Q&A: What are the different types of risk assessment and when are they appropriate?

There are a number of different types of risk assessment that may be completed to inform remedial decisions; however, the risk assessment approach will depend primarily on the project’s regulatory framework.

Screening Level Risk Assessment
Whenever chemical concentration data is compared to numeric, risk-based screening levels, an informal assessment of risk takes place. A screening level risk assessment can be performed by calculating the ratio of the chemical concentration to the screening level and converting the result to a risk probability or hazard quotient. This type of risk assessment is the least complex and is used to quickly differentiate sites in need of regulatory attention from sites with negligible public health risks. Screening levels are calculated using generic, conservative exposure assumptions that may not be appropriate for every site; thus, the reduced complexity could result in unnecessary site cleanup.

Site-Specific Risk Assessment
Many state cleanup programs and the RCRA Corrective Action Program allow site-specific risk assessment. A site-specific risk assessment offers the flexibility to estimate the health effects associated with exposure consistent with current conditions or anticipated future use. A site-specific risk assessment begins with a conceptual site model (CSM) that identifies chemical sources, transport mechanisms, exposure media, human receptors and their potential exposure pathways (e.g., ingestion). The site-specific risk assessment can often incorporate existing or proposed institutional and engineering controls, and can be used to evaluate the health-protectiveness of a proposed remedy. When a site-specific risk assessment is conducted, the regulatory cancer risk and non-cancer hazard thresholds become the metric for determining if remedial action is warranted.


Baseline Risk Assessment
A baseline risk assessment evaluates risk in the absence of remediation and institutional controls, and is required to support development of Superfund remedial alternatives. EPA will use the results of a baseline risk assessment to determine if a site presents an “imminent or substantial” endangerment and make no-action decisions. To provide consistency across sites in the Superfund program, undeveloped areas are typically evaluated under a conservative, future residential land use assumption.

Each of the risk assessments described above are “forward” risk assessments that use chemical data to estimate potential health effects. It is also possible to conduct site-specific and baseline risk assessments in the “backward” direction to develop health-protective, numeric remediation goals.

About Emily Strake
Emily has nearly 20 years of experience in chemistry and human health risk assessment. Her experience includes assessing the potential adverse health effects to humans from exposure to contaminants in soil, sediment, groundwater, surface water, ambient and indoor air, and various types of animal, fish, and plant materials.  She has been the primary author of risk assessment reports and screening evaluations for projects governed under USEPA RCRA and CERCLA, and state programs in Pennsylvania, California, Delaware, Connecticut, Oregon, and Maryland.

Langan Remediation Summit Recap: “Managing Risk at Legacy Sites – Insights for Success”

The three-day Summit highlighted the latest technical and scientific developments with an emphasis on practical experience and solutions for remediation and redevelopment.

“All presenters were asked to share positive developments and insights in their presentations.  We wanted attendees to understand not only the new issues that we face in remediation, but also the progress taking place to address difficult sites,” said Nick DeRose on the goals for the Summit.  This goal was evident in a collaborative and lively session on “emerging contaminants” (more information on this below), as well as a presentation from Dr. Bernie Kueper of Queens University on current research trends in “Methods for Minimizing Contaminant Rebound Including Current Developments in Back Diffusion Phenomena Research,” a critical concern for on-going remediation projects.

For insights into creative mechanisms to manage remediation liability, Curt Toll of Greenberg Traurig and Gary Silversmith of P&L Investments XX teamed to present “Remediation Risk Management, Including Risk Financing and/or Risk Transfer.”

For more information on the presentations, and including obtaining copies, please contact Nick DeRose, Managing Principal at Langan, at nderose@langan.com or 215-491-6510 .

View the full agenda and see what you missed!

Is soil liquefaction a risk in the Middle East?

Soil liquefaction is a phenomenon primarily associated with saturated loose granular soils such as sands, some gravels, and non-plastic silts located close to the ground surface where in situ confining stresses are relatively low.  During earthquake shaking, loose, saturated granular soils tend to contract which can cause an increase in the pore water pressure of the soil particles.  If the shaking is strong enough to increase the pore water pressure beyond the effective confining stress of the soil, the pressure may force the soil particles apart and the soil will then behave similar to a liquid – hence the term “liquefaction”.  Liquefaction can result in a significant reduction in the soil’s shear strength, as well as other ground distress such as sand boils, excessive settlement, and lateral movements.


Yas South Development, Abu Dhabi, UAE

Soil liquefaction can be a risk in the Middle East as groundwater levels are typically high within one to two kilometers of the coast.  The phenomenon is potentially problematic in man-made land reclamation zones, as well as in areas where natural coastal loose sand deposits are encountered.

The liquefaction risk is often exaggerated, as engineers tend to overlook several risk mitigating circumstances, like the high content of fines (silt and clay) within the soil material; the additional surcharge (and hence increased confining stress) due to the subsequent construction of embankments; and also the existence of a surficial crust of dense sand that prevents the liquefaction induced settlement from reaching the surface. In some cases the relatively small thickness of the liquefiable sand layers means that even under a design earthquake event, the actual induced settlements are manageable from a serviceability perspective. Reclaimed areas may or may not be susceptible to liquefaction, depending on the quality of the sand compaction during reclamation and the content of the sand in fines.  Typically, the reclamation can be performed in wet conditions by use of the hydraulic fill method, where the material is deposited by a flowing stream of water, or in dry conditions by compacting the imported fill material in layers. In the first case, the compaction of the reclaimed material typically takes place by use of the vibro-compaction method, while in the second case by the use of impact or vibration rollers. Hydraulic fills tend to be more susceptible to liquefaction, as the material usually lacks fines and as the compaction is performed following fill placement, so is therefore more difficult to achieve. Conversely, reclamation fill placed in dry conditions tend to be less susceptible to liquefaction as the material is compacted in layers and the compaction quality control is performed during fill construction.

In a recent case in Abu Dhabi, authorities accepted Langan’s view that the above mentioned mitigating circumstances eradicated the soil liquefaction risk, which resulted in cost savings of millions of dollars in ground improvement related construction costs.

About Alexandros Yiagos, Ph.D 
U.S. educated (Princeton University) and native of Athens, Greece, Alexandros has 25 years of experience in the design and construction of earth dams, highways (embankments, slopes, and bridges), buildings, thermal power plants, refineries, hydraulic structures, marine structures, airports, wind farms, mines and environmental projects. As a senior project manager for Langan International in Dubai during the past three years, he has been involved in geotechnical engineering consulting for the design of high-rise and low-rise residential, office, hotel, hospital, and education buildings in the United Arab Emirates, Saudi Arabia, Oman, Qatar and India.

What were some of the challenges and rewards associated with working in the Golden Gate National Recreation Area and specifically the Presidio of San Francisco?

The most rewarding aspect of working within the Golden Gate National Recreation Area (GGNRA), and specifically the Presidio, is being part of a team that transformed a former US Army base into a spectacular National Park.

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Battery East – Before

Our role as the environmental consultant began more than 16 years ago. At that time, the US Army base at the Presidio had recently transferred to the National Park Service with the Presidio Trust in charge of managing the interior park lands. The National Park Service  would control coastal lands.

Some of our projects included assessing and achieving clean closure at landfills on or near the coast of the Presidio, cleaning up soil impacted with lead near the Golden Gate Bridge, assessing water quality in habitat ponds to support the resurgence of the red-legged frog, and performing remediation on former landfills to assist in bicycle and pedestrian trail development.


Battery East – After

Our biggest challenge was navigating the complex regulatory structure associated with working within the park to clean-up previously contaminated sites and obtain closure. Some of the government agencies with jurisdiction in the GGNRA are the Regional Water Quality Control Board, Department of Toxic Substance Control, Golden Gate Bridge Highway and Transportation District, National Park Service, and Presidio Trust. Another critical component to successfully manage a park project is to understand land use and applicable cleanup standards, whether they be commercial, ecological, recreation, or residential. Different areas of the park have different cleanup criteria, which are based on land use, exposure assumptions, and background conditions.

The GGNRA now consists of over 80,000 acres of ecologically and historically significant landscapes in the greater San Francisco Bay Area.  Over 14 million people visit and enjoy the GGNRA each year making it one of the largest urban parks in the world. We at Langan are proud to have helped open many areas to the public.

About Joshua Graber, CHMM
Joshua is a senior project manager with nearly 20 years of environmental consulting experience.  His responsibilities include geologic, hydrogeologic, and chemical analytical evaluations; Superfund site management; vapor intrusion assessments and mitigation; soil and groundwater remediation; litigation support; remedial excavation, waste classification, and disposal; and technical report preparation. He currently manages the Presidio-wide groundwater monitoring program, GGNRA projects, in addition to other projects in Northern California.

How do multi-disciplinary firms help solve the challenges of complex PPP (concession) projects overseas?


Langan serves as technical advisor to the lenders (LTA) for EKPPT Motorway in Peloponnese, Greece.

By nature, public–private partnership (PPP or 3P or P3) projects are collaborative and multi-disciplinary. PPP projects have numerous stakeholders, multiple success criteria, longer time horizons, and greater risks in procurement and delivery. The ultimate goal is achieving a balance between risk and return. Therefore, the PPP project model requires numerous specialists to access and address a variety of technical, environmental, contractual, and financial aspects.


EKPPT Motorway will link Athens and Korinthos to the western end of the Peloponnese.

The role of the Lender’s Technical Adviser in a PPP not only requires excellent technical background, but also an understanding of the bigger picture.  During the tender and construction phases, Langan liaises with the involved parties and provides lenders with risk assessments for environmental permitting, designs and construction methods, project schedule, and robustness of CAPEX and OPEX. As a multidisciplinary firm with extensive experience in complex construction projects, Langan has been able to provide high quality Lender’s Technical Adviser services, help cross-disciplinary and cross-functional conflicts, and move the project forward.

About Tasos Papathanasiou, PE
Tasos has over 18 years of diversified experience managing large scale multi-disciplinary projects, including geotechnical and environmental investigations, site evaluations, foundation design, bulkhead design, construction oversight, and stormwater management. He has provided technical advisory services for motorway and airport concession projects in Greece, Cyprus, and Eastern Europe.

What challenges did you encounter while working on the SFMOMA project?

Project Background and Challenges
The expanded San Francisco Museum of Modern Art (SFMOMA), designed by lead architect Snøhetta, opened last month. The 10-story steel-framed structure stands 210 feet above the adjacent streets.

Originally designed in 1991, the museum’s foundation system consisted of a relatively thin mat that extended beyond the structure’s limits to support a future seven-story expansion. Two decades later, expansion plans revealed that the museum needed more space than originally planned.

The expansion combines the existing mat foundation with the new foundation. The project also added a basement, which required a 30-foot-deep excavation in a heavily dense urban area.

Langan faced the following geotechnical challenges:

  • Differential settlement between the existing and new foundations
  • Temporary support of the adjacent 32-story W Hotel during the planned excavation for the new basement
  • Weak and potentially liquefiable soil underlying the new mat foundation
  • Presence of relatively thick deposit of moderately compressible soil

Construction at the SFMOMA site.

Our Solutions
Langan was a key member of the project team, working closely with Magnusson Klemencic Associates (project structural engineer) and Webcor Builders (project general contractor). As the geotechnical, earthquake, and environmental engineers, we developed performance-based seismic design criteria and foundation solutions so the project could move forward.

To address the geotechnical challenges, we recommended deep soil-cement mixing (DSM) to improve the ground beneath the new basement and provide temporary shoring. The objective of the ground improvement was to: (1) reduce the potential for liquefaction, (2) reduce the potential for disturbing the weak underlying soils during construction, and (3) transfer building loads to deeper competent layers.

The DSM panels provided appropriate subgrade bearing for the mat and brought the anticipated differential settlement to acceptable levels. For the original mat foundation, MKA developed a system of stiff shear walls through the basement to spread heavy column loads to meet Langan’s geotechnical and foundation design criteria. This structural system not only supported the original mat without overstressing it, but it also allowed the structural connection to the new mat foundation.

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SFMOMA reopened in May 2016. The transformed museum, with its new (white) addition visible behind the distinctive original building, has twice the amount of exhibition space as before. (Credit: Michael Layefsky)

For the required 30-foot-deep excavation, we developed geotechnical design criteria for a stiff soldier beam and raker system to support the neighboring 32-story W Hotel. Ground improvement was also used to strengthen and stiffen the subgrade soil supporting the shoring. Small measured excavation-induced displacements confirmed the success of this approach.

With our interactive solution-oriented approach with the design and construction teams, we overcame project challenges. The majestic SFMOMA is a testament to our innovative and adaptable foundations systems.

Answer provided by Scott Walker, PE, GE, Associate
Scott has over 17 years of experience in providing geotechnical investigation, design, consultation, earthquake engineering, and construction observation services for projects throughout California and southwestern Montana. He specializes in providing innovative geotechnical solutions to challenging sites. His experience includes: commercial and residential buildings, high-rises, sports facilities, museums, schools, and resort development.

How important is community engagement in construction or remediation projects?

Including the local community in construction or remediation projects is extremely beneficial for all involved and can result in acceptance versus opposition. Although this may not always be a regulatory requirement or even considered to be “critical” to a project’s success, often times this type of proactive inclusion can result in time and money saved, and reduced liability.

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Environmental remediation at a Langan project

Most individuals are curious about ongoing construction projects that are taking place in their own (or neighboring) towns and they wonder about the rationale or ultimate purpose of the project, yet they rarely have any information. Individuals potentially impacted by remediation projects have greater concerns and fears.  The lack of knowledge frequently raises questions, doubts, or even cynicism about the project, especially if the project causes inconveniences that disrupt their daily routines, such as commuting or even being able to send a child out to play.  On the other hand, if the impacted community has the facts about the nature of the project, and understands the benefits or risks to their families, friends, and lifestyle they are less likely to be frustrated and confrontational.  For these reasons, any type of proactive information sharing and allowing residents to feel included in major project stages is of key importance to project management success. Additionally, proactively sharing information (possibly in the form of a fact sheet) also allows the party conducting the work control of the message and can dispel concerns.

Gaining greater project acceptance, and more importantly, obtaining the least community resistance, is your goal. This can only happen by voluntarily sharing information. While it is important to do so with the general public, it is equally, if not more, important to include community leaders – both elected and those who are simply well known and trusted civic leaders. Communication may occur formally (newspapers, planning committee meetings) or informally (social media, social gatherings). Taking steps to proactively educate supporters and opponents will help garner support for your project.

The key components to be communicated include, but are not limited to:

  • The nature of the final project, such as new stores, office buildings, a park or housing
  • The reason for the project, the ultimate purpose/rationale
  • The temporary impacts of construction regarding inconveniences, detours, delays, etc.
  • Permanent changes beyond the construction phase including land use/loss and transportation issues such as roadway changes, traffic, noise
  • Benefits such as increased jobs, easier access to stores, better housing, a cleaner environment, increased revenues and improved transportation
  • The most critical component of community relations is allowing for open discussions, and truly listening to concerns as every community has different needs and issues
  • Ultimately providing feedback on a timely basis, and incorporating appropriate components of their recommendations into a final project

By building strong relationships within your project’s community and easing concerns, the project team can save time, money, unwanted bad press, reduce liability, and pave the way for future successful projects in neighboring communities.

About Irene S. Kropp, Senior Environmental Consultant 
A universally respected leader in the New Jersey environmental community, Irene Kropp brings 30 years of regulatory, technical, administrative, and management experience in all areas of environmental protection to Langan’s environmental practice. Prior to joining Langan, Kropp served as the Deputy Commissioner of the New Jersey Department of Environmental Protection. Additionally, she managed multiple offices in the NJDEP including Water Resources, Compliance and Enforcement, Information Resources Management, Management and Budget, and Science and Site Remediation. She has worked closely with other state agencies, the legislature, local governments, the USEPA, other state environmental agencies, developers, corporations, and many New Jersey business and industry associations.