Ursus has the expertise to evaluate a variety of treatment alternatives in a number of scenarios. Chemical oxidants and reductive dechlorination chemistries can be evaluated depending on the site geochemistry, contaminants of concern, and contaminant concentration. Data generated during an organic study is used to assist in the design for In Situ Chemical Oxidation (ISCO) remediation.
Organic studies are conducted on soil and groundwater from the site. The materials are treated in a manner to simulate the proposed remediation approach. Varying approaches may include chemical injection, physical mixing, and batch treatment.
Ursus can conduct the studies using a variety of methods that best meet the remediation objectives. A description of common methods used is shown below.
Oxidant Demand Testing
Oxidant demand tests are useful for initial screening of oxidant treatment chemistries to determine the amount of chemical needed to remediate the test material. When a chemical oxidant is added to a contaminated soil, for example, the oxidant will react with both the contaminant and any other soil component that can be readily oxidized by the chemistry. These other soil components act as an oxidant sink and the addition of chemical oxidant is required to overcome the demand of both the contaminant and other soil components (the other soil components include reduced metals and naturally occurring organic matter that can be readily oxidized). The study is generally conducted over a 48 to 96 hours period but longer times and more frequent analysis can be conducted.
Oxidant demand tests can be referred to by various different names including Natural Oxidant Demand (NOD), Soil Oxidant Demand (SOD), and Total Oxidant Demand (TOD).
Batch testing is a simple means of evaluating the effectiveness of the treatment chemistry when mixed with the test sample. Varying levels of measurement can be performed with a batch test including, contaminant mineralization, kinetic data on contaminant destruction, residual oxidant level and soil attenuation data.
Column testing involves either pumping or gravity feeding a treatment chemical through a column of soil. Effluent from the column can be tested to determine treatment effectiveness of dissolved constituents as well as soil testing directly from the column to measure adsorbed contaminant levels. This procedure is useful in engineering chemical oxidant reactive barrier walls.
The rate of contaminant destruction when reacted with the treatment chemistry can be useful in designing the remediation approach. Ursus can analyze the test sample at varying time periods to assess the rate of contaminant destruction and measure the residual treatment chemistry. Based on this data, the treatment can be modified to meet the study objectives.
Using chemical oxidation can significantly change the geochemistry of the soil and groundwater treated. As a result, the system can become unstable resulting in the mobilization of various soil components. For example, oxidation of naturally occurring chromium (III) to chromium (VI) can occur after a chemical oxidant is added, resulting in an increase of dissolved chromium. Another example includes reducing the soil and groundwater pH to a range of 3 to 5 for optimum Fentonís Reagent conditions. The low pH can mobilize naturally occurring metals and increase dissolved levels. Ursus can test the samples to determine the extent of mobilization for the chemical oxidant used as well as measure the ability of the soil to attenuate the mobilized metals after the system has reached equilibrium.
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