Technology Description

For low-flow and no-purge sampling methods, simple modifications to the current sample collection procedures will serve to reduce monitoring variability. When using low-flow sampling, purging a pre-defined constant volume for each rather than purging to parameter stability will reduce variability. For low-flow and no-purge sampling methods, variability can be reduced by collecting the samples from exactly the same depth within the well (high precision sampler placement). For stratified wells, a low-energy in-well mixing procedure prior to sample collection will further reduce variability for both low-flow and no-purge sampling methods. For sampling methods that require transfer of the sample from the collection device to the sample container, specific transfer procedures will reduce variability associated with volatile loss. The field demonstration will validate these four improved sampling procedures.

When the observed monitoring result is a function of a long-term concentration trend plus random variability that occurs over a much shorter time scale, low frequency monitoring is more efficient and effective for characterizing the long-term trend (in other words, high frequency sampling provides little or no additional information about long-term trends). As a result, at a site with relatively rapid long-term attenuation and low random variability, frequent monitoring can accurately characterize the true long-term trend. However, less frequent monitoring is appropriate at a site with a slow long-term source attenuation rate because random variability will dominate the apparent concentration trend obtained from more frequent monitoring. This project will demonstrate a method that uses past monitoring results to determine the random variability and long-term rate of change and then uses these site-specific characteristics to establish an optimized monitoring program.

The random variability associated with groundwater monitoring results can significantly distort apparent concentration trends in long-term monitoring records. During remedy effectiveness evaluations, this variability is often mistaken for poor spatial remedy effectiveness resulting in the incorrect conclusion that the remedy is failing to achieve the remediation goals. The demonstration will include an improved method for distinguishing between random variation in apparent concentration trends between wells and true spatial variability in remedy effectiveness.