Pesticides are used to destroy pests. They contain chemical pollutants which can enter the ground water and wells from gardens and lawns. MCL levels have been assigned to these organic chemicals, three of which are lindane, methoxychlor and oxamyl. Lindane, which may cause liver or kidney problems, has a MCL of .0002 milligrams per liter (mg/L); methoxychlor, which may cause reproductive problems, .04 mg/L; and oaxmyl, which can cause slight nervous system problems, .02 mg/L.
Many other organic chemicals exist which have EPA-designated MCLs. Included among them are benzene, chlorobenzene and dioxin. Benzene, caused by factory discharges and landfill leaching, may increase cancer risk and cause anemia. MCL is .005 mg/L. Chlorobenzene, a possible cause of liver or kidney difficulties, comes largely from chemical-factory discharges. It has a MCL of .1 mg/L. Dioxin, which causes increased cancer risk and reproductive problems, comes largely from waste incineration. MCL is .00000003 mg/L.
Construction and mining near water wells may release inorganic chemicals from heavy metals into the groundwater. They may also come from natural sources like rock and soil. They may contain arsenic, cadmium and lead. Arsenic, with a MCL of .010 mg/L, may increase cancer risk and circulatory difficulties. Cadmium, possibly causing kidney damage, has a MCL of .005 mg/L. Lead, which may lead to childhood developmental delays and adult kidney difficulties, has an MCL of .015 mg/L.
Nitrates are inorganic compounds which usually come from human and animal waste as well as from nearby landfills and garbage dumps. Infants under six months could become seriously ill and, if not treated, die when they drink water with nitrate levels above the acceptable MCL rate of 10 mg/L.