What is contaminant dispersion?
Contaminant movement is also controlled by the process of mechanical dispersion. Dispersive mixing causes some contaminant molecules to move ahead of (longitudinal to) the average advective velocity along the hydraulic gradient and some molecules to move laterally (tranverse) to the hydraulic gradient.
What is dispersion in groundwater?
Advection refers to the bulk movement of solutes carried by flowing groundwater. Dispersion refers to the spreading of the contaminant plume from highly concentrated areas to less concentrated areas.
What are ways to remediate contaminated groundwater?
Techniques include biological, chemical, and physical treatment technologies. The traditional approach is “pump and treat” which is physically pumping out the contaminated groundwater using a vacuum pump and then purifying the groundwater using materials that absorb the contaminants.
What factors influence the movement of a contaminant through the groundwater system?
Leaching is a concern because of the potential for a chemical to move through the soil and contaminate the groundwater. Many factors affect whether or not a chemical leaches in soil, including solubility of the chemical, biodegradation, hydrolysis, dissociation, sorption, volatility, rainfall, and evaporation.
How far can contaminated groundwater travel?
The average documented distance traveled for GRO and DRO were 295 and 140 feet, respectively. The average MTBE travel distance was 300 feet. The maximum distance documented between a discharge source and a contaminated well was 1670 feet.
What is contaminant transport?
The most important mechanisms of transport of contaminants through soil are volatilization, leaching, and erosion or suspension of soil particles. Mechanisms that control transport may be the same that control availability to organisms, and thus contaminant fate.
What is the velocity of groundwater?
A velocity of 1 foot per day or greater is a high rate of movement for ground water, and ground-water velocities can be as low as 1 foot per year or 1 foot per decade. In contrast, velocities of streamflow generally are measured in feet per second. A velocity of 1 foot per second equals about 16 miles per day.
What are remediation techniques?
Remediation techniques play a key role in fully cleaning up the contaminants in soils and groundwater. Techniques frequently used are: containment, pump-and-treat, extraction, stabilization/solidification, soil washing, air stripping, precipitation, vitrification, thermal desorption, and bioremediation.
What are three examples of groundwater remediation techniques?
Some of the biological treatment techniques include bioaugmentation, bioventing, biosparging, bioslurping, and phytoremediation.
What happens when groundwater is contaminated?
Contamination of ground water can result in poor drinking water quality, loss of water supply, degraded surface water systems, high cleanup costs, high costs for alternative water supplies, and/or potential health problems.
How is groundwater naturally contaminated?
Industrial discharges, urban activities, agriculture, groundwater pumpage, and disposal of waste all can affect groundwater quality. Contaminants can be human-induced, as from leaking fuel tanks or toxic chemical spills.
Which is the best method for groundwater remediation?
Pump-and-treat (P) is one of the most common methods for remediation of groundwater contami- nated by hazardous wastes. However, this method suffers from serious disadvantages, due a series of subsurface processes.
How is the diffusion of contaminants related to dispersivity?
The amount of spreading is related to the dispersivity of the rock or sediment, the advective velocity of groundwater flow, and the molecular diffusion of the contaminant in the water in the pore space. The amount of diffusion is a function of the concentration gradient and the porosity of the materials.
Why is dispersed low level contamination a challenge?
Dispersed low level contamination poses a particular challenge to those charged with its remediation. Many techniques are not efficient below certain concentration thresholds or entail more severe impacts on certain environmental compartments than the contamination itself.
What is the retardation rate of contaminants in aquifers?
This is especially true in shallow aquifers of glacial-fluvial origin as at Woburn. Retardation rates of contaminants are highly variable and typically range from 0 to 10 times slower than the advective groundwater velocity. Expensive field tests are needed to pin down site-specific values.