Assessment Comments
Assessment is based on: (1) results of IDNR/UHL chemical/physical/bacteriological monitoring from May 2004 through November 2006 conducted at the County Road W4B crossing (STORET station 15030010) as part of the Yellow River Watershed Project, (2) results of an IDNR fish kill investigation in March 2000, and (3) results of IDNR/UHL biological monitoring conducted in 2006 and 2007.
Basis for Assessment
[Note: Prior to the current (2008) Section 305(b) cycle, this stream segment was classified only for general uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters. Thus, for the current (2008) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed state water quality criteria. The presumptive Class B(WW1) aquatic life uses are assessed (monitored) as “partially supported” based on results of a fish kill investigation in March 2000. Results from the IDNR/UHL biological monitoring in 2006 and 2007 suggest a potential impairment of the aquatic life uses. An additional potential impairment remains based on results from the IDNR/UHL water quality monitoring from 2005 and 2007 that show high levels of total dissolved solids and chloride in this stream. The sources of data for this assessment include (1) results of IDNR/UHL chemical/physical/bacteriological monitoring from May 2004 through April 2007 conducted at the County Road W4B crossing (STORET station 15030010) as part of the Yellow River Watershed Project, (2) results of an IDNR fish kill investigation in March 2000, and (3) results of IDNR/UHL biological monitoring conducted in 2006 and 2007.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are 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 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 Section 305(b) assessments and Section 303(d) listings.
The geometric mean of E. coli in the 47 samples collected at the monitoring station near the county road W4B crossing (station 15030010) during the recreational seasons of 2004 through 2006 was 1,883 orgs/100 ml. This geometric mean far exceeds the Class A1 criterion of 126 orgs/100 ml. Forty-four of the 47 samples (94%) exceeded Iowa’s 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 the geometric mean of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). In addition, due to the availability of weekly data for E. coli at the W4B monitoring station, five-sample, 30-day geometric means were calculated for the recreation seasons of 2004 and 2006 (weekly sampling was not conducted during the 2005 recreation season). All 13 geometric means for the 2005 season, and all 17 geometric means from the 2006 recreation season, violated the Class A1 criterion of 126 orgs/100 ml. The minimum five-sample, 30-day geometric means for the 2004 and 2006 recreational seasons were 1,085 and 462 orgs/100 ml, respectively.
The results of IDNR/UHL water quality monitoring from 2004-2007 at station 15030010 suggest additional water quality problems for this stream due to high levels of total dissolved solids (TDS), chloride, and due to low levels of dissolved oxygen. The previous Iowa water quality standard for TDS of 750 mg/l to protect general uses is no longer in effect. The 2006 version of the Iowa Water Quality Standards (the basis for Iowa’s 2008 Integrated Report) states that acceptable levels of total dissolved solids (TDS) and constituent cations and anions will be established on a site-specific basis as described in the “Supporting Document for Iowa Water Quality Management Plans,” Chapter IV as revised on June 16, 2004: This rule-referenced document states that 1,000 mg/l of TDS is the threshold in-stream level at which negative impacts to the uses of a receiving stream may begin to occur. Results of ambient monitoring at IDNR/UHL station 15030010 from May 12, 2005 through April 30, 2007 show that TDS levels in 50% of the 42 samples collected exceed this 1,000 mg/l threshold. The following are the summary statistics for the 42 samples collected: mean: 1,160 mg/l; median: 1,150 mg/l, maximum sample value: 4,950 mg/l. Although the 1,000 mg/l threshold is not a water quality criterion—and is thus not appropriate for identifying Section 303(d) impairments—levels of TDS in Hecker Creek that routinely exceed the 1,000 mg/l threshold value certainly suggest a water quality concern.
Results of IDNR/UHL monitoring at station 15030010 also indicate high levels of chloride. Based on the 61 samples analyzed for chloride from May 2005 through April 2007, 52% of the samples collected exceed Iowa DNR’s draft chronic chloride criterion to protect aquatic life uses of 353 mg/l. Forty-eight percent of the samples exceeded Iowa DNR’s draft acute aquatic life criterion for chloride of 556 mg/l. The following are the summary statistics for chloride in the 61 samples collected: mean: 645 mg/l; median: 410 mg/l, maximum sample value: 671 mg/l. Until they are adopted into the Iowa WQ Standards and are approved by EPA, these draft criteria for chloride are not appropriate for identifying Section 303(d) impairments. Following the EPA approval of these criteria, however, the existing data suggest a chloride-based Section 303(d) impairment for this stream.
Results of IDNR/UHL ambient at this monitoring station also suggest a water quality problem due to low levels of dissolved oxygen. Eight violations of the Class B(WW1) criterion for dissolved oxygen (5.0 mg/l) occurred in the 52 samples collected. The minimum dissolved oxygen value was 1.1 mg/l. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as dissolved oxygen, the aquatic life uses should be assessed as impaired (see pgs 3-33 to 3-35of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, however, the results from station 15030010 do not indicate that significantly greater than 10% of the samples exceed the Class B(WW1) criterion for dissolved oxygen.
Results of IDNR/UHL biological monitoring in 2006 and 2007 suggest potential impairment of the aquatic life uses of this stream. This monitoring was conducted in 2006 and 2007 as part of the IDNR/UHL stream biocriteria project and TMDL sampling. 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 2006 FIBI score was 54 (good) and the BMIBI score was 61 (good). The 2007 FIBI score was 30 (fair) and the BMIBI score was 70 (good). The FIBI average was 42 and the BMIBI average was 65.5. The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established 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. Even though this site failed the FIBI BIC and met the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small headwater stream and doesn’t fall in the calibrated watershed size. Note that results of IDNR/UHL biocriteria monitoring are not typically used to develop "monitored" (i.e., high confidence) assessments because the assessment metrics are based on historical data from larger wadeable streams and rivers and are thus not strictly appropriate for assessing ecological conditions in the typically intermittent headwater streams. For these reasons, headwater stream reaches that show a failure to meet regional expectations for aquatic biota (fish or aquatic macroinvertebrates) will not be added to Iowa’s 2008 Section 303(d) list of impaired waters (Category 5 of the Integrated Report). The assessment type for these assessed waters will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to “monitored" (indicating an assessment with relatively high confidence). Such waters will be placed in either Category 2b or 3b of the IR and thus will be added to the state’s list of “waters in need of further investigation”.
This stream was also investigated as part of a fish kill that occurred on the Yellow River on March 17, 2000. An estimated 4,800 fish were killed; no cause or source of the kill was identified. The following account is from the IDNR fish kill database and includes comments from the IDNR staff that investigated the kill: "Dead fish were observed both upstream and downstream of the Smith Road bridge on the Yellow River, but only below the confluence with the unnamed tributary in section 17 [i.e., Hecker Creek]. North of Postville: Water turbid and green, with high flow. The kill affected a 3.1 mile segment of the Yellow River. Dead fish were not observed in the unnamed tributary that enters into the Yellow River in Section 17." According to DNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill indicates impairment of the aquatic life uses. Pollutant-caused kills where the source of pollution was not identified justify addition of the affected stream segment to Iowa's Section 303(d) list of impaired waters.
