDNR/UHL ambient monthly monitoring from 2002-04 west of Jefferson.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "not supported" due to high levels of indicator bacteria (E. coli). The Class B(WW) aquatic life uses are 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 2002 through 2004.
EXPLANATION: The Class A uses are assessed (monitored) as "not supported" due to levels of indicator bacteria (E. coli) that exceed U.S. EPA assessment guidelines. Due to recent changes in Iowa’s Water Quality Standards, Iowa’s 2006 assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses: the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff." Due to a change in the Standards in July 2003, E. coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E. coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.” Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E. coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of the 2006 Section 305(b) assessments and Section 303(d) listings.
The geometric mean level of indicator bacteria (E. coli) in these 24 samples collected during recreational seasons of 2002, 2003, and 2004 (168 orgs/100ml) exceeds the Iowa Class A water quality criterion of 126 orgs/100ml, and thus suggests an impairment of the Class A uses. In addition, nine of the 24 samples (38%) exceeded Iowa’s single-sample maximum value 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(WW) uses are assessed (monitored) as "fully supported". Results of IDNR/UHL ambient chemical/physical monitoring at the Jefferson station during the 2002-2004 assessment period show no violations of Class B(WW) (aquatic life) water quality criteria in the 36 samples analyzed for pH and ammonia, in the seven samples analyzed for pesticides, or in the 10 samples analyzed for toxic metals. One of the 36 samples analyzed for dissolved oxygen, however, violated the Class B(WW) 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 percentages of violations of the dissolved oxygen criterion at this station (3%) 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 are "fully supported."
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.
