Frequently Asked Questions About MicroPurge Sampling These questions and answers are excerpted from the MicroPurge Sampling Methods FAQ, authored by David Kaminski. 1. Is MicroPurge equipment unique to QED? QED coined the term as a means of promoting the practice of low-impact sampling. While QED did not invent the process, we have been instrumental in bringing information on the MicroPurge concept to the marketplace... 2. Why should I go to MicroPurge sampling systems? What are the advantages? * ...sample quality and accuracy are improved through reduced turbidity, minimized degassing and volatilization. * ...low-rate, low-volume pumping reduces mixing and dilution effects on the concentration of contaminants... * Sampling systems are simpler and less expensive to operate, without the need for high rate purge pumps... * ...it extends the useful life of a monitoring well and preserves the integrity of the filter pack... * ...reduced exposure of field personnel to potentially-contaminated purge water... 3. Is the screen zone of a well really "flushed" by the aquifer? If there is any ground water movement in the well screen zone, then water should pass continuously through the screen. In most cases, even minimal ground water flow is sufficient to maintain an exchange of water in the well screen to provide representative samples with minimal purging... 4. Are there wells or sites that are not candidates for low-flow sampling? Every site is a candidate for low-flow sampling, if it is accepted in your region. Even if you're replacing existing equipment, low-flow sampling will usually yield savings after no more than 6 sampling events. If you're installing a new system, or if purge water handling/disposal costs or purge labor times are high, dedicated low-flow systems can pay for themselves in as little as 2-4 sampling events. 5. What about low yield wells that draw down even at very low pumping rates? If the yield of a well is too low to maintain minimal drawdown in the well at a very low pumping rate the well could be sampled using a dedicated pump by purging only the volume of the sampling device and tubing (passive sampling)... 6. Does a sample taken with MicroPurge equipment represent the entire screen zone, or just the area near the pump intake? Low-flow samples typically represent only the area of the well and surrounding formation immediately adjacent to the intake of the pump... 7. What flow rate is used for low-flow sampling? ...it should be based on the ability to establish a low flow rate at an acceptable level of drawdown (0.2 - 0.3 feet)... 8. Why do I need to monitor the water level when sampling with MicroPurge equipment? Since the goal of low-flow sampling is to obtain a sample from the well screen zone, excessive drawdown of the water column in the well would cause mixing of water from above the sampling point with the zone of interest... 9. How do I get a water level reading without disturbing the water column in the well? Carefully inserting a water level probe into the well shouldn't significantly disturb the water column. A dedicated water level measurement system could be a solution... 10. What is a sufficient purge volume when MicroPurge sampling equipment is used? For low-rate pumping, typical volumes are as little as 2 liters or as much as 10 liters. In passive sampling, the purge volume is dictated by the volume of the sampling device and tubing... 11. What are indicator parameters, and why are they measured during purging? Indicator parameters are water quality measurements, such as pH, conductivity, dissolved oxygen, and oxidation-reduction potential that can be used to identify relative changes in water chemistry. Measuring these parameters continuously during purging can identify when purging is completed... 12. What exactly is stabilization? How do I know when my readings are stable? Stabilization can be defined as the point during purging when purge water indicator parameters remain within a designated range of values. Stabilization criteria are typically user-defined or determined by regulatory guidance... 13. Isn't turbidity an indicator parameter? What role does it play in low-flow sampling? Turbidity is not an indicator of water chemistry, and therefore is not an indicator of a change in ground water chemistry. Turbidity is a general indicator of water quality and the level of turbidity in a ground water sample could affect the ability to determine the concentration of organic or inorganic analytes in a sample... 14. What if my parameters don't stabilize? If stabilization does not occur, it may be the result of excessive pumping rates that caused drawdown and mixing within the water column...