Assessment Comments
Assessment is based on results of IDNR/UHL monitoring in 2001 in support of TMDL development.
Basis for Assessment
SUMMARY: Class A (primary contact recreation) uses remain assessed (monitored) as "not supported" based on levels of indicator bacteria that violate state water quality standards. The Class B(WW) aquatic life uses remain assessed (evaluated) as "fully supported" based on results of ambient physical/chemical monitoring. Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment. The source of data for this assessment is the results of IDNR/UHL monthly monitoring conducted from March to November, 2001, near Osborne (Site 34) and Volga (Site 35) in support of TMDL development for this river segment.
Note 1: except for the use of E. coli as the indicator bacterium, this is the same assessment as that developed for the 2004 reporting/listing cycle. Although the impairment of the Class A uses in this river segment was originally based on levels of fecal coliform bacteria (see assessments for the 2002 and 2004 reporting/listing cycles), a 2003 change in Iowa’s Water Quality Standards required that the data for E. coli be summarized to justify continuing this impairment. Thus, the data for E. coli at Volga River stations 34 and 35 were summarized and compared to Iowa’s revised Class A criteria for E. coli.
Note 2: A TMDL for pathogen indicators in this segment of the Volga River was prepared by IDNR and approved by EPA in 2006. Because the primary Section 303(d) impairment identified for the 2006 assessment/listing cycle (indicator bacteria) is addressed by the TMDL, this waterbody is moved from IR Category 5a from the 2004 assessment/listing cycle to IR Category 4a (impaired; TMDL approved) for the 2006 cycle.
EXPLANATION: 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) at both Volga River monitoring stations in 2001 exceeded in exceeded the Iowa Class A water quality criterion of 126 E. coli orgs/100ml, thus suggesting continued impairment of the Class A uses in this segment of the Volga River. The geometric mean of E. coli for the nine samples collected at Volga River station 35 was 276 orgs/100 ml; the geometric mean for the nine samples collected at Volga River station 304 was 245 orgs/100 ml. Both of these geometric means far exceed the Iowa Class A criterion of 126 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, 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). Although the IDNR assessment/listing methodology requires at least 10 samples collected over a three-year period in order to develop a "monitored" assessment appropriate for Section 303(d) listing, the numbers of samples at Volga River stations 34 and 35 (nine samples at both stations) are considered sufficient to extend the impairment originally based on levels of fecal coliform bacteria.
The Class B(WW) aquatic life uses were assessed as "fully supported" due to the lack of violations of state water quality criteria for pH and dissolved oxygen in the nine samples collected from each of the two Volga River TMDL monitoring stations during 2001. These samples were not analyzed for either ammonia, toxic metals, or toxic organic compounds.
The fish consumption uses remain "not assessed" due to the lack of recent fish tissue monitoring in this river reach.
