Sampling the Environment Sampling Water Matrices n n

Sampling the Environment

Sampling Water Matrices n n 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.

Sampling Water Matrices n 1. 2. 3. 4. 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

Sampling Water Matrices n n n 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.

Sampling Water Matrices n When sampling precipitation, timing is important because precipitation effectively ‘scrubs’ the atmosphere in the early stages of an event.

Sampling Water Matrices n n n 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.

Sampling Water Matrices n n n 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.

Sampling Water Matrices n n 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.

Sampling Water Matrices n n 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.

Sampling Air Matrices n n n n Analytes may be gases, aerosols, or particulates. Sources include: outdoor 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.

Sampling Air Matrices n n n 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.

Sampling Air Matrices n n 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.

Sampling Soils n n Best reference is: Martin Carter, ed. , Soil Sampling and Methods of Analysis, 1993. [S 593/S 7425 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.

n n 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.

Sampling Soils n n n 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.

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

Sampling Soils n n n 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.