Introduction to Air and Water Quality issues.
Hazardous Waste contains chemicals that may harm human health or the environment. Dumping these wastes into a MSW landfill or a vacant lot results in the immediate contamination of the dump site. Often after the initial release, the chemicals flow into the surface water, leach into the groundwater, cling to airborne dust particles, or volatilize into the air. RCRA provides a system of "cradle to grave" control of hazardous waste with the intent of preventing these discharges, but its authority is limited to "solid" wastes, including liquid in tanks and gasses in cylinders.
Many industries take water from lakes and rivers, use the water in some sort of process, then return the water to the water body. Likewise industrial stacks, flares, and vents discharge chemicals to the air. RCRA does not deal with industrial processes that release chemicals into the water or air as part of their normal industrial process. These are regulated, just not by RCRA.
Here is a brief slide show about the distinctions.