API PUBL 4730:2003 pdf download.Groundwater Remediation Strategies Tool
Potential impacts on groundwater receptors and the need for and relative benefits of alternative remedial measures may be evaluated on the basis of the mass flux of contaminants from the source zone to the receptor. This mass-based approach to site assessment and remediation has been described by various researchers (Einarson & Mackay, 2001 a,b; Gallagher et al, 1 995) and identified by USEPA as a key consideration in the evaluation of natural attenuation remedies (USEPA, 1 998). Under this approach, groundwater flow and contaminant concentration data are combined to estimate the rate of contaminant mass transfer (e.g., grams per day) past selected transects through an affected groundwater plume. Strictly speaking, this is a mass discharge rate; however the term “mass flux” is typically used to describe mass discharge, and this convention will be used in this document. Results from one or more such transects can then be used to evaluate: i) potential water quality impacts on downgradient supply wells (as determined from a mass balance analysis of the supply well pumping rate), ii) the natural attenuation of the contaminant mass with distance downgradient of the source (as defined by the reduction in mass flux between transects), and iii) the relative benefits of alternative remedies (based on their anticipated reductions in mass flux from source to receptor).
1.1 Transport Compartments
Several researchers have identified how remediation efforts can focus on individual components of a release site. For example, Gallagher, et al. (1 995) developed a “Mass-Based Corrective Action” approach where the masses in different “compartments” (soil, smear zone, and dissolved plume) were estimated and the cost per pound to remediate these masses was estimated. The concept of different transport compartments is well suited for the mass flux approach, and the conceptual remediation framework described in this document is based on evaluating the vadose zone, smear zone, and several “transect zones” in the dissolved plume.
1.2 Mass Flux and Remediation Timeframe
A logical extension of the mass flux approach is to use mass flux estimates with approximations of source masses to derive order-of-magnitude estimates of remediation timeframe. With this approach, remediation efforts can focus on the change in two key process variables: 1) The change in mass flux in different transport compartments; 2) The change in remediation timeframe. Although estimating remediation timeframe involves considerable uncertainty, relative changes in remediation timeframe can be performed with some degree of accuracy. The conceptual remediation framework described in this document discusses methods to estimate source masses and remediation timeframes in different transport compartments.