Peter K. Joesten

Monitoring engineered remediation with borehole radar

The success of engineered remediation is predicated on correct emplacement of either amendments (e.g., vegetable-oil emulsion, lactate, molasses, etc.) or permeable reactive barriers (e.g., vegetable oil, zero-valent iron, etc.) to enhance microbial or geochemical breakdown of contaminants and treat contaminants. Currently, site managers have limited tools to provide information about the distribution of injected materials; the existence of gaps or holes in barriers; and breakdown or transformation of injected materials over time.

Application of Cross‐Borehole Radar to Monitor Field‐Scale Vegetable Oil Injection Experiments for Biostimulation

Cross-borehole radar methods were used to monitor a field-scale biostimulation pilot project at the Anoka County Riverfront Park (ACP), located downgradient of the Naval Industrial Reserve Ordnance Plant, in Fridley, Minnesota. The goal of the pilot project is to evaluate biostimulation using emulsified vegetable oil to treat ground water contaminated with chlorinated hydrocarbons. Vegetable oil is intended to serve as substrate to naturally occurring microbes, which ultimately break down chlorinated hydrocarbons into chloride, carbon dioxide, and water through oxidation-reduction reactions. In support of this effort, cross-borehole radar data were acquired by the U.S Geological Survey in five site visits over 1.5 years. This paper presents level-run (zero-offset profile) and time-lapse radar tomography data collected in multiple planes. Comparison of preand post-injection data sets provides valuable insights into the spatial and temporal distribution of both emulsified vegetable oil and also the extent of ground water with altered chemistry resulting from injections—information important for understanding microbial degradation of chlorinated hydrocarbons at the site. In order to facilitate data interpretation and test the effectiveness of radar for monitoring oilemulsion placement and movement, three injection mixtures with different radar signatures were used: (1) vegetable oil emulsion, (2) vegetable oil emulsion with a colloidal iron tracer, and (3) vegetable oil emulsion with a magnetite tracer. Based on petrophysical modeling, mixture (1) is expected to increase radar velocity and decrease radar attenuation relative to background—a water-saturated porous medium; mixtures (2) and (3) are expected to increase radar velocity and also increase radar attenuation due to their greater electrical conductivity compared to native ground water. Radar slowness (inverse radar velocity) tomograms and level-run profiles show decreases in slowness in the vicinity of injection wells. Slowness anomalies are observed only in planes connected to injection wells, indicating that the emplaced emulsified vegetable oil does not migrate far after injection. In contrast to the localization of slowness anomalies, attenuation anomalies are observed in all level-run profiles, particularly those downgradient of the injection wells. Despite the expected signatures of different tracers, increases in attenuation are observed downgradient of all three injections; thus, we infer that the attenuation changes do not result from the iron tracers. One viable explanation for the observed attenuation changes is that products of oil-enhanced biodegradation (for example, ferrous iron) increase electrical conductivity of ground water and thus radar attenuation. Application of radar methods to data from the ACP demonstrated the utility of radar for monitoring biostimulation. Results of level-run and tomographic surveys identified (1) the distribution of emulsified vegetable oil, and (2) the distribution of ground water with oil-affected chemistry. Ongoing research efforts include simultaneous tomographic inversion of radar data from multiple planes, petrophysical modeling, geostatistical interpolation, and development of an integrated interpretation considering conventional borehole logs and surface-to-borehole radar data.

Characterization of fractures and flow zones in a contaminated crystalline-rock aquifer in the Tylerville section of Haddam, Connecticut

The U.S. Geological Survey, in cooperation with the Connecticut Department of Energy and Environmental Protection, investigated the characteristics of the bedrock aquifer in the Tylerville section of Haddam, Connecticut, from June to August 2014. As part of this investigation, geophysical logs were collected from six water-supply wells and were analyzed to (1) identify well construction, (2) determine the rock type and orientation of the foliation and layering of the rock, (3) characterize the depth and orientation of fractures, (4) evaluate fluid properties of the water in the well, and (5) determine the relative transmissivity and head of discrete fractures or fracture zones. The logs included the following: caliper, electromagnetic induction, gamma, acoustic and (or) optical televiewer, heat-pulse flowmeter under ambient and pumped conditions, hydraulic head data, fluid electrical conductivity and temperature under postpumping conditions, and borehole-radar reflection collected in single-hole mode. In a seventh borehole, a former water-supply well, only caliper, fluid electrical conductivty, and temperature logs were collected, because of a constriction in the borehole. This report includes a description of the methods used to collect and process the borehole geophysical data, the description of the data collected in each of the wells, and a comparison of the results collected in all of the wells. The data are presented in plots of the borehole geophysical logs, tables, and figures. Collectively these data provide valuable characterizations that can be used to improve or inform site conceptual models of groundwater flow in the study area.

Borehole radar interferometry revisited

Single-hole, multi-offset borehole-radar reflection (SHMOR) is an effective technique for fracture detection. However, commercial radar system limitations hinder the acquisition of multi-offset reflection data in a single borehole. Transforming cross-hole transmission mode radar data to virtual single-hole, multi-offset reflection data using a wave interferometric virtual source (WIVS) approach has been proposed but not fully demonstrated. In this study, we compare WIVS-derived virtual single-hole, multi-offset reflection data to real SHMOR radar reflection profiles using cross-hole and single-hole radar data acquired in two boreholes located at the University of Connecticut (Storrs, CT USA). The field data results are similar to full-waveform numerical simulations developed for a two-borehole model. The reflection from the adjacent borehole is clearly imaged by both the real and WIVS-derived virtual reflection profiles. Reflector travel-time changes induced by deviation of the two boreholes from the vertical can also be observed on the real and virtual reflection profiles. The results of this study demonstrate the potential of the WIVS approach to improve bedrock fracture imaging for hydrogeological and petroleum reservoir development applications.

Geophysical and hydrologic analysis of an earthen dam site in southern Westchester County, New York

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USE OF ELECTROMAGNETIC INDUCTION METHODS TO MONITOR REMEDIATION AT THE UNIVERSITY OF CONNECTICUT LANDFILL: 2004-2011

Time-lapse geophysical surveys using frequency-domain electromagnetics (FDEM) can indirectly measure time-varying hydrologic parameters such as fluid saturation or solute concentration. Monitoring of these processes provides insight into aquifer properties and the effectiveness of constructed controls (such as leachate interceptor trenches), as well as aquifer responses to natural or induced stresses. At the University of Connecticut landfill, noninvasive, electromagnetic induction (EMI) methods were used to monitor changes in subsurface electrical conductivity that were related to the landfill-closure activities. After the landfill was closed, EMI methods were used to monitor changes in water saturation and water quality. As part of a long-term monitoring plan to observe changes associated with closure, redevelopment, and remediation of the former landfill, EMI data were collected to supplement information from groundwater samples collected in wells to the south and north of the landfill. In comparison to single-point measurements that could have been collected by conventional installation of additional monitoring wells, the EMI methods provided increased spatial coverage, and were less invasive and therefore less destructive to the wetland north of the landfill. To monitor effects of closure activities on the subsurface conductivity, EMI measurements were collected from 2004 to 2011 along discrete transects north and south of the landfill prior to, during, and after the landfill closure. In general, the results indicated an overall decline in subsurface electrical conductivity with time and with distance from the former landfill. This decline in electrical conductivity indicated that the closure and remediation efforts reduced the amount of leachate that originated from the landfill and that entered the drainages to the north and south of the landfill.

Geohydrologic assessment of fractured crystalline bedrock on the southern part of Manhattan, New York, through the use of advanced borehole geophysical methods

Advanced borehole-geophysical methods were used to assess the geohydrology of fractured crystalline bedrock in 31 of 64 boreholes on the southern part of Manhattan Island, NY in preparation of the construction of a new water tunnel. The study area is located in a highly urbanized part of New York City. The boreholes penetrated gneiss, schist, and other crystalline bedrock that has an overall southwest-to northwest-dipping foliation. Most of the fractures intersected are nearly horizontal or have moderate- to high-angle northwest or eastward dip azimuths. Heat-pulse flowmeter logs obtained under nonpumping (ambient) and pumping conditions, together with other geophysical logs, delineated transmissive fracture zones in each borehole. Water-level and flowmeter data suggest the fractured-rock ground-water-flow system is interconnected. The 60 MHz directional borehole-radar logs delineated the location and orientation of several radar reflectors that did not intersect the projection of the borehole. A total of 53 faults intersected by the boreholes have mean orientation populations of N12°W, 66°W and N11°W, 70°E. A total of 77 transmissive fractures delineated using the heat-pulse flowmeter have mean orientations of N11°E, 14°SE (majority) and N23°E, 57°NW (minority). The transmissivity of the bedrock boreholes ranged from 0.7 to 870 feet squared (ft2) per day (0.07 to 81 metres squared (m2) per day).

Steam injection pilot study in a contaminated fractured limestone (Maine, USA): modeling and analysis of borehole radar reflection data

AbslructSteam-enhanced remediation (SER) has been successfully used to remove DNAPL and LNAPL contaminants in porous media. Between August and November 2002, SER was tested in fractured limestone at the former Loring Air Force Base, in Maine, USA. During the SER investigation, the U.S. Geological Survey conducted a series of borehole radar surveys to evaluate the effectiveness of radar methods for monitoring the movement of steam and heat through the fractured limestone. The data were collected before steam injection, 10 days after the beginning of injection, and at the end of injection. In this paper, reflection-mode borehole radar data from wells JBW-7816 and JBW-7817A are presented and discussed. Theoretical modeling was performed to predict the variation of fracture reflectivity owed to heating, to show displacement of water and to assess the effect of SER at the site. Analysis of the radar profile data indicates some variations resulting from heating (increase of continuity of reflectors, attenuation of deeper reflections) but no substantial variation of traveltimes. Spectral content analysis of several individual reflections surrounding the boreholes was used to investigate the replacement of water by steam in the fractures. Observed decrease in radar reflectivity was too small to be explained by a replacement of water by steam, except for two high-amplitude reflectors, which disappeared near the end of the injection; moreover, no change of polarity, consistent with steam replacing water, was observed. The decrease of amplitude was greater for reflectors near well JBW-7817A and is explained by a greater heating around this well. John W. Lane Jr., Peter K. Joesten U.S. Geological Survey, Branch of Geophysics 11 Sherman Place, Unit 5015, Storrs Mansfield, CT 06269, United States jwlane@usgs.gov , pjoesten@usgs.gov

Application of Borehole‐Radar Methods to Image Two Permeable Reactive‐Iron Walls at the Massachusetts Military Reservation, Cape Cod, Massachusetts

A pilot-scale study was conducted at the Massachusetts Military Reservation, Cape Cod, Massachusetts, to assess the use of a hydraulic-fracturing method to create vertical permeable walls of zero-valent iron to remediate ground water contaminated with chlorinated solvents at depths exceeding the range of conventional iron-wall installation methods. At the test site, ground-water contamination extends from 24 to 37 meters (m) below land surface. A treatment zone consisting of two parallel reactive-iron walls 12 m long, 13 m high, and 0.15 m thick, separated by about 6 m, was designed to intersect and remediate a portion of the CS-10 plume. The U.S. Geological Survey used a cross-hole, common-depth radar scanning method to test the continuity and estimate the lateral and vertical extent of the two reactive-iron walls. The cross-hole radar surveys were conducted in boreholes on opposite sides of the iron injection zones. Significant decreases in the amplitude of the radar pulse observed in scans traversing the injection zones were interpreted by comparing radar field data to results of twodimensional, finite-difference, time-domain models and laboratory-scale physical models developed to predict the effects of wall edges and discontinuities on common-depth cross-hole radar measurements. As part of a feasibility study, single-hole radar reflection data was used successfully to image the walls.