Unnamed Tributary to Unnamed Tributary to Dry Run Creek IA 01-UIA-6555

from mouth (T97N R9W Sec3) to headwaters (T97N R9W Sec15) Winneshiek 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 2012 - 2014
Stream/River Water Quality Data	CY 2012 - 2014
Lake Water Quality Data	CY 2010 - 2014
Biological Sampling Data	CY 2010 - 2014*
Fish Kill Data	CY 2010 - 2014
Fish Tissue Sampling Data	CY 2010 - 2014
Continuous Dissolved Oxygen Sampling Data	CY 2010 - 2014
*Biological sites sampled in both 2009 and 2013 were also assessed.

Open Segment Map
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Cycle: 2016
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Unknown
Created: 5/26/2016 3:37:41 PM
Updated: 11/21/2016 3:43:14 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

2014

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Special project/study: Iowa DNR

TMDL Priority

Tier III

Class BWW1

Presumptive Use

Aquatic Life - Warm Water Type 1

Fully Supported

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as “not supported” (IR 5p) due to violations of Iowa water quality criteria for indicator bacteria. The presumptive Class B(WW1) aquatic life uses remain assessed as "fully supporting" (IR 2a) based on results of chemical/physical water quality monitoring. The source of data for this assessment remains the results of monitoring at STORET station 15960023 (Dry Run Creek Watershed Site 13a) conducted as part of a Clean Water Act Section 319 water quality project from August 2010 through October 2011.

Assessment Explanation

The presumptive Class A1 uses remain assessed (monitored) as “not supported" due to levels of indicator bacteria (E. coli) that exceeded the Class A1 geometric mean criterion. The geometric means of indicator bacteria (E. coli) in the 21 samples collected at Site 13a during the recreation seasons of 2010 and 2011 were as follows: The 2010 geometric mean was 2,625 orgs/100 ml, and the 2011 geometric mean was 3,385 orgs/100 ml. Both geometric means far exceed the Class A1 criterion of 126 orgs/100 ml. All 21 samples (100%) 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 IDNR’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 indicated impairment of presumptive Class A1 uses at this monitoring site. Note: The monitoring conducted as part of this watershed study included sampling for indicator bacteria (E. coli) immediately (within 24 hours) following rainfall runoff events. About half the samples in each of 2010 and 2011 were collected under such conditions. See the following journal article for more information: Witttman et al. 2013. Evaluation of land use and water quality in an agricultural watershed in the USA indicates multiple sources of bacterial impairment. Environ. Monit. Assess (2013) 185:10395-10429.

Results of chemical/physical monitoring at Site 31a during the 2010-12 period suggested "full support" of the presumptive Class B(WW1) aquatic life uses. None of the approximately 20 samples analyzed from August 2010 to October 2011 violated the Class B(WW1) criteria for ammonia, pH or temperature. Two of 23 samples (9%) violated the Class B(WW1) criterion for dissolved oxygen of 5 mg/l. 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 dissolved oxygen suggests impairment of aquatic life uses. Based on IDNR’s assessment methodology, however, these results suggested that the frequency of violations is not significantly greater than 10 percent; thus, these results did not suggest impairment of the Class B(WW1) aquatic life uses.

Monitoring and Methods

Assessment Key Dates

8/10/2010

Fixed Monitoring Start Date

10/10/2011

Fixed Monitoring End Date

Methods

220

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

420

Indicator bacteria monitoring