1 of 35 The EPA 7-Step DQO Process Step 4 - Specify Boundaries (30 minutes) Presenter: Sebastian Tindall Day 2 DQO Training Course Module 4

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The EPA 7-Step DQO Process

Step 4 - Specify Boundaries

(30 minutes)

Presenter:

Sebastian Tindall

Day 2 DQO Training CourseModule 4

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Step Objective:

To define the spatial and temporal boundaries that the data must represent to support the decision statement

Step 4: Specify Boundaries

Step 4: Specify Boundaries

Step 2: Identify Decisions

Step 3: Identify Inputs

Step 1: State the Problem

Step 5: Define Decision Rules

Step 6: Specify Error Tolerances

Step 7: Optimize Sample Design

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Information IN Actions Information OUT

From Previous Step To Next Step

Define the spatial boundaries of the decision statement

Step 4- Specify Boundaries

Unit of Decision Making

Define the temporal boundary of the problem

Define the scale of decision making

Identify any practical constraints on data collection

Information Needed to Resolve Decision

Statements

Define the population of interest

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How Many Samples do I Need?

REMEMBER:

HETEROGENEITY

IS THE RULE!

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Background

It is difficult to make a decision with data that have not been drawn from a well-defined population

The term “population” refers to the total universe ofobjects to be studied, from which an estimate will be made.

Example: The total number of objects (samples of soil or sludge or sediment or air, etc.), that are contained within the spatial unit to be studied.

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Background

It is difficult to make a decision with data that have not been drawn from a well-defined population

In order to be well-defined and representative, a populationalso needs a characteristic to represent it.• Concentration of a chemical in media (soil, water, air, etc.)• Activity of a radionuclide in media• Permeability of a soil• Etc.

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Spatial Boundaries:

– Define the physical area/volume to which the decision will apply and from where the samples should be taken

Background

Temporal Boundaries

– Describe the timeframe that the data will represent and when the samples should be taken

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Boundaries will be used to ensure that: The data are representative of the population

Background

The data collection design incorporates:

– The areas or volumes that should be sampled

– The time periods when data should be collectedA boundary unit containing a large area/volume may actually contain two or more smaller boundary units (sub-populations) each of which have some relatively homogenous characteristic.

Sampling within the larger unit will not likely yield datawhich is representative of these sub-populations, leading to decision errors.

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Practical Constraint:

Any hindrance or obstacle that may interfere with the full implementation of the data collection design

Background

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Statements


Examples: The universe of:• Surface soil samples (3”x3”x6”) within the area of interest• Subsurface soil samples (3” x 3” x 6”) within the area of interest to a depth of 15 feet • Surface water samples (1 liter) within perimeter boundaries of the pond• Sediment samples (1 kg) from the top 6 inches of lake bottom• Direct surface activity measurement areas (100 cm2) on the building wall surfaces


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Statements


Define the geographic area/volume to which the decision statement applies. Note, the population describedabove resides within this area/volume.

The geographic area is a region distinctively marked by some physical feature, such as:

• Area (surface soil to a depth of 6 inches in the Smith’s backyard) • Volume (soil to a depth of 20 feet within the area of the waste pit)• Length (the pipeline)• Some identifiable boundary (the natural habitat range of a particular animal/plant species)


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Statements


Divide the population into strata (statistical) that have relativelyhomogeneous characteristics

Dividing the population into strata is desirable for the purpose of:• Addressing sub-populations • Reducing variability• Reducing the complexity of the problem (breaking it into more manageable pieces)


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What is the One Phenomenon that Causes

ALL Sampling Error?

HETEROGENEITY

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1

1

1

1

12 2

2

2

2

2

2

2

1 1

1

51 51 5252

51 51 5252

51 51 5252

51 51 5252

SD = 0.516 SD = 0.516

Combined SD = 25.41

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REMEMBER:

HETEROGENEITY

IS THE RULE!

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Statements

Define the population of interestDetermine the timeframe to which the decision applies.

Is it always possible to collect data over the full time period to which thedecision will apply? No One performs a risk assessment that covers the time a normal resident or worker would be exposed in their lifetime.This is a ‘sampling’ of the timeframe to which the decision applies.


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Statements


Example:

“The hexavalent chromium concentration leaching into groundwater over a period of a hundred years.”


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Statements


Determine When to Collect Data• Determine when conditions will be most favorable for collecting data • Select the most appropriate time period to collect data that reflect those conditions


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Statements


Why:Conditions (factors) may vary over the course of data collection.

• May affect: - Success of collecting the data- Interpretation of the data


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Statements


Factors may include: - Weather - Temperature - Humidity - Amount of sunlight - Wind/direction - Rainfall - Etc.


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Statements

Define the population of interestExample:A study to measure ambient airborne particulate matter may give misleadinginformation if the sampling is conducted in the wetter winter monthsrather than the drier summer months.


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Statements


Define the basis for selecting thedecision unit.

• Risk• Permits/regulatory conditions• Technological considerations• Financial scale• Other


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Statements


Define the smallest, most appropriate subsets of the population (sub-populations) for which decisions will be made based on the spatial ortemporal boundaries.


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Statements

Define the population of interestExposure Unit: An area/volume which has a size that correspondsto the area/volume where the receptors derive the majority of theirexposure. (EXAMPLE: A play area or an average residential lot size.)

Remediation Unit: An area/volume which has been determined to be the most cost-effective area/volume for remediation. (EXAMPLE: The volume of a dump truck or a railroad car, the surface area of each building wall.)


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REMEMBER:

HETEROGENEITY

IS THE RULE!

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Statements


Identify any constraints or obstacles that could potentially interfere withthe full implementation of the data collection design, such as:

• Seasonal or meteorological conditions when sampling is not possible• Inability to gain site access or informed consent• Unavailability of personnel, time, or equipment


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Statements


Example:

Population: Total number of soil samples within the spatial boundary that could potentially be collected and measured for lead contentSpatial Boundary: Top 6 inches of soil within the backyard of the Smith’s propertyTemporal Boundary: 8 years (average length of residence)Unit of Decision: Top 6 inches of soil within the backyard of the Smith’s property over the next 8 years


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Areas to be InvestigatedCS

Plan View

Former PadLocation

RunoffZone

0 50 100 150 ft 0 15 30 46 m

BufferZone

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Spatial and Temporal BoundariesCS

Spatial Boundary

Geographic Unit Decision Unit

Temporal Boundary

DS #

Population of Interest

Area or Volume

Relatively Homo-geneous

Statistical Strataa

Exposure Remediation Time- frame

When to Collect Data

Practical Constraints

1a All possible surface soil samples

125 ft diameter foot print of the pad & run-off area (227 yds3)

Yes 125 ft diameter foot print & run-off area of the pad

125 ft diameter foot print of the pad & run-off area (227 yds3)

years Collect any time except winter

Permafrost makes sample collection impossible to access site in winter.

1b All possible surface soil samples

70 ft radial buffer to a depth of 6 inches (794 yds3)

Yes 95ft radial buffer to a depth of 6 inches (940 yds3)

70 ft radial buffer to a depth of 6 inches (794 yds3)



2a All possible subsurface soil samples

125 ft diameter foot print of the pad from 6” to a depth of 10 ft (4318 yd3)

Yes not apply 125 ft diameter foot print of the pad from 6” to a depth of 10 ft (4318 yd3)



2b All possible subsurface soil samples

70 ft radial buffer from 6” to a depth of 10 ft (15084 yds3 )

Yes not apply 70 ft radial buffer from 6” to a depth of 10 ft (15084 yds3 )



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Scale of Decision MakingCS

DS # Scale of Decision Making

(Population, Spatial, and Temporal Boundaries)

1a All possible surface soil samples to a depth of 6 inches within the perimeter of the footprint of the pad and the run-off area, 227 yds3, collected any time except winter.

1b All possible surface soil samples to a depth of 6 inches within the buffer area excluding the footprint of the pad and the run-off area, 794 yds3, collected any time except winter.

2a All possible subsurface soil samples to a depth of 6” to 10’ within the perimeter of the footprint of the pad and the run-off area, 4318 yd3, collected any time except winter.

2b All possible subsurface soil samples to a depth of 6” to 10’ within the buffer area excluding the footprint of the pad and the run-off area, 15,084 yd3, collected any time except winter.

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Summary Population is the TOTAL universe (N)

We cannot measure the entire population (perform a census)

Population must be sampled to provide an estimate

Identification of strata decreases variance, and may allow a smaller sample size (n)

Stratification presents huge opportunities to manage uncertainty

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Statements



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End of Module 4

Thank you

Documents

1 of 35 The EPA 7-Step DQO Process Step 4 - Specify Boundaries (30 minutes) Presenter: Sebastian Tindall Day 2 DQO Training Course Module 4