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 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.gov/Portals/idnr/uploads/water/standards/files/swcdoc2.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 (2012) 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) remain assessed (evaluated) 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 remain assessed (evaluated) as "partially supported" (IR Category 5a) based on results of ambient monitoring for indicator bacteria (E. coli). 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. Levels of indicator bacteria were very low in this assessment segment throughout most of the 2002-2003 assessment period. 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 less than the applicable state criteria, the contact recreation uses should be assessed as "fully supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Thus, these data suggest that the Class A1 uses should be assessed as “fully supported.” These guidelines, however, also suggest that if more than 10% of samples exceed the single-sample maximum criterion for indicator bacteria, the primary contact recreation uses should be assessed as "partially supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, the monitoring data from 2002-03 suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum criterion, thus suggesting that the Class A1 uses should be assessed as “partially supported/impaired.” Because these data are now more than five years old, and because as data age beyond five years they are less able to represent current water quality conditions, the assessment type is changed from “monitored” (a higher confidence assessment) to “evaluated” (lower confidence assessment.)
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.
