New Mexico Geological Society Annual Spring Meeting
April 13, 2018
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Hydrogeologic-Framework, Water-Supply Well Pumping, and Acequia-Irrigation Controls on Subsurface-Water Flow and Contaminant Transport in Santa Fe Group and Alluvial-Terrace Deposits Beneath Historic Santa Fe, New Mexico
John W. Hawley1 and Baird H. Swanson2
Between 1609 and 1880 the Historic center of the present City of Santa Fe (COSF) was a small Colonial-Provincial-Territorial Capital sustained by acequia-irrigation agriculture, livestock and timber production, and a military-post/trade-route location. The vital roles played by Santa Fe (SF) River and its interlinked acequia system are of special environmental interest. Significant anthropogenic groundwater contamination, however, dates to the SF Railroad’s arrival in February 1880 and the expansion of automotive tourism soon thereafter. More serious environmental problems (EPs) are related to accelerated urbanization that occurred soon after 1942 when the ATSF Railyards became the primary staging area for Manhattan Project-LANL construction. The 1942 to 1952 period also coincided with public water-supply (PWS) well and SF-River dam construction, and essential cessation of acequia irrigation. Besides the former Railyards District, adjacent parts of COSF include at least 20 other EP sites that are known or potential sources of groundwater contamination in Santa Fe Gp (SFG) aquifer system and overlying SF River-terrace deposits. The former PNM Santa Fe Generating Station (SFGS) Site is one of them. Contaminants detected in PWS wells and monitor wells (MWs) include gasoline/diesel-fuel and chlorinated-solvent derivatives. Source areas include bulk-fuel storage facilities, gas stations, dry cleaners, and a drywell disposal site. From the perspective of geohydrologic, and hydrochemical mechanisms of subsurface-water flow and contaminant transport, the hydrogeologic framework of the SFG-Tesuque Fm aquifer and overlying vadose-zone material beneath central COSF has two primary components: 1. Lithologic and structural—with hydraulic and chemical properties determined by standard geoscience-based methods (e.g. geology-geomorphology, geophysics, and geochemistry); and 2. Anthropogenic—where acequias and/or large-production wells form the primary controls on the location and timing of vadose-zone/saturated-zone potentiometric transitions in subsurface-water flow regimes.
This presentation focuses on a 2 mi2 area of central COSF where a logged-borehole data base allows preparation of 1:3,000-scale hydrogeologic maps and fence-diagram grids based on records from 1) four exploratory and PWS wells with depths ranging from 1,200 to 2,660-ft, and 2) more than 150 MW boreholes at major EP sites, some of which are in the 300 to 500-ft depth range. Primary hydrogeologic-framework components are illustrated at multiple scales: 1. A conceptual perspective of a mid-Miocene piedmont landscape includes a reconstruction of the Tesuque Fm-Lithosome S (Tts) fluvial fan and its ancestral Santa Fe-Range sediment-source area (Google Earth® image). 2. The internal fractal fabric of fan-distributary channel and inter-channel facies is shown on an idealized fan- piedmont diagram. 3. Study Area framework depiction includes a 1:1, 1:6000-scale block diagram that shows its basic Tts west-tilted structural and fluvial-fan lithofacies framework to a 3,500 ft amsl base elevation. 4. Hydrostratigraphic and structural relations at the most-detailed level are illustrated by 1:3,000-scale maps and a 1,000-ft fence-diagram grid of 26 cross-sections on a 2-ft contour base; with surficial-geologic and “post-Tesuque Erosion Surface” structure-contour maps included. 6. A 7,000-ft long, 3,000-ft deep cross section, with potentiometric-surface drawdown timelines, schematically illustrates the hydraulic/hydrologic impacts of about 62 years of SF-PWS-well pumping on an ever-diminishing saturated thickness of westward-dipping Tts deposits.
2018 New Mexico Geological Society Annual Spring Meeting
April 13, 2018, Macey Center, New Mexico Tech campus, Socorro, NM