By Richard Arnold, P.E., C.P.G.
Director of Engineering & Remedial Action Services
Published November 2008 Real Estate New Jersey Magazine
Richard.Arnold@ewma.com

At the outset of remedial action project, risk management is a key discussion topic. Standard remedial action risks should be discussed, project controls should be agreed upon, and projects should proceed after the needed controls are implemented. But risks to the integrity of existing buildings may not always be included in pre-remedial planning efforts. And there are cases where these risks can be severe.

Structural risks to existing buildings during remedial action projects are often very real, and are not well understood and anticipated. Many buildings are fairly rigid. Key elements of a building such as roofs and walls are often supported by concrete footings that rest on soil foundations, and less critical but still important elements such as building slabs or pavements often rest on soil foundations. If the soil foundation heaves or subsides beneath a footing or a slab, and if the consequent movement of that building element exceeds the amount that a building can tolerate, then there can be substantive damage. For instance: 

• A wall may develop cosmetic or structural cracks and other imperfections. This damage may adversely affect the structural integrity of the building, it may reduce the building value, and it may impact interior environmental control systems;
• The relative elevations of roof sections may change, the roof may no longer shed rainwater as designed, and the roof may become overloaded with collected water and may fail;
• The relative elevations of slab sections may change, the slab may no longer be workable for support of process or storage systems, and it may no longer be suitable for transit by personnel or transporters.

So why do these things happen? Simply put, the soils that commonly support building footings are not manmade, rigid materials. They are composed of granular soil particles, fine grained soil particles, and void spaces between the particles that can be partially or completed filled with mixtures of water, various gases, and contaminants. When the balance of subsurface soil voids is changed, or when horizontal or vertical earth pressure changes occur in a soil zone, soil particles may move relative to one another. The individual particle movements may not be substantive, but as a mass of many particles, the soil may expand or contract, much like a spring will expand or contract under changing loads.

Many remedial technology applications can cause subsurface changes that may result in adverse soil movements. Some examples are listed below:

•  Air or gas injections can result in unexpected soil heave;
• Remedial excavation can result in loss of soil foundation support;
• Improperly placed backfill can result in subsequent soil settlement;
• Ground water extraction can result in soil settlement;
• Contaminant extraction from pore voids can result in soil settlement;

And the list goes on.
Fortunately, it is both possible and practical to minimize the adverse soil movements that can result from application of a range of remedial technologies discussed above. A range of project control options are available, each with demonstrated effectiveness. Some of these project control options are presented below as they may apply to the listed remedial technologies:

• Air or gas injection – monitoring, injection pressure limitation, overpressure controls; 
  Excavation – earthwork evaluation, construction constraints, earth support systems;
• Backfilling – earthwork evaluation, soil compaction, use of select backfill materials;
• Groundwater extraction – soils evaluation, pumping and drawdown constraints; 
  Contaminant extraction – soils evaluation, extraction rate and pressure limitations.

In summary, the risk of structural damage to existing buildings during a remedial action can be substantive, and should be reduced by early risk management planning. In this way, there should be ample opportunity to identify site specific risks to existing buildings, to develop and reach agreement on project controls, and to ensure that project controls are effectively designed, implemented and maintained during remediation.

Mr. Arnold is with EWMA’s Headquarters Office in Parsippany, NJ. He is expert in remedial technology screening, remedial alternative evaluations, feasibility studies, and remediation process pilot testing under a wide range of surface, subsurface and contaminant conditions. For additional information or to discuss your concerns please contact Mr. Arnold at 800-969-3159 ext. 174 or