Midterm Flashcards
Which sampling method has least amount of bias
Random
Selection of appropriate sampling points requires consideration of what variables?
Spatial and Temporal
What are 3 main sampling approaches?
Random, systematic random, and judgemental
Random Sampling
Every sample of population has an equal chance of being selected. Tradeoff: very expensive yet unbiased.
Systematic Random Sampling
Divide population into homogeneous groups (decrease variance), then divide this into cells using a cartesian grid. Tradeoff: slightly larger bias. Used in: land-based sites, drill wells and biological sampling.
Semi-variogram
Tool used to determine the number of samples required for a program to be considered statistically random. Theory: Increasing distance between samples increases randomness (decreases correlation).
Key factors to consider when deciding a sampling strategy are…
Type of pollutant, sampling device and end use of data.
DQO Steps
- State problem
- Identify decision
- Identify inputs to decision
- Define study boundaries
- Develop a decision rule
- Specify limits on decision errors
- Optimize design for obtaining data
Major activities of DQO (2)
Identify:
- Question that needs to be answered
- Amount of uncertainty tolerated
Types of Sampling Programs (3)
Intuitive, statistical, and protocol
Intuitive Sampling Program
Based on judgement of experts.
Statistical Sampling Program
Independent of judgement.
Protocol Sampling Program
Follow legally mandated plans.
Grab Samples
Discrete. Useful in looking at a specific time and locations, particularly for analytes at maximum concentrations. Assumes no change over distance.
Types of Control Site (2)
Area and local
Area Control Site
In same area as sampling site, not adjacent to it.
Local Control Site
Adjacent to sampling site, immediately up-gradient. Preferable because closer to sampling site, so more likely of being identical (except for analyte).
Which type of sample would best represent a heterogeneous sample?
Composite
Three examples of field measurements are…
pH, conductivity, and DO
What 3 areas should be included in a SOP of a sampling plan?
Preservation, labelling and sample collection.
What QC sample is used to measure the precision of a sampling technique?
Duplicate Sample
What type of QC sample is used to detect an error caused by presence of contamination by improperly cleaned sampling equipment?
Sampling Equipment Blank
Three types of error in sampling and analysis process?
Design phase, implementation and lab analysis.
Design Phase (Definition)
Identification of where and how to collect samples.
Implementation (Definition)
Sampling technique, storage and transfer of samples.
Lab Analysis (in relation to error)
Best controlled source of error.
What are 4 compartments in soil where individual pollutants may be found?
Air, water, soil, and free product.
Different types of sampling plans (2)?
Exploratory/surveillance and monitoring/assessment.
Name three of the different natural physical and chemical mechanisms that influence the migration of pollutants.
Climate, respiration, time, surface area, and composition.
Air Cycle
plants -> O2 -> humans -> CO2 -> plants
Water Cycle
Purification system: sun heats the ocean -> water evaporates and collects in clouds -> clouds release water as rain during precipitation
Soil Cycle
Organic matter -> organisms break down
What are the three partitioning mechanisms?
Volatilization, dissolution, and sorption.
Horizontal Stratification
Migration of pollutant from the source of contamination.
Vertical Stratification
Dependant on nature of pollutant (ex., density).
Sources of Interference
Sample collection, transport and storage, preservation, and analysis.
What questions should be asked before sampling?
Is the area homogenous or heterogeneous? Is there horizontal or vertical stratification?
NAPL
Non-Aqueous Phase Liquids
How do LNAPLs act in groundwater?
Spill travels through soil -> to groundwater -> floats on water table surface.
How do DNAPLS act in groundwater?
Spill sinks to bedrock -> collect in bottom in pools
Biomagnification
Increase of pollutant concentration as you move up the food chain. Pollutant exceeds the concentration expected at equilibrium between an organism and its environment.
List partitioning mechanisms in increasing volatility.
Sorption < Dissolution < Volatilization
Why preserve samples?
Chemical compounds can become unstable with changes in/exposure to: time, light, air, and temperature.
List three methods of sample preservation.
Chemical addition, temperature control, and using the correct container.
Problem vs. Preservation Technique: Volatilization (3)
Minimize headspace and agitation, keep sample cool and don’t use vacuum filtration.
Problem vs. Preservation Technique: Adsorption (2)
Choose correct sample bottles (add acid if necessary) or do field tests and preserve quickly.
Problem vs. Preservation Technique: Diffusion (2)
Proper container (want inertness, line with teflon coating) and minimize headspace.
Diffusion
Migration of chemicals from higher to lower concentrations.
Problem vs. Preservation Technique: Precipitation (1 + how)
Use acid, add immediately after sampling or else extreme loss of analyte will occur.
Problem vs. Preservation Technique: Biodegradation
Store at reduced temperature or extreme pH
Biodegradation
Analytes can degrade over time due to interaction with biological components in sample.
Holding Time
Length of time a sample can be stored after collection and preservation without significantly altering analytical results.
Matrix
Surrounding substance within which something else originated/develops/is contained.
Interferences
Cause error in measurement.
Types of Interferences
Additive, subtractive, and multiplicative.
Additive Interference
Generate a signal that adds to the analyte signal.
Subtractive Interference
Generate a signal the takes away from analyte signal (reacts with reagents which prevents reaction with analyte).
Multiplicative Interference
Add to analyte signal without generating a signal of its own. This changes slope.
Volatilization
A dissolved substance is vaporized.
Sources of Interference (4)
Matrix, analyte, other compounds, and reagent.
How to mitigate interferences? (What + examples)
Quality Control: Accuracy and precision, quality control charting, spikes, audits, and EMS).
Bioconcentration
Intake and retention by respiration from water in aquatic systems, or from air in terrestrial systems.
Bioaccumulation
Build up of toxins in an organism from environment and diet.
Ways an organism can uptake pollutants (3).
Uptake is by all possible means, including contact, respiration, and ingestion.
Finish this sentence: Preservation begins in the…
Field and continues in the lab.
Field Preservation Techniques (3)
Chemical addition, temperature, and correct container.
Lab Preservation Techniques (3)
Holding time, refrigeration, and exposure + sectioning.
Goal of preservation?
Minimize physical and chemical changes to the sample before analysis.
Sections of a Sampling Plan. (14)
- Project scope and objective.
- Type of plan.
- Site ID and map.
- Sample source.
- Number and type of samples.
- Frequency of sampling.
- Sampling approach.
- Collection method.
- Analytical parameters and lab methods.
- Field measurements
- Field QC
- Sampler
- Post sampling activities
- Documentation
DQO
Data Quality Objectives. Objectives that outline the overall uncertainty that can be tolerated in a project.
DQOs are balanced against cost of sampling and analysis, there is an inverse relationship between cost and uncertainty.
Sampling Plan Components: Project Scope and Objective
What is included and excluded, qualitative vs quantitative.
Sampling Plan Components: Type of Plan
Surveillance/exploratory or monitoring/assessment.
Sampling Plan Components: Number and Type of Samples
Test/control, grab/composite/discrete, duplicate/split, and local/area
Control Sample
Determine background levels, in terms of composition and concentration. Collected first.
Composite Sample
Multiple grabs, same location but at different times or different locations at same time. Variation is lost, less information.
Sampling Plan Components: Analytical Parameters
Primary or secondary analytes, lab methods (sensitivity, sample mass).
QA
Quality Assurance. A system of monitoring, evaluating, and documenting that lends proof of analysis.
QA Examples
Education and evaluation of employees, result reporting.
Quality Management
Made up of QA, QC, and Qassess
Quality Management Examples
Maintain Quality System Manual (QSM), planning and implementation of QA/QC program.
QC
Quality Control. The day-to-day monitoring of accuracy and precision at the lab level.
QC Examples
SOPs, blanks, calibrations, spikes, QC charting
Qassess
Quality Assessment. Evaluate QA and QC to see how well they are operating.
Qassess Examples
External and internal programs, accreditation, audits, Certification Reference Materials (CRMs), blinds, round robins.
Accuracy
Proximity to the true value. Determined by comparing value against a QC sample of known value.
Precision
How close results are to each other. Determined by comparing duplicate results.
Bias
Judgemental analysis, influencing results. Seen as trending from true value.
What are the two types of error.
Systemic and indeterminant (random).
Systemic Error
Inaccuracies are in the same direction, affecting data average.
Indeterminant/Random Error
Statistical fluctuations that add variability, but don’t affect average.
Spikes
Used to evaluate changes in analyte response from sampling to result. Created by adding a known amount of analyte to a matrix then analyzing.
