Water Quality

In most areas, the water in the Denver Basin aquifer system meets the drinking water standards set by the United States Environmental Protection Agency.The quality of our ground water is affected by its depth from the surface, the source of new water flowing into the ground, and characteristics of the underground rocks and soils.Geological processes have led to the formation of two distinctively different types of aquifers.

Alluvial aquifers follow the course of present and ancient streams.Sand and gravel are the principal water-yielding materials in the alluvial aquifer, and depth to water usually ranges from 0-40 feet.The surface water in streams and reservoirs and water used for irrigation purposes are the principal sources of recharge for these aquifers.Depth to water in the bedrock aquifer generally ranges from 0-250 feet, but can be as great as 500 to 1000 feet in deeper parts of the aquifer.Sandstone and conglomerate are the principal water yielding material in the bedrock aquifer.

In the alluvial aquifer, the shallow depth of the water table and the permeable nature of the soil allow pollutants to easily enter the aquifer.As a result, chemical quality of the water is not generally suited for public or domestic supply.Water from the alluvial aquifer often has a large concentration of dissolved solids, hardness, and localized concentrations of iron, nitrate and sulfate.Deeper water tables and relatively impermeable clay and shale layers above the water table restrict downward movement of contaminants into the bedrock aquifer.The bedrock aquifer generally contains water that is of good chemical quality for public and domestic use.

Water quality is also variable between the four aquifers that make up the Denver Basin system.Hard water is caused by calcium and magnesium bicarbonates, calcium and magnesium sulfates, and calcium and magnesium chlorides.Water in the Dawson aquifer is a calcium bicarbonate type, has small sulfate concentrations, and is moderately hard.Water in the Denver aquifer is also of the calcium bicarbonate type near the center of the aquifer.As water moves through the Denver and underlying aquifers, an ion exchange process naturally softens it.The processes of ion exchange and dissolution cause water in the Arapahoe to be softer and have greater concentrations of sulfate than the Denver aquifer. Generally, water is softer at greater depths.Hard water is undesirable because it causes a hard mineral deposit to form on the inside of pipes and water heaters, requires more soap to make a good lather, while leaving behind a soapy scum.
In addition to hardness, calcium sulfate in water containing little or no oxygen will often be reduced to sulfides by bacteria.This reaction results in the release of hydrogen sulfide gas.Hydrogen sulfide is common in wells that penetrate sandstone and shale, and tends to make the water corrosive to pipes, and smell like rotten eggs.

Water quality near the margins of the aquifers is somewhat degraded by surface recharge containing sulfate and other chemical constituents leached from soluble minerals in the overlying soil and rock.

Dissolved iron concentrations are greatly variable in the Denver Basin Aquifer System.When water that contains large concentrations of dissolved iron is exposed to oxygen, the dissolved iron will precipitate out staining laundry and plumbing fixtures.Precipitated iron may cause the water to appear cloudy and have an unpleasant taste.

Problem	Probable Cause
Difficulty productin soap suds, mineral deposits on the inside of pots and in piping	Hard Water (calcium bicarbonate, magnesium bicarbonate, calcium sulfate, magnesium sulfate, calcium chloride, magnesium chloride)
Red to brown or black stains on laundry and plumbing	Iron or Manganese in water
Rotten Egg Odor, Black stains on laundry	HydrogenSulfide