WSP09428

• File Number: 8449.926
• Description: South Metro Water Supply Study
• State: CO
• Basin: South Platte
• Date: 2/1/2004
• Author: SMWSS Board
• Title: South Metro Water Supply Study
• Water Supply Pro - Doc Type: Publication

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brown precipitate that discolors water and may stain laundry and dishes. Many of the districts are
treating Denver Basin ground waters with a variety of processes to meet secondary (aesthetic)
water quality standards.

The concentrations of dissolved solids varies widely from less than 100 milligrams per liter in
the Dawson aquifer to over 2,000 milligrams per liter in the Laramie-Fox Hills aquifer.

Ground water in the Dawson formation is a calcium carbonate type with low sulfate
concentrations and is moderately hard. Ground water in the Denver aquifer generally contains
100 to 1000 milligrams per liter of dissolved solids. The water is a calcium bicarbonate type near
the center of the aquifer and a sodium bicarbonate or sodium sulfate type near the aquifer
margins. Natural cation exchange occurs as ground water percolates through this aquifer causing
higher sodium concentrations and lower calcium concentrations with depth - the Denver basin
aquifers generally are softer with depth.

Water in the Arapahoe aquifer is generally a sodium bicarbonate or sodium sulfate type with a
dissolved solids concentration ranging from 200 to 1,400 milligrams per liter.

Water in the Laramie-Fox Hills aquifer is also a sodium bicarbonate or sodium sulfate type. The.
dissolved solids concentrations in this aquifer range from 200 to 2,000 milligrams per liter with
the higher concentrations occurring near the aquifer margins. In some parts of the Laramie Fox
Hills aquifer, hydrogen sulfide and methane gases exist causing pumped water to effervesce and
have a putrid odor. The Laramie-Fox Hills is also characterized by high temperatures that are
from 920 F to 960 F in many places throughout the basin. Use of the Laramie-Fox Hills as a
municipal water source therefore frequently requires blending or treatment before connection to
the distribution systems.

Alluvial well systems are frequently used as a point of diversion for either surface water rights or
to capture retum flows under various augmentation plans. While water quality in these alluvial
wells typically meets drinking water standards, it is seen that increasing use and pollution loads
along Cherry Creek and PI um Creek will degrade that water quality. Recent studies by ACWW A
and Cottonwood have addressed treatment needs for alluvial waters in the future. In their case, it
is expected that a reverse osmosis process will be used to treat alluvial water with the reject
water stream being treated at a wastewater plant.

1.3.4 Recbarge of Denver Basin Aquifers - The western outcrops of the Denver Basin aquifers
have some connection with the South Platte River alluvium. In this area, there is the opportunity
for discharges to and from the Denver Basin aquifers. There is also a migration of some surface
precipitation through the aquifers providing some recharge. The total rate of recharge to the
Denver Basin has been estimated to be very small. The modeling herein estimates this total
recharge to be on the order of 35,000 to 40,000 acre-feet per year.

Ground water in the Denver Basin aquifers discharges from the bedrock formations through
overlying alluvial aquifers. During the period 1958 - 78, about 26,000 acre-feet per year was
discharged from the aquifers by natural discharge to alluvial aquifers, springs and evaporation.
About 4,800 acre-feet of water percolated from the Dawson Formation to the Denver Formation

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