Typically, site investigation is carried out by using handheld or transportable field instruments coupled with offsite lab analyses. When using field instruments, the data generated represents a snapshot in time and space. Often, as with a PID or FID, data is presented as a total of contaminates present at that time and place. More sophisticated field equipment such as GC/MS can provide speciation, but still suffer from poor spatial and temporal resolution.
As an alternative, investigators can choose methods such as Summa canisters that sample for a fixed period, say 24 hours, followed by lab analysis. The data generated provides speciation but the concentrations represent an average for the sampling period.
Investigators are aware that environmental conditions such as pressure, temperature, water level and air movement substantially affect concentrations on a range of timescales, therefore uncertainty will always exist when using methods that lack temporal resolution.
The presentation describes instrumentation that provides real time continuous data both down hole and ambient for multiple parameters such as VOCs, methane, oxygen, carbon dioxide, hydrogen sulfide and carbon monoxide together with atmospheric and borehole pressure. Data is presented from field work carried out by, among other, the Maine DEP, for applications such as vapor intrusion, recovery well monitoring and landfill gas migration.
A comparison between spot sampling and continuous monitoring raises questions about the value of limited spot sampling.
Smith, Thomas H.; Hewiit, Geoff; Selleck, John M.; and Morris, Peter
"New Continuous Monitoring Technologies for Vapor Intrusion,,"
Proceedings of the Annual International Conference on Soils, Sediments, Water and Energy:
Vol. 17, Article 14.
Available at: http://scholarworks.umass.edu/soilsproceedings/vol17/iss1/14