Seasonal Fluctuations in the Phreatic Surface – Vadose and Saturated Zone Hydrologic Interaction
Alton Day Stone, PE, LSP, LSE, Alton Engineering, Sterling, MA

Characterization of Multiple Chlorinated Solvent Plumes due to the Impact of TCE Screening Level Reduction
James R. Dickson, P.E., CTI and Associates Inc., Cleveland, WI
Andrew Lonergan, PG, CTI and Associates Inc., Brighton, MI Rob Stenson, CPG, TI and Associates Inc., Cleveland , WI
Chris Winklejohn, P.E., CTI and Associates Inc., Brighton, MI

Natural Attenuation of Detached Contaminated Groundwater Plumes: Application of Seasonal Kendal’s Tau Analysis
Joseph E. Haas II, M.Sc., P.Eg.P.Hg., New York State Department of Environmental Conservation, Stony Brook, NY
Donald A. Trego, Environmental Assessment & Remediations, Patchogue, NY

Seasonal Fluctuations in the Phreatic Surface – Vadose and Saturated Zone Hydrologic Interaction
Alton Day Stone, PE, LSP, LSE, Alton Engineering, 10 Rugg Road, Sterling, MA 01564, Tel:  978-422-8014, Email: adaystone @verizon.net
Paul P. Mathisen, Ph.D, PE, WPI Department of Civil and Environmental Engineering, 100 Institute Road, Worcester, MA 01609-2280, Tel: 505-831-5343, Email: mathisen@wpi.edu

Transport of materials from the soil surface downward through the vadose zone to the saturated zone, and thence through the saturated zone, is dependent upon the amount of precipitation that infiltrates into the soil column, the downward percolation of water to the saturated zone, and subsequent advective flow through the saturated zone.  Massachusetts receives approximately 43 inches of total annual precipitation, which is not evenly distributed during the year.  Estimates on amount that actually recharges the saturated zone range from 16 to 22 inches, with variation dependent upon the hydrologic regime – e.g. soil, land use, depth to impervious surface.  In response to the infiltration and downward percolation of precipitation, aquifers commonly exhibit a “seasonal high” water table (phreatic surface) in the early spring season.  In response to advective flow, evapotranspiration, and other losses the water table drops to a “normal” mid season level in June or July.  In dry summers a seasonal “low” water table is often observed in August through October that may be several feet lower than the normal water table.  The changes in water table elevations result in a defined loss of water from the soil column that, depending upon soil type, may be considerable and affect transport processes.  Where does the lost water go, where does it end up, and what are the potential effects on materials transport?  Major losses include discharge via advective flow and evapotranspiration.  The dominance of one process may have a significant impact on materials fate and transport.  Control volume analysis and analytical and computer groundwater modeling are used to characterize vadose and saturated zone water budgets and the hydraulic interaction between the two zones for different soil types, hydrologic settings and land uses.  Guidelines are provided for use in evaluating site-specific transport processes.

Characterization of Multiple Chlorinated Solvent Plumes due to the Impact of TCE Screening Level Reduction

James R. Dickson, P.E., CTI and Associates Inc., 1202 West Washington Ave. (PO Box 276), Cleveland, Wisconsin 53015-0276, USA, Tel: 920-560-1820, Fax: 414-433-4812, Email: jdickson@cticompanies.com
Andrew Lonergan, PG, CTI and Associates Inc., 12482 Emerson Drive, Brighton , Michigan 48116 , USA , Tel: 248-264-4015, Fax: 248-486-5050, Email: dlonergan@cticompanies.com
Rob Stenson, CPG, CTI and Associates Inc., 1202 West Washington Ave. (PO Box 276), Cleveland, Wisconsin 53015-0276, USA, Tel: 920-560-1820, Fax: 414-433-4812, Email: rstenson@cticompanies.com
Chris Winklejohn, P.E., CTI and Associates Inc., 12482 Emerson Drive, Brighton , Michigan 48116 , USA , Tel: 248-264-4038, Fax: 248-486-5050, Email:cwinklejohn@cticompanies.com

The reduction in the trichloroethylene (TCE) vapor phase screening level by USEPA in 2004 prompted a reevaluation of groundwater contaminant source areas, transport mechanisms, and commingling of multiple CVOC plumes within a complex River Basin.  A USEPA Administrative Order of Consent (AOC) dictated the manufacturing facility to investigate and perform residential and commercial vapor phase removal action to the revised indoor air and subslab action levels without regard for contaminant source area, transport, or commingled contaminants.  In response, a comprehensive reevaluation of the River Basin hydrogeology and groundwater CVOC distribution was completed by the manufacturer to facilitate demarcation of the AOC vapor phase removal action boundary to minimize investigation of contaminants not attributable to the facility. In 2007, an integrated investigation and review of remediation reports filed with state regulators, USGS hydrogeologic reports, and historical groundwater elevation data was conducted. The data were evaluated to identify additional CVOC source areas, map known CVOC plumes, establish groundwater flow transport pathways, and determine the potential for commingled CVOC plumes.  Understanding the complex groundwater flow regime, strongly influenced by river stages, flood control structures, municipal well field production, and engineered recharge basins was critical to resolving the migration pathway of multiple CVOC plumes. All data collected was compiled into a series of CVOC overlay maps to provide a working River Basin model of CVOC distribution and migration based on groundwater flow. The resulting distribution of CVOC source areas and migration pathways results in numerous instances of CVOCs plumes becoming commingled due to the groundwater flow patterns.  As a result, the manufacturer recommended the reduction of the AOC vapor phase removal action boundary area by over 60% thus limiting the action area to immediately downgradient of the facility based on groundwater flow.

Natural Attenuation of Detached Contaminated Groundwater Plumes: Application of Seasonal Kendal’s Tau Analysis
Joseph E. Haas II, M.Sc., P.Eg.P.Hg., New York State Department of Environmental Conservation, SUNY @ Stony Brook, 50 Circle Road, Stony Brook, NY 11790-3409, Tel: 631-444-0332, Email: jehaas@gw.dec.state.ny.us 
Donald A. Trego, Environmental Assessment & Remediations, 225 Atlantic Avenue , Patchogue , NY 11772 , Tel: 631-447-6400, Email: Trego@ENVIRO-ASMNT.COM

The reliance upon the combined assessment of multiple distinct, but converging lines of evidence to demonstrate monitored natural attenuation (MNA) has become common practice. The American Society of Testing and Materials (ASTM) recognizes contaminant of concern (COC) data defining a plume as either shrinking, stable or expanding as a primary line of evidence in MNA evaluations. Often the analysis of the COC data takes the form of trend analysis at individual monitoring locations and/or between monitoring locations along a common transport pathway. However, such simple methods of data analysis are often not applicable for COC plumes that have detached from their source and continue to migrate down gradient.  In such cases these methods frequently yield conflicting results indicating the presence of both increasing and decreasing COC trends. More sophisticated methods, such as the analysis of total dissolved mass loss, have been employed to evaluate historical COC data for COC plumes that have detached from their source and continued to migrate down gradient. However, this method is limited to plumes for which more than one round of monitoring data has been obtained from locations that fully define the distribution of the COC. To overcome the limitations associated with total dissolved mass loss analysis at such sites, Seasonal Kendal’s Tau analysis of historical COC data was applied. The applications of Seasonal Kendal’s Tau analysis returned statistically significant overall trends which were consistent with documented fate of the COC’s evaluated. Therefore, it is suggested that Seasonal Kendal’s Tau analysis of historical COC data can be an appropriate primary line of evidence for evaluating MNA as part of combined assessment of multiple distinct but converging lines of evidence.