Groundwater Treatment
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Fresh water infiltrates into the ground from precipitation and melting ice. Infiltrated water that moves through soil and rock prior to meeting the groundwater table is considered unsaturated flow, evident in varying degrees of soil moisture. The groundwater table is defined by the first depth at which all soil and rock void spaces are completely filled with water, at atmospheric pressure. Water below the groundwater table behaves as saturated flow, where the soil and rock voids are completely filled with water, and pressure increases with greater depth. Groundwater will move from areas of greater to lesser hydraulic pressure along flow nets which can be predicted by understanding the types of soils present, and determining the elevation of the groundwater table at specific site locations. Flow nets will often transition groundwater back to the earth’s surface by connecting into lakes, rivers and springs. Groundwater is the source of well water for millions of people, and represents about one fourth of the world’s total freshwater supply.
Topic Summary
The first steps involved in any groundwater remediation project are to assess the nature and extent of the contamination present through a combination of field work and research. A review of a site’s known history will provide an initial understanding of the type of contamination present. The items that need to be specifically determined are the type (chemical composition), phase (liquid, solid, and/or vapor), and volume of contaminates present. Additionally important is an assessment of where contaminates have been introduced relative to the soil surface and groundwater table, where they have migrated, and the types of soils present. This will require the installation of sampling wells, and extracting soil samples at various depths throughout the site. Laboratory analysis of soil and groundwater samples provides initial data from which remediation decisions can then be made. Groundwater remediation projects often involve government entities such as the EPA that have jurisdiction over clean-up standards. Prior to beginning a remediation project, target clean-up standards are generally understood and aide in remedial technology selection.
Groundwater treatment projects are often conducted in concert with soil remediation projects, since cross-contamination between the two is a likely occurrence. Tracts of contaminated soils may be removed or treated during groundwater remediation efforts. Groundwater remediation methods include general categories of mechanical, chemical, and biological treatment techniques, or any combination of these. A routine groundwater treatment method is called “pump and treat”. Groundwater is pumped to the surface where it can be processed thorough an array of charcoal filters to strip out contaminates, or another treatment technology applied at the surface, depending on the nature of contamination present. After remediation above ground, the groundwater is discharged at the surface, or recharged into the ground. Bioremediation is a routine approach, where living microbes are introduced (or existing microbes’ growth is stimulated) that will break down contamination as part of the microbes’ life-cycle functions. Bioremediation is a popular approach to address hydrocarbon contamination. The introduction of hydrogen peroxide into the groundwater is an example of a chemical remedial technique. Hydrogen peroxide will react with specific contaminates, resulting in benign chemical by-products.
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