By Jim Bailey
Environmental remediation involves the cleanup of contaminated ground water and/or soils impacted by a variety of contaminates. The predominate contaminates over the years have been petroleum hydrocarbons from leaking underground storage tanks and surface spills, as well as solvents and other volatile organic compounds (VOCs) from industrial processes. Today, the most effective, practical, and common ways of remediation have generally been pumping the contaminated ground water from a recovery well(s) to an air stripper for treatment, product recovery pumping, soil vapor extraction, air sparging, and dual phase extraction.
In the early to mid 1980s, the typical approach to ground water remediation was simply pump and treat. Contaminated soil was either excavated and hauled off to a treatment facility, composted or thin spread on-site for natural/biodegradation, incinerated on-site, or not addressed. By 1990, many environmental consulting and engineering firms were utilizing vacuum blowers to improve hydraulic recovery in pumping wells, which in part lead way to soil vapor extraction.
Blowers were connected to a number of vapor extraction wells that were screened above the water table. The VOCs in the soil were then captured under vacuum.
Air sparging was added to assist in the capture of volatiles in the soil, and to provide in-situ aeration enhancing the naturally occurring microbes that breakdown hydrocarbons in ground water. Air sparge or injection points are wells that have a screened interval below the water table.
An air blower or compressor is connected to the air sparge wells providing enough pressure to overcome the static water level and line losses, and supply typically five to 10 SCFM per point. Air molecules rise to the surface of the static water level carrying dissolved VOCs. A vapor extraction blower then captures these VOCs above the water table under vacuum.
Dual phase extraction is the extraction of air and water from monitoring or recovery wells. High vacuum is applied to most commonly tighter formations with low hydraulic conductivity.
The air emissions have usually been discharged directly, treated through carbon vessels, or passed through a thermal or catalytic oxidizer for destruction. The fate of the emissions is most notably governed by the levels of fume concentrations and by air pollutant emissions permits.
There are certainly other more innovative ways of effective treatment, including various means of bio-remediation, chemical treatment and injection, UV oxidation, and the use of ozone. All sites are unique in their type, level, age, and extent of contamination, soil and ground water characteristics, as well as access and political concerns that effect the best suited overall remediation approach.
Jim Bailey is an Applications Specialist for EPG Companies Inc. heading the Remediation and Thermal Oxidizer Divisions.