Evaluation of NAPL Migration Resulting from Big Dig Activities
Frank Ricciardi, Weston & Sampson Engineers, Inc., Peabody, MA

DNAPL Dissolution- Evaluating Natural Depletion Over Time
Jeffrey A. Johnson, The RETEC Group, Inc., Houston, TX 

Vadose Zone Hydraulic Processes – Infiltration and Percolation – and their Function in Hazardous Materials Transport

Alton Day Stone, PE, LSP, Alton Engineering, 10 Rugg Road, Sterling, MA 01564, Tel: 978-422-8014, Fax: 978-422-8014, Email: adaystone@verizon.net
James C. O'Shaughnessy, Ph.D., PE, Civil Engineering Department, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA 01609, Tel: 508-831-5309, Fax: 508-831-5808, Email: jco@wpi.edu

The release of most hazardous materials occurs through spillage or other deposition on the ground (soil) surface, either in the liquid-phase - e.g. gasoline or solvent spill, or solid-phase - e.g. lead paint chips, and deposition of atmospheric particulates.  The transport of surface deposited hazardous materials to an underlying water supply aquifer is of great concern, and necessitates liquid and dissolved-phase transport through the vados or unsaturated zone.  Vadose zone flow is very complex, being a function of several interdependent (and dependent) variables, that is not easily described or modeled and commonly is not well understood by environmental professionals.  The importance of unsaturated flow cannot be ignored; risk characterization models and associated substances-specific risk levels, involve vadose zone transport modeling at some level.  Understanding of vadose zone processes permits adaptation of site-specific data to the general transport models.  This paper describes the basic mechanisms of vadose zone flow, in particular infiltration and percolation, and their relationship to hazardous materials transport.  Infiltration is the movement of water through the soil surface into the underlying soil column.  Percolation is the subsequent movement of water, usually downward, through the subsurface soil.  Both mechanisms involve two hydraulic phenomenon – gravity drainage through macorpores and capillary flow through micropore - that are highly dependent on soil type and structure.  This paper focuses on one-dimensional downward vertical flow (∂v/∂z) as described by the Buckingham-Darcy and Richards Equations.  One-dimensional flow is adequate for practical description of most common engineering applications.  The results of bench scale experiments using soils common to New England, including outwash sands, marine clay and till, are used to illustrate transport mechanisms.   

Evaluation of NAPL Migration Resulting from Big Dig Activities

Frank Ricciardi, P.E., Project Manager, Kelley Race, P.G., LSP, Associate, Ken Bisceglio, CHMM Project Manager, Weston & Sampson Engineers, Inc., 5 Centennial Drive Peabody, MA 01960, Tel: 978-532-1900

The Big Dig required numerous complex construction projects to complete arguably one of the biggest civil engineering projects of mankind. One of these projects involved the installation of an access road to service the numerous construction vehicles through a dense, highly populated area of South Boston. This road was installed adjacent to a bus maintenance facility that contained several feet of light non-aqueous phase liquid (LNAPL - Diesel#1 and gasoline) over a 2.5-acre area. LNAPL migration from this site was influenced by a myriad of complex urban subsurface conditions including:

• Numerous active and abandoned utility ducts and conduits

• An MBTA red-line tunnel

• An active aboveground rail line and bus maintenance facility

• A regional stormwater pump station

• Underdrain system to control groundwater for the newly installed Big Dig access road and

• Complex, heterogeneous urban stratigraphy including urban fill and interbedded clay lenses

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