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Early Bird Rates apply through June 11:
TAGD Members – $375
Non-Profit/Agency Staff – $375
TGWA Members – $375
Non-Members – $425
BOOK A ROOM HERE
Book in the Texas Groundwater room block for a reduced rate!
Standard King: $143
Standard Double: $143
SPONSORSHIP OPPORTUNITIES
Show your support for groundwater science and policy in Texas by sponsoring the Summit! Contact julia@texasgroundwater.org to reserve your package.
EXHIBITOR REGISTRATION
TAGD Member Exhibit – $550
Non-Profit/Agency Exhibit – $650
TGWA Member Exhibit – $650
Non-Member Exhibit – $750
STUDENT SCHOLARSHIPS
Student scholarships are funded by member districts that are passionate about the potential of students in fields related to groundwater management.
The Texas Groundwater Summit is the premier groundwater event in the state, bringing together a diverse group of groundwater professionals over three days to discuss emerging trends and new research. The event provides a mix of expert presentations on all areas of groundwater management, as well as networking opportunities for the groundwater community. We expect to have over 350 groundwater industry leaders, community stakeholders, agency representatives, and elected officials in attendance. You won’t want to miss it!
Texas Alliance of Groundwater Districts (TAGD) looks forward to gathering the statewide groundwater community once again at the 10th Annual Texas Groundwater Summit! This year’s event will take place in person August 31-September 2, 2021 at the Hyatt Regency Hill Country Resort in San Antonio, TX. A livestream option is also available for those participants that are unable to travel or uncomfortable with an in-person conference.
Click here to view a schedule at-a-glance of Summit events.
Who should attend the Texas Groundwater Summit?
Groundwater Conservation District staff and board members
Well drillers and well technology companies
Water providers and planners
Groundwater stakeholders, including agriculture, oil & gas, environmental and industrial
Attorneys, hydrogeologists, and engineers working in the water field
Groundwater technology experts and vendors
Undergraduate and Graduate Students
Anyone interested in the future of groundwater in Texas
Thank you for attending the 9th Annual Texas Groundwater Summit, held September 1-3, 2020, as an interactive webinar event. We appreciate all of our sponsors!
View the 2020 Texas Groundwater Summit agenda here.
To view the presentation slides, click on the title of the presentation. View sessions on our Youtube channel here.
Tuesday, September 1
Groundwater Sustainability & Stewardship
Trey Mixon, Natural Resources Manager, Nestle Waters North America
Innovative GCD Management Strategies Panel
Moderator: Drew Satterwhite, General Manager, North Texas GCD/Red River GCD
Troupe Brewer, Principal, Lloyd Gosselink Rochelle & Townsend PC
Ty Edwards, General Manager, Middle Pecos GCD
Mike Keester, Project Manager/Hydrogeologist, LRE Water
Produced Water as Water Supply Panel
Moderator: Adam Friedman, Partner, McElroy Sullivan Miller & Weber LLP
Brian Bohm, Environmental Sustainability Advisor, Apache Corporation
Bridget Scanlon, Senior Research Scientist, Bureau of Economic Geology
Trey Gerfers, Board Chairman, Presidio County UWCD
Keynote Address
Brooke Paup, Director, Texas Water Development Board
GAMs, the Next Generation Panel
Moderator: Wade Oliver, Senior Hydrogeologist, INTERA
Natalie Ballew, Groundwater Technical Assistance Manager, Texas Water Development Board
Andy Donnelly, Senior Hydrogeologist, Daniel B. Stephens & Associates
John Ellis, Supervisory Hydrologist, United States Geological Survey
Wednesday, September 2
Sarah Kirkle, Director of Policy & Legislative Affairs, Texas Water Conservation Association
Transparency Under COVID and Related Issues
Jennifer Smith, Attorney, SledgeLaw Group
William Gamblin, Groundwater Resources Supervising Engineer, WSP
Underground Disposal Wells and Water Quality Considerations for GCDs
Matthew Uliana, Principal Hydrogeologist, INTERA
Advances in Agricultural Conservation & the North Plains Water Conservation Center
Nicholas Kenny, Agricultural Engineer, North Plains GCD
A Path Forward for Sustainable Crop Production on the Texas High Plains
Ronnie Hopper, Director, High Plains Water District
Diversifying the Water Portfolio for Agriculture in the Rio Grande Basin
Allen Berthold, Senior Research Scientist, Texas Water Resources Institute
The Why and How of Water Communications
Janet Rummel, Public Relations & Communications Officer, NTMWD
Building Effective Education Programs
Melissa Mullins, Environmental Education Specialist, Baylor University
From the GCD Perspective: BGPZ Rules under HB 722
Mary Sahs, Principal, Mary K. Sahs PC
Jason Coleman, General Manager, High Plains Water District
TWDB Update on Brackish Groundwater Production Zones
Erika Mancha, Manager of Innovative Water Technologies, Texas Water Development Board
Thursday, September 3
The Past, Present, and Future of Comanche Springs
Robert Mace, Executive Director, Meadows Center for Water & the Environment
Lessons Learned: Accountability and the Petition for Review Process Panel
Moderator: Bill Dugat, Partner, Bickerstaff Heath Delgado Acosta LLP
Tom Koeneke, Board Vice President, Starr County GCD
Kelly Mills, Water Availability Division Assistant Director, Texas Commission on Environmental Quality
Lynn Smith, General Manager, Mesquite GCD
Keynote Address
Dr. Larry Schooler, Senior Fellow, National Civic League
Moderator: Greg Ellis, Attorney, GM Ellis Law Firm PC
Stacey Reese, Attorney, Stacey Reese Law PLLC
Deborah Trejo, Partner, Kemp Smith Law
Agenda
View the 2019 Texas Groundwater Summit agenda here.
2019 Summit Presentations
To view the 2019 presentation slides, click on the title or an individual speaker’s name to view a PDF of the summit slides. View sessions on our Youtube channel here.
Day 1 – Tuesday, August 20
Welcome Address
Leah Martinsson, Executive Director, Texas Alliance of Groundwater Districts
County Commissioners & Judges Panel
Moderator: The Honorable Jan Roe, Former Robertson County Judge and Current Board President, Brazos Valley GCD
Tim Brown, Former Bell County Commissioner
Will Conley, Former Hays County Commissioner
The Honorable Joe Shuster, Pecos County Judge
The Earth Genome
Glen Low, Founder, The Earth Genome
Finding Meaning in the Numbers: Groundwater Data Panel
Moderator: Glen Low, Founder, The Earth Genome
Erin Atkinson, Vice President, GIS / Technology Practice Leader, HalffAssociates, Inc.
Robert Mace, Interim Executive Director & Chief Water Policy Officer, Meadows Center for Water and the Environment
Suzanne Pierce, Research Scientist, Dynamic Decision Support Systems, Data Management & Collections Group, Texas Advanced Computing Center
Mike Turco, General Manager, Harris-Galveston Subsidence District
Water Valuation & Water Markets Panel
Moderator: Carlos Rubinstein, Principal, RSAH2O
Gabe Collins, Baker Botts Fellow in Energy & Environmental Regulatory AffairsBaker Institute for Public Policy, Rice University
Sharlene Leurig, Chief Executive Officer, Texas Water Trade
Harry Seely, Principal, WestWaterResearch
Keynote Address
Kathleen Jackson, Director, Texas Water Development Board
Day 2 – Wednesday, August 21
Welcome Address
Dirk Aaron, President, Texas Alliance of Groundwater Districts
Adapting to a Changing Landscape: Stakeholders Panel
Moderator: Jason Coleman, General Manager, High Plains Water District
Maurice Hall, Associate VP, Ecosystems – Water, Environmental Defense Fund
Allison Strube, Water Utilities Director, City of San Angelo
Ben Weinheimer, Vice President, Texas Cattle Feeders Association
Karen Work, Water Management Supervisor, ConocoPhillips
Legislative Debrief Panel
Moderator: Leah Martinsson, Executive Director, Texas Alliance of Groundwater Districts
Ty Embrey, Partner, Lloyd Gosselink Attorneys at Law
Greg Ellis, Attorney, GM Ellis Law Firm, PC
Brian Sledge, Managing Partner, SledgeLaw Group, PLLC
Keynote Address
John Sharp, Chancellor of the Texas A&M University System
Legislator Panel
Moderator: Leah Martinsson, Executive Director, Texas Alliance of Groundwater Districts
Representative Tracy King, District 80, Texas House of Representatives
Representative Lyle Larson, District 122, Texas House of Representatives
Representative Poncho Nevárez, District 74, Texas House of Representatives
Senator Charles Perry, District 28, Texas State Senate
Track 1: Stretching the Resource: Innovative Projects
Prospects for Managed Aquifer Recharge from Stormwater for Harris County and Beyond
Gretchen Miller, Associate Professor, Zachry Department of Civil and Environmental Engineering, Texas A&M University
Creative Solutions to Meeting the City of Wolfforth’s Water Demands
Darrel Newsom, City Manager, City of Wolfforth
Calculating Recoverability in ASR Projects
Steven Young, PHD, PE, PG, CGWP, Principal Geoscientist, INTERA
Track 2: Data: Sometimes You Got It, Sometimes You Don’t
Case Study: Technological and Web-Based Solutions to Data Collection, Analysis, and Application in the Houston-Galveston Region
Jason Ramage, Hydrologist, Texas Water Science Center, US Geological Survey
Estimating Use from Exempt Wells
Natalie Ballew, Manager, Groundwater Technical Assistance, TWDB
Quantifying Potential Changes in Recharge from Changes in Weather Patterns
Nick Martin, Principal Scientist, Southwest Research Institute
Track 3: Workshop: Board & Staff Training
Hydrogeology 101
Mike Keester, Project Manager and Hydrogeologist, LRE Water, LLC
Chapter 36 Essentials
F. Keith Good, Shareholder, Lemon Law Firm
Board Governance
Steve Kosub, Senior Water Resources Counsel, San Antonio Water System
Effective Education Programs
Greg Wukasch, External Relations Manager, San Antonio Water System
Track 1: Conserve, Preserve, & Protect: Groundwater Contamination
Reporting Groundwater Contamination. Who’s on first?
Cary Betz, Manager, Permit Support, Compliance, and Groundwater Section, TCEQ
Regulatory Framework Groundwater Contamination from Coal Ash Deposits
Kimberly Mireles, Vice President of Environmental Services, Luminant
Risk Assessment of Oil and Gas Activities on Groundwater Resources
Ron Green, Ph.D., P.G., Institute Scientist, Earth Science Section, Space Science and Engineering Division, Southwest Research Institute
Track 2: Drilling Down: Water Wells
Tracing the Source of Groundwater Through Well Profiling
Noah Heller, President, BESST Inc.
Innovation Software for Permit, Inspections and Production Reporting
Paul Wickman, Director of Applied Technology, RESPEC
A Lower Trinity PWS Case Study
William Gamblin, Associate Principal, Environmental/Water Resources Manager, Braun Intertec
Day 3 – Thursday, August 22
Brackish Groundwater Panel
Moderator: Zach Holland, General Manager, Bluebonnet GCD
Neil Blandford, Senior Vice President and Principal Hydrogeologist, Daniel B. Stephens and Associates
John Meyer, Technical Lead Brackish Resource Aquifer Characterization System, TWDB
Steve Walden, Principal, Steve Walden Consulting
Hope Wells, Water Resources Council, San Antonio Water Systems
Where Do You Draw the Line? Surface Water/Groundwater Interaction
Moderator: John Dupnik, Deputy Executive Administrator, Water Science & Conservation, TWDB
James Beach, Senior Supervising Hydrogeologist and Area Manager, WSP
James Kowis, Principal Owner, James Kowis Consulting
Dave Mauk, General Manager, Bandera County River Authority & Groundwater District
Joe Yelderman, PhD, Professor, Department of Geosciences, Baylor University
Case Law Panel
Moderator: Mike Gershon, Partner, Lloyd Gosselink Attorneys at Law
Natasha Martin, Attorney, Graves Dougherty Hearon and Moody
Edmond McCarthy, Partner, McCarthy & McCarthy, LLP
Drew Miller, Partner, Kemp Smith
2018 Summit Presentations
To view the 2017 presentation slides, click on the speakers’ name or the panel title to view a PDF of the Summit slides. Video of perentations will be available on TAGD’s YouTube channel here.
Day 1 – Tuesday, August 28
Welcome Address
Sarah Rountree Schlessinger, Executive Director, Texas Alliance of Groundwater Districts
Moderator: Sarah Rountree Schlessinger, Executive Director, Texas Alliance of Groundwater Districts
Gabriel Eckstein, Director, Program in Natural Resources Systems and Director, International Water Law Project, Texas A&M University School of Law
Robert Mace, Associate Director and Chief Water Policy Officer, The Meadows Center for Water and the Environment
Stacey Steinbach, Assistant General Manager, Texas Water Conservation Association
Groundwater Availability
Moderator: Sarah Rountree Schlessinger, Executive Director, Texas Alliance of Groundwater Districts
Van Kelley, PG, Sr. Vice President; Principal Hydrogeologist, INTERA
Darrell Peckham, Principal, Peckham P.G., LLC
Justin C. Thompson, Doctoral Student, Jackson School of Geosciences, University of Texas at Austin
Keynote Address
Senator Charles Perry, District 28, Texas State Senate
Optimizing the Edwards Aquifer: the next 20 years and beyond
Roland Ruiz, General Manager, Edwards Aquifer Authority
Marc Friberg, Executive Director of External & Regulatory Affairs,
Mark Hamilton, Executive Director of Aquifer Management Services
Groundwater Management in Denmark
Jacob Vind, Counsel General and Head of the Danish Water Technology Alliance in the US, Royal Danish Consulate General
Day 2 – Wednesday, August 29
Opening Remarks
Dirk Aaron, President, Texas Alliance of Groundwater Districts
Groundwater Management Toolbox
Moderator: Dirk Aaron, General Manager, Clearwater UWCD
Vanessa Escobar, Senior Regulatory Compliance Coordinator, Barton Springs Edwards Aquifer CD
Greg Sengelmann, General Manager, Gonzales County UWCD
Gary Westbrook, General Manager, Post Oak Savannah GCD
Moderator: Michael A. Gershon, Principal, Lloyd Gosselink Attorneys at Law
Greg Ellis, Attorney, GM Ellis Law Firm, PC
Stacey Reese, Attorney, Stacey Reese Law PLLC
Celina Romero, Partner, Duggins Wren Mann & Romero, LLP
Representative Lyle Larson, District 122, Texas House of Representatives
Groundwater Transactions
Moderator: Kodi Sawin, Principal, Sawin Group
Kristen Fancher, Attorney, Fancher Legal, PLLC
Jason Hill, Attorney, JT Hill & Co.
John Tracy, Ph.D, Director, Texas Water Resources Institute
TAGD Awards
Workshop: Board & Staff Training
Steve Kosub, Senior Water Resources Counsel, San Antonio Water System
Personnel and Employment Policies for GCDs
Jennifer Smith, Attorney, SledgeLaw Group PLLC
FAQs on the Public Information Act & Open Meetings Act
Kimberly Grinnan Kelley, Attorney, Bickerstaff Heath Delgado Acosta LLP
Groundwater Data & Technology
Sam Hermitte, Assistant Deputy Executive Administrator, Water Science & Conservation, TWDB
Erin Atkinson, Vice President, Halff Associates
Enabling Your Groundwater Data through Dynamic Web Applications & Visualization Tools
Daniel Pearson, Data and Spatial Studies Chief, US Geological Survey
Know Your Aquifer
Wade Oliver, PG, Senior Hydrogeologist, INTERA
Using Remote-Sensed Data to Improve Recharge Estimates
Ron Green, Ph.D., P.G., Institute Scientist, Earth Science Section, Space Science and Engineering Division, SwRI
Single District Groundwater Quality Studies
Paul Kirby, Project Geologist, Daniel B. Stephens & Associates, Inc.
All the Wells & Whistles
Adam Foster, Hydrologist, WWD/PI Program, Texas Department of Licensing and Regulation
Raymond Straub, President, Straub Corporation
Water Well Drillers FAQs
Bobby Bazan, Water Resource Specialist, Post Oak Savannah GCD
Pete Brien, Owner, Brien Water Wells
Emerging Groundwater Management Trends
Managed Recharge – Beyond the ASR Well
Stephanie Moore, Senior Hydrologist, Daniel B. Stephens & Associates, Inc.
Aquifer Subsidence Vulnerability
Mike Keester, Project Manager and Hydrogeologist, LRE Water, LLC
How and Why GCDs Might Support the Oil and Gas Wastewater Recycling Efforts
Adam Friedman, Associate, McElroy, Sullivan, Miller & Weber, LLP
Day 3 – Thursday, August 30
Conservation & Stewardship in Texas Groundwater
Moderator: Vanessa Puig-Williams, Puig-Willaims Law, PLLC
Grant Ellis, Natural Resources Manager, Parks and Recreation Department, City of San Antonio
Blair Fitzsimmons, Chief Executive Officer, Texas Agricultural Land Trust
Roel R. Lopez, Ph.D., Director, Texas A&M Natural Resources Institute
Lori Olson, Executive Director, Texas Land Trust Council
Legislator Panel
Senator José Rodríguez, District 29, Texas Senate
Representative Paul Workman, District 47, Texas House of Representatives
GCD Innovation & Inspiration: Stories from the field
Moderator: Ronnie Hopper, Board Member, High Plains Water District
North Plains Master Irrigator Program
Kirk Welch, Assistant General Manager-Outreach, North Plains GCD
Horizontal: An Innovative Supply Well
Jason Coleman, Manager, High Plains Water District
Visualizing Your Aquifer using Geophysical Characterizations at Multiple Scales
Scott Ikard, Hydrologist, Texas Water Science Center, US Geological Survey
Layne Marlow, Field Technician, South Plains GCD
Mitchell Sodek, General Manager, Central Texas GCD
Andrew Teeple, Hydrologist and Geophysics and Subsurface Analysis Unit Team Lead, Texas Water Science Center, US Geological Survey
To view the 2017 presentation slides, click on the speakers’ name or the panel title to view a PDF of the Summit slides. If there is a presentation missing that you’d like added or if there is a problem with the file, please email groundwater@iemshows.com. View sessions on our Youtube channel here.
Day 1 – Tuesday, August 29
Welcome Address & Opening Remarks
Sarah Rountree Schlessinger, Executive Director, TAGD
100 Year Anniversary of the 1917 Conservation Amendment
Moderator: Ken Kramer, Water Resources Chair and Legislative Advisor, Sierra Club – Lone Star Chapter
Carole Baker, President/CEO, Texas Water Foundation
Karen Guz, Conservation Director, San Antonio Water System
Carlos Rubinstein, Principal, RSAH2O, LLC
Andy Sansom, Executive Director, The Meadows Center for Water and the Environment
Thales Smith, University of Texas School of Law
The Value of Groundwater: Market Valuation & Assessment
Peter Lake, Director, Texas Water Development Board
Amy Hardberger, Esq., Associate Dean, St. Mary’s University School of Law
Charles R. Porter Jr., Ph.D., College of Education, St. Edward’s University
David W. Yoskowitz, Ph.D., Associate Director & HRI Endowed Chair for Socio-Economics, Harte Research Institute, Texas A&M University-Corpus Christi
Groundwater Users – Correlative Rights, Existing Use, & Curtailments
Moderator: Alan Day, General Manager, Brazos Valley GCD
Charles Bowers, Ag Producer and Board Member, Panhandle GCD
David Coleman, Director of Water Services, City of College Station
Ronald Gertson, Board Member, Texas Rice Producers Legislative Group
Lara Zent, Executive Director and General Counsel, Texas Rural Water Association
Planning Ahead: Current Groundwater Projects for Tomorrow’s Needs
Moderator: Bobby Bazan, Water Resources Management Specialist, Post Oak Savannah GCD
David Collinsworth, Regional Manager, Brazos River Authority
Dana Porter, Program Leader and Associate Dept. Head, Texas A&M AgriLife Extension Services
Tom Ray, Water Resources Programs Manager, Lockwood, Andrews & Newman, Inc.
John Seifert, Project Manager, LBG-Guyton Associates
Day 2 – Wednesday, August 30
Welcome & Opening Remarks
Joe B Cooper, President, TAGD
Keynote Address
Senator Charles Perry, District 28, Texas State Senate
Similar Rules: a Discussion with Groundwater Management Areas
Moderator: Sarah Rountree Schlessinger, Executive Director, TAGD
Ronald Fieseler, General Manager, Blanco-Pedernales GCD
Dave Mauk, General Manager, Bandera County RA & GD
Jim Totten, General Manager, Lost Pines GCD
Gary Westbrook, General Manager, Post Oak Savannah GCD
Keynote Address
Honorable Nathan L. Hecht, Chief Justice, Supreme Court of Texas
Legislative Debrief
Moderator: Sarah Rountree Schlessinger, Executive Director, TAGD
Greg Ellis, Attorney, GM Ellis Law Firm PC
Ty Embrey, Attorney, Lloyd Gosselink Attorneys at Law
Monique Norman, Attorney
Brian Sledge, Attorney, SledgeLaw PLLC
Hope Wells, Corporate Counsel, San Antonio Water System
Luncheon Keynote Address
Dr. Leyon Greene, Hydrologist and Meteorologist, TexMesonet, TWDB
Breakout 1, Track 1: Groundwater Research and Science
Moderator: C.E. Williams, General Manager, Panhandle GCD
Water Level Monitoring Networks and Analysis of Data for Assessing DFCs
Jevon Harding, P.G., Hydrogeologist, INTERA
Use of Coupled Surface Water/Groundwater Models in Managing Water Resources
Ronald Green, Ph.D., P.G., Institute Scientist, Southwest Research Institute
Influence of Urban Pumping on Groundwater Quality
Peter Knappett, Assistant Professor, Department of Geology & Geophysics, Texas A&M University
Breakout 1, Track 2: Getting Deep: Water Wells
Moderator: Steve Walthour, General Manager, North Plains GCD
Look Before You Drill
Doug Laymon, Geophysical Services Manager, Collier Consulting, Inc.
Protecting Your Groundwater Assets
Dan Haddock, Principal Engineer, INTERA
Educating the Well Owner
Drew Gholson, Water Resources Program Specialist, Texas A&M AgriLife Extension
Breakout 2, Track 1: GCD Board Member Training
Moderator: Zach Holland, General Manager, Bluebonnet GCD
The Intricacies of Chapter 36
Shauna Fitzsimmons, Attorney, SledgeLaw PLLC
Russ Johnson, Attorney, McGinnis Lochridge
Application of Oil & Gas Principles to Groundwater Law
Bill Dugat, Attorney, Bickerstaff Heath Delgado Acosta
Board Member Responsibility & Liability
Drew Miller, Attorney, Kemp Smith LLP
Breakout 2, Track 2: Groundwater Databases & Data Collection
Bobby Bazan, Water Resources Management Specialist, Post Oak Savannah GCD
How Technology Can Help GCDs Fulfill Their Missions
Michael Keester, P.G., Project Manager and Hydrogeologist, LRE Water, LLC
Dave Colvin, P.G., Project Manager, LRE Water, LLC
Using Your Data Efficiently and Effectively
Suzanne Pierce, Research Scientist, Texas Advanced Computing Center, UT Austin
Day 3 – Thursday, August 31
Welcome Address & Introductions
Sarah Rountree Schlessinger, Executive Director, TAGD
The Impact of DFC Monitoring & Implementation on Planning
James Beach, Senior Vice President, LBG-Guyton Associates
DFC Tracking Panel
Moderator: James Beach, Senior Vice President, LBG-Guyton Associates
Dirk Aaron, General Manager, Clearwater UWCD
Greg Sengelmann, General Manager, Gonzales County UWCD
Steve Walthour, General Manager, North Plains GCD
Case Law Update
Moderator: Susana Canseco, Attorney, Branscomb PC
Troupe Brewer, Attorney, Lloyd Gosselink Attorneys at Law
Kristen Fancher, Attorney, Fancher Legal, PLLC
Vanessa Puig Williams, Attorney, Puig Williams Law
Emily Rogers, Attorney, Bickerstaff Health Delgado Acosta LLP
Advanced Groundwater Technology Panel
Moderator: Sarah Rountree Schlessinger, Executive Director, TAGD
Texas A&M ASR Initiative
Dr. Gretchen Miller, Water Management and Hydrological Science Program Faculty, Texas A&M University
Brackish Desal – Beyond the Bad Water Line
Stephen Hoff, GIS Analyst, Bexar County Information Technology
3-D Modeling, Visualization, and Management
Gabe Collins, Baker Botts Fellow in Energy & Environmental Regulatory Affairs, James A. Baker III Institute for Public Policy, Rice University
Bill Mullican, Principal, Mullican & Associates
Michelle Sutherland, Independent Researcher, Michelle A. Sutherland LLC
Nathan Toll, Senior Research Scientist, Southwest Research Institute
Michael Turco, General Manager/CEO, Harris-Galveston Subsidence District