How many groundwater samples are needed after decommissioning if a release to groundwater is confirmed?

After decommissioning a UST when a release to groundwater is confirmed, it is essential to collect adequate groundwater samples to assess the extent of contamination and understand its impact. The correct answer indicates that three samples should be taken: one from an upgradient location and two from downgradient areas.

Collecting a sample from an upgradient site is critical because it serves as a baseline for comparing with the downgradient samples. This helps in determining whether any contamination detected in the downgradient samples is due to the confirmed release from the UST or if it originated from another source. The requirement for two downgradient samples ensures a more comprehensive evaluation of the contamination plume in the direction of groundwater flow. By taking multiple samples, it allows for a better assessment of the concentration of contaminants and helps identify the spread and potential impacts on surrounding areas.

This sampling approach aligns with regulatory guidelines aiming to ensure that sites are remediated effectively and that any risk to human health and the environment is adequately managed. It emphasizes thoroughness and precision in understanding how a confirmed release affects groundwater quality.