Bigalks Creek IA 01-UIA-284

Alternate name(s) for this segment: Nichols Creek

mouth (S18 T100N R10W Winneshiek Co.) to west line of S23 T100N R11W Howard 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.

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Cycle: 2020
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Unknown
Created: 10/1/2020 3:05:25 PM
Updated: 10/15/2020 11:47:49 AM

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

2008

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Watershed project monitoring

TMDL Priority

Tier III

Class A2

Presumptive Use

Recreation - Secondary 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

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2012

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Watershed project monitoring

TMDL Priority

Tier III

Class BCW1

Aquatic Life - Cold Water Type 1

Partially Supported

Temperature: Thermal Modifications

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

2014

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Watershed project monitoring

TMDL Priority

Tier IV

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 presumptive Class A1 and the presumptive Class A2 uses remain assessed as “not supported” due to levels of indicator bacteria (E. coli) that exceeded state water quality criteria. The Class BCW1 use remains assessed as "partially supported" due to violations of the Class BCW1 criterion for temperature. 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 2012-2014	191910001	Bigalk Creek - Site 7

Presumptive Class A1 - Indicator Bacteria: Historical

Site ID	Data Source ID	# Samples / # Years	2012 Geometric Mean	2013 Geometric Mean	2014 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
191910001	6	21/3	155.6	940.3	1063.5	Yes	15	71%	Yes	Evaluated	Not

Presumptive Class A2 - Indicator Bacteria: Historical

Site ID	Data Source ID	# Samples / # Years	2012 Geometric Mean	2013 Geometric Mean	2014 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
191910001	6	21/3	155.6	940.3	1063.5	Yes	4	19%	No	Evaluated	Not

Class BCW1 - Conventional Parameters: Historical

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
191910001	6	Ammonia	7/1	0.3	0.09	0.05	0 / 0	0% / 0%	No	Evaluated	Full
191910001	6	pH	13/2	10.08	8.36	8.29	1 / 0	8% / 0%	No	Evaluated	Full
191910001	6	Temperature	14/2	20	14.19	16.1	0 / 0	0% / 0%	No	Evaluated	Full

According to Iowa’s IR methodology, removal of an existing impairment due to violation of Iowa’s numeric water quality criteria requires that monitoring data show full support of the previously impaired beneficial use for two consecutive cycles. Although results of monitoring for the current IR cycle do not suggest an impairment of the Class BCW1 uses due to temperature, this impairment will remain in effect.

Class BCW1 – Trout Natural Reproduction:

Based on the January 2020 trout reproduction in Iowa streams summary prepared by the DNR Fisheries Bureau, the Class BCW1 coldwater aquatic life use of Bigalk Creek was assessed as "fully supported". According to the updated summary, this stream was placed in Category II: streams that exhibit recent but inconsistent reproductive success and occasional stocking may be needed to maintain the trout population.

Class HH - No Data

Monitoring and Methods

Assessment Key Dates

4/3/2012

Non-fixed Monitoring Start Date

10/7/2014

Non-fixed Monitoring End Date

1/1/2020

Biological Monitoring

Methods

120

Surveys of fish and game biologists/other professionals

150

Monitoring data more than 5 years old

220

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

330

Fish surveys

420

Indicator bacteria monitoring