Field Sampling Techniques

In an effort to educate clients about the inner workings of an environmental testing lab, Patricia McIsaac from Test America presented few pointers in a recent webinar.  The following is a summary of the materials presented:

Throughout the process of a water or soil sampling project there should be constant communication with the lab with all documents and information being shared.  While setting up a projects the lab would first like to know if there are known hazards. This is can be solved by properly labeling samples and providing background information.  Some important information to provide would be; what matrices should be used, certifications, compounds of interest, levels of sensitivity, methods, number of samples, Quality Assurance / Quality Control (QA/QC) requirements and timeframe.  When labs and field samplers work together they are able to minimize errors.

Collection of field quality control samples are important for every sampling event.  The following may be provided.  One temperature blank will be provided for each cooler to verify the cooler temperature (<6 degrees C) upon receipt.  Some labs have switched to infrared guns to take direct temperature samples, in this case, no temp blank would be necessary.  One trip blank per day for VOCs with analyte free water will be provided to assess if contaminants are introduced while samples are handled in the field or in transit. Typically, one field blank/ equipment blank/ rinsate blank is provided per day per matrix type.  These contain analyte-free water collected from the surface of the decontaminated sampling equipment to verify cleanliness, the water should be supplied by the lab.  Co-located samples/ field duplicates/ field splits are collected at same time and sampling location as primary sample.  Field duplicates are useful in documenting precision.  Finally, matrix spike [MS] and matrix spike duplicates [MSD] are sent at a frequency of one set per twenty field samples for each matrix type.  These are used to determine accuracy of the method.

Chain of Custody (COC) procedures are another important aspect of the sampling project.  Environmental samples can become legal evidence at any time, therefore, their possession must be traceable.  The field samplers initiate COC and the lab signs off when received and notes condition, number, details, etc.  Traditionally, the Laboratory will supply a COC prompting the field staff to supply the necessary information.  sampling1

There are a couple main bottle types used in sampling; high density polyethylene (HDPE) plastic, amber and or clear glass, and EnCore/TerraCore/Core N’ One.   Holding Time is the length of time a sample can be stored after collecting and prior to analysis without affecting the results.  Holding times vary greatly depending on the analyte, sample matrix or analytical method.   While holding times appear adequate to protect samples, relevant data for individually defined holding time is sparse.  Check out more information about holding times on the EPA website at http://www.epa.gov/nerlesd1/cmb/tasks/holding.htm.

Different preservatives are used for different samples but holding times should still be assessed.  Use of preservatives should be discussed with the lab prior to sampling.  Some common preservation techniques include; refrigeration, nitric acid, hydrochloric acid, sulfuric acid, sodium hydroxide and zero headspace. Refrigeration slows microbial activity, slows chemical reactions, maximizes solubility of gasses/volatiles and minimizes volatilization.  Nitric acid solubilizes metals.  Hydrochloric acid and Sulfuric acid minimize microbial activity.  Sodium hydroxide raises pH to maintain solubility of cyanides and sulfides and zero headspace minimizes volatilization.  These should all be documented on the COC and packed the appropriate way in the coolers.

Whesampling2n packing your samples you want to make sure that the samples will not break or leak before arriving to the lab.  First, you want to pick an appropriate cooler size then place an absorbent pad at the bottom of the cooler with bubble wrap above it.  Add a liner (large clear bag) above the bubble wrap for all samples to go in.  All bottles should be wiped clean and placed in bags for protection with glass bottles in bubble wrap and plastic bottles in zip lock bags.  Make sure there is a temperature blank in each cooler and fill each cooler with ice (all samples need to be at <6 degrees C).  Take into consideration where the samples are being shipped and how long it will take and add more ice or bubble wrap accordingly.  Secure the contents and tie the liner in a knot, place bubble wrap over the top of the liner where the cooler will be shut.  Complete the COC and place it in a plastic bag near the top of the cooler. Remember to take off any unnecessary labels or markings.  The cooler should be closed with sealed with packaging tape as well as tamper evidence seal.

Once the samples arrive to the lab they must go through the acceptance procedure.  The laboratory personnel will first check that the COC is properly completed and that the samples are labeled and in good condition.  Then samples are preserved according to the requirements of the method and the specific holding times.  For volatile organic analysis, a trip blank must be submitted with the samples.

Thank you to Test America for the original presentation on this material.

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