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    AUTHOR:
 MONO AUTH: White, Nicholas E.
MONO TITLE: Integrated geophysical investigation of a shallow aquifer at
            Rocky Mountain Arsenal, Denver, Colorado
 CORP INFO: Colorado School of Mines; Golden, CO; United States
            Master's
    SOURCE: 146
REFERENCES: 26
      YEAR: 1995
  LANGUAGE: English
  PUB TYPE: Thesis, Monographic
    FORMAT: illus.
  ABSTRACT: This document evaluates the feasibility of integrating several
            geophysical methods to characterize geologic and hydrologic
            features, that are associated with a shallow paleochannel in the
            Denver Formation near Rocky Mountain Arsenal (RMA), Denver
            Colorado. The site is located in Section 13, Township 2 South,
            Range 67 West of the Rocky Mountain Arsenal's Offpost Study
            Area. The application of geophysical methods is desired to
            supplement geologic data, derived from soil borings and wells,
            pertaining to shallow groundwater aquifers (approximately 20 to
            100 ft depth) at RMA. Surveys were designed, implemented, and
            evaluated for five geophysical methods; seismic refraction,
            seismic reflection, direct current (DC) resistivity, gravity,
            and frequency-domain electromagnetics (EM). Survey design was
            aided by the creation of forward models and by field testing.
            Data acquisition was carried out along three intersecting
            profiles, one of which is near five soil boring locations. Data
            interpretation began with a geophysical model that was created
            from existing geologic information. Results from the five
            geophysical methods were then integrated to form an interpreted
            geologic model that correlates with existing borings and wells.
            The subsequent evaluation of the geophysical methods reveals
            that P-wave refraction is successful in delineating the surface
            of the groundwater aquifer within the boundaries of the
            paleochannel, and is successful in delineating the surface of
            the Denver Formation in regions where it subcrops above the
            aquifer surface (outside of paleochannel boundaries). The S-wave
            refraction method is shown to be useful in defining the surface
            of the unweathered Denver Formation. DC soundings alone yield
            ambiguous information on the depths and resistivities of the
            Denver Formation and overlying alluvial units. However, when DC
            sounding interpretations are constrained with the depth of the
            Denver Formation, known from borings and seismic methods, a
            complex alluvial structure is defined with more detail than any
            of the other four methods. The gravity method is used to
            delineate the surface of the Denver Formation. Frequency-domain
            EM profiles are successful in defining the shape of the Denver
            Formation, but are not successful in determining accurate depths
            to its surface. Seismic reflection methods (P-wave and S-wave),
            as implemented in this study, are shown to be ineffective tools
            for characterization of the shallow paleochannel.
DESCRIPTOR: Adams County Colorado; aquifers; buried channels; buried
            features; Cenozoic; Colorado; Cretaceous; Denver Formation;
            direct-current methods; elastic waves; electromagnetic surveys;
            fluvial features; geophysical surveys; ground water; Mesozoic;
            Paleocene; Paleogene; Rocky Mountain Arsenal; seismic surveys;
            shallow aquifers; surveys; Tertiary; United States; Upper
            Cretaceous; velocity structure
 LATITUDES: N394000; N395000
LONGITUDES: W1044500; W1045500