Purpose: One of the major obstacles preventing cost-effective cleanup of many Department of Defense (DoD) sites is the current inability to accurately locate and quantify residual nonaqueous phase liquid (NAPL) contamination. Monitoring NAPL remediation is desirable to quantify the extent of cleanup achieved and to verify the cost-effectiveness of the applied technology. Common tracer methods for estimating NAPL saturation require the addition of partitioning tracers to the subsurface and the creation of a flow field, such as a well-to-well test. The recently developed natural radon-222 (Rn) tracer method has the potential to provide a rapid, low-cost, and noninvasive routine-use method for quantifying residual NAPL saturation. Since Rn is already present in the subsurface due to the decay of radium-226, its addition is not required. In its simplest form, the method requires monitoring radon concentrations in subsurface fluids to evaluate the progress of NAPL remediation. Description: The method is based on Rn&146;s high solubility in organic NAPL. In the absence of NAPL contamination, aqueous Rn concentrations reach background levels that depend on aquifer porosity and mineralogy. In the presence of NAPL, aqueous Rn concentrations are substantially reduced as the Rn partitions into the residual NAPL. The resulting &145;Rn deficit&146; can be quantitatively correlated to the degree of NAPL saturation. Thus, it is possible to quantify the presence of residual NAPL and assess the effectiveness of remediation efforts by measuring the Rn concentration in groundwater produced from existing monitoring wells. The transport of Rn is also retarded due to the partitioning of Rn into the NAPL phase. Thus, Rn can be used as a natural partitioning tracer in dynamic transport experiments. The radon method will be evaluated at several DoD sites where NAPL contamination is being remediated. Once demonstrated and validated, an ESTCP technical protocol will be issued. Benefits: The radon method may provide a low-cost noninvasive approach for monitoring the progress of NAPL remediation. The method can also be used in combination with other partitioning tracer methods to provide an additional tool for NAPL detection and characterization. (Project Completed - 2006) Contacts: Technical Contact:
Dr. Lewis Semprini
Department of Civil, Construction, and
Environmental Engineering
Oregon State University
Corvallis, OR 97331-2302
Telephone: (541) 737-6895
Fax: (541) 737-3099
E-mail: lewis.semprini@orst.edu DoD Liaison Officer:
Mr. Holmes Don Ficklen
HQ AFCEE/ERS
3300 Sidney Brooks Road
Brooks AFB, TX 78235
Telephone: (210) 536-5290
Fax: (210) 536-4330
E-mail: Holmes.Ficklen@brooks.af.mil
| 
