Andy Zdon, PG, CEG, CHG

Technical Director


Contact Information

Phone: (415) 967-6000


Location: Oakland, CA

LinkedIn Profile





Numerical Modeling

Environmental Forensics


BS, Geology - Northern Arizona University

Andy Zdon, PG, CEG, CHG

Technical Director

Andrew (Andy) Zdon has more than thirty years of experience in a variety of geology and hydrogeology-related projects. He is a California Professional Geologist, Certified Hydrogeologist, and Certified Engineering Geologist, and is also a licensed Geologist in Arizona and Utah. Mr. Zdon was also appointed in 2013 by the Inyo County Superior Court as Watermaster for a surface water system in the Owens Valley. His specialties include basin analyses and relationships with spring systems; numerical groundwater modeling including flow; and groundwater/surface water interactions including spring flow, contaminant transport, and dual-phase flow in both basin fill and fractured rock environments. Investigations in these areas can be in support of CEQA/NEPA analyses, water resource development evaluations, or providing third-party review.


He has served as an expert witness on many cases and has provided both depositions and court testimony. Mr. Zdon was appointed to serve on the first Technical Advisory Committee for the California Board for Engineers, Land Surveyors, and Geologists, and has served as a Subject Matter Expert for the Board for multiple tasks.

representative projects

Technical Expert – Hydrogeology of Proposed Yucca Mountain Nuclear Waste Repository, Nevada. Technical expert representing the County of Inyo, California relating to potential impacts to water resources in the County of Inyo, including downgradient groundwater/spring water users in the communities of Shoshone and Tecopa, and ecological resources associated with springs, the federally-designated Amargosa Wild and Scenic River, and Death Valley National Park. Work has included reviewing existing numerical groundwater flow and transport modeling for the region, and running the carbonate-aquifer model (which covers portions of California, Nevada, and Utah) developed by the U.S. Geological Survey to evaluate the effect of pumping related to Southern Nevada Water Authority water rights and applications on vertical hydraulic gradients beneath Yucca Mountain, and preparation of comments to Supplemental Environmental Impact Statement for Groundwater (prepared and submitted during 2015).


Spring Survey, Mojave and Sonoran Deserts, San Bernardino, Los Angeles, Kern, and Inyo Counties, California. Principal investigator for Mojave Desert-wide spring survey for the Barstow, Needles, and Ridgecrest U.S. Bureau of Land Management (BLM) Districts. Also included lands owned by project partner land trusts. Work consisted of records search (inclusive of technical data, water rights information, BLM records search, and cultural historic information), field inspection of more than 300 springs, and preparation of a comprehensive report and catalog of springs that serves as the most comprehensive and temporally consistent investigation of springs ever to occur in the region. Field data included refining location information; field water quality parameters; flow, collection, and analysis of water samples for stable isotope analysis; identification of vegetation present including invasive species; identification of wildlife use, including use by non-native animals; types of spring disturbance; and general geological observations. Subsequent work has included extensive isotopic characterizations, including stable isotope, tritium, and radiocarbon analyses to evaluate regional aquifer connections with springs, and working cooperatively with biologists conducting vegetation mapping and environmental DNA analyses on selected springs. This project was reported in several publications, including USA Today.


Hydrogeologic Characterization and Flow Modeling, Big Valley Groundwater Basin, Lake County, California. Conducted numerical modeling analysis of the Big Valley Groundwater Basin (inclusive of Soda Bay) in Lake County, California as part of an environmental review/feasibility study related to using the Kelseyville water system as an alternative water supply for the Soda Bay area. The Soda Bay area is in complex volcanic terrain, and has been previously served primarily by surface water from Clear Lake, which is seasonally problematic due to water quality issues. Additionally, the numerical modeling provided estimates of streamflow depletion in Kelsey Creek due to groundwater pumping addressing concerns related to the Clear Lake Hitch, a California-state listed threatened species fish (also under federal review).

  • State of California Water Resources Control Board, Office of Administrative hearings, Draft Cease and Desist Order issued against Bluetriton brands, inc. relating to spring capture in San Bernardino County, California. Declaration and Oral Testimony (2022).

  • Eddie Falzon and S. Jo Falzone v. Wack, Casey, Carey Williams,, in Superior Court for the State of California, County of Inyo. Physical Solution, appointment as Watermaster (Representative of the Court), 40-Acres Water System.

  • Orange County Water District v. Sabic Innovative Plastics US LLC; Brenntag West, Inc., Gallade Chemical, Inc.;, In the Superior Court for the State of California in and for the County of Orange, Case No. 30-2008-00078246-CU-TT-CXC, Deposition (2013).

  • State of California Energy Resources Conservation and Development Commission, Application for Certification for the Hidden Hills Solar Energy Generation Project; Intervenor Amargosa Conservancy, Docket No. 11-AFC-2, Declaration and Oral Testimony (2013).

  • Southern California Gem Industries v. Roth, in the Superior Court of the State of California, County of San Diego. Expert Report (2009).

  • Garry N. Holdgrafer,, v. Unocal Corporation, A Delaware Corporation, Union Oil Company of California, Unocal California Pipeline Company, 76 Products Company, Superior Court of the State of California, County of San Luis Obispo. Deposition and Court Testimony (2003).

  • Fraga, N.S. Fraga, Brian S. Cohen, Andy Zdon, Maura Palacios Mejia, Sophie S. Parker "Floristic Patterns and Conservation Values of Mojave and Sonoran Desert Springs in California," Natural Areas Journal, 43(1), 4-21.

  • Love, A.H., Zdon, A., Fraga, N., Cohen, B., Palacios Mejia, M., Maxwell, R. and Parker, S.S. (2022) “Statistical Evaluation of the Similarity of Characteristics in Springs of the California Desert, USA. Frontiers in Environmental Science, p. 2101.

  • Zdon, A., Love, A.H. (2020). “Groundwater Forensics Methods for Differentiating Local and Regional Springs in Arid Eastern California, USA.” Environmental Forensics.

  • Parker, S.S., Zdon, A., Christian, W.T., Cohen, B.S., Mejia, M.P., Fraga, N.S., Curd, E.E., Edalati, K., and Renshaw, M.A. (2020). “Conservation of Mojave Desert Springs and Associated Biota: Status, Threats and Policy Opportunities.” Biodiversity and Conservation.

  • Zdon, A., Rainville, K., Love, A.H., Buckmaster, N., and Parmenter, S. (2019). “Identification of source-water mixing in the Fish Slough spring complex, Mono County, California, USA.” Hydrology 2019, 6. 26.

  • Love, A.H., Zdon, A. (2018). “Use of Radiocarbon Ages to Narrow Groundwater Recharge Estimates in the Southeastern Mojave Desert, USA.” Hydrology 2018, 5, 51.

  • Zdon, A., Davisson, M.L., and Love, A.H. (2018) “Understanding the source of water for selected springs within Mojave Trails National Monument, California.” Environmental Forensics, Volume 19, No. 2, 99-111.

  • Zdon, A. (2017). “Water in the Desert? A Survey of Springs 2015-2016.” Desert Report: News of the Desert from Sierra Club California and Nevada Desert Committee. June.

  • Potter, Christopher, Zdon, A., and Weigand, J. (2017) “Monitoring Springs in the Mojave Desert using Landsat Time Series Analysis. International Journal of Water Resources and Environmental Management, Volume 8, No. 2. December.

  • Zdon, A., Davisson, M. L., and Love, A.H. (2015) "Testing the Established Hydrogeologic Model of Source Water to the Amargosa River Basin, Inyo and San Bernardino Counties, California." Environmental forensics, v. 16,.4 pp. 344-355.

  • Zdon, A. (2014) “Wading Deep: The Importance of Hydrological Monitoring.” California Council of Land Trusts, Conservation Frontiers, Volume 5.3, July. 8 p.

  • Traylor, R.L., Zdon, A., Zawadki, A. (2001) "Identification of Areas for Potential Recharge Projects, New Well Siting Areas and Basin Source Water Assessment." Proceedings of the XXXI International Association of Hydrogeologists Congress Munich, Germany, 10-14 September 2001: New Approaches Characterizing Groundwater Flow. Pages 657-661.