Preliminary Assessment of the Preliminary Assessment of the Importance of Mountain Block Importance of Mountain Block Faults to Groundwater Flow in Faults to Groundwater Flow in

the Carbonate-Rock Aquifers of the Carbonate-Rock Aquifers of the Southern Great Basinthe Southern Great Basin

Douglas B. Blatchford, PEDouglas B. Blatchford, PEHarding Lawson AssociatesHarding Lawson Associates

Steve A. Mizell, PhDSteve A. Mizell, PhDDesert Research InstituteDesert Research Institute

BackgroundBackground

Geologic HistoryGeologic History– Carbonates deposited during PaleozoicCarbonates deposited during Paleozoic– Compression placed older formations Compression placed older formations

over younger during Mesozoicover younger during Mesozoic– Extensional deformation and volcanism Extensional deformation and volcanism

occurred during Cenozoicoccurred during Cenozoic– Present day physiography Present day physiography

characterized by structural basinscharacterized by structural basins

BackgroundBackground Previous WorkPrevious Work

– Cole, et al. (1992) completed steady-state Cole, et al. (1992) completed steady-state simulation of Tikaboo Valleysimulation of Tikaboo Valley

– Brothers, Buqo, and Tracy (1993) completed Brothers, Buqo, and Tracy (1993) completed steady-state simulation of Coal and Garden steady-state simulation of Coal and Garden ValleysValleys

– Dettinger et al. (1995) described the Dettinger et al. (1995) described the distribution of carbonate rock aquifersdistribution of carbonate rock aquifers

– Prudic, Harrill, and Burbey (1995) provided a Prudic, Harrill, and Burbey (1995) provided a conceptual evaluation of regional ground water conceptual evaluation of regional ground water flowflow

NEVADAUTAH

CALIFORNIA

ARIZONA

IDAHOOREGO N

Limit ofGreat Basin

LAS VEGAS

CARBONATE ROCK PROVINCE

GARDEN

PENOVER

COAL

TIKABOO

Four Basin ModelFour Basin Model Four basins modeled included Four basins modeled included

Penoyer, Garden, Coal, and Tikaboo Penoyer, Garden, Coal, and Tikaboo ValleysValleys

One square mile discretizationOne square mile discretization Four basin grid 115 rows x 60 columnsFour basin grid 115 rows x 60 columns Results calibrated against regional Results calibrated against regional

model by Prudic, Harrill, and Burbey model by Prudic, Harrill, and Burbey (1995)(1995)

DiscretizationDiscretization

ResultsResults

Worthington ModelWorthington Model

1/8 square mile discretization1/8 square mile discretization Penoyer Valley fault on western Penoyer Valley fault on western

flank, Garden Valley fault on flank, Garden Valley fault on eastern flankeastern flank

Results generated for:Results generated for:– No fault zonesNo fault zones– Low conductivity faultsLow conductivity faults– High conductivity faults High conductivity faults

DiscretizationDiscretization

PENOVER VALLEY FAULT

GARDEN VALLEY FAULT

No Fault ZonesNo Fault Zones

Low ConductivityLow Conductivity 5075 ft

5000 ft

4975 ft

4950 ft

4925 ft

4900 ft

5050 ft

5000 ft

4975 ft

5075 ft

5025 ft

4950 ft

4925 ft

4900 ft4875 ft

5025 ft

5050 ft

5075 ft

5000 ft

4975 ft

4950 ft

4925 ft

4900 ft

5025 ft

5050 ft

High ConductivityHigh Conductivity5025 ft

5000 ft

4975 ft

4950 ft

4925 ft

4900 ft

5025 ft

5000 ft

4975 ft

5050 ft

Timpahute ModelTimpahute Model

1/6 square mile discretization1/6 square mile discretization Penoyer Valley, Penoyer Springs, Penoyer Valley, Penoyer Springs,

Tikaboo Valley, Schofield Pass, and Tikaboo Valley, Schofield Pass, and a Range Bounding fault modeleda Range Bounding fault modeled

Results generated for:Results generated for:– No fault zonesNo fault zones– Low conductivity faultsLow conductivity faults– High conductivity faultsHigh conductivity faults

DiscretizationDiscretization

PENOVER VALLEY FAULT

RANGE BOUNDING FAULT

PENOVER SPRINGS FAULT

TIKABOO VALLEY FAULT

SCHOFIELD PASS FAULT

No Fault ZonesNo Fault Zones

Low ConductivityLow Conductivity

High ConductivityHigh Conductivity

ConclusionsConclusions Sub-region flow models reflect regional Sub-region flow models reflect regional

models at a gross levelmodels at a gross level Low conductivity faults accentuate Low conductivity faults accentuate

mounding below mountainsmounding below mountains Low conductivity faults perpendicular Low conductivity faults perpendicular

to regional flow do not impact flow to regional flow do not impact flow directiondirection

High conductivity faults parallel to High conductivity faults parallel to regional flow act as drainsregional flow act as drains