Walnut Creek IA 04-RAC-1120

mouth (S13 T78 R25W Polk Co.) to Interstate 35/80 in S33 T79N R25W Polk 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: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trend: Unknown
Created: 11/4/2016 8:45:26 AM
Updated: 11/4/2016 8:45:26 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

4a - Pollutant-caused impairment. TMDL has been completed.

Cause Magnitude

High

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2010

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Volunteer monitoring

Class BWW2

Aquatic Life - Warm Water Type 2

Not Assessed

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 (primary contact recreation) uses remain assessed (evaluated) as “not supported” (IR 4a) based on data from Iowa Geological Survey snapshot monitoring from 2004-2008. The Class B(WW-2) aquatic life remain “not assessed” (IR 3a) due to lack of recent biological data upon which to base an assessment. The source of data for this assessment remains the results for E. coli monitoring from 2006-2008 at two monitoring stations sampled as part of Iowa Geological Survey Watershed Snapshot monitoring: station 977102 in West Des Moines at the road crossing on 73rd Street and station 977111 in West Des Moines at the road crossing on NW 114th Street. The IDNR/SHL biological sampling from 1998 are now considered too old (greater than 10 years) to characterize current water quality conditions.

Assessment Explanation

Note: A TMDL for pathogen indicator (E. coli) impairments in the Raccoon River basin was prepared by IDNR and approved by EPA in June 2008. Thus, this impairment is placed into Category 4a of Iowa’s Integrated Report.

EXPLANATION: The Class A1 uses remain assessed (evaluated) as “not supported” due to levels of indicator bacteria (E. coli) that exceed state water quality criteria. The geometric mean levels of indicator bacteria (E. coli) in the 10 recreational season samples collected at each station as part of snapshot monitoring events from 2006-2008 (983 orgs/100ml at station 977102 and 1,107 orgs/100 ml at station 977111) both far exceed the Iowa Class A1 water quality criterion of 126 orgs/100ml. All 10 samples at each station exceeded the Iowa single-sample maximum Class A1 criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).

Although previously assessed as “fully supporting”, the Class B(WW-2) aquatic life uses are now considered “not assessed” due to the age of the biological data (greater than 10 years) upon which the previous assessments were based.

Monitoring and Methods

Assessment Key Dates

8/26/1998

Biological Monitoring

8/26/1998

One-time Chemical Monitoring

5/24/2006

Non-fixed Monitoring Start Date

10/8/2008

Fixed Monitoring End Date

Methods

150

Monitoring data more than 5 years old

220

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

315

Regional reference site approach

330

Fish surveys

380

Quantitative physical habitat assessment

420

Indicator bacteria monitoring