Dry Creek IA 02-CED-507

mouth (S1 T83N R7W Linn Co.) to confluence with unnamed tributary in S15 T84N R7W Linn Co.

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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Cycle: 2018
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Unknown
Created: 8/2/2019 1:34:07 PM
Updated: 8/2/2019 1:34:16 PM

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

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2008

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Special project/study

TMDL Priority

Tier III

Class BWW2

Aquatic Life - Warm Water Type 2

Fully Supported

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The presumptive Class A1 uses remain assessed (monitored) as “not supported” (IR 5p) due to high levels of indicator bacteria. This impairment continues the Class A1 impairment identified for the 2008 Integrated Reporting cycle based on overwhelming evidence of impairment. The Class B(WW2) aquatic life uses remain assessed (monitored) as “fully supporting” (IR 2a) based on ambient monitoring in 2010 and 2011. The source of data for this assessment remains the results of ambient water quality monitoring conducted at station 15570005 at Donnelly Park from May 2010 to July 2011.

Assessment Explanation

The presumptive Class A1 (primary contact recreation) uses remain 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 11 samples collected at station 15570005 during the recreational season of 2010 (1,121 orgs/100 ml), and the geometric mean of the 11 samples collected during the recreation season of 2011 (1,170 orgs/100 ml) both far exceeded the Class A1 criterion of 126 orgs/100 ml. Twenty of the combined 22 samples (91%) exceeded Iowa’s 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).

The Class B(WW2) aquatic life uses are assessed (monitored) as “fully supported.” No violations of Class B(WW2) water quality criteria for dissolved oxygen, pH, or temperature occurred in the 22 samples collected at Station 15570005 and analyzed from May 2010 to July 2011.

Monitoring and Methods

Assessment Key Dates

5/24/2010

Fixed Monitoring Start Date

7/25/2011

Fixed Monitoring End Date

Methods

220

Non-fixed station physical/chemical monitoring (conventional pollutant only)

420

Indicator bacteria monitoring