session 3c - simple methods of water quality & quantity determination
TRANSCRIPT
Fundamentals of Environmental Sampling
Jodi Sangster
Operator• Knowledge• Experience
Equipment• Detection
limits• Size• Power needs
On-Site• Difficulty of
sampling• Time
There are no absolutes. Each project is different.
Data Quality Objectives (DQO)
Amount and Quality of Data
Develop a sampling plan based on what you are testing for
Representative Sample
Plan and organize so that least contaminated site is sampled first
Avoid disturbance at the sampling site Avoid contamination
Clean and dry collection / testing equipment Use new or clean containers Wear gloves
Types of Samples
A Composite Sample is a mixture of grab samples taken at different times or locations and pooled together to provide one sample.
A Grab Sample is a snap shot of the quality of the water at the exact time and place the sample was taken.
Grab Samples
Composite Sample
What Now?
Interactions with air Oxidation Out gassing
Chemical reactions during storage or transport Filtering and cold storage Acid preservation Prompt analysis
Evaporation Cap tightly
pH and carbonates are sensitive to CO2 out gassing and CaCO3 precipitation.Dissolved oxygen is sensitive to gain from air and loss due to microbial.Reduced compounds are susceptible to oxygen increases from air.
Equipment Calibration
Thermometers – annual check Manufacturers User Manual Calibrate DO, pH, on daily or before use basis. Full pH check should be done weekly Conductivity/Salinity checked on daily/before use basis
(Std. @ 20oC) Use a QC check standard on daily or before use basis Record data on Calibration Sheet or Field Sheet
Know the limitations and interferences for each test!!!
Quality Assurance and Control
Quality control refers to activities used to monitor and minimize error QC Samples – blanks,
spikes, duplicates Quality control = error
control Quality assurance is the
QC management system
Blank
deionized water processed like any of the samples and used to "zero" the instrument
Calibration BlankCan be rechecked often to make sure equipment is not showing signs of drift or losing calibration.
Type How prepared?What does it tell
you?
Field (ambient) blank
Container filled with “analyte-free” water in the field
Transport, storage, and field handling
Rinsate or equipment blank
Container filled with “analyte-free water which has been passed
through sample collection equipment
Contaminated equipment
Trip blank (volatiles only)
Container filled at laboratory sent out in the field and returned with
samplesContamination
during transport
Common Blanks
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 More0
2
4
6
8
10
12
14
16
18
Nitrate – N (ppm)
Freq
uenc
y
Example Data – Field Reagent Blanks
Method Detection
Limit
Duplication
Field duplicates or replicates FD1 and FD2
Permit calculation of error due to heterogeneity, sampling method, and analytical method
Precision expressed as relative percent difference (RPD) or range (R)
X 100
Spikes
Checking “known” samples
Reinforced Blank Reinforced Duplicate
Varies depending on DQO Typically depends on the type of project and
how the data will be used Most common Field QC samples (frequency)
Blanks (1/20, 1/10, or once per day) Field Duplicates (1/20, 1/10, or once per day) Spikes (1/10 or once per day)
Frequency of Field QC Samples
Every sample collected increases project cost
Must balance cost of collection with data quality requirements
Additional samples do not always insure that the data will be of high quality
Cost of Field QC