Assessment Comments
Assessment is based on: (1) IDNR monthly fixed station monitoring near Elkport (station 10220002) from January 2006 through August 2008 and (2) results of IDNR/UHL biological monitoring in 1999-2002, 2006 & 2008.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to high levels of indicator bacteria (E. coli) and frequent violations of Iowa’s water quality standards. The Class B(WW1) aquatic life uses are assessed (monitored) as "partially supported" based on results of IDNR/UHL biological monitoring in conducted in 1999-2002, 2006 & 2008. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river reach. Sources of data for these assessments include results of (1) IDNR monthly fixed station monitoring near Elkport (station 10220002) from January 2006 through August 2008 and (2) results of IDNR/UHL biological monitoring in 1999-2002, 2006 & 2008.
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) was addressed by the TMDL, this waterbody was moved from IR Category 5a from the 2004 assessment/listing cycle to IR Category 4a (impaired; TMDL approved) for the 2006 cycle. Subsequent biological monitoring indicated a biological impairment not covered by the TMDL; thus, this waterbody was placed in Category 5b-v of the 2010 Integrated Reporting cycle.
EXPLANATION: The Class A1 (primary contact recreation) uses remain assessed (monitored) as "not supported" due to high levels of indicator bacteria and frequent violations of the relevant Iowa water quality standard. Twenty-one samples from this station were analyzed for indicator bacteria (E. coli) during recreational seasons of 2006 through 2008. The geometric mean of E. coli bacteria in the 21 samples was 450 orgs/100 ml. This geometric mean exceeds the state Class A1 water quality criterion of 126 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and the IDNR assessment/listing methodology, if the geometric mean is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). This river reach has a history of high levels of indicator bacteria, with assessments of either "partial support" or "nonsupport" of the primary contact recreation uses made since the 1992 report.
Due to the availability of weekly bacteria data for the recreation seasons of 2004 and 2005 at the IDNR/UHL ambient station at Elkport (10220002), the 30-day/5-sample geometric means were calculated for these two recreation seasons (in 2006, the sampling frequency at this monitoring station returned to monthly). In the 2004 recreation season, 15 of the 27 30-day geometric means exceeded Iowa’s Class A1 criterion of 126 orgs/100 ml. In the 2005 recreation season, 10 of the 26 geometric means exceeded the Class A1 criterion. As noted above, U.S. EPA guidelines for Section 305(b) reporting and the IDNR assessment/listing methodology state that a single geometric mean greater than the state criterion of 126 orgs/100 ml. suggests that the Class A1 uses are “not supported.” Thus, when assessed either on the basis of an overall (3-year) geometric mean or on the basis of 30-day/5-sample geometric means, the data for indicator bacteria at this station suggest nonsupport of the Class A1 uses.
The results of IDNR ambient water quality monitoring from 2006 through 2008 suggest "full support" of the Class B(WW1) uses due to the lack of violations of state water quality criteria for pH, dissolved oxygen, and ammonia-nitrogen in the approximately 32 samples during this three-year period. In addition, no violations of Class B(WW1) chronic criteria occurred in the 2 samples analyzed for pesticides and toxic metals during this three-year period.
However, results of IDNR/UHL biological monitoring conducted in 1999-2002, 2006 & 2008 as part of IDNR/UHL stream biocriteria and REMAP projects, suggests “partial support” of the Class B(WW1) aquatic life uses. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (F-IBI) and a benthic macroinvertebrate index (BM-IBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 1999-2002 BMIBI scores were 49, 39, 42 (fair) and 57 (good). The 2006 FIBI score was 78 (excellent) and the 2006 BMIBI score was 75 (good). The 2008 BMIBI score was 42 (fair). The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61. This segment passed the FIBI BIC 1/1 times in 2006 and passed the BMIBI BIC 1/6 times in the last 10 years. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. This aquatic life use assessment is considered "monitored" because there were two or more BMIBI samples collected in multiple years from 2004-2008.
The fish consumption uses remain "not assessed" due to the lack of recent fish tissue monitoring in this river reach.
