Drilling an Array of Columns to 95 Feet to Install Deep ZVI Permeable Reactive Barrier
Wednesday, May 7, 2014: 10:15 a.m.
Platte River Room (Westin Denver Downtown)
Sarah Conkle
,
CH2M HILL, Denver, CO
Casey Hudson, PE
,
CH2M HILL, Atlanta, GA
Mike Perlmutter, PE
,
CH2M HILL, Atlanta, GA
The Wyoming Air National Guard Base is part of the Cheyenne Municipal Airport, approximately 2 miles north of downtown Cheyenne, Wyoming. As a result of historic solvent use for aircraft maintenance operations, a groundwater plume with carbon tetrachloride (CCl
4) and trichloroethylene (TCE), two orders of magnitude above remedial goals, extends 1200 feet offsite. CH2M HILL installed a 95-foot deep zero valent iron (ZVI) permeable reactive barrier (PRB) to intercept the groundwater at the base boundary and accelerate the attenuation of the off-base plume.
A Continuous Flight Uncased Hollow Stem Auger method was used to install the ZVI PRB, which is made up of 192 three-foot-diameter columns, placed in two offset rows perpendicular to groundwater flow. The columns were installed on five-foot centers (two feet between columns) to create a PRB with an aggregate length of 480 feet. Based on groundwater modeling, this configuration would provide the same residence time and treatment effectiveness as a conventionally installed three-foot-wide trench.
Because of site and plume characteristics, each column included three vertical layers to address the horizons of interest: Layer 1 (40-65 feet bgs) included up to 100 percent iron and the reciprocal volume of sand; Layer 2 (52-84 feet bgs) included a low permeability grout to limit downward vertical groundwater migration through the columns; and Layer 3 (72-95 feet bgs) included 15 percent ZVI and 85 percent sand. The amount of ZVI was based on the groundwater velocity and column study results.
The presentation will review the critical design elements for the drilled column ZVI PRB and key challenges associated with its construction. Groundwater data from the first year of monitoring will also be presented.
Sarah Conkle, CH2M HILL, Denver, CO
Sarah Conkle is a junior environmental engineer in CH2M HILL's Denver, Colorado office. She has five years of experience supporting the design, construction, operation, and evaluation of remediation systems for both federal and commercial clients. Conkle received her BSCE from the University of Michigan.
Casey Hudson, PE, CH2M HILL, Atlanta, GA
Casey Hudson has 24 years of experience as a professional engineer and senior project manager working in the environmental consulting industry. He specializes in project management, remedial action design and implementation, and technology evaluation. Hudson received a Bachelor of Science degree from Southern Illinois University in mechanical engineering and a master’s degree from the Georgia Institute of Technology in environmental engineering.
Mike Perlmutter, PE, CH2M HILL, Atlanta, GA
Mike Perlmutter is a senior environmental engineer in CH2M HILL’s Atlanta, Georgia office. He has more than 15 years of experience designing, constructing, operating, and evaluating a wide range of remediation systems. Perlmutter received his BSCE from Georgia Tech and MSE from the University of Texas at Austin.
