WSP08952

• File Number: 8449.870
• Description: SB 996-153 Phase I - Economic Life of the Denver Basin
• State: CO
• Basin: South Platte
• Date: 11/13/1996
• Author: CWCB/SEO
• Title: Economic Life of the Denver Basin Final Report
• Water Supply Pro - Doc Type: Publication

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Denver basin were each treated individually. The models are set up to be run with the
MODFLOW model (McDonald-Harbaugh, 1988).

Under the Senate Bill 5 requirements, calculation of depletion for the purpose of definition
of the location of nontributary groundwater is done assuming that the water level in the aquifer
has been lowered to the top of the aquifer. Thus these models are designed as change models
with initial groundwater level in each aquifer as a flat surface. Any pumping produces
groundwater movement in the aquifer and induces recharge from the surface water streams. This
depletion in surface water flow is tracked in analysis of the model results and used to determine
stream depletion in response to pumping.

The models are required by Senate Bill 5 to ignore water in confined storage in the
aquifers and cannot calculate actual expected changes in water level in the aquifers. As such, they
are unsuited for use in an analysis of the economic life of the aquifers. Horizontal flow within the
aquifers and vertical leakage between the aquifers are calculated by these models. In developing
these models, extensive geologic and hydrologic data were gathered and compiled. This data will
be of use in the Phase 2 analysis for this project.

4.2 Robson's Denver Basin Model

A modeling project performed by S. G. Robson of the U.S.G.S. is described in the report
entitled "Bedrock Aquifers in the Denver Basin, Colorado - A Quantitative Water-Resources
Appraisal", U.S.G.S Professional Paper 1257, 1987. In this project, a single groundwater model
of the four major Denver Basin aquifers was developed, calibrated, and used for simulations of
groundwater level changes expected in response to several water demand scenarios. The model
code was developed by Trescott and Larson (1975) and S.P. Larson (1976).

This is a calibrated hydraulic head model and accounts for: water in both confined and
unconfined storage, leakage between the aquifers in response to changes in groundwater levels in
the various aquifers, induced infiltration from streams, and recharge from precipitation.

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HRS WATER CONSULTANTS, INC