Assessment Comments

Assessment is based on: (1) IDNR monthly fixed station monitoring near Elkport (station 10220002) from January 2004 through December 2006 and (2) results of DNR/UHL biological monitoring in 2002 and 2006.

Basis for Assessment

SUMMARY:  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 were assessed (monitored) as "fully supported" based on results of DNR/UHL chemical/physical monitoring from 2004 through 2006 and on DNR/UHL biological monitoring in conducted in 2002 and 2006.   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 2004 through December 2006 and (2) results of DNR/UHL biological monitoring in 2002 and 2006.  

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 was moved from IR Category 5a from the 2004 assessment/listing cycle to IR Category 4a (impaired; TMDL approved) for the 2006 cycle.   This waterbody remain in IR Category 4a for the 2008 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.   Seventy samples from this station were analyzed for indicator bacteria (E.  coli) during recreational seasons of 2004 through 2006.   Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed.   Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A1 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 of E.  coli bacteria in the 70 samples was 187 orgs/100 ml, with 26 samples (37%) exceeding Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   The geometric mean (187orgs/100 ml) exceeds the state 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 Class A 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 continue to suggest nonsupport of the Class A1 uses.  

The results of IDNR ambient water quality monitoring from 2004 through 2006 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 36 samples during this  three-year period.   In addition, no violations of Class B(WW1) chronic criteria occurred in the 10 samples analyzed for pesticides during this period.   Of the ten samples analyzed for toxic metals, only one sample violated a Class B(WW1) criterion:  one of the ten samples analyzed for lead exceeded the Class B(WW1) criterion of 30 ug/l.   This violation occurred on July 6, 2004; the level of lead in the sample was 60 ug/l.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-18), however, one violation of a water quality criterion for a toxic pollutant in an abundant data set (at least 10 samples over at three-year period) does not indicate an impairment of aquatic life uses.  

Results of DNR/UHL biological monitoring in 2002 and and REMAP monitoring in 2006, conducted as part of the DNR/UHL stream biocriteria project, also suggest “full 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 2002 BMIBI score was 56 (good).   The 2006 FIBI score was 78 (excellent) and the 2006 BMIBI score was 75 (good).   The BMIBI average was 65.5.   The aquatic life use support was assessed as fully supporting (=FS), 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.   The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.

The fish consumption uses remain "not assessed" due to the lack of recent fish tissue monitoring in this river reach.