Subsurface Soils Investigation


A Subsurface Soils Investigation is the physical examination of that which is below what you can stand on or see.  This investigation is without question:

•     the first concern which you should resolve even if you’re addressing a handful of issues simultaneously as you approach a closing date on your land;

•     the easiest issue to address in your due process;

•     one of the least expensive issues you will address;

•     the most-deadly poison pill to overcome if you discover something ugly after you own the property, or during design, permitting, or construction; and

•     the single most important information the engineer who designs your foundation will need.


There are relatively few affordable ways to prove that the ground is economically safe to build on (and unencumbered legally by seemingly esoteric regulations):

•     an archeological dig (a very expensive, poor choice which will only render negative information for the new dental office prospect);

•     dig several pits (usually with a backhoe) at locations determined by the architect who designed your preliminary site plan (note: this is definitely the least expensive method, but it is only moderately effective); or

•     drill/bore several holes (with a truck-mounted drilling rig capable of extracting intact samples from the core) at locations determined by the architect who designed your preliminary site plan. 


Although drill/boring is a somewhat more expensive method, it is ultimately the most efficient method of subsurface testing because the cores can be sent to a geotechnical lab to be tested for soil bearing capacity and evaluated by a Geotechnical Engineer who will produce written (and sealed) foundation design recommendations for the Structural Engineer to follow.  Assuming the Subsurface Soils Investigation determines that the soils are typical, it is difficult to say whether it would have been ultimately less expensive to forego the testing and just use the worst-case-scenario for soil bearing pressure found in the Building Code…but if you discover a problem early, it will be the smartest money you ever spent.


Some Frequently Asked Questions and musings about Subsurface Soils Investigation


Q:   Why do owners typically put off Subsurface Soils Investigation?

A:   From an architect's standpoint, there is virtually no good reason to postpone soils testing, but we have heard some remarkably trivial explanations from unhappy owners faced with very significant costs and delays.   Here are some of the examples: "it's a perfectly flat cornfield that's never been developed before," or "it would show up in the Seller's disclosure if it was a problem," or "my real estate agent says recently-completed neighboring buildings have experienced no particular difficulty," or "our Building Dept doesn't require it," or "I wanted to get the GC to deal with it so I could get it rolled into my construction financing," or “I figured that if it became a problem, it was the general contractors problem”.  If any of these sound familiar, please reconsider because it may affect the structural design or the costs of your project.


Q:   What are some of the uglier scenarios ArchiPelago’s doctor/clients have encountered over the years? 

A:   Abandoned underground fuel storage tanks which did not show up on a title insurance report; Native-American burial grounds; EPA ‘wetlands’ designation evoked by a 5-year change in fluctuating ground water from large municipal detention ponds nearby; expansive clay soils 16” below surface; artesian wells contaminated by coal tar from a natural gas pumping station ¼ mile away; solid bedrock 20” below surface on a project designed to have a full basement; root structure of a huge, protected, historic tree on a neighboring parcel.  Feel free to call us for references if you’d like to hear some of these stories directly from the doctor/owner.