Which of the following factors can alter the quality of a groundwater sample taken from a monitoring well?

• A. Drilling fluid
• B. Improperly stored and handled casing
• C. Solvent used to weld PVC casing together
• D. All of the above

Answer: (D)

Contaminants can be introduced at various stages of well construction and handling, which can change the composition of the groundwater sample you collect. Drilling fluid can leave residues or introduce salts, hydrocarbons, or other additives into the wellbore or formation, potentially biasing the sample if the well isn’t properly purged and decontaminated. If casing is stored or handled improperly, lubricants, oils, solvents, rust, or other residues can transfer to the water during sampling, altering its quality. The solvent used to weld PVC casing can leave volatile residues that volatilize into the sample or dissolve into it, affecting VOC measurements and overall sample integrity. Because each of these scenarios has the potential to introduce substances not originally present in the groundwater, all of the above can alter sample quality.