Big Hollow Lake IA 02-ICD-6496

Approximately 5 miles southwest of Mediapolis IA in S-17 T-71N R-3W Des Moines 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 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: Unknown
Created: 1/5/2022 11:27:28 AM
Updated: 1/6/2022 11:26:23 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Slight

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 I

Turbidity: Secchi Disk Transparency

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Slight

Status

New

Source

Other: Sediment Resuspension

Source Confidence

Low

Cycle Added

2022

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier I

Class BLW

Aquatic Life - Lakes and wetlands

Not Supported

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Slight

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 I

Class HH

Human Health -

Fully Supported

Impairment Delistings

Cycle Added	Class	Cause	Data Source	Rationale
2016	Class A1	Algal Growth: Chlorophyll a	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 the presence of aesthetically objectionable conditions caused by non-algal turbidity and violations of the Class A1 criterion for pH. The Class BLW use was assessed (monitored) as “not supported” due to violations of the Class BLW criterion for pH. The Class HH (fish consumption) use was assessed (evaluated) as "fully supported" based on turtle tissue sampling data.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2016-2019	22290002	Big Hollow Lake
Iowa DNR	6	WQ	CY 2019-2019	14000296	Big Hollow 1
Iowa DNR	6	FT	See Below	346	Big Hollow Lake	Big Hollow Recreation Area

Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples per Year (2018/ 2019/2020)

2018 Geometric Mean

2019 Geometric Mean

2020 Geometric Mean

Violates Annual Geometric Mean?

# 2018 SSM violations / SSM Violations needed for impairment

# 2019 SSM violations / SSM Violations needed for impairment

# 2020 SSM violations / SSM Violations needed for impairment

Violates Annual SSM Significantly >10% Rule?

Assessment Type

Support Level

22290002

3/3/0

0 / NA

Evaluated

Full

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
14000296	6	11 / 1	7.6	9.8	8.8	4	3	YES	Monitored	Not
22290002	6	23 / 4	7.5	9.7	8.6	5	5	YES	Monitored	Not

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
22290002	6	Chlorophyll a TSI	24 / 4	31	76	62	NO	Monitored	Full
22290002	6	Secchi TSI	12 / 4	36	80	68	YES	Monitored	Not
22290002	6	Total Phosphorus TSI	24 / 4	50	90	71	NA	NA	NA
22290002	6	Fixed suspended solids	12 / 4	0.3	15	0.7	NA	NA	NA

DNR's assessment methodology indicates that at least two assessment/listing cycles with a TSI value less than or equal to 63 are necessary to suggest de-listing of an impairment. The chlorophyll a TSI value for the 2016 assessment listing cycle was 65, 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 2020 assessment/listing cycle was less than the trigger of 65 (2020 listing for chlorophyll a was 58), and because the TSI value for the current listing cycle is also 62, based on DNR's methodology, these values suggest "full support" of the Class A1 use protecting against aesthetically objectionable conditions and the impairment (5a) for chlorophyll a is suggested for delisting for the 2022 assessment/listing cycle.

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
14000296	6	Ammonia	10 / 1	0.02	0.35	0.1	NA	0 / 0	3	NO	Monitored	Full
22290002	6	Ammonia	22 / 4	0.0003	0.37	0.06	NA	0 / 0	5	NO	Monitored	Full
14000296	6	Dissolved Oxygen	11 / 1	7.6	18.8	11.7	0	NA / NA	3	NO	Monitored	Full
22290002	6	Dissolved Oxygen	23 / 4	7.4	20.6	11.4	0	NA / NA	5	NO	Monitored	Full
14000296	6	pH	11 / 1	7.6	9.8	8.8	4	NA / NA	3	YES	Monitored	Not
22290002	6	pH	23 / 4	7.5	9.7	8.6	5	NA / NA	5	YES	Monitored	Not
14000296	6	Temperature	11 / 1	10.08	28	21.59	0	NA / NA	3	NO	Monitored	Full
22290002	6	Temperature	23 / 4	13.6	28.4	23.1	0	NA / NA	5	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 Concentration = 75th Percentile	Assessment Type	Support Level
22290002	6	6	48.83944727	70.05%	5.780237	31.85%	NO	Evaluated	NA

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)
346	shoulder	2015	snapping turtle	3	28.3	0.16	0.02	0.06
Support Level	Full

Monitoring and Methods

Assessment Key Dates

5/25/2016

Fixed Monitoring Start Date

10/1/2019

Fixed Monitoring End Date

8/13/2015

Fish Tissue Monitoring

Methods

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