The environmental fate and transport of an organic compound in the subsurface environment is controlled by the compound's physical and chemical properties and the physical, chemical, and biological nature of the subsurface media through which the compound is migrating. Several processes are known to cause a reduction in the concentration and/or mass of a contaminant dissolved in groundwater. To see a Table summarizing these processes click here. Those processes that result only in the reduction of a contaminant's concentration, but not of the total contaminant mass in the system, are termed nondestructive. Those processes that result in the degradation of contaminants are referred to as destructive. Nondestructive processes include advection, hydrodynamic dispersion (mechanical dispersion and diffusion), sorption, dilution, and volatilization. Destructive processes include biodegradation and abiotic degradation mechanisms. Biodegradation may be the dominant destructive attenuation mechanism acting on a contaminant, depending upon the type of contaminant and the availability of electron donors or carbon sources. Abiotic degradation processes (e.g., hydrolysis) are also known to degrade chlorinated solvents; where biodegradation is not occurring, these may be the only destructive processes operating. However, the rates of abiotic processes generally are slow relative to rates of biodegradation.