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

2 of 35 Step Objective: To define the spatial and temporal boundaries that the data must represent to support the decision statement 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

3 of 35 Information INActions 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

4 of 35 How Many Samples do I Need? REMEMBER: HETEROGENEITY IS THE RULE!

5 of 35 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 of objects 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.

6 of 35 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 population also 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.

7 of 35 n Spatial Boundaries : –Define the physical area/volume to which the decision will apply and from where the samples should be taken Background n Temporal Boundaries – Describe the timeframe that the data will represent and when the samples should be taken

8 of 35 Boundaries will be used to ensure that: n The data are representative of the population Background n The data collection design incorporates: –The areas or volumes that should be sampled –The time periods when data should be collected A 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 data which is representative of these sub-populations, leading to decision errors.

9 of 35 Practical Constraint: Any hindrance or obstacle that may interfere with the full implementation of the data collection design Background

10 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 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 cm 2 ) on the building wall surfaces Step 4- Specify Boundaries

11 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 Define the geographic area/volume to which the decision statement applies. Note, the population described above 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) Step 4- Specify Boundaries

12 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 Divide the population into strata (statistical) that have relatively homogeneous 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) Step 4- Specify Boundaries

13 of 35 What is the One Phenomenon that Causes ALL Sampling Error? HETEROGENEITY

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15 of SD = Combined SD = 25.41

16 of 35 How Many Samples do I Need? REMEMBER: HETEROGENEITY IS THE RULE!

17 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 Determine the timeframe to which the decision applies. Is it always possible to collect data over the full time period to which the decision 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. Step 4- Specify Boundaries

18 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 Example: “The hexavalent chromium concentration leaching into groundwater over a period of a hundred years.” Step 4- Specify Boundaries

19 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 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 Step 4- Specify Boundaries

20 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 Why: Conditions (factors) may vary over the course of data collection. May affect: - Success of collecting the data - Interpretation of the data Step 4- Specify Boundaries

21 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 Factors may include: - Weather- Temperature - Humidity- Amount of sunlight - Wind/direction- Rainfall - Etc. Step 4- Specify Boundaries

22 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 Example: A study to measure ambient airborne particulate matter may give misleading information if the sampling is conducted in the wetter winter months rather than the drier summer months. Step 4- Specify Boundaries

23 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 Define the basis for selecting the decision unit. Risk Permits/regulatory conditions Technological considerations Financial scale Other Step 4- Specify Boundaries

24 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 Define the smallest, most appropriate subsets of the population (sub- populations) for which decisions will be made based on the spatial or temporal boundaries. Step 4- Specify Boundaries

25 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 Exposure Unit: An area/volume which has a size that corresponds to the area/volume where the receptors derive the majority of their exposure. (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.) Step 4- Specify Boundaries

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27 of 35 How Many Samples do I Need? REMEMBER: HETEROGENEITY IS THE RULE!

28 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 Identify any constraints or obstacles that could potentially interfere with the 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 Step 4- Specify Boundaries

29 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 Example: Population: Total number of soil samples within the spatial boundary that could potentially be collected and measured for lead content Spatial Boundary: Top 6 inches of soil within the backyard of the Smith’s property Temporal 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 Step 4- Specify Boundaries

30 of 35 Areas to be Investigated CS Plan View Former Pad Location Runoff Zone ft m Buffer Zone

31 of 35 Spatial and Temporal Boundaries CS

32 of 35 Scale of Decision Making CS

33 of 35 Summary n Population is the TOTAL universe (N) n We cannot measure the entire population (perform a census) n Population must be sampled to provide an estimate n Identification of strata decreases variance, and may allow a smaller sample size (n) n Stratification presents huge opportunities to manage uncertainty

34 of 35 Information INActions Information OUT From Previous Step To Next Step Define the spatial boundaries of the decision statement 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 Step 4- Specify Boundaries

35 of 35 End of Module 4 Thank you