Long Term Performance Assessment of a Permeable Reactive Barrier at Former Naval AITR Station Moffett Field

Abstract

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden to Department of Defense, Washington Headquarters Services, Directorate for Information SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITORS ACRONYM(S) ESTCP SPONSOR/MONITOR'S REPORT NUMBER(S)Environmental Security Technology Certification Program 901 North Stuart Street, Suite 303 Arlington, VA 22203 DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release; distribution is unlimited. SUPPLEMENTARY NOTES ABSTRACTThe primary objective of this report is to describe the results of the last round of monitoring conducted in July 2004, their relationship to the results of pervious rounds, and their implications for the longevity and hydraulic performance of the permeable reactive barrier (PRB). ii ACKNOWLEDGEMENTS This study was funded by the Department of Defense's (DoD) Environmental Security Technologies Certification Program (ESTCP) through the Naval Facilities Engineering Service Center (NFESC). Battelle, under contract to NFESC conducted the laboratory and field investigation associated with the study. The authors also acknowledge the support provided by Mary Parker from Navy's Southern Division and by several staff from Tetra-Tech EMI, the on-site Navy contractor, who provided additional field support. SUBJECT TERMSiii EXECUTIVE SUMMARYA permeable reactive barrier (PRB) filled with zero-valent iron (ZVI) was installed at former Naval Air Station (NAS) Moffett Field in April 1996 and monitored periodically for the next 8 years. This pilot-scale PRB intercepts the more concentrated core of a relatively large regional groundwater plume of CVOCs that is approximately two miles long and a mile wide. The primary objective of this report is to describe the results of the last round of monitoring conducted in July 2004, their relationship to the results of pervious rounds, and their implications for the longevity and hydraulic performance of the PRB.The primary contaminant in the plume is trichloroethylene (TCE). Considerable amount of cis-1,2 dichloroethylene (DCE) is also present in the groundwater, thus indicating that some natural attenuation through anaerobic reductive dechlorination is underway at the site. The cleanup targets for these two compounds are the same as the federal drinking water standards or maximum contaminant levels (MCL) of 5 ppb (TCE) and 70 ppb (DCE).The long-term monitoring of this PRB showed that the ZVI continues to react strongly with the chlorinated volatile organic compounds (CVOC), primarily TCE and DCE, present in the groundwater. For the first time in July 2004, there were signs that a treated water front was exiting the PRB, fl...

Evaluation of five strategies to limit the impact of fouling in permeable reactive barriers

“…Spatial variability in aquifer hydraulic properties has been shown to affect the distribution of flows in PRBs and the rate and distribution at which minerals precipitate in pores [18]. In specific field groundwater chemistry and flow velocity condition, regions with high flow rates may not show significant pH increases and more mineral precipitation [7].…”

“…In specific field groundwater chemistry and flow velocity condition, regions with high flow rates may not show significant pH increases and more mineral precipitation [7]. For simplified, this study assumes that regions with high flow rates tend to accumulate minerals more quickly and foul more rapidly than regions where flows are slower under same geochemistry condition [18]. These regions of more rapid mineral accumulation can be minimized or eliminated when flows in the PRB are equalized.…”

“…These regions of more rapid mineral accumulation can be minimized or eliminated when flows in the PRB are equalized. One strategy to equalize flows is to install pea gravel zones along the up gradient and down gradient faces of the ZVI [18].…”

“…The pea gravel zones had the same lateral and vertical dimensions as the PRB (25-m wide and 10-m deep). Thickness and hydraulic conductivity of gravel zones were selected to be consistent with the gravel zones used for the PRB at Moffett Federal Airfield [18].…”

“…Thus, considerable interest exists regarding strategies to limit fouling and its impact on long-term performance of PRBs [10]. Five proposed are evaluated in this paper: (i) pea gravel equalization zones up gradient and down gradient of the reactive zone to equalize flows [4,18], (ii) placement of a sacrificial pre-treatment zone upstream of the reactive medium [17,19], (iii) pH adjustment [3,19], (iv) use of larger ZVI particles [3], and (v) periodic mixing of the ZVI to break up and redistribute secondary minerals [10,20]. Table 1 summaries the five strategies proposed to address fouling in the long-term performance of PRBs and their related laboratory studies and field applications.…”