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