“Toe” of a Slope Definition The “toe” of a slope is essentially the bottom, or baseline section, of the soil mass comprising the slope. It is also defined as the outermost margin of displaced material during a landslide. The toe of a slope is farthest away from the head scarp.

Confined Aquifer Confined Aquifer: In the hydrogeology branch of geology, a confined aquifer is an aquifer that is overlain (and underlain) by a layer of low permeability, such as clay, shale, or silty clay. In fact, the two confining layers contain the storage and flow of groundwater, such that the aquifer maintains hydraulic pressure (or…

Natural Gas Natural Gas: In geology, natural gas means combustible hydrocarbon gas that forms by natural geological or biological processes. To illustrate, natural gas that forms by geological processes is the thermal decomposition of buried organic materials. Whereas natural gas that forms via biological processes entail the microbial decomposition of buried organic material. Natural gas…

Maximum Soil Screening Levels (MSLs) Maximum Soil Screening Levels (MSLs): MSLs are a list of risk-based hydrocarbon concentrations for soil pollution evaluations, that is developed by the California Regional Water Quality Control Board. These screening levels are based on the Leaking Underground Fuel Tanks (LUFT) Manual, for cleaning up soil contamination from leaking USTs. However, MSLs…

Gravel Blanket in Methane Mitigation A gravel blanket is a 2-inch or 4-inch thick layer of gravel, sand, or approved material that transmits methane soil gas to the horizontal sub-slab perforated pipes and verticle vent riser of a passive methane mitigation system.