Unnamed Tributary to Unnamed Tributary to Yellow River IA 01-YEL-6575
from mouth (T96N R7W Sec15) to headwaters (T96N R7W Sec21) Winneshiek Co.
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 7/12/2019 2:52:39 PM
- Updated
- 7/12/2019 2:53:48 PM
The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to violations of Iowa water quality criteria for indicator bacteria and for pH. The presumptive Class B(WW1) aquatic life uses are assessed as “partially supporting" due to violations of water quality criteria for pH. The source of data for this assessment is the results of monitoring at STORET station 15960038 (Unnamed Creek at 130th Ave., Site 6) conducted as part of a Clean Water Act Section 319 water quality project from April through October 2011. Station 15960038 was also monitored for indicator bacteria (E. coli) from April to October 2014. Monitoring at station 15960038 during 2014 did not include analysis for parameters other than indicator bacteria.
The presumptive Class A1 uses are assessed (monitored) as “partially supported" due to levels of indicator bacteria (E. coli) that exceed the Class A1 geometric mean criterion. The geometric mean of indicator bacteria (E. coli) in the 20 samples collected at Site 6 during the recreation season of 2014 was 293 orgs/100 ml. Fourteen of the 20 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 DNR’s assessment/listing methodology, if a recreation season geometric mean is greater than the respective criterion (126 orgs/100 ml for Class A1, the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). In addition, the percentage of samples with levels of E. coli that exceeded Iowa single-sample maximum criteria indicates impairment of presumptive Class A1 uses at this monitoring site. Note: The 2012 TMDL for bacteria impairments for streams in the Yellow River basin does not apply to the bacteria impairment in this assessment segment.
Results of chemical/physical monitoring at Site 6 during 2011 suggest impairment of the presumptive Class A1 and the presumptive Class B(WW1) aquatic life uses due to violations of water quality criteria for pH. At Site 6, none of the 14 samples analyzed from April to October 2011 violated the Class B(WW1) criteria for dissolved oxygen or temperature, and none of the eight samples collected violated the Class B(WW1) criteria for ammonia. Five of the 14 samples collected (36%), however, violated the Class A1 & B(WW1) criterion for pH (all violations were greater than 9 pH units). 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 suggests impairment of aquatic life uses. Based on DNR’s assessment methodology, these results suggest that the frequency of violations is significantly greater than 10 percent; thus, these results suggest impairment of the Class A1 and Class B(WW1) uses.