Exploring the SVE Pilot Test: What it is, why it is a Benefit, and the Viable Alternatives
The United States Environmental Agency defines a pilot test as a "preliminary test or study of the program or evaluation activities to try out procedures and make the necessary changes or adjustments." In this installment, we'll explore exactly what this means, what a pilot test entails, why it can be beneficial to your overall remediation plan, and if there are any viable alternatives to performing a pilot test.
The Anatomy of a Pilot Test for a Basic SVE Remediation System
In essence, a pilot test is the stage of a remediation plan where preliminary information is gathered. It is a way to gain site specific information, and to evaluate the feasibility and effectiveness of a particular remediation plan or treatment system.
In the simplest terms, a pilot test for a soil vapor extraction (SVE) system includes an extraction well located within the contaminated area, one with similar construction located in an area of no documented contamination, and a number of corresponding observation wells. Other important parts of the pilot test configuration may include a portable blower or vacuum extractor, well sample ports, measuring instruments for the extraction wells, and sample collection equipment. Common measuring instruments include a photo-ionization (PID) meter, which measures the quantity of volatile compounds being released, a number of vacuum gauges or airflow meters to help determine the radius of influence for each extraction well, and temperature gauges to help determine the temperature of the soil vapor, which can affect the overall airflow rate. Sample equipment can include tedlar bags and portable air pumps for collecting influent or effluent samples, and disposable bailers for collecting water or product samples from observation wells.
The extraction wells are an integral part of a SVE remediation system pilot test. These wells are a way for contamination to be removed from the vadose zone through the creation of a negative pressure gradient. The contamination is "sucked" towards the extraction well because there is a lesser amount of pressure at the extraction well. The key in any remediation plan that utilizes vapor extraction as a removal technique is to determine the correct amount of change in the pressure gradient that is needed to be effective. A pilot test is a common way to determine such information.
Of course, if you only sample at the extraction wells, the picture you gain will be an incomplete one. While observations at the extraction wells will provide information of how the conditions are changing at the site of extraction, it might not extend much beyond that. That's where observation wells are so important. Observation wells, which are screened in similar fashion to their corresponding extraction wells will provide information such as ground-water fluctuation, vapor pressure gradients, and even changes in the migration of the contaminated plume. By taking regular samples and measurements, at both the observation and extraction wells, a scientist can gain a more complete and specific picture than either part could provide alone. Ideally the measurements taken should include the ground-water level as measured with a water level indicator, the thickness of any free phase product as measured with an interface probe, and the concentration of VOCs as determined by a photo-ionization meter. Samples taken should include influent and effluent equipment air samples, and any off-gases associated with the proposed treatment of the vapor extracted. These samples collected should be tested in a laboratory setting for analyses such as volatile organic compounds (VOC), and total petroleum hydrocarbons (TPH). The specific analysis needs will vary from state to state, so it's a good idea to contact the local regulatory authority for guidance if needed.
There is a third part to the pilot test and the resultant remediation system; that of the equipment being used. In one sense, a pilot test can be considered as a "trial run" of the equipment that you want to use in your remediation system. Whether you are considering using a classic SVE system, as is being discussed here, or a combination of a SVE system and bioremediation, making sure your system is running efficiently can save you hundreds if not thousands of dollars over the life of the remediation system.
Why Conduct a Pilot Test?
One of the most overlooked reasons to conduct a pilot test is that sometimes it is required by regulatory agencies. More and more states, such as Florida, are requiring that a pilot test of a particular remediation system be performed prior to approval for reimbursement. If you're not sure, be sure to check with your state environmental agencies; they'll be happy to provide you with the necessary information. The second reason is an easy one to recognize. A pilot test can provide you with the necessary information to conduct your remediation plan in the most efficient way for your specific conditions. By understanding how the system parameters such as the amount of applied pressure, and spacing of the extraction wells can be adjusted, for your situation, your remediation system can be run in the most cost effective way.
There Are Alternatives
Performing a pilot test for your remediation system is the ideal, both in long term remediation and economic sense. However, as every consultant knows, there are times when the client and the situation demands quicker action. In these situations, there are other options available. While they might not be as ultimately cost effective as running a few preliminary tests prior to installation, they have been known to provide acceptable results.
The first alternative to performing a pilot test is to simply install a temporary remediation system at the site and start the remediation process right away. Technology advances today have produce smaller, more versatile SVE systems, and many are offered on a rental basis. These smaller, mobile systems allow for changes to be made if necessary.
The second alternative to conducting a pilot test is to use generalized reference information about the site to estimate the site characteristics. If the lithology and basic extent of the contamination is known, then grain size analysis can be used to estimate the permeability of the soil, and eventually the air flow. This "back of the envelope" method is good for areas of relatively small amounts of contamination. The disadvantages of this method are that sometimes the perceived physical and chemical parameters are not the same site wide, and there is a marked difficulty evaluating layered geological conditions. In addition, if the remediation system involves air emissions, the estimates of air concentrations would not be available prior to implementation.
Whether you're just at the preliminary stages of your remediation planning, or if you've been brought in mid-stream, knowing the characteristics of the site is paramount for an effective solution. A pilot test is just one of the ways to gain information about the radius of influence, necessary system vacuum pressure, and the chemical nature of the off-gas emissions, so that your system can operate effectively. We would be more than happy to discuss the options available for you to meet your needs.