Geode Lake IA 03-SKU-896

Henry County S36T70NR5W 4 mi. SW of Danville.

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 2018 - 2020
Stream/River Water Quality Data	CY 2018 - 2020
Lake Water Quality Data	CY 2016 - 2020
Biological Sampling Data	CY 2016 - 2020*
Fish Kill Data	CY 2016 - 2020
Fish Tissue Sampling Data	CY 2016 - 2020
Continuous Dissolved Oxygen Sampling Data	CY 2016 - 2020
*Biological sites sampled in both 2015 and 2019 were also assessed.

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Cycle: 2022
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 12/22/2021 2:44:16 PM
Updated: 1/5/2022 9:52:07 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Support Level

Not Supported

Impairment Code

4a - Pollutant-caused impairment. TMDL has been completed.

Cause Magnitude

Slight

Status

Continuing

Source

Natural: Flooding

Source Confidence

Low

Cycle Added

2006

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Ambient monitoring: Iowa DNR-lakes

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

4a - Pollutant-caused impairment. TMDL has been completed.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2006

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Beach monitoring: Iowa DNR WQMA

Class BLW

Aquatic Life - Lakes and wetlands

Not Supported

Support Level

Not Supported

Impairment Code

4a - Pollutant-caused impairment. TMDL has been completed.

Cause Magnitude

Slight

Status

Continuing

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Low

Cycle Added

2006

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Ambient monitoring: Iowa DNR-lakes

Class C

Drinking Water -

Not Assessed

Class HH

Human Health -

Not Supported

Fish Consumption Advisory: Mercury

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

High

Status

Continuing

Source

Agriculture

Source Confidence

N/A

Cycle Added

2010

Impairment Rationale

Fish consumption advisory in effect: no more than 1 meal/week

Data Source

Fish contaminant monitoring: Iowa DNR

TMDL Priority

Tier IV

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use remains assessed as “not supported” due to high levels of bacteria that exceeded the Class A1 standard. High levels of pH that exceeded the state water quality criterion also contributed to the impairment at this lake. The Class BLW use remains assessed as “not supported” due to high pHs levels that exceeded the state water quality criterion. The Class HH (fish consumption) use remains assessed (monitored) as “not supported” (IR 5a) based on fish tissue sampling data and due to the issuance of a fish consumption advisory at this lake. Note: A TMDL for bacteria and pH at Geode Lake was prepared by DNR and approved by EPA in 2009. Because not all of the Section 303(d) impairments identified for this assessment/listing cycle (mercury) are addressed by the TMDL, this waterbody remains in IR Category 5a (impaired; TMDL required) for the current assessment/listing cycles.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2016-2017	22290001	Lake Geode
Iowa DNR	6	WQ	CY 2016-2017	21440001	Geode Lake Beach (Geode State Park)
Iowa DNR	6	FT	See Below	70	Lake Geode	E of Lowell

Class A1 - Indicator Bacteria: Historical

Site ID	Data Source ID	# Samples / # Years	2016 Geometric Mean	2017 Geometric Mean	2018 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
21440001	6	24 / 2	41.76	36.49	NA	No	5	21%	YES	Monitored	Not

Class A1 - pH:

Site ID	Data Source ID	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	# Violations	Violations needed for impairment	Violates Significantly >10% Rule?	Assessment Type	Support Level
22290001	6	6 / 2	8.4	8.9	8.7	0	3	NO	Evaluated	Full

According to DNR's methodology, a lake must meet water quality standards for two consecutive cycles to suggest de-listing. Therefore, the Class BLW use of Lake Geode will remain listed for the 2022 cycle as "not supported" due to pH.

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
22290001	6	Chlorophyll a TSI	6 / 2	36	73	42	NO	Evaluated	Full
22290001	6	Secchi TSI	6 / 2	37	67	56	NO	Evaluated	Full
22290001	6	Total Phosphorus TSI	6 / 2	42	57	54	NA	NA	NA
22290001	6	Inorganic suspended solids	6 / 2	0.3	4	2.2	NA	NA	NA

Class BLW - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	# Violations	# Acute / Chronic Violations	Violations needed for impairment	Violates Significantly >10% Rule?	Assessment Type	Support Level
22290001	6	Ammonia	6 / 2	0.0003	0.082	0.03	NA	0 / 0	3	NO	Evaluated	Full
22290001	6	Dissolved Oxygen	6 / 2	6.4	16.4	12	0	NA / NA	3	NO	Evaluated	Full
22290001	6	pH	6 / 2	8.4	8.9	8.7	0	NA / NA	3	NO	Evaluated	Full
22290001	6	Temperature	6 / 2	18.6	27	23.9	0	NA / NA	3	NO	Evaluated	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 Concentration = 75th Percentile	Assessment Type	Support Level
22290001	6	4	19.54	89.2%	5.68	58.4%	NO	Evaluated	NA

Class C - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	Median Value	# Violations	Violates Significantly >10% Rule?	Assessment Type	Support Level
22290001	6	Inorganic nitrogen (nitrate and nitrite)	6 / 2	0.8	5.1	2.8	2.6	0	NO	Evaluated	Full
22290001	6	pH	6 / 2	8.4	8.9	8.7	8.7	0	NO	Evaluated	Full

Class HH - Fish Tissue Sampling:

Site ID	Biopart	Year	Species	# in sample / # of samples	Avg Length (cm)	(Avg) Hg (ppm)	Chlordane (ppm)	Sum PCBs (ppm)
70	fillet	2009	largemouth bass	5	NA	0.437
70	shoulder	2009	snapping turtle	2	NA	0.284	0.03	0.09
Support Level	Not	A one meal/week mercury consumption advisory for largemouth bass exists on this segment. Based on IR Methodology, the Class HH (fish consumption) use was assessed as “not supported.”

Monitoring and Methods

Assessment Key Dates

5/25/2016

Fixed Monitoring Start Date

8/20/2017

Fixed Monitoring End Date

9/16/2009

Fish Tissue Monitoring

8/13/2009

Fish Tissue Monitoring

9/25/2009

TMDL Completed

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

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)

420

Indicator bacteria monitoring