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Title: Estimating the Impact of Vadose Zone Sources on Groundwater to Support Performance Assessment of Soil Vapor Extraction

A generalized conceptual model approach was developed that can be used to estimate the impact of volatile contaminant sources in the vadose zone on groundwater for sites where soil vapor extraction (SVE) operations have diminished source strength. The model has the potential to be broadly applicable for sites where vapor-phase transport dominates. The primary target for this conceptual model and related numerical modeling estimate of groundwater impact is for sites where contaminants have been removed from readily accessible portions of the subsurface, but where contaminants may persist in localized portions of the vadose zone. This paper describes the conceptual model, uses numerical simulations to evaluate the parameters controlling impact to groundwater, and presents estimated results for a range of input conditions. Over the implied ranges, the compliance well concentrations showed (inverse) proportionality with source concentration, Henry’s Law constant, and well screen length. An increase in site recharge caused a linear response in well concentration, with slopes dependent on the groundwater velocity. All other tested parameters resulted in nonlinear responses. The functional relationship between dimensional and transport parameters and resulting groundwater concentrations provide a basis for establishing a structured approach to evaluating the potential risk to groundwater posed by a vadosemore » zone source. This type of evaluation is particularly important to sites where SVE has been applied and reduced contaminant concentrations, but has reached a condition of diminishing returns such that a site must consider whether continuation of SVE, remedy modifications, or closure is warranted.« less
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Publication Date:
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Report Number(s):
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Resource Type:
Journal Article
Resource Relation:
Journal Name: Ground Water Monitoring and Remediation, 34(2):71-84
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
Sponsoring Org:
Country of Publication:
United States
soil vapor extraction; vadose zone; remediation