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on the other hand, may yield as much as 2,000 gallons of water per minute because vast amounts of water I ie between the sand and grains and pebbles. Crystal I ine rocks, like granite, appear to have no avai lable water when an individual rock is examined. Yet, moderate amounts of water can be contained in fractures Interlacing an extensive rock mass. decause of great hydrologic variation in rocks and soi Is, and the d j f ferences in the rates at wh i ch aqu i fers recharge, there is a great range in the amount of water ava i I ab I e from location to location, season to season, and year to year. Ground water aquifers may provide a sustained yield of less than a gallon to several thousand gallons of water per minute. Aggravating Circumstances &Consequences I f water is pumped out of an aqu i fer faster than It is recharged, the water I eve I in the aqu i fer--the ground water table--is said to drop. Seasonal fluctuations from irrigation or changes in recharge are quite common. If the excess i ve wi thdrawa I :::>f water cant i nues over an extended period of time and the natural recharge does not offset the total amount of water extracted, it is said the ground water is being l'mined.'1 There Is ev i dance that once vast amounts of water are withdrawn from deep aquifers at rates exceeding recharge, the aquifers never again can be recharged with the original volume of water. Consol idation and subsidence processes can fi II in the space once occupied by water. Efforts to artificially recharge underground aquifers have met with I i m I ted success. Human activities greatly affect the avai labi I ity of ground water in some areas. Widespread and excessive pumping of underground waters can lower the ground water table under many square miles. This is the situation in some irrigated farming areas in eastern Colorado. In many areas wells have had to be deepened to obtain sufficient water as a ground water table drops. The lower the ground water table, the more it costs to drill a well and to pump the water to the surface. It eventually may cost more to pump water than the water is worth, especially for agricultural and industrial app 1 i cat ions us; ng large vo I urnes of water. Paving large areas, altering or removing vegetation, grading, sand and gravel mining, diverting storm runoff away from establ ished channels and other manipulation of the land and surface hydrology can change recharge rates in the immediate vicinity, thus altering ground water levels. Mitigation An adequate understanding of the ground water system is the best measure of protection from property damage and devaluation from a reduction or loss of water supply. 3y using such knowledge, construction and property development can be accomplished without encountering unexpected ground water situations. Hydrogeologic investigations can reveal notonlysp'ecificcharacteristics, butths interrelationships between and among human endeavors and natura I factors. Know I edge of the amount of water 'II i thdrawn per year, the recharge rates and other facts may requ i re the amount af water withdrawn annually from wells to be restricted and tne number of wells limited to keep the wells from drying up. Restrictions on land development may be needed to preserve recharge from natural sources and thus maintain the ground water supply and protect land investments. Land Use In semi-arid Colorado ground water considerations are increasingly considered in maKing land use decisions. Norma 11 y I and uses are not restr i cted, a I though they may entail construction modifications to protect or enhance ground water supp I y and re I ated property va lues. Too much or too II tt I e ground water, year around or seasona 11 y, can be compensated for ordinari Iy through geologic investigation and responsive planning. Developments which rely on ground water should be permitted only after it is established that sufficient water exists and that the necessary amounts can be withdrawn indefinitely without jeopardizing the supply. 21