Twelve Mile Creek Lake IA 05-GRA-1367

Union County S12T72NR30W approx 4 mi E of Creston.

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.
Trophic: Eutrophic
Trend: Stable
Created: 8/21/2020 2:40:49 PM
Updated: 10/14/2020 2:49:16 PM

Use Support

Class A1

Recreation - Primary contact

Fully Supported

Class BLW

Aquatic Life - Lakes and wetlands

Not Supported

Organic Enrichment: Low Dissolved Oxygen

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

2016

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier IV

Class C

Drinking Water -

Not Assessed

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 use is assessed (monitored) as “fully supported.” The Class BLW use is assessed (monitored) as "not supported" due to violations of the Class BLW criterion for Dissolved Oxygen. The Class C use remains “not assessed” due to a lack of enough information upon which to base an assessment. All other designated uses are “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 2014-2018	22880004	Twelve Mile Lake	Lake Deep Point

Class A1 - Indicator Bacteria: No Data

Class A1 - pH:

Site ID	Data Source ID	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
22880004	6	15 / 5	9.1	8.4	8.4	1	7%	NO	Monitored	Full

Class A1 - Lake TSI's

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Median Value	Median TSI Violation	Assessment Type	Support Level
22880004	6	Chlorophyll a TSI	15 / 5	36	70	60	NO	Monitored	Full
22880004	6	Secchi TSI	15 / 5	46	70	62	NO	Monitored	Full
22880004	6	Total Phosphorus TSI	22 / 5	51	84	72	NA	NA	NA
22880004	6	Inorganic suspended solids	15 / 5	0.3	15	2.8	NA	NA	NA

Class BLW - Conventional Parameters:

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
22880004	6	Ammonia	15 / 5	0.31755	0.07	0.02	0 / 0	0% / 0%	NO	Monitored	Full
22880004	6	Dissolved oxygen	15 / 5	13.2	7.2	7.1	NA / 4	NA / 27%	YES	Monitored	Not
22880004	6	pH	15 / 5	9.1	8.4	8.4	1 / NA	7% / NA	NO	Monitored	Full
22880004	6	Temperature	15 / 5	26.6	23.49	23.3	0 / 0	0% / 0%	NO	Monitored	Full

Class BLW - Lake Planktonic Cyanobacteria:

Site ID	Data Source ID	# Samples	Maximum Cyanobacteria Wet Mass	Maximum Cyanobacteria % Composition	Median Cyanobacteria Wet Mass	Median Cyanobacteria % Composition	Median Cyanobacteria Wet Mass = 75th Percentile	Assessment Type	Support Level
22880004	6	11	91.317	99.6 %	15.779	90.7 %	NO	Evaluated	NA

Class C - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
22880004	6	Inorganic nitrogen (nitrate and nitrite)	22 / 5	1.1	0.19	0.05	0	0%	NO	Monitored	Full

The Class C uses are not assessed due to the lack of data sufficient for developing a valid assessment of support of the Class C uses.

Class HH - No data

Monitoring and Methods

Assessment Key Dates

4/22/2014

Fixed Monitoring Start Date

8/22/2018

Fixed Monitoring End Date

Methods

120

Surveys of fish and game biologists/other professionals

222

Non-fixed-station monitoring (conventional during key seasons and flows)

260

Fish tissue analysis

270

PWS chemical monitoring (ambient water)

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)