Surface monitoring is used to check the integrity of caps on waste and check on borehole monitoring. It may give preliminary indications of the migration of gas off-site. The typical regulatory limit of methane is 500 parts per million (ppm) by volume (in California, AB 32 may push this limit down to 200 ppm). In the UK the limit for a final landfill cap is 1*10−3 milligrams per square metre per second, and for a temporary cap it is 1*10−1 mg/m2/s (as measured using the Environment Agency's " Guidance on Monitoring landfill gas surface emissions " LFTGN 07, EA 2004). Surface monitoring can be broken down into Instantaneous and Integrated. Instantaneous monitoring consists of walking over the surface of the landfill, while carrying a flame ionization detector (FID). Integrated consists of walking over the surface of the landfill, while pumping a sample into a bag. The sample is then read with a FID or sent to a lab for full analysis. Integrated regulatory limits tend to be 50 ppm or less.