Minor Creek IA 01-UIA-283
mouth (S10 T99N R10W Winneshiek Co.) to confluence with unnamed tributary in E 1/2 S1 T99N R11W Howard Co.
- Cycle
- 2016
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 6/20/2016 1:11:56 PM
- Updated
- 11/29/2016 10:45:06 AM
The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as “not supported” (IR 5p) due to levels of indicator bacteria that exceed state water quality criteria. The Class B(WW2) aquatic life uses remain assessed (evaluated) as “fully supported” (IR 2a) based on results of water quality monitoring from April 2011 to May 2012. The data used for this assessment are from Minor Creek Site 3 at 318th Avenue (STORET station 15960043). Note: no water quality data are available for this monitoring station beyond May 2012.
The presumptive Class A1 (primary contact recreation) uses remain assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 10 samples collected during the recreational seasons of 2011 and 2012 at monitoring station 15960043 were as follows: the 2011 geometric mean of six samples was 612 orgs/100 ml and the 2012 geometric mean of four samples was 3,582 orgs/100 ml. Both geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Seven of the 10 samples (70%) exceeded the Class A1 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 a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”
Results of chemical/physical water quality monitoring in 2011 and 2012 suggest "full support" of the Class B(WW2) aquatic life uses. Monitoring at station 15960043 showed no violations of Class B(WW2) water quality criteria for ammonia or pH in the six samples analyzed from April to June of 2011 (note: this amount of data is not sufficient for a higher confidence (“monitored”) assessment; thus, the assessment of the Class B(WW2) aquatic life uses is considered “evaluated” (of lower confidence)). One of the six samples analyzed for dissolved oxygen violated the Class B(WW2) criterion of 5 mg/l. The sample collected on June 28, 2011, contained 3.7 mg/l of dissolved oxygen and thus violated the Class B(WW2) standard. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as pH and dissolved oxygen suggests impairment of aquatic life uses. Based on IDNR’s assessment methodology, however, these results suggest that the frequency of violations is not significantly greater than 10 percent; thus, these results do not suggest impairment of the Class B(WW2) aquatic life uses. Thus, the Class B(WW2) aquatic life uses are assessed (evaluated) as “fully supported”.