Volga River IA 01-VOL-294
confluence with Brush Cr. (S26 TT93N R7W Fayette Co.) to east corporate limit of Fayette (NE 1/4 S28 T93N R8W Fayette Co.)
- Cycle
- 2016
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 6/22/2016 1:07:57 PM
- Updated
- 11/29/2016 10:57:36 AM
The Class A1 (primary contact recreation) uses remain "not assessed" (IR 3a) due to lack of information on levels of indicator bacteria in this river segment. The Class B(WW1) aquatic life uses are now considered “not assessed” (IR 3a) due to lack of recent data upon which to base an assessment. Fish consumption uses remain assessed (monitored) as “partially supported” (IR 5a) based on fish contaminant monitoring. The source of data for this assessment is the results of fish contaminant monitoring conducted near the Volga River Recreation Area in 2001 and 2005, 2007, 2008, 2012, and 2014 as part of U.S. EPA/IDNR or IDNR fish contaminant (RAFT) monitoring.
The Class A1 (primary contact recreation) uses remain "not assessed" due to lack of information on levels of indicator bacteria in this river segment.
While the Class B(WW1) aquatic life of this segment were previously assessed (evaluated) as "fully supported" based on results of TMDL monitoring and IDNR biological monitoring in 2000, these data are now considered too old (greater than 10 years) for assessing current water quality conditions. Thus, the Class B(WW1) aquatic life uses are not considered “not assessed”. As water quality data age, they become less able to represent current water quality conditions. Thus, according to IDNR’s assessment/listing methodology, waterbodies with assessments based on data older than ten years will be considered “not assessed” unless the previous assessment indicated impairment of the assessed use.
For the 2001 RAFT sampling, the composite samples of fillets of smallmouth bass contained 0.326 ppm of mercury. The level of mercury in the sample of 2005 composite sample smallmouth bass fillets was 0.545 ppm which also exceeded the IDNR/IDPH advisory trigger level of 0.3 ppm for a one meal per week advisory. According to the IDNR/IDPH advisory protocol, if two consecutive samplings show that contaminant levels are above the trigger level in fillet samples, issuance of a consumption advisory is justified. This advisory was issued by IDNR and IDPH in January 2006 and covered the segments of the Volga River upriver from the county road C2W bridge at Volga in western Clayton County. Follow-up monitoring was conducted as part of the RAFT program in 2007 and 2008. The 2007 samples of smallmouth bass fillets contained 0.24 ppm of mercury; the 2008 sample of smallmouth bass fillets contained 0.33. Because the level of mercury in the 2008 sample exceeded the IDNR/IDPH advisory trigger level of 0.3 ppm, the advisory issued in 2006 continued. Results of from the 2012 RAFT showed that levels of mercury in the five smallmouth bass sampled ranged from 0.16 to 0.27 ppm with an average level of mercury of 0.214 (standard deviation of 0.051 ppm). This level of mercury is below Iowa’s threshold for a one mean/week advisory of 0.3 ppm of mercury. According to Iowa’s consumption advisory protocol, however, two consecutive samplings that show levels of fish contaminants are below the advisory threshold are needed to rescind an existing advisory. Thus, follow-up monitoring was conducted in 2014 to better define levels of mercury in this segment of the Volga River and to determine whether the existing advisory should be rescinded. The average level of mercury in tissue plugs from three smallmouth bass was 0.29 ppm. This level of mercury is sufficiently close to the advisory threshold of 0.3 ppm to justify continuing the existing consumption advisory and mercury impairment.