Assessment Comments
Assessment is based on results of IDNR ambient monthly monitoring east of Grimes from 2004 through 2006.
Basis for Assessment
[Note: Prior to the current (2008) Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life 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. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2008) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) 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 violate state water quality criteria. The Class B(WW2) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient chemical/physical water quality monitoring from 2004-06 that show (1) good chemical water quality and (2) no violations of Iowa’s general use criterion for total dissolved solids. The source of data for this assessment is the results from the IDNR/UHL ambient monthly monitoring station on Beaver Creek east of Grimes (STORET station 10770001 (formerly station 420307) from 2004 through 2006.
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). 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 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 Section 305(b) assessments and Section 303(d) listings.
The geometric mean level of indicator bacteria (E. coli) in the 24 samples collected (338 orgs/100ml) during the recreational seasons of 2004 through 2006 exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Fourteen of the 24 samples (58%) exceeded Iowa’s single-sample maximum criterion 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 should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).
Monitoring at the IDNR/UHL station east of Grimes showed no violations of Class B(WW2) water quality criteria during the 2004-2006 assessment period for pH or ammonia-nitrogen in the 36 samples analyzed, for toxic metals in the ten samples analyzed, or for pesticides in the seven samples analyzed. One of the 36 samples analyzed for dissolved oxygen during the 2004-06 period, however, violated the Class B(WW2) criterion of 5.0 mg/l. This violation occurred on February 4, 2004 (4.1 mg/l). According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), however, a violation frequency of less than 10 % for conventional parameters such as dissolved oxygen nonetheless suggest "full support" of aquatic life uses. Thus, the percentages of violations of the dissolved oxygen criterion at this station (3%) does not suggest an impairment of aquatic life uses in this stream segment.
This stream segment has been previously identified as Section 303(d)-impaired due to levels of total dissolved solids that exceeded Iowa’s general water quality of 750 mg/l. Four of the 36 samples analyzed for total dissolved solids at the IDNR/UHL monitoring station from 2000 through 2002 exceeded Iowa’s general use criterion of 750 mg/l. These samples were collected on October 11, 2000 (960 mg/l), January 10, 2001 (880 mg/l), October 9, 2001 (780mg/l), and January 8, 2002 (860 mg/l). Based on these results, this stream segment was assessed as “partially supported” for the 2004 assessment/listing cycle and added to Iowa’s 2004 Section 303(d) list. A review of TDS data from 2002 through 2004 for the 2006 assessment/listing cycle, however, showed no violations of Iowa’s general use criterion in the 35 samples collected from February 2002 through December 2004 (maximum value = 650 mg/l). Although retained on Iowa’s 2006 Section 303(d) list, IDNR’s 2006 assessment for this stream noted that if subsequent monitoring during the next [2004-2006] assessment period continued to show a lack of these violations, good cause would exist for removing this waterbody from Iowa’s Section 303(d) list due to existence of more recent and accurate data that demonstrates that this waterbody meets and maintains applicable water quality standards.
A review of IDNR/UHL monitoring data for the 2004-2006 period shows a maximum TDS level of 570 mg/l (mean = 438 mg/l; median = 450 mg/l) in the 36 samples collected. Thus, the results from monthly ambient monitoring from February 2002 through December 2006 show no violations of the TDS criterion and thus suggest good cause for removal of this impairment. In addition, the Iowa Water Quality Standards no longer contain the 750 mg/l general use criterion for TDS but rather specify a site-specific approach to identifying TDS toxicity to aquatic life. As approved by U.S. EPA in 2004, the Iowa Water Quality Standards state the following: “Acceptable levels of total dissolved solids (TDS) and constituent cations and anions will be established on a site-specific basis. The implementation approach for establishing the site-specific levels may be found in the “Supporting Document for Iowa Water Quality Management Plans,” Chapter IV, July 1976, as revised on June 16, 2004.” In an IDNR issue paper on TDS toxicity, the in-stream level of TDS that triggers the need for site-specific criteria is 1,000 mg/l (see http://www.iowadnr.com/water/standards/files/tdsissue.pdf). None of the levels of TDS in Beaver Creek approach this trigger level.
As part of the revisions to the TDS general use criterion of 750 mg/l, dissolved solids constituents such as chloride and sulfate were also considered. Levels of both of these TDS constituents in this segment of Beaver Creek are low relative to proposed water quality criteria for these constituents. For chloride, the CWA Section 304a chronic criterion is 230 mg/l; this level is above maximum chloride levels seen in Beaver Creek. For the 2004-2006 period, the maximum level of chloride in the 36 samples collected at the IDNR/UHL monitoring station was 60 mg/l (mean=34 mg/l; median=32 mg/l). For the period 2001 through 2006, the maximum value was 170 mg/l in the 71 samples collected. Although final aquatic life criteria have not yet been adopted into the Iowa Water Quality Standards, the chloride levels seen in Beaver Creek over the last six years do not suggest a toxicity problem. For more information on the issue of chloride toxicity specific to the Iowa Water Quality Standards, see the following IDNR issue paper: http://www.iowadnr.com/water/standards/files/cissue.pdf.
Federal water quality criteria do not exist for sulfate, and the state of Iowa has never adopted a sulfate criterion to protect aquatic life. An IDNR issue paper on aquatic life criteria for sulfate (see http://www.iowadnr.com/water/standards/files/sulfateissue.pdf) suggests that an sulfate criterion to protect aquatic life in Iowa surface waters might be 2,000 mg/l. This level is well above sulfate levels seen in this segment of Beaver Creek. For the 2004-2006 period, the maximum level of sulfate in the 36 samples collected at the IDNR/UHL monitoring station was 65 mg/l (mean=33 mg/l; median=29 mg/l). For the period 2001 through 2006, the maximum sulfate value in the 70 samples collected was 140 mg/l. Although final aquatic life criteria have not yet been adopted into the Iowa Water Quality Standards, the sulfate levels seen in Beaver Creek over the last six years do not suggest a toxicity problem.
