2019 NGWA Conference on Fractured Rock and Groundwater: Alphabetical Content Listing
Ranjeet Nagare, Ph.D., P.Eng.
Characterizing Contaminant Transport in a Dual Aquifer System with Intervening Vadose Zone for Remedy Selection
A CSM was further developed by implementing a 72-hour pumping test. The objectives of the pumping test were to refine the existing bedrock hydrostratigraphic model, determine orientation and extent of pumping influences, identify the hydraulic connection between the bedrock and overburden aquifers, and define an appropriate remedy for the site.
Analysis of the pumping test data was performed through curve matching techniques in Aqtesolv, and visualization of head change over time. Further development of the CSM informed remedy design for commingled plumes from various stakeholders across this multiple property site. Validation of the new CSM included various communications with all stakeholders and modification to the regulatory framework, and will result in developing an appropriate groundwater remedy for both the bedrock and overburden aquifer.
Comparison Of CSMs For Bedrock PFAS Impacts At A Former Manufacturing Facility And A Former Military Base
David Sherman, PG
From 2005 to 2015, soil vapor extraction (SVE) was implemented to treat impacted soil and reduce the CVOC concentrations in perimeter area groundwater; however, clean-up goals were not achieved. Following the SVE remedy, additional Site characterization indicated that groundwater is likely not perched, overburden material remains highly impacted, and DNAPL was observed in one SVE well. Groundwater underlying the source has CVOC concentrations that were much higher than the perimeter monitoring wells.
The initial characterization was not detailed and led to a remedy that could not complete cleanup of the Site. To develop a robust conceptual site model, the extent of contamination will be further delineated, and the processes that control transport of CVOCs will be evaluated, with an eye towards effective remedy design and implementation.
Brent Aigler, P.G.
Allen Shapiro, Ph.D.
TCE analyses of rock core are an integral part of characterizing the magnitude and spatial distribution of contaminant mass in the rock matrix. Analyses of cores from seven closely spaced coreholes in a mudstone aquifer show a complex vertical and lateral TCE distribution. Phase partitioning calculations for TCE in the rock matrix show that most TCE is adsorbed to solid surfaces because of the large organic carbon fraction (foc) in the mudstone; however, large TCE content in some core samples also suggest the presence of NAPL in the rock matrix and proximity to a TCE source zone. A probability of NAPL occurrence, PNAPL, in core samples can be calculated by accounting for variability in matrix porosity and foc in the phase partitioning calculations. The distribution of PNAPL along the closely spaced coreholes identifies a configuration attributed to a TCE source zone.
Pat Quinn, PhD
Jessica Meyer, Ph.D.
Delineation of aquitard hydrogeologic units (HGUs) is critical to the development of conceptual site models (CSMs) for contaminated sites. However, aquitards are often delineated assuming a strong correlation between lithology and hydraulic conductivity. This assumption has not been rigorously tested in bedrock where fracture characteristics control bulk hydraulic conductivity. The objective of this research was to identify HGUs for a contaminated sedimentary rock site using a direct hydraulic dataset. Twelve boreholes were continuously cored to between 53 and 152 m bgs, comprehensively characterized, and instrumented with high-resolution multilevel systems. Head profiles were measured at each location several times per year over multi-year periods. The position/thickness of distinct vertical gradients occurred consistently in each profile indicating multiple, thin intervals of rock functioning as aquitards. The position of these aquitards was not predicted by lithostratigraphy but was strongly associated with sequence stratigraphy. The hydraulic contrasts identified by the head profiles were combined with sequence stratigraphy to delineate 6 aquitards and 4 aquifers. This hydraulically calibrated geologic framework was independently verified against the DNAPL and dissolved phase contaminant mass distributions. These HGUs now serve as the framework for numerical models which are needed to predict future conditions and evaluate remediation feasibilities and timeframes.
Scaled Bioaugmentation Injection Strategy for Remediation of Mixed Chlorinated VOCs in a Fractured Shale Aquifer
Kevin Kelly, PG
The mile-long commingled VOC plume in bedrock extends through a densely populated area located in the Newark Basin of northern New Jersey. Bioaugmentation was first applied in a 2015 pilot study primarily because of the lack of naturally-occurring bacteria in the bedrock aquifer. Three years of performance metrics showed significant mass reductions and informed the final 2019 remedial design; scaled 2019 bioaugmentation injections into eight bedrock wells, with geochemical reduction as an alternative. The injection design was optimized by modifying the volume of carbon substrate in bedrock to mitigate methane production, selecting of an alternative buffer to optimize pH, and the use of two different substrate products. We utilized geochemical conditions to degrade chlorinated solvents by biotic as well as abiotic methods (ferrous iron released from the matrix precipitated as iron sulfide).
Hank Andolsek, C.G.
Inspection of water level measurement data quality by means of a digital elevation model variogram analog
Joe Guggenberger, PhD, PE, RG
Robert Bond, P.G.
Samuel Jacobson, BSc
Evaluation of High Resolution Methods for Contaminant and Flux Distributions in Igneous / Metamorphic Rock Settings
Steven Chapman, M.Sc., P.Eng.
Integrated Use of Data and Numerical Models for Site Conceptual Model Development In Complex Hydrogeologic Systems
Donald Reeves, Ph.D.
Conceptual Site Model Evaluation to Support Focused Site Characterization – Rockland County, New York
Bedrock production well testing in 1999 identified site contaminants of concern (COCs ). Site assessments were conducted which identified COCs above groundwater standards in overburden and bedrock groundwater. The original CSM indicated a sole source of contamination originating from the leachfield.
A RI was undertaken to evaluate and address data gaps identified in the original CSM. Data quality objectives and sampling techniques were selected to evaluate contaminant distribution under current site conditions.
Evaluation of the RI data indicates multiple source areas. COC distribution in the bedrock is influenced by the production well pulling contamination downward and against natural groundwater flow. Refinement of the CSM included targeted geophysical logging, aquifer hydraulic testing, and discrete sampling to evaluate fractures and flow potential in the bedrock including matrix diffusion of COCs as a continual source.
James Marolda, CPG, PG
At a former Manufactured Gas Plant (MGP) site in the northeast, a stratigraphic horizon was identified and correlated across the site using natural gamma logging; this horizon coincides with a water-bearing fracture zone. Hydraulic responses observed in nearby wells during drilling indicate a high degree of fracture connectivity within the zone, which serves as a primary migration pathway for MGP residuals and associated dissolved-phase contaminants. These findings yielded development of a reliable conceptual site model and will add efficiency to supplemental subsurface investigation efforts.
Nathan Vogan, PG
A site characterization investigation identified contaminants of concern (COCs) including metals and polychlorinated biphenyls within the fill materials, overburden groundwater, and seeps on the steep slopes. A central bedrock knob was identified in direct contact with fill materials. A remedial investigation was conducted to evaluate the extent of contamination and refine the CSM. Water level measurements indicated radial horizontal flow consistent with topography, however overburden groundwater was not observed in the northern and eastern portions of the site. The contributing source of COCs identified at seeps on the steep slopes was undetermined.
A data gap investigation evaluated if bedrock groundwater is a source to the seeps. Geophysical logging identified transmissive fractures that would be unlikely contributing to seeps. The CSM and geochemical comparisons ruled out bedrock groundwater as a source and therefore, does not require remedial action which simplified site cleanup objectives.
Integrating Borehole-, Outcrop-, and Map-Scale Data to Construct a 3-D Model for PFOA Transport in Bennington, VT
Using acoustical borehole imaging, the orientations of structures in bedrock wells were determined. In addition, structures were identified as bedding, foliations, or fractures through borehole camera surveys and direct comparison with structures at nearby outcrops, including field measurements. By integrating borehole structural data with 1) temperature, conductivity, gamma, caliper, and heat-pulse flowmeter logs, 2) detailed structural data from outcrops, 3) the spatial analysis of well driller reports, and 4) bedrock geologic maps, the 3-D architecture of the FRA was constructed.
Significant findings are: A) Borehole structures strongly correlate with those at all scales and strongly influence the regional hydrogeology, B) One thrust fault is a barrier and the other is a conduit for groundwater flow, C) Steeply-dipping fracture zones bring up PFOA-free groundwater in areas surrounded by high-PFOA wells.