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 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: 7/29/2020 2:51:26 PM
Updated: 10/14/2020 10:25:33 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 -

Partially Supported

Fish Consumption Advisory: Mercury

Support Level

Partially 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

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 uses are assessed (monitored) as “partially supported” due to high levels of bacteria that exceed the Class A1 standard. High levels of pH that exceed the state water quality criterion also contribute to an impairment at this lake. The Class BLW uses are assessed (monitored) as “not supported” due to high pHs that exceed the state water quality criterion. The Class C uses remain “not assessed” (IR 3a) due to a lack of enough information upon which to base an assessment. The Class HH uses are assessed (monitored) as “partially supported” (IR 5a) 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

Sources of Data:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2016-2017	21440001	Geode Lake Beach (Geode State Park)
Iowa DNR	6	WQ	CY 2014-2017	22290001	Lake Geode
Iowa DNR		FT	See Below	70	Lake Geode

Class A1 - Indicator Bacteria:

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	Partial

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
22290001	6	12 / 4	9.51	8.74	8.9	2	17%	NO	Monitored	Full

According to DNR's methodology, a lake must meet water quality standards for two consecutive cycles to suggest de-listing. Therefore, Lake Geode will remain listed for the 2020 cycle as "not supported" its Class A1 uses 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	12 / 4	36	73	52	NO	Monitored	Full
22290001	6	Secchi TSI	12 / 4	37	67	56	NO	Monitored	Full
22290001	6	Total Phosphorus TSI	12 / 4	42	73	54	NA	NA	NA
22290001	6	Inorganic suspended solids	12 / 4	0.3	9.5	2.2	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
22290001	6	Ammonia	12 / 4	0.082	0.03	0.01	0 / 0	0% / 0%	NO	Monitored	Full
22290001	6	Dissolved oxygen	12 / 4	16.4	11.5	11.2	NA / 0	NA / 0%	NO	Monitored	Full
22290001	6	pH	12 / 4	9.51	8.74	8.9	2 / NA	17% / NA	NO	Monitored	Full
22290001	6	Temperature	12 / 4	27	23.8	24.8	0 / 0	0% / 0%	NO	Monitored	Full

According to DNR's methodology, a lake must meet water quality standards for two consecutive cycles to suggest de-listing. Therefore, Lake Geode will remain listed for the 2020 cycle as "not supported" its Class BLW uses due to pH.

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
22290001	6	10	83.481	98.9 %	7.290	72.05 %	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
22290001	6	Inorganic nitrogen (nitrate and nitrite)	12 / 4	5.1	1.92	1.9	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 – Fish Tissue Sampling:

Site ID

Date

Species Name

Biopart

# in sample

chlordane result

chlordane violation?

PCBs result

PCBs violation?

Hg result

Hg violation?

Assessment Type

Support Level

9/16/09

snapping turtle

shoulder

<0.03

<0.09

0.284

Evaluated

Full

8/13/09

largemouth bass

fillet

0.437

Yes

Evaluated

Partial

9/13/06

largemouth bass

fillet

0.51

Yes

Evaluated

Partial

9/18/08

largemouth bass

fillet

0.267

Evaluated

Full

Monitoring and Methods

Assessment Key Dates

5/28/2014

Fixed Monitoring Start Date

8/23/2017

Fixed Monitoring End Date

9/16/2009

Fish Tissue Monitoring

8/13/2009

Fish Tissue Monitoring

9/18/2008

Fish Tissue Monitoring

9/13/2006

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