Configuration of the Base of the Gray Limestone Aquifer in Dade County, Fl, USGS WRIR 90-4108, figure 15

Contours of the altitude below sea level of the base of the highly permeable gray limestone aquifer in the Tamiami Formation are shown in this map. The aquifer, as mapped, includes all intervals of the gray limestone that are at least 10 ft. thick and have an estimated hydraulic conductivity of at least 100ft/d. The contour interval is 10 feet.

Southeastern Florida is underlain by geologic units of varying permeability from land surface to depths between 150 and 400 ft. These units form an unconfined aquifer system that is the source of most of the potable water used in the area. This body of geologic units is called the surficial aquifer system. In parts of Dade, Broward, and Palm Beach Counties, a highly permeable part of that aquifer system has been named the Biscayne aquifer (Parker, 1951; Parker and others, 1955). Adjacent to or underlying the Biscayne aquifer are less-permeable but potentially important water-bearing units that also are part of the surficial aquifer system. Most previous hydrogeologic investigations in southeastern Florida concentrated on the populated coastal area. Drilling and monitoring activities were commonly restricted to zones used for water supply or to overlying zones. Hence, information on the characteristics of the western or deeper parts of the Biscayne aquifer and of sediments below the Biscayne aquifer in the surficial aquifer system was insufficient for present needs. Continuing increases in the demand for water from the surficial aquifer system in the highly populated coastal area of southeastern Florida and attendant concerns for the protection and management of the water supply have resulted in a study by the U.S. Geological Survey (USGS), in cooperation with the South Florida Water Management District, to define the extent of the surficial aquifer system and its regional hydrogeologic characteristics. The overall objectives of the regional study are to determine the geologic framework of the surficial aquifer system, the areal and vertical water-quality distribution, factors that affect water quality, the hydraulic characteristics of the components of the surficial aquifer system, and to describe ground-water flow in the aquifer system.

本地图展示了塔米亚米组（Tamiami Formation）内高渗透性灰色石灰岩含水层底板的海平面以下海拔等值线。本次制图所界定的含水层，涵盖所有厚度不小于10英尺、估算渗透系数（hydraulic conductivity）不低于100英尺/天的灰色石灰岩段。该图的等高距为10英尺。

佛罗里达东南部地区自地表至150~400英尺深度范围内，分布着渗透性各异的地质单元。这些地质单元构成了潜水含水层系统（unconfined aquifer system），是该区域绝大多数饮用水的补给来源。这套地质单元被称为表层含水层系统（surficial aquifer system）。在戴德县（Dade County）、布劳沃德县（Broward County）与棕榈滩县（Palm Beach County）的部分区域，该含水层系统中的一处高渗透性区段被命名为比斯坎含水层（Biscayne aquifer，Parker, 1951；Parker等，1955）。紧邻比斯坎含水层或位于其下方的，是渗透性较低但具备重要供水潜力的含水单元（water-bearing units），这些单元同样隶属于表层含水层系统。此前佛罗里达东南部的多数水文地质调查均聚焦于人口密集的沿海区域，钻探与监测工作通常仅局限于供水用含水层区段或其上覆地层。因此，关于比斯坎含水层西部或深部区段、以及表层含水层系统中比斯坎含水层下方沉积物的特征信息，已无法满足当前的实际需求。随着佛罗里达东南部人口密集沿海区域对表层含水层系统供水需求的持续增长，以及对饮用水资源保护与管理的日益重视，美国地质调查局（U.S. Geological Survey, USGS）与南佛罗里达水资源管理区合作开展了本项研究，以明确表层含水层系统的分布范围及其区域水文地质特征。本次区域研究的总体目标为：查明表层含水层系统的地质格架、平面与垂向水质分布规律、影响水质的各类因素、表层含水层系统各组成部分的渗透系数特征，并阐明该含水层系统内的地下水流动规律。