Low Flow (Low Stress) Sampling: is it environmental?

The goal of the low flow groundwater sampling is to collect samples that reflect the actual organic and non-organic components in the water, with minimal alterations from sampling operations. Low flow groundwater sampling minimizes the mixing of water from above and below the soil formation and also helps in minimizing aeration of the groundwater sample as it is extracted from the sampling well.

Groundwater is drawn from a well at a rate of 500 mL per minute to less than 100 mL per minute. To regulate the low flow of water while sampling, the environmental technician needs a pneumatic bladder or electric submersible pump.

The groundwater monitoring well is purged of stagnant water first, then the samples are taken when readings for turbidity and other water quality parameters (like dissolved oxygen, temperature, pH, and conductivity) meet pre-defined criteria. The readings from the monitoring parameters tell the environmental technician when the water has changed from stagnant well water to water coming in from the adjacent aquifer. That is the signal for the groundwater sampling to begin.

Low-flow sampling offers certain benefits over the higher-flow sampling options.

· Improves sample quality.

· Enhances sample representativeness.

· Reduces the amount of wastewater created by the purging process.

· Reduces field time by not creating turbulence with high-flow operations.

· Allows for automation of the sampling process.

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