Low flow groundwater sampling has become the norm for collecting groundwater samples during preliminary groundwater investigations, long-term groundwater monitoring, and during remedial activities. By using low flow purging and sampling techniques groundwater samples can be collected from a monitoring well that are representative of the groundwater within the formation adjacent to the well screen without generating large volumes of investigation derived wastes that can be costly to dispose of and unsightly while remaining onsite awaiting analytical tests results, waste classification, and arranging waste disposal. With low flow groundwater purging and sampling, the volume of waste can be as little as a few liters as opposed to tens or hundreds of gallons.
Low flow purging and sampling typically involves the use of a bladder pump, peristaltic pump, or a submersible pump with a variable speed controller that can be adjusted to a flow rate of less than 1.0 L/min. or commonly recommended between 0.1 and 0.5 L/min. The pumping rate is determined by measuring the water level in the monitoring well and determining the point at which stabilized drawdown occurs.
While purging the well, water quality parameters are monitored using a multiparameter water quality instrument to determine when sample collection should occur. These water quality parameters include pH, conductivity, ORP, dissolved oxygen, and may or may not include turbidity. The values for these parameters are typically written down on a well purge log by the field technician at a predetermined time increment or after each volume of the flow system is purged. Once the parameters have stabilized, the field technician then collects their samples and records the sample collection time as well as any other notes on the well purge log.
In-Situ, Inc. has developed software to assist the field technician by automatically recording information such as calibration reports and water quality parameter readings. This saves the technician time in the field, centralizes data storage, and saves time back at the office by eliminating the need to transpose data from well purge logs into an electronic format. In-Situ, Inc.’s TROLL 9500 and Flow-Sense software allows the user to create well purge logs in advance or in the field by following a simple software wizard. The software calculates the time it takes to purge one flow system volume and uses this or a user defined timeframe to log water quality stabilization parameters automatically on a laptop or In-Situ, Inc. Rugged Reader. Once stabilization occurs, the user simply saves the well purge log file and enters any notes associated with it. Once back at the office the user can simply export the data into a professional looking well purge log to add as an addendum in your report to the customer.
In-Situ, Inc. Low Flow Sampling Systems are available for purchase or rental and can be shipped to any location.