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Quality Characteristics There is a tremendous range of ground water qua Ii ty because of the chern i Cd I character i st i cs of recharge water and the geologic formations through which ground water travels. Some ground water aquifers yield water nearly as pure as disti lied wat'3r. Others may be sa 1 tier than seawater and st i I I others may be natura II y rad i aaet i ve or character i zed by some particular chemical constituent or combination of them. DifferencGS In ground water qual ity are often predictable from geologic and geochemical knowledge. Aggravating Circumstances &Consequences In Colorado the most common natural water qual ity problems are hardness and salinity because of minerals dissolved In the wat.ar. rlard water can be softened with chern I ca I treatment. The second most prevalent situation, and an Increasingly serious one as the state's limited water suppl ies are called upon to meet the demands of growth, is the contamination of good ground water with sewage, Industrial and agricultural chemicals and other wastes. Malfunctioning sewage disposal systems, seepage fro~ dumps and landfi 115, Improper waste disposal methods, mineral exploration and production are jeopardizing drinkabls water supp lies and i ncreas i n9 the cost of treat i n9 them before they can be used. Depending upon the type and volume of contam i nants, rehab i II tat I on of a po II uted ground wat3r supply may take several years or an undetermined amount of tlme--if it can be achieved at all. Mitigation A thorough understanding of the ground relationship to human activities Is water system and its the first step in protecting water qual ity, mini:nizlng treatment costs and providing people with safe water for drinking and growing food. Proper construct i on, operat i on and ma i ntenance of sewage disposal systems, neutral Izingor isolating harmful chemicals prior to disposal and revised manufacturing processes are basic protective measures. Land Use Whi Ie land uses which contaminate ground water wi II always exist, hydrogeologic investigations are fundamental to managing both 13nd and water and ensuring their value. Case History In the 1940's and 50's, the U.S. Rocky Mountain Arsenal in western Adams County deposited a complex mixture of chemical wastes from the manufacture of pesticides, herbicides, and some chemical warfare agents into unl ined holding ponds. It also injected wastes into subsurface zones through a deep disposal well. i""ore than 30 square mi les of a shallow fresh water aquifer were contaminated by toxic substances (aldrin and dieldrin) in the vicinity of the ponds. Losses from this disposal of toxic wastes over a permeable ground water zone exceeded $2,165,000, including payments to ranchers and farmers for well contamination and crop losses. Adequate geological investigations could have anticipated the prob I em and Ii n i ng of the d Isposa I ponds cou I d have prevented seepage contamination. wastes a 150 were injected into the subsurface zones through a deep d i sposa I we II. Mil d earthquakes recorded in the vicinity of the well were attributed to deep well InJections. The earth tremors were not experienced prior to injection and gradually ceased after injection disposal was terminated. In June, 1978, a U.S. Senate subcommittee approved $6.5 mi II ion to continue cleanup Nark at the arsenal. 23