DON'T TAKE WATER SUPPLY FOR GRANTED

                         Roanoke Times
                 Copyright (c) 1995, Landmark Communications, Inc.

DATE: THURSDAY, February 6, 1992                   TAG: 9202050157
SECTION: CURRENT                    PAGE: NRV-11   EDITION: NEW RIVER VALLEY 
SOURCE: JOE HUNNINGS
DATELINE:                                 LENGTH: Medium
DON'T TAKE WATER SUPPLY FOR GRANTED
Almost one-third of Montgomery County's citizens depend on ground water as their primary source of drinking water. Yet, because it is a resource hidden from sight, it is often taken for granted.
However, ground water is too critical and vulnerable a resource to ignore. All citizens must be aware of how our activities affect the quality and quantity of ground water resource.
Everyone has heard of ground water, but few people are familiar with its properties. For example, most people would be surprised to learn that there is more fresh water underground than in lakes, rivers and streams.
Most of the county's precipitation, an average of 40 inches per year, seeps into the ground. This water flows downward to a zone where all pores or open spaces are filled with cold water called the saturation zone.
The upper level of this zone is called the water table. Water in the saturated zone is known as ground water. If this saturated zone will yield water in usable quantities to wells or springs it is known as an aquifer.
A common misconception about ground water is that it occurs in the form of underground lakes and rivers. This does not occur. Ground water collects in the open spaces between unconsolidated or loose particles of rock, gravel, sand or soil; and in the pores, cracks and solution channels of consolidated or solid rock masses.
The coastal plain of Virginia is made up mostly of unconsolidated deposits. Montgomery County is underlain by consolidated rocks. In fact, the county has two regions composed of different types of rocks. The rock type can have an important impact on the quality and quantity of ground water.
The largest part of the county is valleys and ridges and the dominant rocks are limestone shale and sandstone. Limestone tends to predominate in the valleys and sandstone in the ridges. Where limestone dominates, ground water yields are high. Those areas underlain by sandstone and shale often yield only enough water for domestic supplies.
Natural ground-water quality is affected by the chemical composition of the rock formations. Limestone, for example, increases the hardness of the water.
The ground-water pollution potential is very high in the valley and ridge portion of the county. Streams and surface runoff entering sinkholes and underground channels contribute to the recharge of the aquifers, providing direct conduits for contaminants.
The southern part of the county, south of Paris Mountain to the Floyd County border, is in the Blue Ridge Province. It is underlain by igneous and metamorphic rocks such as granite, gneiss and schist.
Ground-water use is primarily limited to domestic needs. Springs are common and are used as private water supplies. Wells in this area usually yield less than 20 gallons a minute.
Ground water in the Blue Ridge Province is not highly mineralized because, unlike limestone, the rocks are relatively insoluble. However, the iron content of the water can be high in some locations.
Next week's Hoein' and Growin' will look at threats to our ground-water quality and how you can do your part for its protection.
Another opportunity to learn more about our ground-water resource would be to attend two programs sponsored by the Museum of Natural History on Feb. 13 and 19. Call the museum for more details.

Joe Hunnings is the Virginia Cooperative Extension Service agent for agriculture in Christiansburg. If you have questions call the Montgomery County extension office at 382-5790.

by Bhavesh Jinadra by CNB