Assessment Comments
Assessment remains based on results of IDNR/UHL monitoring in 2001 at two sites (Volga and Osborne) in support of TMDL development.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses remain assessed (evaluated) as "not supported" based on levels of indicator bacteria that violate state water quality standards. The Class B(WW1) 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 remains 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. The water quality data upon which these assessments are based are now more than five years old; therefore, these assessments are now considered "evaluated" (of lower confidence) instead of "monitored" (of higher confidence). Despite the age of the data used for this assessment, the impairment of the Class A1 uses remains until more recent data suggest a good cause for de-listing.
Note: 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; this waterbody remains in IR Category 4a for the 2010 cycle.
EXPLANATION: The Class A1 (primary contact recreation) uses remain assessed (evaluated) as "not supported" due to high levels of indicator bacteria. The geometric mean level of indicator bacteria (E. coli) at both Volga River monitoring stations in 2001 exceeded in exceeded the Iowa Class A1 water quality criterion of 126 E. coli orgs/100ml, thus suggesting continued impairment of the Class A1 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 exceed the Iowa Class A1 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" [higher confidence] 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 justify this impairment. Note: because the data from Arbuckle et al. (2000) are now older than five years, the assessment category is changed from a “monitored” (i.e., a higher confidence assessment) to “evaluated” (i.e., lower confidence assessment).
The Class B(WW1) aquatic life uses remain assessed (evaluated) 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.
