Surface impoundments are relatively shallow ponds or lagoons used by industries and municipalities to store, treat and dispose of liquid wastes. As many as 180,000 surface impoundments exist in the United States. The standards that existed when many small sewage lagoons were first built in Pennsylvania have changed as we learned more about groundwater flow and contamination. Like landfills, new surface impoundments are usually required to have liners and monitoring wells for leak detection.