Soil Gas Survey of Porter Ranch Community Following Aliso Canyon Storage Facility Gas Leak

HUB 302-#107

Methane (a component of natural gas) is an important greenhouse gas that has recently garnered some interest as increased oil/gas production has led to documented events of leaking methane to shallow aquifers and the atmosphere. Yet, there is still a lack of research that attempts to understand the migration of gasses in the subsurface to shallow aquifers and soils. This project attempts to understand the effect, if any, of the natural gas leak at the Aliso Canyon Storage Facility on soil gas concentrations by conducting a soil gas survey of the Porter Ranch community, south of the facility. Eight soil gas survey wells were installed in public areas for weekly analyses of relative gas concentrations by a photoionization detector (PID) as a function of time (between May and October 2016). Soil gas data was compared with available natural gas sampling of air collected by the South Coast Air Quality Management District (AQMD) in parallel. Results indicate that soil gasses were highest in the eastern portion of the study area at 6.3 parts per million (ppm) in May 2016, possibly consistent with concurrent AQMD data. Furthermore, soil gas concentrations decreased in all sampling locations consistently to values that averaged between 0.4 and 0.7 ppm. The decreasing trend may be consistent with the migration of natural gas from depth following the capping of the leak at the storage facility (as of February 2016). Sampling will continue as the facility is brought back online in the near future. More work needs to be done to understand what effects if any, subsurface migration of gasses may have.