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Using Environmental Tracers to Help study areaModel of CalibrateThe a Ground-Water The Middle Rio Grande Basin Ward Sanford and Niel Plummer USGS National Research Program, Reston, VA Doug McAda, Laura Bexfield & Scott Anderholm USGS Water Science Center, Albuquerque, NM Information Used to Construct and Calibrate the Model • Geologic Information • Hydrologic Information • Geochemical Information • MODFLOW, MODPATH and UCODE Geologic Information Geologic Studies were used to Develop the Model Geometry and Zonation Geologic model of the Middle Rio Grande Basin constrained by gravity data (Grauch) Inner Valley Alluvium River Gravels Ceja Gravels Layer 1 Layer 2 Medium to Coarse Sand Silts Medium Sand Fine to Medium Sand Eolian Sand Volcanic Sand Piedmont Slope Deposits Volcanic Flows Volcanic Intrusions Inner Valley Alluvium River Gravels Ceja Gravels Layer 5 Layer 6 Medium to Coarse Sand Silts Medium Sand Fine to Medium Sand Eolian Sand Volcanic Sand Piedmont Slope Deposits Volcanic Flows Volcanic Intrusions Rio Grande alluvium Layer 1 Layer 1 Fine sand Paleochannel sand & gravel Very fine Sand Ceja gravels Proximal volcanic sand Northern fluvial sand & gravel Northern proximal volcanic sand Central fluvial sand & gravel Southern fluvial sand & gravel Southern proximal volcanic sand Central fine & very fine sand faults Rio Grande alluvium Geologic Model Fine sand Medium Sand Paleochannel sand & gravel Very fine Sand Northwest medium sand Central medium sand Ceja gravels Proximal volcanic sand Northeast medium sand West central medium sand East central coarse sand Northern medium sand Northern proximal volcanic sand Northern fluvial sand & gravel Ground-Water Southern proximal Flow Model Central fluvial sand & gravel Southern fluvial sand & gravel volcanic sand Central fine & very fine sand faults N Medium to coarse sand scale 0 10 20 km Southwest medium sand Southeast coarse sand Piedmont slope deposits silts Extrusive volcanic rocks Intrusive volcanic rocks Hydrologic Information Middle Rio-Grande Basin Water Table in 1960 N Albuquerque Boundary Conditions Jemez Mountain-Front Recharge and Underflow Jemez River Western Basin Underflow Basin Underflow Rio Puerco Rio Grande Middle Rio-Grande Basin Boundary Tijeras Arroyo Eastern Mountain - Front Recharge Southwestern Basin Underflow Abo Arroyo Rio Salado Geochemical Information Deuterium Carbon-14 Middle Rio-Grande Basin Boundary pmC 100 per mil 80 -120 -110 60 -100 40 -90 -80 20 -70 -60 0 -50 Bounda ry of the Middle Rio-Gra nde Basin Edge of the finite-difference model grid Albuquerque Local northwest recharge Northern MF Recharge Hagan basin underflow Jemez underflow Rio Puerco Rio Grande Eastern Mountain Front Ladron Peak Abo Arroyo Basin Discharge Results Recharge Estimates 120,000 100,000 Rio Grande 80,000 Acre-feet per Year Mountains 60,000 40,000 20,000 0 Kernodle (1995) Sanford (2003) Creating a “Trough” with Low Recharge Western Recharge Northwestern Recharge River Water Northeastern Recharge Eastern Recharge 40 km Water Levels For Layer 2 Estimating Paleorecharge Rates Summary and Conclusions • Environmental Tracers are an important source of data to use in addition to geology and water levels to calibrate regional groundwater models • Recharge in the Middle Rio Grande Basin is much less than previously estimated, but was higher in the past. • The lower recharge rates can explain spatial features in both the water table and geochemical zones
