Both cities straddle the Fall Line. Urban areas associated with Washington, D.C. are located in the Potomac River Basin in both the Piedmont and the Coastal Plain. The urban area associated with Wilmington, Delaware is located in the Coastal Plain in the northern part of the Delmarva Peninsula. Both areas are experiencing rapid development and growth. The PODL includes several other smaller cities that are also undergoing urban growth and industrialization to varying degrees.
Drinking water is supplied from both surface water and ground water.
The distribution of water use closely follows population. Most of the use is in urban areas around Washington, D.C. with most withdrawals from the Potomac River. Ground water is the predominant source of supply in the Coastal Plain and the Great Valley Carbonate. Surface-water sources also supply drinking water to parts of the Coastal Plain adjacent to the Fall Line where distribution systems draw from reservoirs and rivers located in the Piedmont, and from the Shenandoah River in the Great Valley Carbonate. Similar to Cycle I, each group will be intensively studied for three years, followed by six years of low-intensity assessment.