WorldWide Drilling Resource

Can Chemical Oxidation Help with Soil and Well Contaminations? Adapted from Information by the United States Environmental Protection Agency Chemicals or mixtures of chemicals which are heavier than water and are only slightly soluble in water are called dense nonaqueous phase liquids (DNAPLs). When these chemicals are released into the environment in suffi- cient quantity, they will move through soils and groundwater until they encounter a resistant layer, which will impede further vertical movement and allow the liquid to pool. These chemicals are the most common form of contamination or spill encountered, and the resulting pools become slowly dissolving sources of ground- water and soil vapor contamination. In situ chemical oxidation (ISCO) is an aggressive remediation technology which has been applied both to DNAPL source zones and to the dissolved-phase chemicals coming from the source zones. Chemical oxidation typically involves reduction/oxidation (redox) reactions which chemically convert hazardous contaminants to nonhazardous or less toxic compounds. These new compounds are more stable, and either less mobile or not mobile at all. There are several oxidants capable of degrading contaminants. Commonly used oxi- dants include potassium or sodium permanganate, Fenton's catalyzed hydrogen peroxide, hydrogen peroxide, ozone, and sodium persulfate. Each oxidant has advantages and limita- tions. While applicable to soil contamination and some source zone contamination, they have been applied primarily toward the remediation of groundwater. The selection of an oxidant for site cleanup involves the following key concepts: • Is the oxidant capable of degrading the contaminant of concern? Is a catalyst or other addi- tive required to increase effectiveness? • What is the soil oxidant demand? Soil oxidant demand is a measure of how the naturally occurring materials in soil affect the performance of some of the oxidants. For nonselective oxidants, more oxidant will be required so the cost of cleanup will be increased. • What is the naturally occurring pH of the soil/groundwater system? Some oxidants require an acidic environment to work. If the soil is basic, an acid needs to be applied in addition to the oxidant. • How will the decomposition rate of the oxidant affect application strategies? Some unreacted oxidants may remain in the subsurface for weeks to months, while others naturally decompose within hours of injection. The type of delivery system used for the oxidants depends upon the depth of the contaminants, the physical state of the oxidant (gas, liquid, solid), and its decomposition rate. Backhoes, trenchers, and augers have been used to work liquid and solid oxidants into contaminated soil and sludge. Liquids can be delivered either by gravity through wells and trenches, or by injection. Pressurized injection of liquids or gases, either through the screen of a well or the probe of a direct-push rig, will force the oxidant into the formation. The direct- push rig offers a cost-effective way of deliv- ering the oxidant. If needed, the hole can be completed as a small-diameter well for later injections. Potassium permanganate and other solid-phase chemical oxidants have also been added by hydraulic or pneumatic fracturing. Oxidation technologies have the potential for achieving significant removal of subsurface contaminants; however, the results of field and laboratory work indicate complete removal of contami- nants may not be achieved with these technologies even under optimal condi- tions. Innovators are combining the benefits of using ISCO with compatible technologies, such as solvent flushing and bioremediation, to maximize reme- diation potential. Drilling sample of a dense nonaqueous phase liquid, courtesy of U.S. Geological Survey. Hi Ronnie & Michele, . . . As I have told Jan and Ed numer- ous times, I really respect how WWDR operates - great publication, great people, and you don’t inundate us with e-mails like some other organizations. Thanks! Jeff Hoffer Sales Manager Allegheny Instruments, Inc. Vermont / Virginia WTR 15 WorldWide Drilling Resource ® JANUARY 2019