Andrew J Long
Andy Long has more than 30 years of experience assessing groundwater flow and transport through numerical and conceptual modeling, analyzing ambient and injected tracers, and geophysical methods.
Professional Experience
Groundwater Specialist, USGS Washington Water Science Center (July 2015 – present) –
Advise and train scientists and technicians on interpretive studies and data collection and management. Advise managers in building and guiding the groundwater program. I conduct scientific investigations involving conceptual and numerical modeling.Chair and Vice Chair, Washington Hydrogeology Symposium (2017 – 2022)
Research Hydrologist, USGS Dakota Water Science Center (DWSC; 2009 – 2015) –
Developed innovative methods to better understand, quantify, and test hypotheses related to groundwater flow and transport in karst aquifers. Topics include groundwater age dating, lumped-parameter models, aquifer classification, hydrochemical evaluation, heat transport, and groundwater recharge.Adjunct Assistant Professor, South Dakota School of Mines and Technology (SDSMT; Oct 2005 – 2018) –
Served on eight graduate advisory committees for M.S. and Ph.D. students and gave numerous guest lectures.Hydrologist, USGS DWSC (Jan 1999 – Oct 2009) –
This involved numerical modeling of groundwater flow and solute transport, dye tracing experiments in karst aquifers, aquifer pumping tests, and development of new research models.Consultant (1994–1998) –
Conducted GIS analysis and groundwater modeling with MODFLOW related to a proposed low-level nuclear-waste site for the Boyd County Monitoring Committee in Nebraska. Consulted for Terra Nitrogen in Sergeant Bluff, Iowa and simulated groundwater flow and transport with MODFLOW, MOC, and GIS analysis to assess the movement of ammonia contamination.
Research assistant, SDSMT (1995–1998) –
Developed and wrote the FORTRAN computer code for a three-dimensional groundwater model to simulate dual-porosity flow in karst aquifers. Collaborated with a team of researchers on the design of a numerical model to simulate surface-water and groundwater flow, dynamically linked to atmospheric processes.
Hydrologist, Rapid City Water Department (1994-1995) –
Collaborated with the USGS to simulated groundwater flow in karst aquifers.
Science and Products
Skagit Ground Water Model
Conceptual model of the uppermost principal aquifer systems in the Williston and Powder River structural basins, United States and Canada
Hydrogeologic framework of the uppermost principal aquifer systems in the Williston and Powder River structural basins, United States and Canada
A framework for assessing water and proppant use and flowback water extraction associated with development of continuous petroleum resources
Two approaches for incorporating climate change into natural resource management planning at Wind Cave National Park
Comparison of a karst groundwater model with and without discrete conduit flow
Prediction, time variance, and classification of hydraulic response to recharge in two karst aquifers
Microgravity methods for characterization of groundwater-storage changes and aquifer properties in the karstic Madison aquifer in the Black Hills of South Dakota, 2009-12
Multivariate statistical approach to estimate mixing proportions for unknown end members
Groundwater flow, quality (2007-10), and mixing in the Wind Cave National Park area, South Dakota
Multivariate analyses with end-member mixing to characterize groundwater flow: Wind Cave and associated aquifers
Simulated groundwater flow in the Ogallala and Arikaree aquifers, Rosebud Indian Reservation area, South Dakota – Revisions with data through water year 2008 and simulations of potential future scenarios
Numerical groundwater-flow model of the Minnelusa and Madison hydrogeologic units in the Rapid City area, South Dakota
Science and Products
- Science
Filter Total Items: 13
Skagit Ground Water Model
State and local water-resource managers in Lower Skagit/Samish Water Resource Inventory Area (WRIA-3) face two water-availability issues that are common throughout Washington State. First, they must reserve water for domestic wells that are exempt from the water rights system without harming river and stream ecosystems in the lower Skagit River basin. Skagit County, which would be responsible for... - Data
- Publications
Filter Total Items: 29
Conceptual model of the uppermost principal aquifer systems in the Williston and Powder River structural basins, United States and Canada
The three uppermost principal aquifer systems of the Northern Great Plains—the glacial, lower Tertiary, and Upper Cretaceous aquifer systems—are described in this report and provide water for irrigation, mining, public and domestic supply, livestock, and industrial uses. These aquifer systems primarily are present in two nationally important fossil-fuelproducing areas: the Williston and Powder RivAuthorsAndrew J. Long, Katherine R. Aurand, Jennifer M. Bednar, Kyle W. Davis, Jonathan D.R.G. McKaskey, Joanna N. ThamkeHydrogeologic framework of the uppermost principal aquifer systems in the Williston and Powder River structural basins, United States and Canada
The glacial, lower Tertiary, and Upper Cretaceous aquifer systems in the Williston and Powder River structural basins within the United States and Canada are the uppermost principal aquifer systems and most accessible sources of groundwater for these energy-producing basins. The glacial aquifer system covers the northeastern part of the Williston structural basin. The lower Tertiary and Upper CretAuthorsJoanna N. Thamke, Gary D. LeCain, Derek W. Ryter, Roy Sando, Andrew J. LongA framework for assessing water and proppant use and flowback water extraction associated with development of continuous petroleum resources
The U.S. Geological Survey is developing approaches for the quantitative assessment of water and proppant involved with possible future production of continuous petroleum deposits. The assessment approach is an extension of existing U.S. Geological Survey petroleum-assessment methods, and it aims to provide objective information that helps decision makers understand the tradeoffs inherent in resouAuthorsSeth S. Haines, Troy Cook, Joanna N. Thamke, Kyle W. Davis, Andrew J. Long, Richard W. Healy, Sarah J. Hawkins, Mark A. EngleTwo approaches for incorporating climate change into natural resource management planning at Wind Cave National Park
Wind Cave National Park (WICA) protects one of the world’s longest caves, has large amounts of high quality, native vegetation, and hosts a genetically important bison herd. The park’s relatively small size and unique purpose within its landscape requires hands-on management of these and other natural resources, all of which are interconnected. Anthropogenic climate change presents an added challeAuthorsAmy J. Symstad, Andrew J. Long, John Stamm, David A. King, Dominque M. Bachelet, Parker A. NortonComparison of a karst groundwater model with and without discrete conduit flow
Karst aquifers exhibit a dual flow system characterized by interacting conduit and matrix domains. This study evaluated the coupled continuum pipe-flow framework for modeling karst groundwater flow in the Madison aquifer of western South Dakota (USA). Coupled conduit and matrix flow was simulated within a regional finite-difference model over a 10-year transient period. An existing equivalent poroAuthorsStephen P. Saller, Michael J. Ronayne, Andrew J. LongPrediction, time variance, and classification of hydraulic response to recharge in two karst aquifers
Many karst aquifers are rapidly filled and depleted and therefore are likely to be susceptible to changes in short-term climate variability. Here we explore methods that could be applied to model site-specific hydraulic responses, with the intent of simulating these responses to different climate scenarios from high-resolution climate models. We compare hydraulic responses (spring flow, groundwateAuthorsAndrew J. Long, Barbara MahlerMicrogravity methods for characterization of groundwater-storage changes and aquifer properties in the karstic Madison aquifer in the Black Hills of South Dakota, 2009-12
A study of groundwater storage in the karstic Madison aquifer in the Black Hills of South Dakota using microgravity methods was conducted by the U.S. Geological Survey in cooperation with West Dakota Water Development District, South Dakota Department of Environment and Natural Resources, and Lawrence County. Microgravity measurements from 2009 to 2012 were used to investigate groundwater-storageAuthorsKarl R. Koth, Andrew J. LongMultivariate statistical approach to estimate mixing proportions for unknown end members
A multivariate statistical method is presented, which includes principal components analysis (PCA) and an end-member mixing model to estimate unknown end-member hydrochemical compositions and the relative mixing proportions of those end members in mixed waters. PCA, together with the Hotelling T2 statistic and a conceptual model of groundwater flow and mixing, was used in selecting samples that beAuthorsJoshua F. Valder, Andrew J. Long, Arden D. Davis, Scott J. KennerGroundwater flow, quality (2007-10), and mixing in the Wind Cave National Park area, South Dakota
A study of groundwater flow, quality, and mixing in relation to Wind Cave National Park in western South Dakota was conducted during 2007-11 by the U.S. Geological Survey in cooperation with the National Park Service because of water-quality concerns and to determine possible sources of groundwater contamination in the Wind Cave National Park area. A large area surrounding Wind Cave National ParkAuthorsAndrew J. Long, Marc J. Ohms, Jonathan D.R.G. McKaskeyMultivariate analyses with end-member mixing to characterize groundwater flow: Wind Cave and associated aquifers
Principal component analysis (PCA) applied to hydrochemical data has been used with end-member mixing to characterize groundwater flow to a limited extent, but aspects of this approach are unresolved. Previous similar approaches typically have assumed that the extreme-value samples identified by PCA represent end members. The method presented herein is different from previous work in that (1) endAuthorsAndrew J. Long, Joshua F. ValderSimulated groundwater flow in the Ogallala and Arikaree aquifers, Rosebud Indian Reservation area, South Dakota – Revisions with data through water year 2008 and simulations of potential future scenarios
The Ogallala and Arikaree aquifers are important water resources in the Rosebud Indian Reservation area and are used extensively for irrigation, municipal, and domestic water supplies. Drought or increased withdrawals from the Ogallala and Arikaree aquifers in the Rosebud Indian Reservation area have the potential to affect water levels in these aquifers. This report documents revisions and recaliAuthorsAndrew J. Long, Larry D. PutnamNumerical groundwater-flow model of the Minnelusa and Madison hydrogeologic units in the Rapid City area, South Dakota
The city of Rapid City and other water users in the Rapid City area obtain water supplies from the Minnelusa and Madison aquifers, which are contained in the Minnelusa and Madison hydrogeologic units. A numerical groundwater-flow model of the Minnelusa and Madison hydrogeologic units in the Rapid City area was developed to synthesize estimates of water-budget components and hydraulic properties, aAuthorsLarry D. Putnam, Andrew J. Long