Several localized areas of groundwater contamination exist around landfills and other pollution sources that are not being cleaned-up. These areas must be monitored to see that the contamination does not spread to drinking water wells. Groundwater contamination often results from human activity, but it can occur naturally, too. Generally most metals detected in our groundwater are naturally occurring and in low levels. Silver, cadmium, chromium, lead, and selenium exceed standards in the Tucson basin in several isolated areas.
Nitrate contamination is one of the most common forms of groundwater pollution.
Agriculture, industry, and sewage are generally the most common causes. Nitrate levels that exceed drinking water standards are found in localized areas along the Santa Cruz River near Green Valley, Sahuarita, and northwest of Marana. Undeveloped desert areas have the lowest levels of nitrate. When found in groundwater, they usually come from industrial waste disposal or landfills. The groundwater at that site is being stripped of all VOCs and incorporated into the City of Tucson's water supply.