T.E. McHugh, Ph.D., D.A.B.T., corresponding author, is at GSI Environmental Inc., 2211 Norfolk, Suite 1000, Houston TX 77098; 713-522-6300; email@example.com.
Cutting-Edge Technical Papers
Influence of Shallow Geology on Volatile Organic Chemical Attenuation from Groundwater to Deep Soil Gas
Article first published online: 6 MAY 2013
© 2013, National Ground Water Association
Groundwater Monitoring & Remediation
Volume 33, Issue 3, pages 92–100, Summer 2013
How to Cite
McHugh, T. E., Beckley, L. and Bailey, D. (2013), Influence of Shallow Geology on Volatile Organic Chemical Attenuation from Groundwater to Deep Soil Gas. Groundwater Monitoring & Remediation, 33: 92–100. doi: 10.1111/gwmr.12013
- Issue published online: 9 AUG 2013
- Article first published online: 6 MAY 2013
Vapor intrusion pathway evaluations commonly begin with a comparison of volatile organic chemical (VOC) concentrations in groundwater to generic, or Tier 1, screening levels. These screening levels are typically quite low reflecting both a desired level of conservatism in a generic risk screening process as well as limitations in understanding of physical and chemical processes that impact vapor migration in the subsurface. To study the latter issue, we have collected detailed soil gas and groundwater vertical concentration profiles and evaluated soil characteristics at seven different sites overlying chlorinated solvent contaminant plumes. The goal of the study was to evaluate soil characteristics and their impacts on VOC attenuation from groundwater to deep soil gas (i.e., soil gas in the unsaturated zone within 2 feet of the water table). The study results suggest that generic screening levels can be adjusted by a factor of 100× at sites with fine-grained soils above the water table, as identified by visual observations or soil air permeability measurements. For these fine-grained soil sites, the upward-adjusted screening levels maintain a level of conservatism while potentially eliminating the need for vapor intrusion investigations at sites that may not meet generic screening criteria.