Application of a Conceptual Site Model for Groundwater Contamination in a Bedrock Municipal Well System

Monday, September 23, 2013: 11:35 a.m.
Lisa Campbell , CDM Smith, New York, NY
John N. Dougherty, PG , CDM Smith, Edison, NJ
Mike Valentino , CDM Smith, San Juan, PR
Adalberto Bosque , Caribbean Environmental Protection Division, U.S. EPA, Santurce, PR
Diana M. Cutt, PG , Office of Research and Development, USEPA Region 2, New York, NY

This paper describes how a conceptual site model (CSM) was developed and used by EPA to identify the sources of volatile organic compounds affecting municipal water supply wells completed in the bedrock aquifer at a Superfund site in Puerto Rico. The site is underlain by Cretaceous age volcanic rocks of the Pre-Robles Formation, which consist mostly of massive volcanic breccia. Chemical weathering has resulted in an overlying saprolite layer, which is a major water-bearing unit that stores water and provides recharge to the underlying bedrock aquifer. The saprolite is semi-confined by the overlying silty clay soils in the overburden.

The CSM was developed over the course of a multi-staged investigation, which included the following activities:

  • Soil investigations of potential source areas, including discrete-depth soil sampling through the overburden.
  • A hydrogeologic investigation using borehole geophysics, heat pulse flow meter logging, and packer testing to determine the frequency and orientation of bedding, fractures, and joints and to identify water-bearing zones in six bedrock boreholes. These data were used to design a multilevel well for each location.
  • Investigation of the saprolite zone, which had been found during the bedrock drilling activity to be a major water-bearing unit. The investigation included installation and sampling of 11 single-screened wells to determine the extent of contamination in this zone.
  • An evaluation of the groundwater-surface water interaction in the river downgradient of the contaminated supply wells. Stream gauges were installed and measured, and surface water and sediment samples were collected.
  • Preparation of cross-sections using the results of this program to develop the bedrock CSM.

These data were compiled and evaluated to develop and refine the CSM of the groundwater flow system. The CSM was then used in conjunction with the soil data to identify two sources of the groundwater contamination.

Lisa Campbell, CDM Smith, New York, NY
Lisa Campbell is a senior geologist at CDM Smith, where she has worked since 1996. Campbell focuses on hydrogeologic characterization of Superfund sites in Region II, which include those situated in fractured bedrock terrain in New Jersey, New York, and Puerto Rico. Her experience includes planning and executing many aspects of site investigations, including soil and groundwater sampling, borehole geophysical logging to characterize fractured bedrock hydrogeology, conventional and multilevel monitoring well design and installation, and use of matrix diffusion data for site characterization.


John N. Dougherty, PG, CDM Smith, Edison, NJ
John Dougherty is a hydrogeologist with 28 years of experience in environmental consulting and has been working at CDM since 1999. At CDM he has been concentrating on hydrogeologic characterization of U.S. EPA Superfund sites in Region II. Many of these sites are situated in fractured bedrock terrain. He has experience in many aspects of site investigation, borehole geophysical investigations, and has designed and supervised the installation of monitoring wells at Superfund sites around the United States. Dougherty holds a B.S. in Geosciences from Pennsylvania State University.


Mike Valentino, CDM Smith, San Juan, PR
Mike Valentino is a hydrogeologist with 22 years of experience in environmental consulting and has been working at CDM since 1990. At CDM Valentino has worked on hydrogeologic characterization of U.S. EPA Superfund sites in Region II. Currently he is a Project Manager working at CDM’s San Juan, Puerto Rico office. Valentino holds a B.S. degree in Geology from Duke University and an M.S. degree in Hydrogeology from San Jose State University.


Adalberto Bosque, Caribbean Environmental Protection Division, U.S. EPA, Santurce, PR
Adalberto Bosque is an engineer and Remedial Project Manager working at the U.S. EPA's Caribbean Environmental Protection Division in Puerto Rico. He is responsible for managing site investigation and remediation projects.


Diana M. Cutt, PG, Office of Research and Development, USEPA Region 2, New York, NY
Diana Cutt, PG, is Superfund and Technology Liaison for the EPA Region 2 Office of Research and Development.