WATER RESOURCES OF ORANGE COUNTY 23
The irregularities in the surface of the Eocene limestone may have been caused by deep erosion, but the contours on the top of the Avon Park Limestone strongly suggest a fault in the St. Johns River valley. Movement along this fault probably started in post-Eocene time and continued into Miocene time.
HYDROLOGY
CHEMICAL QUALITY OF WATER
All waters except distilled water contain dissolved materials in varying amounts. The type and amount of dissolved materials is influenced by many factors such as source, movement, geology, topography, climate, biological action, and cultural changes.
Rain falling through the atmosphere picks up small quantities of dust particles, atmospheric gases, and windblown salts. In areas near the ocean, the amount of salts picked up by rain may be appreciable especially if it is blown inland from the ocean. In industrialized areas the atmosphere generally contains exhaust gases and particles that are readily picked up by rain. The type and amount varies with the industry. Rain may also pick up radioactive fallout from nuclear explosions. To date, however, the amount of radioactive materials in water has remained far below tolerable limits.
When rain reaches the earth, it begins to dissolve or pick up in suspension varying amounts of the materials contacted. The carbon dioxide dissolved from the atmosphere and from decaying organic matter- on the earth's surface react with the water to form a weak carbonic acid. Carbonic acid greatly increases the ability of water to dissolve inorganic materials especially limestone such as underlies Orange County.
Surface water moves more rapidly than ground water, consequently, its time of contact with soils and rocks is shorter. This is one reason for lower mineralization in surface water than in ground water. Surface water is usually higher in color than ground water because surface water dissolves -living and decaying organic materials that it contacts. Decaying organic matter consumes dissolved oxygen from the water and releases. carbon dioxide.
When water percolates into the ground, the rate of movement is greatly reduced. When water percolates very far through soils