James D. Doherty, Ph.D., P.E., LSP, Pennoni Associates, Inc., 82 South Street, Hopkinton MA, 01748-2205, Tel: 508-435-8080, Fax: 508-435-4351

Low-flow groundwater sampling has been advocated by the U.S. Environmental Protection Agency (EPA) as well as by a number of state Environmental Protection Agencies as a means of collecting groundwater samples.  However, it is not clear that this sampling method always provides a representitive groundwater sample.  In some cases, traditional sampling methods where samples are collected by bailing 3 to 5 well volumes prior to collecting the sample may provide a sample that is more representitive of average site conditions.  One of the objectives of low-flow sampling is to draw groundwater directly from a small portion of the formation and minimize mixing of formation water with stagnant well casing water.  The EPA has demonstrated that the results of low-flow sampling can produce groundwater contaminant concentrations that vary by over a factor of 10 depending on where the sample is collected within a screened interval.  This variation in groundwater quality along the length of a well screen is likely due to a number of factors including: the nature of the source;  the proximity of the well to the source; the amount of heterogeneity of geologic material; and the nature of the contaminant.  Thus, low-flow sampling may produce sample results that are significantly different than values obtained with samples collected using bailers (which are more representitive of average concentrations along the well screen).  The variability in sample results introduced by using low-flow sampling methods must be accounted for when interpreting the sample results.  In some cases, samples collected using low-flow sampling techniques would be expected to be less representitive of average aquifer concentrations than those collected using bailer methods.

Passive Vapor Diffusion Sampling for Volatile Organic Compounds in a Bayou

Tom Dragoo, Parsons, 1700 Broadway, Ste. 900, Denver, CO. 80290, Tel: 303-764-1953

Fax: 303-831-8208

John Hicks, Parsons, 1700 Broadway, Ste. 900, Denver, CO. 80290, Tel: 303-764-1941 , Fax: 303-831-8208

John Tunks, Parsons, 1700 Broadway, Ste. 900, Denver, CO. 80290, Tel: 303-764-8740 , Fax: 303-831-8208
Raphael Vazquea, AFCEE/ERT, 3207 Sidney Brooks, Brooks City-Base, TX  78235-5344 , Tel: 210-536-1431, Fax: 210-536-4330

Joy Lozano, Booz,Allen & Hamilton, 700 North St. Mary’s St., Suite 700, San Antonio, TX 78205

Tel:  210-536-4980, Fax: 210-536-3609   

Polyethylene-membrane passive vapor diffusion samplers (PVDSs) have been shown to be an effective and economical tool for detecting volatile organic compounds (VOCs) in bottom sediments of surface water bodies in areas of groundwater discharge.  PVDSs were buried in the bottom sediment of a bayou at the former England Air Force Base, Louisiana to assess whether groundwater contaminated with chlorinated aliphatic hydrocarbons was discharging to the Bayou.  A horizontal contaminant profile was developed by analyzing the resulting vapor samples for VOCs.  Details will include a general description of the technology and work performed, a summary of the PVDS results and insights gained into groundwater-surface water interactions at the study site, and a cost analysis.

Use of Innovative Packer Sampling and Geophysical Techniques for Groundwater and Bedrock Characterization

Roger E. Huddleston, CH2M HILL, 8501 W. Higgins Rd., Suite 300, Chicago, IL  60631, Tel:  773-693-3809, Fax: 414-454-8761 
Dakon Brodmerkel, CH2M HILL, 1700 Market Street, Suite 1600, Philadelphia, PA  19103, Tel: 215-563-4244, Fax: 215-563-3828
Andrew Judd, CH2M HILL, 99 Cherry Hill Rd. Suite 304, Parsippany, NJ 07054-1102 , Tel: 973-316-0159, Fax: 973-334-5847

A fractured bedrock groundwater investigation was performed at a former chemical company site in Paterson, New Jersey facility between May and December 2002.  Site conditions were characterized using traditional rock coring and logging techniques, as well as more innovative packer sampling and geophysical tools.  Groundwater samples were collected at approximately 20-foot intervals from 100 to 400 feet below ground surface using a custom-built triple-packer and transducer assembly.  The packer assembly was constructed such that the top and bottom packers inflated simultaneously, while the middle packer could be independently inflated.  By initially inflating the top and bottom packers, evacuating water from the sealed zone, inflating the middle packer, then initiating groundwater purging and sampling from the zone between the middle and bottom packers, the effects of leakage around the packers due to the high hydraulic head at depth was reduced, enabling greater confidence in groundwater quality results.  Geologic formation characteristics were logged using natural gamma, fluid temperature, fluid resistivity, heat pulse flow meter (for vertical borehole flow measurements), high resolution acoustic televiewer, and optical televiewer tools.  In addition, a Model 40 GeoFlow horizontal heat pulse flow meter (provided and operated by K-V Associates, Inc., Mashpee, MA) was used to characterize horizontal gradient flow directions.  Based on these data, a conceptual model was developed indicating that the predominant horizontal groundwater flow occurred in two highly fractured zones at approximate depths of 90 to 120 and 285 to 310 feet below ground surface.  Between about 120 and 285 feet below ground surface, strong downward vertical gradients were observed, with negligible groundwater production.  At depths below about 310 feet, no measurable groundwater flow was observed.  Results were used to select additional well locations and depths, which subsequently verified the gradient data indicated by the geophysical techniques.

Increasing the Accuracy of LNAPL Volume Determinations in the Subsurface

Andrew J. Kirkman, The RETEC Group, Inc., 413 Wacouta Street, Suite 400, St. Paul, MN 55101-1957 Tel: 651-222-0841, Email: akirkman@retec.com

LNAPL observed in the subsurface is frequently thought of as a entirely separate fluid layer, detached from the groundwater.  A “pancake” conceptual model is often thought of where there is some saturation that is constant over the thickness of LNAPL measured in the well (b_o).  In reality the average LNAPL saturation occurs far below 100%.  If assuming a case where the LNAPL has not been significantly smeared by the rising and falling of the water table, LNAPL often starts at low saturations 5%-28% at the oil/water interface, then peaking at 30-50% at the oil air interface and declining back to a residual oil saturation again 5%-28%. Below the oil/air interface total fluids are close to 100%.  Although it is believed some air can be trapped below.   By analyzing representative core plugs for capillary pressure the actual oil saturation profile in the subsurface and a more, realistic original oil in place (OOIP) value can be obtained.  For a given b_o, the specific yield value for LNAPL (Do) having units of (L³/L²), is estimated by integrating the corresponding saturation profile over the soil column instead of multiplying a constant saturation over the length of the product thickness measured.  Once the Do is known for several measured LNAPL thickness, a linear relationship can be obtained between Do and b_o.  The linear relationship can then be used to determine the Do for any measured b_o and the total OOIP for a plume can be estimated by integrating the Do over the plume area.  The presentation of three cross sections of monitoring wells in the subsurface will demonstrate the actual distribution of an LNAPL in the modeled subsurface. 

A Practical Application of the Texas Risk Reduction Program at a DNAPL Contaminated Site

Kiran K. Srinivasan, ENTRIX, Inc., 5252 Westchester, Suite 250, Houston, TX 77005, Tel: 713-662-1920, Fax: 713-666-5227, Email: ksrinivasan@entrix.com
Christina Robinson, ENTRIX, Inc., 5252 Westchester, Suite 250, Houston, Texas 77005 , Tel:  713-662-1912, Fax: 713-666-5227, Email: crobinson@entrix.com              

The recently promulgated Texas Risk Reduction Program (TRRP) is being used at a site to address DNAPL contamination in soil and groundwater.  TRRP is a three-tiered tool that enables contaminated sites to be characterized and closed in a defensible manner using human health and ecological considerations.  A fundamental step in processing sites under TRRP is delineation of the nature and extent of contamination to residential Assessment Levels.  At the DNAPL site, a combination of default and site-specific TRRP Assessment Levels were used to delineate the nature and extent of contamination.  Site-specific levels were calculated using TRRP equations and geotechnical data from site soil samples.  The complex geology of the site, unknown historical release sources, and TRRP’s affected property owner notification requirements, posed challenges to delineation.  These challenges were overcome by a combination of risk assessment and management techniques allowed under TRRP.  Delineation activities, exposure/risk assessment and its results, and possible remedial or “response” actions are being documented in a unique set of TRRP forms constituting an Affected Property Assessment Report.   Several TRRP-approved response actions are being contemplated to manage the groundwater contaminant plume at the site.  One such option is the Plume Management Zone.  Data are being collected to verify that the site meets the conditions in TRRP for a PMZ.  Upon completion of data collection, this response action will be implemented and its effectiveness monitored.  Regulatory closure will be sought upon successful demonstration of the PMZ.  

Increased Accuracy of Site Assessment using Passive Soil Gas Technology

James E. Whetzel, W. L. Gore and Associates, Inc., 100 Chesapeake Blvd, Elkton, MD 21922, Tel: 410-506-4779, Fax: 410-506-4780 

Assessing sites for the presence of organic pollutants typically involves costly soil and/or ground water collection and analyses by one or more analytical methods.  Budgeting constraints can result in limited numbers of samples being analyzed and an increased possibility of missing source areas and plume extents. An alternate approach is the analysis of organic compounds in the vapor phase (soil gas) using passive soil gas technology. A cost-effective passive soil gas survey allows a denser profiling of a site resulting in a more accurate site characterization. A comprehensive soil gas survey can shift subsequent matrix sampling programs from assessment to confirmation.  This presentation will discuss an innovative and cost-effective passive soil gas technology along with case studies showing its success.

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