Assessment Comments
Assessment based on results of (1) 2002/2004 IDNR/UHL biological monitoring FIBI = 54, 65 (good), BMIBI = 62, 72 (good), (2) IDNR/UHL ambient monthly WQ monitoring at Volney from 2002-04, and (3) IDNR/UHL monitoring for indicator bacteria in 2004. FIBI BIC = 52; BMIBI BIC = 61.
Basis for Assessment
SUMMARY: Class A (primary contact recreation) uses were assessed (monitored) as "not supported" due to high levels of indicator bacteria that violate state water quality standards. Class B(WW) aquatic life uses were assessed (monitored) as "fully supported" based on results of (1) IDNR/UHL biological monitoring in 2002 and 2004 and (2) results of IDNR/UHL ambient chemical/physical water quality monitoring from 2002-2004. Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river reach. The sources of data used for this assessment include (1) results of IDNR/UHL monthly ambient water quality monitoring conducted on the Yellow River near Volney (station 10030002) during the 2002-2004 assessment period, (2) results of monitoring for indicator bacteria at IDNR/UHL station 15030002 near Old Mission Road from May to November 2004, and (3) IDNR/UHL biological monitoring conducted in 1998 and 2002.
EXPLANATION: The Class A (primary contact recreation) uses were assessed (monitored) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria. Due to recent changes in Iowa’s Water Quality Standards, Iowa’s 2006 assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A 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 in the 39 samples collected from the IDNR/UHL ambient monitoring station near Volney (10030002) was 81 orgs/100 ml; nine of the 39 samples (23%) exceeded Iowa’s single-sample maximum value of 235 orgs/100 ml. The geometric mean (81 orgs/100 ml) is well below the state water quality criterion of 126 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, however, if more than 10% of the samples exceeds the single-sample maximum value, the primary contact uses should be assessed as “partially supported.” According to IDNR’s assessment/listing methodology, these results suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum value, thus suggesting that the Class A uses should be assessed as “partially supported/impaired”.
The geometric mean of E. coli in the 26 samples collected from the IDNR/UHL monitoring station near Old Mission Road (15030002), however, was 463 orgs/100 ml; thus far exceeding the state water quality criterion of 126 orgs/100 ml. Also, 12 of the 25 samples (48%) exceeded Iowa’s single-sample maximum value of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli 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). Thus, the Class A (primary contact recreation) uses were assessed as "not supported" for the 2000-2002 assessment period.
The Class B(WW) aquatic life uses were assessed (monitored) as "fully supported" based on results of both chemical/physical monitoring and on results of biological monitoring. Results of monthly chemical/physical monitoring from the IDNR ambient station near Volney from 2002 through 2004 showed no violations of Class B(WW) water quality criteria for conventional pollutants or ammonia in the approximately 35 samples analyzed. Of the ten samples analyzed for toxic metals, only one sample violated a Class B(WW) criterion: one of the ten samples analyzed for lead exceeded the Class B(WW) criterion of 30 ug/l. This violation occurred on July 6, 2004; the level of lead in the sample was 40 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.
In addition to chemical/physical monitoring, the assessment of aquatic life uses was also based on biological data collected in 2002 and 2004 as part of the IDNR/UHL stream biocriteria and REMAP projects. 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 2004 biocriteria FIBI score was 65 (good) and the BMIBI score was 72 (good). The 2002 REMAP FIBI score was 54 (good) and the BMIBI score was 62 (good). The FIBI average was 59.5 and the BMIBI average was 67. 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 biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61.
The fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river reach.
