Prairie Creek IA 03-SSK-6598

from mouth (SE1/4 S34 T85N R25W) to headwaters in the NW1/4 S33 T85N R26W.

Assessment Cycle

2018

Release Status

Final

Data Collection Period

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.

Overall IR Category: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Unknown

Created: 7/19/2019 7:24:41 AM
Updated: 7/19/2019 7:25:26 AM

Assessment conducted in accordance with Iowa's 2018 IR methodology

Use Support

Class A1

Recreation

Primary contact

Presumptive Use

Not Supported

Impairments

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

Volunteer monitoring

TMDL Priority

Tier III

Class BWW1

Aquatic Life

Warm Water Type 1

Presumptive Use

Not Assessed

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 as “not supporting” due to levels of indicator bacteria that far exceed Iowa water quality criteria. The presumptive Class B(WW1) aquatic life uses remain “not assessed” due to lack of information upon which to base an assessment. The source of data for this assessment remains the results of monitoring at Iowa DNR monitoring station SC-13 (STORET station 908022) conducted as part of Iowa DNR water quality snapshot monitoring from 2008 through 2012. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment categories are considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).

Assessment Explanation

The Class A1 (primary contact recreation) remain assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric mean of indicator bacteria (E. coli) in the nine samples collected during the recreational seasons of 2008 through 2012 at station SC-13 was 1,070 orgs/100 ml, thus far exceeding the Class A1 criterion of 126 orgs/100 ml. All nine of the 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 DNR’s assessment/listing methodology, if a the geometric mean of at least 10 samples collected over five years of snapshot monitoring exceeds the respective water quality criterion, the contact recreation uses should be assessed as "impaired". Although only nine samples were collected over the five-year period, the relatively high geometric mean and the occurrence of greater than the single-sample maximum criterion (235 orgs/100 ml) in all nine samples suggests that the presumptive Class A1 uses should be assessed as "not supporting" (impaired).

None of the other parameters collected at this station over the 2008-2012 period have Class B(WW1) water quality criteria to which monitoring results can be compared. Thus, the presumptive Class B(WW1) aquatic life uses of this segment remain "not assessed".

Monitoring and Methods

Assessment Key Dates

5/10/2008

Fixed Monitoring Start Date

5/12/2012

Fixed Monitoring End Date

Methods

150

Monitoring data more than 5 years old

420

Indicator bacteria monitoring

830

(VOL.) Bacteriological water column sampling by quality-assured volunteers