2018 assessment for Cedar Creek

Cedar Creek IA 03-SKU-6549

from Lake Geode (T70N R5W Sec25 Henry Co.) to headwaters (T70N R4W Sec5 Des Moines Co.)

2018
Open Data Collection Period Modal

For purposes of developing stream/river water quality assessments for integrated reporting, three years of water quality data are typically used for both conventional pollutant parameters (e.g., indicator bacteria) and the less frequently monitored toxic parameters (e.g., toxic metals). Since the 2004 IR cycle, DNR has used a three-year data gathering period for streams, rivers, and beaches. For most assessments, the use of three years of data increases the number of samples upon which the decision on use support is based and helps address the problem of weather-related year-to-year fluctuations in water quality.

Due to the lower sampling frequency in Iowa’s ambient lake, biological, fish kill, and fish tissue monitoring programs, five years of data are used for developing IR assessments and for identifying Section 303(d) listings.

Data Type	Data Timeframe
Beach Sampling Data	CY 2014 - 2016
Stream/River Water Quality Data	CY 2014 - 2016
Lake Water Quality Data	CY 2012 - 2016
Biological Sampling Data	CY 2012 - 2016*
Fish Kill Data	CY 2012 - 2016
Fish Tissue Sampling Data	CY 2012 - 2016
Continuous Dissolved Oxygen Sampling Data	CY 2012 - 2016
*Biological sites sampled in both 2011 and 2015 were also assessed.

Open Segment Map
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Overall IR

5 - Water is impaired or threatened and a TMDL is needed.

Trend

Unknown

Created

7/12/2019 2:01:00 PM by

Updated

7/12/2019 2:03:42 PM by

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

5p - Impairment occurs on a waterbody with a presumptive A1 or B(WW1) use.

Cause Magnitude

High

303(d) Listing Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2014

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Special project/study

TMDL Priority

Tier III

Class BWW1

Presumptive Use

Aquatic Life - Warm Water Type 1

Not Assessed

General Use

General Use water -

Not Assessed

303(d) Delistings for this Cycle

No delistings for this assessment cycle.

Documentation

Assessment Summary

The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to violations of Iowa water quality criteria for indicator bacteria. The presumptive Class B(WW1) aquatic life uses remain "not assessed" due to the lack of sufficient water quality information upon which to base an assessment. The source of data for this assessment is the results of monitoring from May 2013 through October 2014 at five stations on Cedar Creek upstream from Lake Geode. This monitoring was conducted as part of a Clean Water Act Section 319 water quality project.

Assessment Explanation

The presumptive Class A1 uses are assessed (monitored) as “not supported" due to levels of indicator bacteria (E. coli) that exceed the Class A1 geometric mean criterion. The geometric means of indicator bacteria (E. coli) in the 10 to 16 samples collected during the recreation seasons of 2013 and 2014 at each of the five monitoring stations, as well as the percentages of samples that exceed the Class A1 single-sample maximum (SSMax) criterion of 235 orgs/100 ml, are as follows (arranged in approximate order from upstream (at Hwy 34) to downstream. Note: Only three samples were collected at each of the five stations during the recreation season of 2013. According to Iowa DNR’s assessment/listing methodology, at least seven independent samples per recreation season are needed to calculate a geometric mean appropriate for comparison to the Class A1 geometric mean criterion in the Iowa Water Quality Standards. Thus, only the geometric means for the 2014 recreation season, when from seven to 13 samples were collected at each of the five monitoring stations, are appropriate for comparison to Iowa’s Class A1 geometric mean criterion.

Site A (nr Hwy 34): 2014 geometric mean of seven samples was 98 orgs/100 ml; five of 10 samples (50%) > single-sample maximum criterion.

Site B (at 135th Street): 2014 geometric mean of seven samples was 394 orgs/100 ml; eight of 10 samples (80%) > single-sample maximum criterion.

Site C, at 130 Street: 2014 geometric mean of eight samples was 301 orgs/100 ml; eight of 11 samples (73%) > single-sample maximum criterion.

Site F at Roosevelt Street: 2014 geometric mean of eight samples was 543 orgs/100 ml; eight of 10 samples (80%) > single-sample maximum criterion.

Near Danville: 2014 geometric mean of 13 samples was 1,694 orgs/100 ml; 10 of 13 samples (62%) > single-sample maximum criterion.

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 all five monitoring sites.

Monitoring and Methods

Assessment Key Dates

5/15/2013

Fixed Monitoring Start Date

10/22/2014

Fixed Monitoring End Date

Methods

420

Indicator bacteria monitoring