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Low-flow sampling is a method for taking groundwater samples. This method of sampling uses a strict set of guidelines to ensure that the samples taken are of the highest quality and the best representation of the water present at the sampling level.

For this sampling method, the groundwater is drawn from the aquifer at an extremely low rate, usually at less than 500 mL per minute. That rate is often less than 100 mL per minute in many applications.

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The goal of this sampling technique is to collect samples that reflect the actual organic and non-organic components in the water, with minimal alterations from sampling operations. The slow draw of water minimizes the mixing of water from above and below the soil formation and also helps in minimizing aeration of the sample.  

The sampling process involves purging the well of stagnant water first, then taking the samples. As the stagnant water is drawn up, it is monitored for turbidity and certain parameters. The readings from the monitoring 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.

How Do I Prepare For Low-flow Sampling?

Getting ready for low-flow sampling requires a properly constructed and developed monitoring well. The wellhead must be secured from rain and surface water intrusion.

To regulate the low flow of water while sampling, the environmental technician needs a pneumatic bladder or electric submersible pump. The pump's regulator must offer the ability to adjust the pump's outflow. The bladder pump is lowered into the well and submerged completely below the water at the desired sampling level.

The pump controller must have great precision to maintain a low, constant flow of water for proper sampling. Precise water level monitoring is also essential. The sampling process includes monitoring certain chemical parameters within the water. This requires a multi-parameter probe installed within the water flowing from the pump.

Ideally, sampling should not be done on the hottest days or at the hottest times of the day. It is important that the wellhead and the sampling equipment be kept in the shade. Heat can create thermal flows within the well and affect the ability to get representative samples.

Once the water coming up is cleared for sampling, the environmental technician takes the samples from a diverter outlet located near the top of the well head.

What Are The Benefits Of Low-flow Sampling?

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

  • Improves sample quality.

  • Enhances sample representativeness.

  • Reduces the amount of waste water created by the purging process.

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

  • Allows for automation of the sampling process.

Who Can Help You With Low-flow Sampling On Your Property?

If you need groundwater samples taken, low-flow sampling is a great option in many cases. To speak with an expert about setting up a sampling program on your property, contact Talon/LPE. We provide environmental consulting services all over Texas, Oklahoma, and New Mexico. Let our experts get your sampling program underway.

Topics: Environmental Drilling