North Skunk River IA 03-NSK-853

mouth (S5 T74N R10W Keokuk Co.) to confluence with Cedar Cr. in S15 T75N R12W Keokuk 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
View assessment methodology in new window

Cycle: 2020
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Unknown
Created: 9/9/2020 9:18:46 AM
Updated: 10/12/2020 9:50:59 AM

Use Support

Class A1

Recreation - Primary contact

Partially Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Partially Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2008

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Ambient monitoring: Iowa DNR-rivers

TMDL Priority

Tier IV

Class BWW1

Aquatic Life - Warm Water Type 1

Not Supported

Metals: Chromium

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2010

Impairment Rationale

Violations of acute criterion

Data Source

Ambient monitoring: Iowa DNR-rivers

TMDL Priority

Tier III

Class HH

Human Health -

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 use remains assessed as "partially supported" due to 2014-2016 levels of indicator bacteria that exceeded state water quality criteria. The Class BWW1 aquatic life use remains assessed as "not supported" due to violations of state water quality criteria for chromium during the 2004-06 assessment period. All other designated uses were "not assessed".

Assessment Explanation

Sources of Data:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 04-06, 14-16	10540001	North Skunk River	Site located in Segment 854 and beginning with the 2020 IR, will no longer be used to assess this segment

Class A1 - Indicator Bacteria:

Site ID	Data Source ID	# Samples / # Years	2014 Geometric Mean	2015 Geometric Mean	2016 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
10540001	6	23 / 3	225	219	385	Yes	13	57%	Yes	Monitored	Partial

Class BWW2 - Toxic Parameters:

During the 2004-2006 period, ten samples were analyzed for total chromium. Levels of chromium in two of these samples contained 0.02 mg/l of total

chromium and exceeded the Class BWW1 aquatic life acute criterion of 0.016 mg/l. The remaining eight samples were reported as less than the detection

level of 0.02 mg/l. Based on Iowa DNR’s assessment/listing methodology, more than one violation of an acute water quality criterion for a toxic parameter

over a three-year period suggests impairment of aquatic life uses. Thus, the violations of the chromium criterion suggest that the Class BWW1 aquatic life

use of this assessment segment should be assessed as impaired. Note: Prior to EPA approval in 2009, Iowa’s Class BWW1 acute criterion for chromium was

0.060 mg/l, and the chronic criterion was 0.040 mg/l.

Monitoring and Methods

Assessment Key Dates

1/7/2004

Fixed Monitoring Start Date

12/4/2006

Fixed Monitoring End Date

1/8/2014

Fixed Monitoring Start Date

12/5/2016

Fixed Monitoring End Date

Methods

150

Monitoring data more than 5 years old

230

Fixed station physical/chemical (conventional plus toxic pollutants)

420

Indicator bacteria monitoring