Sampling the Environment

1
Sampling the Environment
2
Sampling Water Matrices

• Sources include precipitation, springs,
  freshwater streams, rivers, ponds, lakes,
  saltwater lakes, oceans.
• Sources are often very heterogeneous spatially
  and temporally obtaining a representative
  sample can be very difficult.
• Some materials float, others sink, some form
  strata horizontally or vertically.
• It will often be necessary to obtain different
  samples for different analytes.

3
Sampling Water Matrices

• When collecting water samples, in addition to
  recording specific location, you should also
  record
• Water temperature
• Depth of sample
• Stream flow rate
• Recent weather events

4
Sampling Water Matrices

• Sampling groundwater must be done carefully to
  avoid contamination by the sampling process.
• Drilling a well may bring contaminants to the
  aquifer.
• If an existing well is used, it should be purged
  by 3-10 volumes to eliminate stagnant water.

5
Sampling Water Matrices

• When sampling precipitation, timing is important
  because precipitation effectively scrubs the
  atmosphere in the early stages of an event.

6
Sampling Water Matrices

• Sampling devices will depend on the body of
  water.
• Manual grab samples are usually taken from
  large bodies of surface water.
• Nissen or other bottles as well as pumps may be
  used to sample water at depth.
• Automatic samplers may be used for discharge
  pipes or temporal characterization.
• Pumping water through adsorption or ion exchange
  tubes may be done to concentrate an analyte from
  a large volume of water.

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Sampling Water Matrices

• Problems with sampling increase as analyte
  concentration decreases.
• Sampling devices and containers are always
  possible sources of contamination or loss.
• Acid-washed plastic is a good material for metals
  but will adsorb organics.

8
Sampling Water Matrices

• When water contains suspended particles, it may
  be desirable to filter if one wishes to study the
  dissolved material only.
• The act of filtration may release materials from
  paper filters resulting in contamination.

9
Sampling Water Matrices

• Time between sampling and analysis varies for
  different analytes and often different
  preservation methods are required for each
  analyte.
• EPA guidelines may be used to determine how long
  a sample may be held before analysis and what the
  best method of preservation will be.

10
Sampling Air Matrices

• Analytes may be gases, aerosols, or particulates.
• Sources include outdoor air, indoor air,
  industrial stacks, auto exhausts, etc.
• Many air chemicals are very reactive and/or
  present in very low concentrations.
• Low concentrations generally required that large
  quantities of air be passed over filters or
  through some sorbing medium to obtain analyzable
  levels.
• Large spatial and temporal variations are
  typical.
• Exploratory screening tests are required before
  starting an assessment program.
• Increasingly, interest is focused on ways of
  measuring analytes in situ, particularly
  spectroscopically.

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Sampling Air Matrices

• Meteorological effects on sampling must be
  considered wind direction and speed, air
  temperature, precipitation are all factors.
• Topography may also be important. Turbulence and
  eddies are influenced by hills, valleys, even
  buildings.
• On-shore breezes may dilute normal analyte
  levels near the sea shore.

12
Sampling Air Matrices

• Gaseous analytes are somewhat more difficult to
  collect and analyze than aqueous ones because of
  the ease with which gases are lost.
• Teflon bags or polished stainless steel
  containers can be used for grab samples of air.
• Inorganic solids, activated carbon and organic
  polymers are all used to collect gases by
  adsorption.
• Aerosols and particles may be collected on
  filters or by the use of impactors which allow
  screening by particle size.

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Sampling Soils

• Best reference is Martin Carter, ed., Soil
  Sampling and Methods of Analysis, 1993.
  S593/S7425 1993
• Soils are very complex and variable.
• Properties change horizontally across the
  landscape and vertically down the soil profile.
• Sampling must take the variability into account.

14

• Sampling can be judgmental or random.
• Judgmental sampling consists of making visual
  assessments of the appropriate places to sample.
  This method is usually chosen for exploratory
  sampling.
• Exploratory sampling is called for to get a
  qualitative assessment of soil properties when an
  environmental impact has occurred or is
  anticipated. The program would be designed
  according to the presumed cause of disturbance.
• The nature of the landscape and the mobility of
  the analyte must be considered. At least two
  control samples will be required, more if the
  landscape has high variability.

15
Sampling Soils

• Simple random sampling eliminates personal bias
  but may miss important areas.
• Stratified random sampling can correct for that
  problem.
• The bases for stratification may be topography,
  vegetative cover, soil type, or estimated
  exposure to contamination.
• Presampling may be required to determine
  important horizontal and vertical strata, but the
  final number of samples required may be fewer
  overall.
• Sampling within strata should be totally random.

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Sampling Soils

• Undisturbed soils should be sampled by horizon.
• Mechanically disturbed soils often show no
  visible stratification and they are simply
  sampled at random depths.

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Sampling Soils

• Most samples will brought to the lab in plastic
  bags.
• The samples may be anything from dry to saturated
  with moisture and the first lab operation is
  usually to dry them.
• Drying temperatures depend upon analytes to be
  found.
• Sometimes soils are ground and screened to pass,
  e.g., a 2 mm screen.
• Dried samples may generally be stored at room
  temperatures for months to years in sealed glass
  jars.