Remedial Performance Evaluation of Dual PRBs Installed in a Historical Arroyo
Wednesday, May 7, 2014: 1:00 p.m.
Platte River Room (Westin Denver Downtown)
Aaron D. Kempf
,
ARCADIS U.S. Inc., Highlands Ranch, CO
Adam C. Griffin, PE
,
ARCADIS U.S. Inc., Seattle, WA
Gaston Leone
,
ARCADIS US Inc., Highlands Ranch, CO
Passive treatment technologies for groundwater remediation are an attractive choice for sites where future use and minimizing operation and maintenance are a priority. Permeable reactive barriers (PRBs) can provide effective groundwater treatment while minimizing site disturbance and long-term interruptions. However, careful design and implementation is required to ensure performance that achieves remedial objectives.
Historical lead and copper smelting operations conducted over 100+ years have resulted in site groundwater primarily impacted with arsenic. Groundwater flow and the majority of arsenic mass flux are concentrated in buried arroyos at the site, which present an opportunity to provide a focused groundwater remedy as part of a larger site restoration strategy. In the largest arroyo, two zero-valent iron (ZVI) PRBs were constructed in series to passively treat site groundwater and reduce the mass flux to sensitive receptors. Pre-design activities included column testing to determine the site-specific ZVI groundwater arsenic uptake characteristics, as well as detailed hydrogeologic and contaminant characterizations.
Site arroyos consist of coarse alluvial deposits resulting in a high-permeability and high flux groundwater flow system, which required PRB designs including both high permeability and widths and iron content consistent with contaminant loading rates and desired treatment longevity. PRBs were constructed of a ZVI and sand backfill with a hydraulic conductivity of greater than 1000 ft/day, and were approximately 8 feet thick to provide sufficient residence time and meet the targeted design lifetime.
Monitoring data including high-resolution water levels, hydraulic conductivity estimates, tracer testing, and water quality analyses are presented and compared to the PRB design parameters and performance objectives, which included effective hydraulic groundwater interception, contaminant removal efficacy, and continued reactivity of the ZVI and positive geochemical indicators. Results indicate that the PRBs are intercepting groundwater and resulting in reductions in arsenic groundwater concentrations.
Aaron D. Kempf, ARCADIS U.S. Inc., Highlands Ranch, CO
Aaron Kempf earned a B.S. in Bioenvironmental Science from Texas A&M University and an M.S. in Environmental Science from the University of Arizona. His background includes experience with the Texas Commission on Environmental Quality and applications of contaminant transport in porous media as it pertains to hazardous material remediation.
Adam C. Griffin, PE, ARCADIS U.S. Inc., Seattle, WA
Adam Griffin is a licensed environmental engineer employed by ARCADIS and works out of the Lakewood, Colorado office. He attended the University of Tennessee in Knoxville and acquired a bachelor’s degree in Civil Engineering and later returned to obtain his master’s degree in Environmental Engineering. He has been with ARCADIS for six years and prior to this was employed at Oak Ridge National Laboratory for two years. Griffin is a staff engineer with ARCADIS and focuses on in-situ biological groundwater remediation and interpretation of complex and high-resolution hydrogeologic data.
Gaston Leone, ARCADIS US Inc., Highlands Ranch, CO
Gaston Leone is a principal hydrogeologist at ARCADIS. He has been conducting hydrogeologic studies at mining facilities for the past 20 years. His areas of expertise include hydrogeologic characterization, and groundwater remediation and modeling.
