Assessment Comments

Assessment is based on: (1) IDNR monthly fixed station monitoring near Elkport (station 10220002) from January 2008 through December 2010 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 2008 through December 2010 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) are assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria.   The geometric means of indicator bacteria (E.  coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at the IDNR/SHL ambient station near Elkport were as follows:  the 2008 geometric mean was 1,337 orgs/100 ml, the 2009 geometric mean was 198 orgs/100 ml and the 2010 geometric mean was 358 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Fourteen of the 21 samples (67%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”   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 Section 305(b) report.  

The results of IDNR ambient water quality monitoring from 2008 through 2010 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 30 samples 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, suggest “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 (FIBI) and a benthic macroinvertebrate index (BMIBI).   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 50, 41, 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 12 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 over a five-year period.  

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