South Raccoon River IA 04-RAC-1181
mouth (S21 T78 R27W Dallas Co.) to confluence with Middle Raccoon R. in S9 T78N R29W near Redfield in Dallas Co
- Assessment Cycle
- 2018
- Release Status
- Final
- Data Collection Period
- Overall IR Category
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 5/29/2019 11:00:00 AM
- Updated
- 7/8/2019 3:03:50 PM
Assessment Summary
The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW1) aquatic life are assessed (monitored) as "fully supported” based on results of ambient chemical/physical water quality monitoring from 2014 through 2016 and on 2012/2013/2015 DNR/SHL biological sampling. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment. The source of data for this assessment are the results of (2) DNR/SHL ambient monthly monitoring during the 2014-2016 assessment period at STORET ambient monitoring station 10250001 (formerly station 429340) located near Redfield approximately 1 mile downriver from the confluence of Middle Raccoon and South Raccoon rivers and (2) 2012/2013/2015 DNR/SHL biological sampling conducted near Redfield.
Assessment Explanation
The Class A1 (primary contact recreation) uses are assessed (monitored) 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 24 samples collected during the recreational seasons of 2014 through 2016 at STORET ambient monitoring station 10250001 were as follows: the 2014 geometric mean was 1921 orgs/100 ml, the 2015 geometric mean was 352 orgs/100 ml, and the 2016 geometric mean was 598 orgs/100 ml. All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Seventeen of the combined 24 samples (71%) exceeded Iowa’s 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 the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (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 "not supported." Results of chemical/physical water quality monitoring at STORET ambient monitoring station 10250001 also suggest “full support” of the aquatic life uses. Monitoring showedno violations of Class B(WW1) water quality criteria for 35 Ammonia samples (maximum = 0.1 mg/L), 36 Dissolved Oxygen samples (minimum = 7.5 mg/L), 35 pH samples (range = 7.2 to 8.7), 36 Temperature samples (maximum = 25.9° c), 36 Chloride samples (maximum = 22 mg/L), or 36 Sulfate samples (maximum = 43 mg/L) occurred during monitoring from January 2014 to December 2016.According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” of the Class B(WW1) aquatic life uses.
Assessment Key Dates
8/8/2012 | Biological Monitoring |
9/6/2013 | Biological Monitoring |
1/9/2014 | Fixed Monitoring Start Date |
12/8/2016 | Fixed Monitoring End Date |
10/8/2015 | Biological Monitoring |
Methods
230 | Fixed station physical/chemical (conventional plus toxic pollutants) |
315 | Regional reference site approach |
320 | Benthic macroinvertebrate surveys |
420 | Indicator bacteria monitoring |