2016 NGWA Groundwater Summit

Using Tracer Test Data to Calibrate a Complex Flow and Solute Transport Model

Monday, April 25, 2016: 3:00 p.m.
Confluence Ballroom A (The Westin Denver Downtown)
Andrew B. Bittner , Gradient, Cambridge, MA
John Kondziolka , Gradient
Peter Nangeroni, P.E. , Woodard & Curran, Dedham, MA
Robert McGrath , Woodard and Curran, Dedham, MA
Manu Sharma , Gradient Corp, Cambridge, MA

Successful calibration of groundwater and solute transport models to field data is critical to ensure their accurate predictive capability. Model calibration generally consists of two steps: a hydraulic flow model is calibrated using hydraulic field data, and then a solute transport model is calibrated using chemical field data. At a National Priorities List site in rural New England, a rare additional step was taken: tracer test data were used to significantly improve the calibration of both the hydraulic and solute transport models.

Three independent, conservative tracers were injected at three separate site locations into two different hydraulic formations. Downgradient concentrations were monitored for one year to develop breakthrough curves. Hydraulic heads and chemistry were monitored site-wide to collect traditional calibration data. The tracer data indicated the presence of a previously uncharacterized, localized preferential flow pathway through highly weathered bedrock.

MODFLOW and MT3DMS were used to simulate the hydraulics and chemical transport for the site and the preferential flow pathway. The three conservative tracers, along with chemical data for the five site constituents, provided eight independent datasets used to calibrate the geometric and hydrogeologic parameters of the preferential flow pathway. One constituent was the daughter product of another, which provided another check on the modeled decay rates. Particle tracking was used to calculate a site-specific dispersivity value.

Using the tracer test data to calibrate both models yielded more robust and accurate calibrations than could have been achieved using only traditional data metrics. Good breakthrough curve matches were achieved at a large number of downgradient wells for all eight solute transport models. The geometry of the preferential pathway conformed well with estimates of weathered bedrock thickness from boring logs, and the site-wide normalized root mean square error for hydraulic heads was less than 5% for all modeled times.

Andrew B. Bittner, Gradient, Cambridge, MA
Andrew B. Bittner is a licensed environmental engineer with more than14 years of experience specializing in the fate and transport of contaminants in porous and fractured media, NAPL transport, groundwater hydrology, groundwater and surface water modeling, remedial investigation and design, and soil vapor intrusion modeling. He has applied these skills to develop cost effective remedial solutions at pharmaceutical facilities, manufacturing plants, and dry cleaning facilities at sites around the world. In particular, Bittner has extensive experience developing risk-based remedial strategies, designing remedial investigations, delineating and characterizing the distribution of environmental pollutants, and overseeing remedial operations in South America.

John Kondziolka, Gradient
John Kondziolka is an environmental engineer at Gradient with experience using physical experiments and numerical simulations to solve unique problems in environmental fluid mechanics and contaminant transport. In particular, he has used a variety of analytical and numerical techniques to understand site histories, develop conceptual site models, support risk assessments, and design and implement remedies at sites both in the U.S. and abroad. Kondziolka also works in the areas of environmental forensic analysis, groundwater and surface water modeling, cost allocation, and litigation support. Before joining Gradient, he worked at the MIT Environmental Fluid Mechanics Laboratory, modeling sediment transport.

Peter Nangeroni, P.E., Woodard & Curran, Dedham, MA
Peter Nangeroni has over 30 years of due diligence, site investigation and remediation, redevelopment planning, environmental engineering, construction management, and solid and chemical waste management experience. He also has extensive experience in the evaluation of remedial alternatives and the management of diverse project teams in the conceptualization, design, permitting, construction, and operation of remedial programs, with an emphasis on PRP-led CERCLA sites.

Robert McGrath, Woodard and Curran, Dedham, MA
Robert McGrath is employed by Woodard and Curran in Dedham, Massachusetts.

Manu Sharma, Gradient Corp, Cambridge, MA
Mr. Sharma consults on a wide range of environmental sciences topics, including water quality, contaminant fate and transport modeling, risk assessment, hazardous waste site cleanups, and environmental response cost liability/allocation. With more than 25 years of consulting experience, he has successfully applied these skills to solve a range of complex problems, from assessing health risks associated with chemicals in products to developing cost-effective remedial solutions at both small and extremely large contaminated sites. He has served as an expert on cases related to multi-PRP liability assessment and cost allocation, contaminant transport, remedial investigation/design, standard of care, and water resource development.