smith deirdre 06 cropped

Stacy B. Ziegler, P.E., LEED AP BD+C, Chief Executive Officer

With over 22 years of experience in the industry, Ms. Ziegler is a proven leader and expert in geotechnical engineering and field services. Her technical experience includes geotechnical analysis, pile capacity, slope stability, design of mechanically stabilized earth structures, specialized geotechnical laboratory testing and pavement evaluations. She also provides oversight/management of a diverse range of construction review projects, building on her years of experience with field review services. Her experience also includes field review of specialized instrumentation, concrete, utilities/piping earthwork, and video inspections, as well as geothermal feasibility evaluations and geothermal vertical closed loop installations.




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Deirdre S. Smith, P.E., LEED AP BD+C, Chief Operating Officer

With over 30 years of experience in civil, water resources and geotechnical engineering, Ms. Smith is responsible for management and oversight of the firm’s civil and site engineering, environmental, hydrogeologic, water resources and natural resources professional staff and projects.  She has also coordinated field review, analysis and report preparation for geotechnical subsurface evaluations, performed and served as the senior reviewer on slope stability analysis geotechnical and civil engineering projects including dikes, embankments and landfills, as well as the installation, field monitoring, data reduction and interpretation, and report preparation for geotechnical instrumentation projects.




Marcozzi 08 croppedGuy Marcozzi, P.E., LEED AP BD+C, President 

Mr. Marcozzi has over 30 years of diverse experience in performing and managing civil, geotechnical and structural engineering. His experience includes geotechnical and structural evaluations and design, land development, transportation and sustainable design with emphasis on effective and incorporation of existing site features into the project and sustainable development.   Mr. Marcozzi’s knowledge of civil engineering, structural engineering, the geosciences and real life construction results in innovative, pragmatic and cradle to grave solutions, which provide unique value to our clients.




bross 2010 croppedJeffrey M. Bross, P.E., LEED AP, F. ACEC, Senior Consultant 

Mr. Bross has consulting and project management responsibility for civil engineering, coastal engineering, water resources, environmental, hazardous waste, and regulatory agency projects.  He has extensive experience in the preparation and attainment of permits and the development of requisite mitigation associated with permitting for difficult and challenging projects.  Mr. Bross has been a principal regulatory negotiator and has a strong working relationship with local, state, and federal regulatory agencies throughout the Mid-Atlantic region.  He was instrumental in drafting the revision of the Unified Development Code (UDC) of New Castle County on behalf of the Consulting Engineers Council of Delaware, Committee of 100, and the New Castle County Chamber of Commerce.  He has authored numerous technical articles and papers, and is a featured speaker on issues involving environmental and construction matters.


Cloonan 04 croppedJames F. Cloonan, P.E., Senior Consultant

Mr. Cloonan has been with Duffield Associates for over 30 years and his responsibilities include coordinating the activities of geotechnical and foundations engineering personnel, contract development, and client interface. As a Senior Consultant, Mr. Cloonan was previously responsible for coordination of the company’s design build projects, contract development, and client interface.  Project Manager responsibilities include all phases of site development, construction management, subsurface soil condition analysis, report preparation, and construction review for the purpose of foundation, pavement and earthwork design and construction, and materials testing.




Stack 01 croppedW. Hank Stack, P.E., Field Services Division Director 

Mr. Stack’s responsibilities as the Geotechnical and Field Services Division Director include overseeing all field and laboratory operation for the firms multiple offices, including two AASHTO laboratories one of which is authorized to perform testing for the USACE. His responsibilities include management of field drilling programs, geotechnical analysis and preparation of geotechnical evaluation reports, construction consulting for optimizing best practices to add value to client’s needs.  He has served as Project Manager for the firm’s larger sampling, instrumentation, earthwork, concrete, steel, and pavement construction projects.  His experience includes field review of pile, micro pile and caisson installations; geotechnical instrumentation; structural steel review, concrete, masonry, earthwork and sediment and erosion control measures using best management practices.



Stack 01 croppedDavid Small, Environmental Division Director

As Senior Consultant, David Small is part of Duffield’s Environmental group. David recently joined Duffield following a 30-year career with the Delaware Department of Natural Resources and Environmental Control (DNREC) where he served most recently as Cabinet Secretary.






WaltersD. Dwight Walters, P.E., Civil Engineering Division Director

Mr. Walters has over 26 years of experience in design and project management of civil engineering related projects – including civil-site design, municipal engineering, surveying, water resources and water/wastewater practices. He has been leading and managing engineering departments and offices since 1997. These duties included overall supervision of the following departments: Urban Planning & Development, Municipal Engineering, Surveying, Environmental Planning, Environmental Engineering and Construction Inspection. Mr. Walters has managed commercial, industrial and residential projects both in the public and private sector.




HoffmanScott C. Hoffman, P.E., Water Resources Division Director

Mr. Hoffman’s primary responsibilities include all phases of project management of large scale water and wastewater projects for both municipal and industrial clients. His experience with water projects includes potable water treatment plants, both iron and arsenic removal, and distribution systems. His municipal wastewater project experience with New Castle County includes sequential batch and membrane reactors as well as conventional activated sludge. Much of his extensive industrial wastewater treatment experience is for poultry industry upgrades and expansions for spray irrigation disposal systems. Mr. Hoffman also has singular skills for the use of GIS as a tool for data collection, planning, and preliminary engineering.



devine-croppedBrian J. Devine, P.E., Geotechnical Division Director

Mr. Devine serves as a manager in the Field Services Division where he manages multidisciplinary projects including: geotechnical design/analysis/reporting and construction review. His geotechnical responsibilities include design and review of field drilling programs, soil and rock core sampling and logging, geotechnical analysis (bearing capacity and settlement, pile analysis), design of ground improvement programs, design of earth retention systems, preparation of geotechnical evaluation reports, and slope stability analyses. His experience also includes the design of articulating concrete block revetment systems, temporary shoring systems and mechanically stabilized earth structures and slopes.



Beringer 99 croppedM. Richard Beringer, P.E., LEED AP, REP,  Senior Environmental Consultant

Mr. Beringer has over 35 years of environmental experience. He is responsible for project management, planning, and technical issues for environmental engineering and science projects. Project experience includes: project planning and permitting assistance; Phase I, and II Environmental Assessments; hydrogeologic investigations, sediment and water quality assessments, remedial investigations, water/wastewater studies, NPDES compliance, environmental impact statements (EIS), state and federal Superfund Sites site evaluation and remediation; emergency response actions; industrial waste landfill design, flood modeling and flood hazard reduction planning; and Brownfield Program Sites.




Jenkins 05 croppedW. Andrews Jenkins, P.G., LEED BD+C, Senior Environmental Project Manager/Senior Geologist

Mr. Jenkins has over 30 years of environmental experience and is a Senior Project Manager in our firm on the environmental services team. Mr. Jenkins performs property evaluations where adverse environmental impacts may have occurred to soil, sediment, surface water, groundwater, or buildings. These projects include historical research, field sampling, analysis, interpretation, attention to industry standards and regulatory requirements, and communications with clients and regulatory agencies.




Whallon-croppedChristopher C. Whallon, Esq., P.G., Senior Environmental Consultant

Mr. Whallon has over 30 years of diverse environmental experience as an attorney, consultant, and contractor working with both public sector and private clients. His technical experience includes: design, performance and evaluation of multi-disciplinary redevelopment projects; site assessments and characterizations; remedial design and oversight; permitting; compliance evaluation and environmental auditing; and emergency response. His environmental management experience includes positions as a line, section and practice group manager (environmental consulting), department manager (environmental contracting), program management for multi-project initiatives, and project manager. His legal environmental experience includes representing clients in litigation and regulatory matters arising under both federal and state law, property transfer matters, and evaluation and counseling regarding environmental risk.




gresh 2012 preferred Jennifer L. Gresh, P.G., Philadelphia Services Leader

Ms. Gresh has 17 years of experience assessing environmental impact to land, air, and water.  In her capacity as the Philadelphia Services Leader and an Environmental Project Manager, Ms. Gresh oversees Phase I and II Environmental Site Assessments, remedial investigation/feasibility studies, Brownfield Investigations, remedial design, health and safety plans, operation and maintenance plans, spill prevention and countermeasure control plans, stormwater plans, aboveground and underground storage tank removals and assessments, and environmental remediation/cleanup projects.




LewandowskiSteven H. Lewandowski, P.E., Senior Project Manager

Mr. Lewandowski has specialized in providing guidance and service to private utility and local government clients.  Currently, Steve is responsible for all phases of project management for potable water and wastewater facilities projects from project conception to completion.  Mr. Lewandowski has managed the design and construction of potable water facilities projects for Tidewater Utilities, including production/treatment plants, storage tanks, and distribution systems funded through the Drinking Water State Revolving Fund.




LewandowskiStephen Gorski, P.E., Senior Project Manager

As the Branch Manager for the Maryland office, Stephen Gorski, P.E. specializes in many facets of civil engineering in Maryland and Delaware. He has over 30 years of experience in the civil engineering profession, including a wide variety of water resources, public infrastructure, and private land development contracts. He provides project management, civil engineering design and land planning services for both public and private sector clientele. His involvement in public works projects include road, water, wastewater, floodplain modelling, stream restoration, and stormwater management design. His private sector experience includes managing, designing, and permitting for several categories of land development, including single family, townhouse, condominium and multi-family residential projects, school and church contracts, distribution centers, office parks and commercial land development projects.