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PollutionEngineering November 2012 : Page 40

Advertorial EOS REMEDIATION, LLC HOWTO: (919) 873-2204 • • Manage Back Diffusion from Low Permeability Zones using EOS XR Problem Chlorinated solvents and other persistent contaminants present in high permeability (K) zones (sands or gravels) will slowly dif-fuse into lower K zones (commonly silts or clays) over decades of exposure (loading phase in Fig. 1a), then gradually diffuse back out (back diffusion phase in Fig. 1b) through a process called matrix diffusion . Low levels of contaminants can be released to groundwater from the low-permeability matrix over decades or even centuries after source removal, dramatical-ly increasing site management costs. Figure 2 shows a common pattern in contaminant concentrations following source removal. for decades, multiple reinjections could be required. If the reinjection frequency could be reduced to once every 10 or 20 years, this could dramatically reduce site management costs. from low K zones extends cleanup times. Increasing the time between reinjections to 10-20 yr can reduce costs by 65% to 95%. Using EOS XR can save a lot of money Figure 1A Solution Injection of an emulsified vegetable oil (EVO) like EOS PRO is an excellent approach for rapidly reducing contaminant concen-trations, and only needs to be injected once every 3 to 5 years. However, if con-taminants slowly diffuse out of low K zones EOS XR EOS XR is a premium, food-grade oil/ water emulsion developed by EOS Remediation, LLC to overcome the chal-lenges of matrix diffusion. EOS XR is the only extended time-released substrate for cost effective management of matrix dif-fusion. EOS XR is a mixture of regular EOS® (fast release soluble substrate and medium release vegetable oil) and a proprietary slow release substrate that slowly ferments to hydrogen and acetate for decades, to treat chlorinated solvents and other persistent contaminants slowly released from low K zones, resulting in fewer substrate reinjec-tions and lower costs. The analysis presented in Figure 3 shows the cumulative costs of using a soluble substrate, a traditional EVO and EOS XR when back diffusion Figure 1B Figure 1. Matrix diffusion process: (A) Loading phase; and (B) Back diffusion phase. Figure 2 Downgradient contaminant concentrations showing tailing resulting from back diffusion from low permeability (K) zones. Figure 3 Cumulative costs for management of a site with a soluble substrate, a traditional EVO and EOS XR. 40 Pollution Engineering NOVEMBER 2012

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