Black Pit IA 02-WIN-1920

Mason City T96N R20W Sec17 NE and T96N R20W Sec8 SE Cerro Gordo 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.

Open Segment Map
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Cycle: 2020
Release Status: Final
Overall IR: 3 - Insufficient data exist to determine whether any designated uses are met.
Trophic: Unknown
Trend: Unknown
Created: 9/1/2020 2:48:32 PM
Updated: 10/15/2020 11:13:16 AM

Use Support

Class BLW

Aquatic Life - Lakes and wetlands

WINOFI

Fish Kill: Caused By Other

Support Level

Further Investigation Needed

Impairment Code

3b - Use potentially impaired based on an evaluated assessment.

Cause Magnitude

Slight

Status

Continuing

Source

Natural: Ordinary Stratification and Bottom-Water Hypoxia/Anoxia

Source Confidence

Low

Cycle Added

2016

Impairment Rationale

Non Pollutant-caused fish kill

Data Source

Fish kill investigation: Iowa DNR

Class HH

Human Health -

Not Assessed

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

This lake is not designated for Class A1 uses. The Class BLW uses are assessed (evaluated) as “partially supported” due to fish kills in July 2015. All other designated uses are “not assessed.”

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 2018-2018	22170003	Black Pit

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
22170003	6	Ammonia	3 / 1	0.146	0.07	0.02	0 / 0	0% / 0%	NO	Evaluated	Full
22170003	6	Dissolved oxygen	3 / 1	15	11.9	14.6	NA / 0	NA / 0%	NO	Evaluated	Full
22170003	6	pH	3 / 1	8.4	8	8	0 / NA	0% / NA	NO	Evaluated	Full
22170003	6	Temperature	3 / 1	22.1	21.2	21	0 / 0	0% / 0%	NO	Evaluated	Full

Class BLW - Fish Kill:

The Class BLW uses are assessed (evaluated) as “partially supported” due to fish kills that occurred in July of 2015. Because the cause of the fish kill was not identified, or the fish kill was attributed to a non-pollutant cause (e.g., winterkill), the assessment type is “evaluated.” Segments assessed using “evaluated” assessments are placed in Category 3b and are added to the state list of waters in need of further investigation. If no additional fish kills are reported in the segment for a 10 year period, the Category will be changed from 3b to 3a (water not assessed).

Details about the 2015 fish kill can be found here:https://programs.iowadnr.gov/fishkill/Events/886

Class HH - No Data

Class HH uses are considered “not assessed” (IR 3a) due to the age of the fish tissue sampling data upon which the previous assessment (“fully supported”) was based.

Monitoring and Methods

Assessment Key Dates

8/27/2018

Fixed Monitoring End Date

6/4/2018

Fixed Monitoring Start Date

7/11/2015

Fish Kill

Methods

140

Incidence of spills and/or fish kills

222

Non-fixed-station monitoring (conventional during key seasons and flows)