Assessment Comments
Assessment remains based on results of water quality monitoring conducted in 2008 at Buffalo Creek Site 3 of the Section 319 water quality monitoring project.
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, 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) uses are “not assessed” (IR 3a) due to the lack of information on indicator bacteria upon which to base an assessment. The Class B(WW2) aquatic life uses are assessed (monitored) as “partially supported” (IR 5a) due to low levels of dissolved oxygen. The source of data for this assessment is the results of water quality monitoring at Buffalo Creek Site 3 of the Section 319 water quality monitoring project (STORET station 15100003). This station is located along 136th Street south of Aurora in Buchanan County.
EXPLANATION: The presumptive Class A1 uses are not assessed: Section 319 monitoring at this site did not include analysis for indicator bacteria.
The Class B(WW2) aquatic life uses remain assessed (monitored) as “partially supported” based on results of Section 319 monitoring at Buffalo Creek Site 3 from June to September 2008. While none of the 12 samples collected contained levels of ammonia, pH, or water temperature that violated Class B(WW1) water quality criteria, levels of dissolved oxygen suggest impairment of the Class B(WW2) aquatic life uses. Four of the 12 samples analyzed for dissolved oxygen violated the Class B(WW2) criterion of 5 mg/l. According to U.S. EPA guidelines for Section 305(b) reporting, if significantly 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, the results from station Buffalo Creek Site 3 indicate that significantly greater than 10% of the samples violated the Class B(WW2) criterion for dissolved oxygen. Thus, these results suggest that the Class B(WW2) uses should be assessed (monitored) as “partially supported.” The four violations ranged from 4.0 mg/l to 4.8 mg/l. All violations occurred in August and early September thus suggesting that low stream flow may have contributed to the occurrence of these violations.
