Powell Creek IA 04-RAC-1803

mouth (at upper end of Little Storm Lake Buena Vista Co.) to headwaters in NW 1/4 S12 T91N R38W Buena Vista 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 2016 - 2018
Stream/River Water Quality Data	CY 2016 - 2018
Lake Water Quality Data	CY 2014 - 2018
Biological Sampling Data	CY 2014 - 2018*
Fish Kill Data	CY 2014 - 2018
Fish Tissue Sampling Data	CY 2014 - 2018
Continuous Dissolved Oxygen Sampling Data	CY 2014 - 2018
*Biological sites sampled in both 2013 and 2017 were also assessed.

Open Segment Map
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Cycle: 2020
Release Status: Final
Overall IR: 3 - Insufficient data exist to determine whether any designated uses are met.
Trend: Unknown
Created: 10/7/2020 7:54:18 AM
Updated: 10/16/2020 11:13:08 AM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Assessed

Class BWW1

Presumptive Use

Aquatic Life - Warm Water Type 1

WINOFI

Toxic Inorganics: Ammonia

Support Level

Further Investigation Needed

Impairment Code

3b - Use potentially impaired based on an evaluated assessment.

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2008

Impairment Rationale

Potential Impairment

Data Source

TMDL monitoring: Iowa DNR

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The presumptive Class BWW1 use remains assessed as “partially supported” based on levels of ammonia that violated state water quality criteria. All other designated uses were "not assessed".

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2004	11110001	Powell Creek	TMDL Site 1
Iowa DNR	6	WQ	CY 2004	11110002	Powell Creek	TMDL Site 2

Presumptive Class A1 – No Data:

Presumptive Class BWW1 - Ammonia:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Acute / Chronic Violations	% Acute/ Chronic Violations	Significantly >10% Violations	Assessment Type	Support Level
11110001	6	Ammonia	6 / 1	16	2.9	0.2	0 / 1	0% / 17%	No	Evaluated	Full
11110002	6	Ammonia	6 / 1	6.9	1.4	0.19	0 / 1	0% / 17%	No	Evaluated	Full
Although these results suggest that the presumptive Class BWW1 aquatic life use should be assessed as “fully supported,” the extremely high levels of ammonia, combined with the limited amount of monitoring, suggest both a potential impairment of the aquatic life use as well as the need for additional monitoring. This amount of data (six samples) does not meet DNR guidelines for Clean Water Act assessment and listing that require at least 10 samples be collected per site over a three-year period. Such assessments are appropriate for addition of segments to IR subcategory 3b and on Iowa’s list of waters in need of further investigation.

Monitoring and Methods

Assessment Key Dates

7/19/2004

Non-fixed Monitoring Start Date

10/20/2004

Non-fixed Monitoring End Date

Methods

150

Monitoring data more than 5 years old

220

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