Beneath the plain lies the Biscayne Aquifer, a natural underground source of fresh water that extends from southern Palm Beach County to Florida Bay, with its highest point peaking around the cities of Miami Springs and Hialeah. Most of the Miami metropolitan area obtains its drinking water from this aquifer. As a result of the aquifer, it is not possible to dig more than 15 to 20 ft (5 to 6 m) beneath the city without hitting water, which impedes underground construction, though some underground parking garages exist. For this reason, the mass transit systems in and around Miami are elevated or at-grade.[citation needed] COUNT 4
QSN1 Along with Miami Springs, where is the highest point of the Biscayne Aquifer? ANS1 Hialeah QSN2 The Biscayne Aquifer stretches from Palm Beach County to where? ANS2 Florida Bay QSN3 After digging how many meters is one sure to reach running water in Miami? ANS3 5 to 6 QSN4 What is limited by Miami's high water table? ANS4 underground construction