How deep should the monitoring wells be

The depth of gas wells is also based on a characterisation of geological and hydrogeological conditions at the site and on the perceived level of risk associated with grormd gas or vapours. The depth of wells should be sufficient to intercept any gas or vapour sources or migration pathways. The present authors have seen several examples where gas has not been encoimtered but where the wells have not been installed deep enough to intercept the source. Examples include  

The local authority determined tiiat (referring to CIRIA guidance), positive gas results encountered during a spike survey are generally 

Installing wells that have response zones in more than one source or pathway is bad practice and should be avoided as it usually makes it very difficult to interpret the gas monitoring results (it is virtually impossible to identify where the gas is coming from). 

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