Briggs Woods Lake IA 04-UDM-1255

Hamilton County S17T88NR25W near Webster City.

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 2020 - 2022
Stream/River Water Quality Data	CY 2020 - 2022
Lake Water Quality Data	CY 2018 - 2022
Biological Sampling Data	CY 2018 - 2022*
Fish Kill Data	CY 2018 - 2022
Fish Tissue Sampling Data	CY 2018 - 2022
Continuous Dissolved Oxygen Sampling Data	CY 2018 - 2022
*Biological sites sampled in both 2017 and 2021 were also assessed.

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Cycle: 2024
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 11/1/2023 8:13:17 AM
Updated: 2/5/2024 11:04:33 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Turbidity: Secchi Disk Transparency

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

New

Source

Other: Sediment Resuspension

Source Confidence

Low

Cycle Added

2024

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier II

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

Class HH

Human Health -

Fully Supported

Impairment Delistings

Cycle Added	Class	Cause	Data Source	Rationale
2012	Class BLW	pH	Ambient monitoring: Iowa DNR-lakes	New data: WQ improvement (chemical / physical / bacterial)
2012	Class A1	pH	Ambient monitoring: Iowa DNR-lakes	New data: WQ improvement (chemical / physical / bacterial)

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as "not supported" due to aesthetically objectionable conditions caused by non-algae turbidity. The Class BLW use was assessed (monitored) as “fully supported.” The Class HH (fish consumption) use was assessed as “fully supported” based on fish tissue sampling data. Note: The DNR TMDL prepared for impairments due to algae and low dissolved oxygen (organic enrichment) was approved by U.S.EPA in July 2012. Additionally the DNR TMDL prepared for pH was approved by U.S.EPA in February 2021. Because not all the impairments identified for this lake are covered by this TMDL (Turbidity Secchi disc transparency), this lake remains in IR Category 5a.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2018-2022	22400004	Briggs Woods Lake
Iowa DNR	6	FT	See Below	1077	Briggs Woods Lake	SE of Webster City

Class A1 - Indicator Bacteria: No Data

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
22400004	6	15 / 5	8.25	9.37	8.79	3	4	NO	Mon	Full

Briggs Woods Lake was assessed as "not supported" for the 2012 assessment/listing cycle due to frequent violations of the state Class A1 criterion for pH. Based on DNR’s assessment methodology the current assessment/listing cycles must have fewer violations of the criterion based on the minimum required by the 10% Rule to propose delisting pH. There were less than 10% of the samples exceeding the single-sample maximum criterion for the 2024 assessment/listing cycle. Therefore, the impairment for pH is suggested for delisting for the 2024 assessment/listing cycle.

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
22400004	6	Chlorophyll a TSI	15 / 5	28	76	61	NO	Mon	Full
22400004	6	Secchi TSI	15 / 5	45	80	70	YES	Mon	Not
22400004	6	Total Phosphorus TSI	15 / 5	37	73	65	NA	NA	NA
22400004	6	Inorganic suspended solids	15 / 5	0.6	13	1.9	NA	NA	NA

DNR's assessment methodology indicates that a TSI value less than or equal to 63 is necessary to suggest de-listing of an impairment. The chlorophyll a TSI value for the 2020 assessment listing cycle was 66, which based on DNR's assessment/listing methodology indicated an impairment based on the narrative criteria protecting against aesthetically objectionable conditions. Because the TSI value for the 2024 assessment/listing cycle is less than or equal to the delisting threshold of 63 (median TSI value for chlorophyll a was 61), based on DNR's methodology, these values suggest "full support" of the Class A1 uses protecting against aesthetically objectionable conditions and the impairment (4a) for chlorophyll a is suggested for delisting for the 2024 assessment/listing cycle.

Class BLW - Binomial 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
22400004	6	Dissolved Oxygen	14 / 5	6.2	17.3	9.8	0	NA / NA	4	NO	Mon	Full
22400004	6	pH	15 / 5	8.25	9.37	8.79	3	NA / NA	4	NO	Mon	Full
22400004	6	Temperature	15 / 5	15.7	29.8	23.8	0	NA / NA	4	NO	Mon	Full

Briggs Woods Lake was assessed as "not supported" for the 2012 assessment/listing cycle due to frequent violations of the state Class BLW criterion for pH. Based on DNR’s assessment methodology the current assessment/listing cycles must have fewer violations of the criterion based on the minimum required by the 10% Rule to propose delisting pH. There were less than 10% of the samples exceeding the single-sample maximum criterion for the 2024 assessment/listing cycle. Therefore, the impairment for pH is suggested for delisting for the 2024 assessment/listing cycle.

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
22400004	6	7	20.93500637	100%	9.832523025	82%	NO	Evaluated	NA

Class BLW - Toxic Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Acute / Chronic Violations	>1 Acute / Chronic Violation	Assessment Type	Support Level
22400004	6	Ammonia	15 / 5	0.456	0.07	0.02	0 / 0	NO	Mon	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)
1077	tissue plug	2019	largemouth bass	11	35.3	0.093
1077	tissue plug	2017	largemouth bass	3	40.4	0.247
Support Level	Full

Monitoring and Methods

Assessment Key Dates

6/19/2018

Monitoring Start

8/23/2022

Monitoring End

5/30/2017

Fish Tissue Monitoring

8/30/2012

TMDL Completed

7/1/2019

Fish Tissue Monitoring

2/2/2021

TMDL Completed

Methods

150

Monitoring data more than 5 years old

200

Physical/Chemical Monitoring

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)