Assessment Comments
Assessment remains based on results of ambient physical/chemical water quality monitoring conducted by (1) IDNR/UHL from 2002-03 in support of TMDL development and (2) the Minnesota Pollution Control Agency in 2000-01.
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 "partially supported" based on results of monitoring for indicator bacteria. The Class B(WW2) aquatic life uses remain assessed (evaluated) as “fully supported” based on results of ambient chemical/physical water quality monitoring. The sources of data for this assessment are the results of water quality monitoring conducted near the Iowa/Minnesota state line by (1) IDNR/UHL during the 2002-2004 assessment period as part of TMDL monitoring (TMDL station 3; STORET station 11600002) and (2) the Minnesota Pollution Control Agency (MPCA) from November 2000 through September 2001 (MPCA STORET station S000-097).
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) as "partially 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 18 samples collected at the IDNR/UHL TMDL monitoring station near the Iowa/Minnesota border during summer recreational seasons of 2002-2003 (104 orgs/100ml) is below, and meets, the Iowa Class A1 water quality criterion of 126 orgs/100ml. Four of the 18 samples (22%) exceed 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 less than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "fully supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). According to U.S. EPA guidelines for Section 305(b) reporting, however, if levels of E. coli exceed the single-sample maximum value in more than 10% of the samples, the primary contact recreation uses should be assessed as “partially supported” (see pgs 3-33 to 3-35of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, the results from the IDNR/UHL TMDL station suggest the percetage of samples exceeding Iowa's single-sample maximum criterion was significantly greater than 10%, thus suggesting that the Class A1 uses should be assessed as “partially supported.” Note: throughout most of the 2002-2003 period, levels of indicator bacteria were very low in this assessment segment. The difference between an assessment of "full support" and "impairment" is one sample value above Iowa's single-sample maximum criterion.
Regarding support of the Class B(WW2) aquatic life uses, results of chemical/physical water quality monitoring conducted by IDNR/UHL during the 2002-04 period in support of TMDL development, and conducted by MPCA from November 2000 through September 2001, suggest relatively good water quality in this stream segment. Results of IDNR/UHL monitoring from March 2002 through December 2003 show that none of the 21 samples collected had levels of dissolved oxygen or ammonia-nitrogen that violated state water quality standards (these samples were not analyzed for other conventional parameters, toxic metals, or pesticides). One of the 11 samples, however, violated the upper Class B(WW) criterion of 9.0 pH units: the sample collected on August 19, 2002 contained a pH of 9.3 units. This violation occurred on a day with an extremely high level of dissolved oxygen (19.9 mg/l) and a water temperature of 25.6 C; these readings correspond to percent DO saturation well in excess of 150%. These conditions suggest that the high level of primary productivity resulted in the high level of pH. Because this violation is more related to natural conditions than to pollution, the occurrence of the high level of pH in this river segment is not seen as a water quality impairment. Regardless, the U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), the percentage of violations at this station during the 2000-2002 period for pH (9%) does not suggest a water quality impairment. These guidelines allow up to 10% violations of conventional parameters such as pH and dissolved oxygen before impairment of water quality is indicated.
Results of MPCA monitoring show that none of the 10 samples collected had levels of pH or ammonia-nitrogen that violated state water quality standards (these samples were not analyzed for toxic metals or pesticides). One of the 10 samples, however, violated the Class B(WW2) criterion for dissolved oxygen of 5.0 mg/l: the sample collected on July 10, 2001 contained only 2.9 mg/l of dissolved oxygen. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), the percentage of violations at this station during the 2000-2002 period for dissolved oxygen (10%) does not suggest a water quality impairment. These guidelines allow up to 10% violations of conventional parameters such as pH and dissolved oxygen before impairment of water quality is indicated. These results, although somewhat limited in terms of parameter coverage, suggest "full support" of the Class B(WW2) aquatic life uses.
