CURRICULUM VITAE
OF
DAVID B. VANCE
 

1701 W. Cuthbert     Midland, Texas 79701

Phone 432-570-5847     Cell  505-235-4637

E-Mail  2the4@2the4.net      Web Site URL 2the4.net



INTRODUCTION

Mr. Vance has more than 28 years of experience in industry and environmental consulting and research. His technical background encompasses geology, hydrogeology, microbiology, and chemistry. Arenas in which Mr. Vance has exercised his technical and consulting skills include: chemical manufacturing; general industrial; mining; construction; commercial real estate; research & development, and government. He has been responsible for the development and application of programs in the environmental service sector such as remediation design, industrial compliance, risk management, and air quality services. At ARCADIS he is responsible for providing leadership for the development reactive colloid technology, anaerobic bio-oxidation systems, in-situ chemical oxidation processes, and has recently been tasked with taking the lead in the development of Carbon Sequestration Services. Mr. Vance maintains a web site at www.2the4.net that contains on-line versions of over 35 published articles and columns, in addition to white papers on innovative technology developments.

SUMMARY OF QUALIFICATIONS

                TECHNICAL

  • Strong background in the physical and biological sciences including: physics, chemistry, microbiology, geosciences, and computer sciences. Greatest strengths lie in diversity of scientific knowledge, understanding the culture of the scientific disciplines, and the ability to communicate complex scientific concepts to lay people.
  • Engineering systems and programs associated with construction, mining, chemical processes, and commercial real estate. An important component is an understanding and experience in the culture of the engineering disciplines.
  • Technology expertise of breadth and depth, that allows for the management of complex multi-disciplinary projects with diverse staff and technical requirements.
  • Fate and transport of organic and inorganic chemicals in surface and subsurface hydrogeologic systems, including detailed risk analysis.
  • Hydrogeology of heterogenetic anisotropic flow systems in fractured and granular media.
  • Biologically mediated remediation and attenuation processes in groundwater and soil.
  • Physical/Chemical/Biological treatment of soil, groundwater or industrial waste water with difficult contaminants or matrices.
  • Carbon sequestration systems, processes, and monitoring.

 

      MANAGEMENT AND OPERATIONS

  • Executive, regional, and project level national and international technical services delivery and business operations.
  • Strategic Analysis for entry into new endeavors and exits from non-productive ones. Including championing the changes amongst upper management as well as other interested and involved internal and external stakeholders or organizations.
  • Program Development that includes training for sales, technical staff and the public. These activities include the creation of computer based training, support, and operations systems to support the roll-out and implementation of new programs.
  • Ability to analyze large volumes of information (paper or digital) to winnow key pertinent facts to support technical, business and financial decisions.
  • The ability to bring about a consensus for action in situations where multiple parties, with diverse interests, are incapable of independent synergistic fruitful cooperation.
    •  

      COMMUNICATIONS, NEGOTIATION AND SALES

  • Seasoned and capable of negotiating with senior level executives in the Board Rooms of New York, or a foreman on a shop floor in Taipei.
  • Demonstrated and articulate oral and written communication skills at the personal level, as well as the public, that includes speeches, seminars and a published column (go to http://www.2the4.net to view over 35 on-line versions of columns and articles).
  • Contract negotiations associated with external stakeholders and internal management or employee issues.
  • Direct sales experience at all levels in diverse markets, sales management and training at the national level.

 

EMPLOYMENT CHRONOLOGY

1998-Present ARCADIS G&M

  • Providing technical and sales support to project staff in the region and nation wide. Leader (including a patent application) in developing nano-scale colloidal iron technology for the treatment of chlorinated hydrocarbons and oxyanionic metals such as chromate and arsenic. Leader in the development of anaerobic biological oxidation systems. Currently leading development of Carbon Capture and Sequestration services. 
    • 1996-1998  2 The 4 Technology Solutions
  • An environmental consulting practice focused on groundwater resources and remediation in conjunction with an effort to seek venture capital to establish a nation wide virtual based environmental consulting services company.
    • 19941996 KTR Environmental Services, Inc., New York, NY
  • Started-up a firm providing technical due diligence services for the real estate and financial industry, as well as niche environmental services in the industrial sector. Established technical service operations in New York and Los Angeles.
    • 19901994 ATEC Associates, Indianapolis, Indiana
  • Corporate Director of Strategic Services in a $100 million, 1500 employee organization. Responsible for Strategic Analysis and Corporate Program Development including training for sales, technical staff and the public.
    • 19881990 Groundwater Technology, Mandeville LA
  • Regional Technical Services Manager. Focus was on sales, staff support, and training in industrial/chemical/petroleum settings for GTI's 10 state Southern Region. Technical Service areas of practice and support included hydrogeology, biosciences, and physical/chemical treatment systems.

SELECT PROJECT EXPERIENCE

Remediation

Assessment, Monitoring and Remediation of Gas Releases from Carbon Dioxide Flood to Drinking Water Aquifers - West Texas
Development of assessment and monitoring programs for management of gas releases from carbon dioxide EOR floods in two areas of a large scale EOR program in West Texas. Includes the development and monitoring of remediation programs. One area involves large scale groundwater recovery with pressure/depressurization cycles, another a treatment system installed on the water supply for a residence.

Bioreductive Dehalogenation of Chlorinated Solvents - Houston, Texas
Remediation of a large chlorinated solvent plume through the addition of soluble carbon substrate to induce biologically driven reductive dehalogenation.

Chemical Oxidation of Chloroform – Pharmaceutical Production Facility - Sao Palo, Brazil
Used hydrogen peroxide injection, the pH buffer profile of the soils, and native iron minerals to stimulate Fenton’s Oxidation of chloroform.. Successful in reducing the chloroform concentration in groundwater from greater than 500 mg/L to less than 100 mg/L (at which point biological processes can take over).

Reductive Dehalogenation of Chlorinated Solvents with PdFe Nano-Scale Colloids - Texas
A phase one field pilot test of nano-scale palladium iron colloids to treat groundwater impacted with chlorinated solvents at an industrial facility on the Southern Gulf Coast of Texas. Control of colloid behavior when mixed with native groundwater and exposed to geologic surfaces is a core component of this project.

Biological In-Situ Chromate Reduction - Dallas, Texas
Remediation of a hexavalent chromium groundwater plume associated with a plating operation. Using injection of soluble carbon substrate to lower redox conditions, stimulate bacteria reduction, and induce abiotic reduction of soluble chromate to the insoluble trivalent chrome.

Development of Anaerobic Bio-Oxidation Program for Terminal Along Houston Ship Channel
Houston, Texas

This is a large complex facility used for storage and transfer operations at the Houston Ship Channel. Performed a biogeochemical evaluation and designed anaerobic bio-oxidation programs for an MTBE plume and a mixed Benzene/DCA plume in another area. An infiltration array was installed beneath two 180 foot diameter replacement tanks. Field pilot studies were successfully implemented, currently in the design stage for full scale application. 

US Navy - Reductive Dehalogenation Pilot Study - Dallas, Texas
Performing a full scale field pilot study to evaluate reductive dehalogenation in a multi-level aquifer. Using the injection of soluble carbon substrate to control redox conditions and stimulate anaerobic reductive dehalogenation.

Pond Closures And Clean-Outs, Petrochemical Sludges - Freeport, Texas
Developed sampling plan and design study for a major international chemical manufacturer for bioremediation of petrochemical sludges that were significantly contaminated with exotic and heavy metals (Co, Ni and Pb) located in a series of 3 emergency dump ponds. Successfully provided client with specific aeration needs, nutrient requirements, optimum operation procedures and anticipated kinetic rates for the construction of an on site biodegradation system for the organic component of the sludges.

Bioremediation at a Superfund Site - Florida
The Dubose Superfund site had 70,000 cubic yards of soil contaminated with PNA's and PCP. Successfully adopted an approach more cost effective than that dictated by the ROD utilizing active cometabolic degradation of the contaminants of concern in conjunction with on-site growth of indigenous organisms for batch inoculation.

In-Situ Treatment of Large Condensate Plume at Pipeline Facility
Kermit, Texas

Designed and installed the 1st stage full scale system that uses circulation well technology and in-situ biodegradation to remediate a 3,000 by 800 foot condensate plume without the need for any groundwater or soil vapor recovery

Aboveground Bioremediation Of Crude Oil Contaminated Soils - Southeast Texas
The facility is part of the Strategic Petroleum Reserve. Contaminated soils (1300 yd3) were excavated and treated using induced aeration and nutrient addition.

Waste Water Sludge Dewatering And Odor Control - Dow Chemical, Midland, Michigan
Retained for technical support regarding the removal and treatment of 650,000 cubic yards of solids from a hazardous waste treatment plant retention pond. These solids included biomass, inorganic precipitates, organic chemicals, and miscellaneous materials (such as IX resins). Aided in the preparation of a closure plan and supporting treatability studies. Issues resolved included dewatering, filtration, treatment of filtrate and odor control

Former Chlorinated Solvent Manufacturing Facility - Baton Rouge, LA
Performed bench scale feasibility study to evaluate the potential for biodegradation of mixed chlorinated solvents impacting clay rich soils. Core of study involved the evaluation of cometabolic degradation (using methane. Followed up with the design for a field scale pilot study.

Waste Water Treatment

Selenium Removal From Waste Water At Glass Manufacturing Facility - Los Angeles, CA
A large national glass manufacturer uses elemental selenium to decolorize their product. The selenium in turn is captured in a scrubber installed on the discharge of the glass furnace. A 10 gpm waste water flow is discharged with over 1.2% TDS and 40 ppm selenium. Designed and applied a process using metallic zinc powder was designed to reduce selenate to selenite followed by ferric iron adsorption, precipitation, coagulation, settling, and filtration. This lowered selenium concentrations to less than 1 ppm meeting the clients discharge requirement.

Invention of Unique Precious Metal Cyanide Treatment System
Developed and applied a treatment system that utilized cationic reductants adsorbed to a stabilized biological granule to split silver and gold from cyanide waste streams. The system eluted free cyanide (which required further treatment) and recovered silver and gold as colloids dispersed in the biogranule matrix.

Invention of an Oxyanionic Sorption Process
Through the use of cell fractionation and activation protocols developed a biological granule that acted as an anionic exchange media. Full development from an "idea" through bench scale refinement, to full scale field operation.

Zinc Galvanizing Operation For Big Three Auto Manufacturer - Longmont, Colorado
Removal of 5 mg/l of mixed metals, primarily zinc (4 mg/l) and nickel (1 mg/l) from plating process rinse waters at an average flow of 12.5 (7200 GPD). Treatment system was a fluidized-bed contactor with a cationic biological adsorption agent.

USGS Analytical Laboratory - Denver, Colorado
Removal of 200 mg/l hexavalent chromium from laboratory waste waters at an average flow of 600 gal/month; using a packed bed canister system containing anionic biological ion exchange media for hexavalent chromium removal. Also removal of 50 mg/l of mercury from laboratory waste waters at an average flow of 350 gal/month.

Utility Company - Northwest New Mexico
Removal of 50 mg/l of chromium (a mixture of trivalent and hexavalent species) from 27,000 gallons of compressor cooling water at two remote locations. The discharge standard was 0.05 mg/l total chromium. Primary treatment consisted of chromate removal with anionic biological ion exchange media. To meet the stringent discharge level, a magnesium oxide precipitation/ adsorption system was designed for removal of soluble and complexed forms of cationic Chromium III that were not removed by the anionic Metal Removal Agent.

Geohydrology

Design Of Groundwater Recovery System Adjacent to Storm Water Piping - Dallas, Texas
An aerospace industrial facility in had multiple contaminant plumes of petroleum and chlorinated hydrocarbons. One of the plumes on the periphery of the site had impacted and infiltrated a large diameter storm water drain off-site. Designed a groundwater recovery system to capture (from on-site) the impacting groundwater.

Ground Water Reinjection At Refinery Boundary - Ponca City, Oklahoma
Evaluation of geochemical interaction of injection water with formation water, leading to formation plugging at a refinery using water mounding to control off-site migration of free phase hydrocarbons. Also recommended chemical treatments for well flushing to remove fouling and inhibit biological activity.

Geochemical Evaluation Of Pulp And Paper Landfill - Central Louisiana
Used geochemical assessment and Stiff plots to prove to the LA DEQ that landfill leachate with high TDS and metals content had not impacted groundwater systems adjacent to the landfill.

Water Resource Evaluation - Southern Colorado
Prepared a review of regional groundwater setting, pumping effects, efficacy of evaluation models, and alternative assessment approaches in support of a permit application for groundwater production required for a cement manufacturing facility.

Risk

Risk Assessment At Industrial Facility - Tricities Area, Virginia
An industrial facility had releases of chlorinated solvents dating to the World War II era. A 200 foot well on the site screened in fractured bed rock was impacted with dissolved chlorinated solvents. A health based risk assessment was prepared to obviate the need for a potentially extremely expensive remediation program for the deep aquifer.

Risk Assessment at Industrial Facility - Indianapolis, Indiana
A leaking underground storage tank containing chlorinated solvents was removed and the pit over-excavated by the client. The excavated soils were stored on site. They received a $750,000 fine for RCRA violations. Prepared a risk assessment for the USEPA Region 5 office in Chicago that proved no harm to the environment, reducing the fine to $220,000.

International Chemical Facility Audits
Coordination of a Fortune 100 chemical manufacturer multi-site audit of facilities in Holland, France, Japan, South Korea, Taiwan, Singapore and the USA. Project duration from notification to project completion was three weeks, as required by the clients tight schedule for a division divestiture.

Expert Legal Support

Remediation Evaluation And Cost Estimate - City of Austin, Texas
The City of Austin has a public park that has been impacted by the migration of petroleum hydrocarbons from multiple off-site bulk storage facilities operated by major oil companies since the 1940s. Retained by the city’s attorneys for two tasks. First, to support the legal case that the hydrocarbon impact in the park did originate from the bulk storage facilities. Secondly, to evaluate remediation approaches, and estimate costs and time frames for the remediation of the park.

Situational Assessment at Mine - Central New Mexico
An old (originally dating to Spanish Colonial and Native American activity) silver/gold/copper mine was being converted to industrial garnet production. Before production began they were stopped by politically driven rezoning. Interviewed the mine development staff, state regulators, legal representatives, and other retained consultants. A report was prepared with suggestions on how to overcome opposition from local "green" groups, as well as deal with the political pressure.

NCP Cost Recovery Action Lead Contaminated Site – Kansas
Retained by defendant’s counsel to review assessment and remediation costs, compliance with NCP procedures, and impact of the lack of thirdparty due diligence during a property transfer. Depositions have taken place, awaiting trial.

Remediation Cost Evaluation for Pipeline Release - West Texas
Prepared cost estimate for remediation costs in support of testifying expert.

Remediation Cost Evaluation for Release at a Natural Gas Plant -West Texas
Reviewed and revised remediation approach and cost estimates in support of testifying expert.

Remediation Cost Evaluaton CVOC Relaease at a Pharmaceutical Facility -West Texas
Developed remediation approach and cost estimate in support of testifying expert.

Expert Legal Support

Remediation Evaluation And Cost Estimate
City of Austin, Texas

The City of Austin has a public park that has been impacted by the migration of petroleum hydrocarbons from multiple off-site bulk storage facilities operated by major oil companies since the 1940s. Retained by the city’s attorneys for two tasks. First, to support the legal case that the hydrocarbon impact in the park did originate from the bulk storage facilities. Secondly, to evaluate remediation approaches, and estimate costs and time frames for the remediation of the park.

Situational Assessment At Mine
Central New Mexico

An old (originally dating to Spanish Colonial and Native American activity) silver/gold/copper mine was being converted to industrial garnet production. Before production began they were stopped by politically driven rezoning. Interviewed the mine development staff, state regulators, legal representatives, and other retained consultants. A report was prepared with suggestions on how to overcome opposition from local "green" groups, as well as deal with the political pressure.

NCP Cost Recovery Action Lead Contaminated Site
Kansas

Retained by defendant’s counsel to review assessment and remediation costs, compliance with NCP procedures, and impact of the lack of third party due diligence during a property transfer. Deposed prior to settlement.

Evaluation of Remediation Costs for Pipeline Release
West Texas

Prepared cost estimate for remediation costs in support of testifying expert.

Evaluation of Remediation Costs for the Release of Light Hydrocarbons at a Natural Gas Plant
West Texas

Reviewed and revised remediation approach and cost estimates in support of testifying expert.

Evaluation of Remediation Costs for the Release of Chlorinated VOCs at a Pharmaceutical Facility
West Texas

Developed remediation approach and cost estimate in support of testifying expert.

Evaluation of Hydrocarbon Impacts on Groundwater from Petroleum Pipeline Release
Midland, Texas

Evaluated biogeochemical and hydrogeologic data to render an opinion on the timing and volume of a crude oil release from a pipeline; and the rate at which the groundwater impact was migrating. This included an assessment of the natural attenuation processes and rates. Deposed before trial. 

Evaluation of Hydrocarbon and Brine Impacts from Petroleum Production Field
Central, Texas

Evaluated hydrocarbon and brine impacts in petroleum production field in which activity dated to the 1940’s. Developed approach to assess extent of impact and remediation costs for multiple crude oil and brine release sites in support of testifying expert.

Evaluation of Hydrocarbon Release from Pipeline
Central, Oklahoma

In support of testifying expert evaluated costs associated with remediation of a pipeline release impacting groundwater.

Forensic Evaluation

Evaluation of Biogenic Acetone at Petrochemical Terminal
Houston Ship Channel

Evaluated biogenic production at a large petrochemical shipping terminal that handled petrochemicals including pure benzene. Provided evidence and arguments that detected acetone was a biogenic degradation product and not an original product release.

Geochemical Evaluation Of Pulp And Paper Landfill And Surrounding Aquifer
Central Louisiana

Used geochemical assessment and Stiff plots to prove to the LA DEQ that landfill leachate with high TDS and metals content had not impacted groundwater systems adjacent to the landfill.

 

EDUCATION

M.S. Geology (Hydrogeology/Geochemistry), Washington State University, Pullman
B.S. Geologic Science, New Mexico State University, Las Cruces

 

PUBLICATIONS

      Vance, David B., 2005. Nanoscale Iron Colloids: The Maturation of the Technology for Field Scale Applications, Pollution Engineering, Vol. 37, No. 7, pp. 16-18, July, 2005.

      Lutes, C.C., Liles, D.S., Suthersan, S.S., Lenzo, F., Hansen, M., Payne, F.C., Burdick, J.V., and Vance, D., 2003. DNAPL Dissolution, Environ. Sci. Technol., Corr./Rebuttal); 2003; V. 37, No. 11, pp. 2618-2619.

      Nyer, Evan K. and Vance, David B., 2001. Nano-Scale Iron for Dehalogenation, Spring 2001, GWMR, Vol. 21, No. 1, pp. 41-46, 2001.

      Nyer, Evan K. and Vance, D.B., 1999. Hydrogen Peroxide Treatment: The Good, the Bad, the Ugly, Summer 1999, GWMR, Vol. 19, No. 3, pp. 54-57, 1999.

      Vance, D.B., 1995. Arsenic - Chemical Behavior and Treatment, the National Environmental Journal, Vol. 5, No. 3.

      Vance, D.B., 1993. Remediation by In-Situ Aeration - The Power of Volatilization and Bio- Oxidation, The National Environmental Journal, Vol. 3, No. 4, pp. 59-62.

      Vance, D.B., 1991. On-site Bioremediation of Oil and Grease Contaminated Soils, The National Environmental Journal, Vol. 1, No. 1, pp. 26-30.

      Vance, D.B. and Matranga, M., 1989. Forced Aeration Biodegradation of Oil and Grease Contaminated Clays in an Aboveground Bioreclamation Cell, Conference Papers, Petro-Safe 89, V. 2, p. 749-760.

      Brierley, J.A. and Vance, D.B., 1987. Recovery of Precious Metals by Microbial Biomass, Biohydrometallurgy International Symp., University of Warwick, Coventry, England.

       

      ENVIRONMENTAL TECHNOLOGY GROUNDWATER COLUMNS

      Groundwater Remediation - First Principles

      Hydrophobic Organic Chemicals and Total Organic Carbon: The Ideal and Reality of Site Clean-Up

      Understanding the Limitations of In-Situ Bioremediation

      Groundwater Injection and Problem Prevention

      Metals and Groundwater Part I: Source and Mobility

      In-Situ Bioremediation of Metals-Contaminated Groundwater

      Remediation of Metals-Contaminated Groundwater Part III: Electrochemical Processes

      Iron: The Environmental Impact of a Universal Element

      Anisotropic Hydrology Part I: Fracture Flow Systems

      Anisotropic Flow in Heterogenetic Granular Media: Analysis of Complex Flow Systems

      Particulate Transport in Groundwater, Part I: Colloids

      Particulate Transport in Groundwater, Part II: Bacteria

      Physical Properties of DNAPLS and Groundwater Contamination

      Site Assessment and Remediation Focus on the Possible

      Groundwater Remediation by No Action the Role of Natural Attenuation

      In-situ Treatment of Groundwater Contaminated with Chlorinated Solvents, Recent Developments

      Risk, Costs and Benefits the New Groundwater Regulatory Paradigm

      Phytoremediation Enhancing Natural Attenuation Processes

      Heat in Groundwater Systems Part I - Fundamentals

      Heat in Groundwater Systems Part II - Effect on Physical Properties and Reaction Kinetics

      Groundwater and Redox Potential

      Life on Mars the Ubiquitous Vigor of Microbiological Systems

      Natural Attenuation and Pump and Treat Remediation

      Natural Attenuation: Transverse Dispersion as the Natural Driving Force

      Natural Attenuation: Methanogenic Systems

      What's Toxic/What's Not

      Reactive Barriers - A Passive Treatment Alternative Adjacent to Source Zones

      Horizontal Wells

      Monitor Wells - To Purge or Not to Purge

      MTBE - Reality and Consequences.

      Application of High Technology to Groundwater Issues.

      Enhanced Groundwater Remediation Part I: Available Reaction Processes.

      Enhanced Groundwater Remediation Part II: Physical Processes.

      New Applications of REDOX Reactions for In-Situ Groundwater Remediation.

      Biofouling of Wells - Causes and Solutions

      Selected Presentations

      February, 1989 - Annual PetroSafe Conference, Houston, Texas: "Forced Aeration Biodegradation of Oil and Grease Contaminated Clays in an Aboveground Bioreclamation Cell."

      May, 1989 - Annual meeting of the Independent Liquid Terminal Association (ILTA), Houston, Texas: "The Typical Hydrocarbon Site - Fate, Transport and Remediation."

      October, 1991 - Civil Engineering Professional Development Seminar, Purdue University, Lafayette, Indiana: "Description and Selection Criteria for On-Site Remediation Technologies."

      October, 1992 - Executive Enterprises, Environmental Regulation Course, Louisville, Kentucky. "Superfund, Sins of the Past, Hope for the Future, and How to Deal with the Present.”

      December, 1995 - New York Department of Environmental Quality, Albany, New York, Seminar on Intrinsic Remediation. 

      November, 1996 - New York Maritime Conference, New York, NY. "Microbiological Remediation Technologies for Treatment of New York Harbor Dredge Spoils."

      August, 2000 - SETMA 2000 - Seminario de Tecnologias para Meio Ambiente - Brazilian Association of Sanitary Engineering, Sao Palo, Brazil. “The Current State of Remediation Technology - Extraction Versus Injection - Advantages and Limitations of Each”

      March, 2002 – American Association of Petroleum Geologists, Annual Meeting, Houston, Texas -Stimulated Anaerobic Degradation of Petroleum Hydrocarbons”

      May, 2002 – Battelle International Conference on Remediation of Chlorinated Solvents and Recalcitrant Compounds, Monterey, CA. – “Chemical Oxidation and Biological Dehalogenation of Chloroform”

      April, 2003 - National Environmental & Safety Conference , National Association of Petroleum Refiners, New Orleans, LA - Anaerobic Oxidation Systems for Hydrocarbons

      March, 2004 – Southwest Section AAPG, El Paso Texas - Anaerobic Bio-Oxidation of MTBE and 1,2-DCA

      March, 2004 – Presentation to the Texas Commission on Environmental Quality (TCEQ) – Practical Aspects of the Use of IRZ Technology to Remediate Chlorinated Solvents

      April, 2004 – ARCADIS sponsored 3 hour presentation at the Petroleum Club in Midland, Texas attended by the industrial and regulatory communities. LNAPL Assessment, Remediation, and Management; the State of the Art.

      April, 2004 – AAPG Annual Meeting, Dallas, Texas - The Effect of Physical, Geochemical, and Microbiological Heterogeneity on the Assessment and Remediation of Contaminated Soil and Groundwater

      October, 2005 – Evaluation of the Control of Reactivity and Longevity of Nano Scale Colloids by the Method of Colloid Manufacture, EPA Nanotechnology for Hazardous Waste Site Remediation Technical Workshop, Washington DC