Modeling Remediation at Visalia

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Remediation with Steam Stripping at Visalia

In-situ Remediation with Thermal Methods has become a hot topic since steam injection, electrical conduction heating, and electrical resistance heating have been used in several successful projects. The most visible of these projects is the Visalia Superfund Project. One million three hundred thousand pounds of creosote, diesel and pentachlorophenol was recovered there by injecting steam into an aquifer 120 feet underground. Less than one pound per day had been recovered in a pump and treat.

The primary recovery mechanism at Visalia is vaporization of diesel diluent, PCP and smaller creosote molecules. In addition, the hydrocarbons that dissolve in the water can be oxidized in a reaction similar to coal-gasification, i.e. oxidation with injected oxygen and hydrolysis by water. Many lessons can be learned by studying the Visalia project with a sophisticated simulator like STARS the Computer Modeling Groups non isothermal compositional finite difference simulator.

These include quantifying the production and destruction mechanisms, Figure 1.

Figure 1 - Production Mechanisms

Simulators like STARS can differentiate between the DNAPL produced as liquid and which components (up to 30) are produced by vaporization. In addition, competitive reactions like oxidation, pyrolysis or bioremediation can be specified for each component in the simulation. Including all mechanisms can help the design team to understand what is important and how to best plan the remediation project.

Figure 2 - Vaporized DNAPL Redistribution

How the DNAPL can be redistributed as it vaporizes can be seen in Figure 2. Since the primary production mechanism is vaporization, the DNAPL moves wherever the steam goes. As the steam cools above the aquifer, or in low pressure zones, the DNAPL can condense. Knowing what could happen before it happens has been a desire of generations of people. Use of simulation as a project design tool can only help to improve projects and reduce cost.

Figure 3 - Increasing Oxidation of DNAPL

The relative value of oxidation via “Hydrous Pyrolysis” can be seen in Figure 3 where coinjecting extra air with the steam does not increase recovery because recovery of vaporized NAPL decreases. However, the lower steam injection rate resulting from increased air-coinjection could reduce the cost of the project.

Figure 4 - Improving Well Locations

The overall efficiency of projects like Visalia can be improved substantially by using a sophisticated simulator to help select placement of wells. Figure 4 shows that adding either a central injector or producer to the project would have cut the time to recover the DNAPL by 50%. The production could be improved because the original design allowed DNAPL to be concentrated between wells. Adding a well where the DNAPL is being concentrated fixes the problem.

Summaries of Visalia

The Visalia work has been presented at numerous seminars and was described in an AIChE paper at Atlanta in March of 2000 and in the Journal of Hazardous Materials [92 (2002), 1-19]. Preprints are available from MKTS. STARS has also been used to model environmental projects as diverse as high temperature thermal conduction (ISTD), steam-surfactant injection, alkaline-surfactant polymer flooding, soil vapor extraction from soil overlaying fractured rock, electrical resistance heating and bioremediation.

To Discuss Possibilities Please Contact Us At

MK Tech Solutions, Inc. - Houston, Tx - Phone: 281 - 564 - 8851, ASKMKTS@MKTechSolutions.com