Cedar River IA 02-CED-449
mouth (S20 T75N R4W Louisa Co.) to confluence with Sugar Cr. in S17 T78N R2W Muscatine 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
- 5/20/2019 1:40:55 PM
- Updated
- 7/11/2019 7:30:49 AM
Cycle Added | Class | Cause | Data Source | Rationale |
---|---|---|---|---|
2014 | Class A1 | pH | Ambient monitoring: Iowa DNR-rivers | New data: WQ improvement (chemical / physical / bacterial) |
2014 | Class BWW1 | pH | Ambient monitoring: Iowa DNR-rivers | New data: WQ improvement (chemical / physical / bacterial) |
Assessment Summary
The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” based on results of ambient monitoring for indicator bacteria. The Class A1 uses are also assessed (monitored) as “partially supporting” due to violations of the Class A1 criterion for pH. The Class B(WW1) aquatic life uses are assessed (monitored) as "partially supporting” due to violations of the Class B(WW1) criterion for pH. The Class B(WW1) aquatic life uses are assessed (evaluated) as "not supporting” due to low benthic macroinvertebrate IBI scores. Fish consumption uses remain “not assessed” due to the lack of recent fish contaminant monitoring in this assessment segment. The sources of data for these assessments are the results of monthly monitoring from 2014 through 2016 at the DNR ambient station located at the County Road G28 bridge NE of Conesville (IDNR station 10700001) and DNR/SHL biological sampling in 2012 and 2013.
Assessment Explanation
[Note: A TMDL for indicator bacteria impairments in nine segments of Cedar River was prepared and approved by EPA in February 2010. Because this segment (IA 02-CED-0010_0) had not been previously impaired due to indicator bacteria, this segment was not included in the EPA TMDL. Thus, this impairment is not covered by the TMDL and is considered appropriate for Category 5a of Iowa's Integrated Report.] The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially 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 station 10700001 were as follows: the 2014 geometric mean was 217 orgs/100 ml, the 2015 geometric mean was 52 orgs/100 ml, and the 2016 geometric mean was 209 orgs/100 ml. Two of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Six of the combined 24 samples (25%) 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 Iowa 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 "partially supported." Results of chemical/physical water quality monitoring at station 10700001 suggest “full support” of the aquatic life uses. Monitoring showedno violations of Class B(WW1) water quality criteria for 36 Ammonia samples (maximum = 1.3 mg/L), 36 Dissolved Oxygen samples (minimum = 6.6 mg/L), 36 pH samples (range = 6.8 to 9), 36 Temperature samples (maximum = 25.8°C), 36 Chloride samples (maximum = 100 mg/L), or 36 Sulfate samples (maximum = 74 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. This evaluated biological assessment was based on data collected in 2011, 2012 and 2013 as part of the DNR/SHL stream nutrient sampling project. A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa collected in the stream sampling reach. The biological metrics were combined a benthic macroinvertebrate index (BMIBI). The index rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2012 BMIBI score was 29 (poor) and the 2013 BMIBI score was 15 (poor). The aquatic life use support was assessed (evaluated) as not supporting (=NS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008. The BMIBI BIC for this ecoregion is 51. This assessment is considered evaluated because the drainage area (7789 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site failed the BMIBI BIC (0/3), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the site used for the assessment doesn’t fall in the calibrated watershed size. According to DNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). DNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).
Fish consumption uses are not assessed due to the lack of recent fish contaminant monitoring in this river segment.
Assessment Key Dates
8/29/2012 | Biological Monitoring |
1/9/2014 | Fixed Monitoring Start Date |
12/1/2016 | Fixed Monitoring End Date |
10/7/2013 | Biological Monitoring |
Methods
230 | Fixed station physical/chemical (conventional plus toxic pollutants) |
315 | Regional reference site approach |
320 | Benthic macroinvertebrate surveys |
360 | HABITAT ASSESSMENT |
420 | Indicator bacteria monitoring |