Advanced surveying techniques probe contaminated petrol station sites

Whether a petrol forecourt is in full operation or it has been run down over the years and is pinpointed for re-development, the contamination of land is an important environmental issue. Disused petrol forecourts offer excellent locations for redevelopment at good prices and remediation of the land should be counted as a net benefit to the environment, says IETG which reports on how its Land Sector deals with such cases.

Petrol forecourt contamination can happen for a number of reasons, fractured fuel lines, failed tanks, poorly maintained drainage systems and incorrect storage and disposal of chemicals are just a few of them. But, overall, there is no need for the sites to carry any additional risk or liability, if the correct surveys are carried out on a regular basis.

The majority of service stations are well maintained and are inspected on a regular basis. However, there are service stations that have cut corners or have simply become run down before final closure. Leakages can also go un-noticed for many years causing a build up of hydrocarbons and a legacy of groundwater pollution problems.

Investigation needed
The requirements of the contaminated land regime, environmental assessment, IPPC and ISO14001 require landowners and users to be more pro-active than ever before about investigating the condition of land being acquired or developed. Working with both the petrochemical companies and the land developers, IETG has developed an approach to sustainable urban development that is gaining wide spread acceptance.

Contaminated land investigation typically consists of discrete stages and petrol forecourt investigation is no different. There is the desk study, using historical information to establish past uses of the site and the surroundings to give a general feel for the likelihood of contaminative risk. In addition, information from statutory bodies and local authorities about the site and surrounding areas is reviewed, including data regarding the location of landfill sites, water quality classifications and site investigation reports. A review of the geology and hydrology of the site is usually taken as part of a geotechnical investigation, and this information is used as a means of identifying the potential residence and migration of contamination to and from the site.

The majority of IETG’s surveyors are appointed under the “Forecourt Passport System”, a voluntary system whereby operatives undergo a two-day course to ensure they understand how to recognise and deal with safe working practices, H&S issues and emergency situations, when working within a petrol forecourt, oil terminal or refinery environment.

Site detection equipment
When carrying out the topographic and geotechnic site investigations on forecourts, modern technology is used, such as radio detection units and ground probing radar, which between them enables not just the location of all services beneath the ground, but also enables sub-surface structures, such as tanks and foundations to be identified.

Once the services have been identified, the ground can be penetrated. IETG uses several techniques for this stage of the surveying from soil vapour samples, which identify hot-spots where gas readings are high, to “windowless sampling”, which gives the engineer a lined geological sample one metre long from a depth up to ten metres, that can be sent to the laboratory for analysis.

The way the data is collated and reported can be flexible depending on the needs of the client. A remotely captured measured site drawing can be produced through using laptop computers, enabling all data to be collated straight into electrical format at site level. But if the client requires further information and database interrogation, a GIS (graphical information system) allows the project manager to look at the data collected using a map-based model.

IETG has put together an integrated service offering answers to the majority of questions raised on petrol forecourt contamination. The “useability”of the services, which incorporates utility location, GPR, SVS, sampling, air emissions testing, data collection and management, enables the company to bring the whole package to the table, allowing the engineer to decide on how much he requires.


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