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 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: Unknown
Created: 9/2/2020 2:46:50 PM
Updated: 1/4/2021 7:20:33 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Algal Growth: Chlorophyll a

Support Level

Not Supported

Impairment Code

5* - 303(d)-impaired last cycle; fully supporting this cycle; potential de-listing.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2016

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier I

Support Level

Not Supported

Impairment Code

5* - 303(d)-impaired last cycle; fully supporting this cycle; potential de-listing.

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 BLW

Aquatic Life - Lakes and wetlands

Not Supported

Support Level

Not Supported

Impairment Code

5* - 303(d)-impaired last cycle; fully supporting this cycle; potential de-listing.

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

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 “not supported” due to the presence of aesthetically objectionable conditions caused by algae blooms and violations of the Class A1 criterion for pH. The Class BLW uses are assessed (monitored) as “not supported” due to violations of the Class BLW criterion for pH. Class HH uses are assessed (monitored) as "fully supported" based on turtle tissue monitoring.

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	22290002	Big Hollow Lake	Lake Deep Point
Iowa DNR		FT	See Below	346	Big Hollow Lake

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
22290002	6	15 / 5	9.6	8.51	8.4	2	13%	NO	Monitored	Full

According to DNR's methodology, a lake must meet water quality standards for two consecutive cycles to suggest de-listing.Therefore, Big Hollow Lake 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
22290002	6	Chlorophyll a TSI	15 / 5	31	74	58	NO	Monitored	Full
22290002	6	Secchi TSI	15 / 5	36	73	63	NO	Monitored	Full
22290002	6	Total Phosphorus TSI	15 / 5	50	81	68	NA	NA	NA
22290002	6	Inorganic suspended solids	15 / 5	0.3	15	1.1	NA	NA	NA

Although the index value for Chlorophyll a is below the impairment trigger of 65 for this assessment cycle, Big Hollow Lake was listed as partially supporting its Class A1 uses due to aesthetically objectionable conditions. Based on DNR's methodology, the median TSI value for Chlorophyll a must be 63 or less for two consecutive assessment/listing cycles before a lake can be removed from the state's Section 303(d) list (IR Category 5). Therefore, Big Hollow Lake will remain listed as "not supported" for the 2020 assessment/listing cycle.

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
22290002	6	Ammonia	15 / 5	0.185	0.04	0.02	0 / 0	0% / 0%	NO	Monitored	Full
22290002	6	Dissolved oxygen	15 / 5	20.2	11.9	10.3	NA / 0	NA / 0%	NO	Monitored	Full
22290002	6	pH	15 / 5	9.6	8.51	8.4	2 / NA	13% / NA	NO	Monitored	Full
22290002	6	Temperature	15 / 5	27.7	23.63	23.98	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
22290002	6	11	48.839	92 %	12.008	70.1 %	NO	Evaluated	NA

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

346

8/13/15

snapping turtle

shoulder

<0.02

<0.06

0.16

Monitored

Full

346

7/5/12

snapping turtle

shoulder

0.329

Yes

Evaluated

Partial

Monitoring and Methods

Assessment Key Dates

5/28/2014

Fixed Monitoring Start Date

8/19/2018

Fixed Monitoring End Date

7/5/2012

Fish Tissue Monitoring

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