Borehole Geophysical Monitoring of Amendment Emplacement and Geochemical Changes During Vegetable Oil Biostimulation, Anoka County Riverfront Park, Fridley, Minnesota, Scientific Investigations Report 2006

Scientific Investigations Report 2006—5199

Borehole Geophysical Monitoring of Amendment Emplacement and Geochemical Changes During Vegetable Oil Biostimulation, Anoka County Riverfront Park, Fridley, Minnesota

Prepared in cooperation with the U.S. Navy

By John W. Lane, Jr., Frederick D. Day-Lewis, Carole D. Johnson, Peter K. Joesten, and Christopher S. Kochiss

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Abstract

The U.S. Geological Survey (USGS) conducted a series of geophysical investigations to monitor a field-scale biostimulation pilot project at the Anoka County Riverfront Park (ACP), downgradient from the Naval Industrial Reserve Ordnance Plant, in Fridley, Minnesota. The pilot project was undertaken by the U.S. Naval Facilities Engineering Command, Southern Division, for the purpose of evaluating biostimulation using emulsified vegetable oil to treat ground water contaminated with chlorinated hydrocarbons. Vegetable oil was introduced to the subsurface to serve as substrate for naturally occurring microbes, which ultimately break down chlorinated hydrocarbons into chloride, carbon dioxide, and water through oxidation-reduction reactions. In support of this effort, the USGS collected cross-borehole radar data and conventional borehole geophysical data in five site visits over 1.5 years to evaluate the effectiveness of geophysical methods for monitoring emplacement of the vegetable oil emulsion and for tracking changes in water chemistry. Radar zero-offset profile (ZOP) data, radar traveltime tomograms, electromagnetic (EM) induction logs, natural gamma logs, neutron porosity logs, and magnetic susceptibility logs were collected and analyzed.

In order to facilitate data interpretation and to test the effectiveness of radar for monitoring oil-emulsion 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) was expected to increase radar velocity and decrease radar attenuation relative to background—a water-saturated porous medium; mixtures (2) and (3) were expected to increase radar velocity and increase radar attenuation because of their greater electrical conductivity compared to background ground water.

Radar ZOP data and tomograms show increased EM velocity in the vicinity of injection wells. Comparison of pre- and post-injection datasets shows that velocity anomalies are observed only in planes connected to injection wells, indicating that the emulsified vegetable oil does not migrate far after injection. In contrast to the localization of velocity anomalies, radar attenuation anomalies are observed in all zero-offset profiles, particularly those downgradient from the injection wells. Despite the expected signatures of different tracers, increases in attenuation are observed downgradient from all three injection wells; thus, we infer that the attenuation changes do not result from the iron tracers alone. Over the period of data collection, the slowness (reciprocal velocity) anomalies are relatively stable, whereas the attenuation anomalies generally increase in magnitude and extent. One explanation for the attenuation changes is that products of vegetable oil-enhanced biodegradation (for example, chloride) increase the specific conductance of ground water and thus bulk electrical conductivity and radar attenuation. This interpretation is supported by the results of EM-induction and magnetic susceptibility logs, which indicate increases in electrical conductivity in the absence of magnetic anomalies that might result from the iron and magnetite.

Based on the geophysical data, conceptual models of the distributions of emulsified vegetable oil and ground water with altered chemistry were developed. The field data indicate that, in several cases, the plume of ground water with altered chemistry would not be detected by direct chemical sampling given the construction of monitoring wells; hence the geophysical data provide valuable site-specific insights for the interpretation of water samples and monitoring of biostimulation projects. Application of geophysical methods to data from the ACP demonstrated the utility of radar for monitoring biostimulation injections.

Abstract

Figures

1. Map showing (A) location of the study area, Anoka County Riverfront Park, Fridley, Minnesota, and (B) location of boreholes at the study area

2. Graphs showing (A) reflective permittivity of vegetable oil emulsions plotted against emulsion water content predicted by the two-phase complex refractive index method (CRIM), (B) electromagnetic (EM) wave radar velocity through quartz sand and saturated by vegetable oil emulsions with different emulsion-to- water ratios plotted against porosity predicted by the three-phase CRIM, and (C) expected slowness difference resulting from injecting a vegetable oil emulsion containing 35 percent oil and 65 percent water into a water-saturated quartz sand for different levels of emulsion pore-space saturation plotted against porosity predicted by the CRIM

3. Diagram showing radar survey geometries for (A) cross-hole zero-offset profiling, and (B) cross-hole tomography

4. Plot showing (A) zero-offset radar slowness, and (B) zero-offset radar amplitude profiles for the MW-1 to INJ-2 plane, Anoka County Riverfront Park, Fridley, Minnesota

5. Diagram showing cross-hole radar tomography raypath geometry for the MW-7 to INJ-3 plane, Anoka County Riverfront Park, Fridley, Minnesota

6. December 2001 cross-hole radar tomograms for the (A) MW-1 to INJ-2 planes, and (B) MW-7 to INJ-3 planes, Anoka County Riverfront Park, Fridley, Minnesota

7. (A) Raypaths corresponding to slowness-difference data of greater than the median value of the dataset, and (B) raypaths corresponding to slowness-difference data showing less than the 30th percentile, Anoka County Riverfront Park, Fridley, Minnesota

8. Diagram showing conceptual diagram of the object-based inversion parameterization of slowness difference (Δs) in the tomographic image plane

9. Radar slowness-difference tomography inversion results from well-pair MW-7 and INJ-3 using the object-based inversion (OBI) method

10. Borehole geophysical logs for MW-1, Anoka County Riverfront Park, Fridley, Minnesota

11. Borehole geophysical logs for INJ-2, Anoka County Riverfront Park, Fridley, Minnesota

12. Interpreted conceptual model of the June 2003 areal distribution of ground water with altered chemistry (blue) and the area where pure-phase vegetable oil emulsion is found in the subsurface (green), Anoka County Riverfront Park, Fridley, Minnesota

13. Interpreted conceptual model of the June 2003 cross-sectional distribution of ground water with inferred, highly elevated total dissolved solids (TDS)(dark blue), moderately elevated TDS (light blue), and the region where pure-phase vegetable oil emulsion is found in the subsurface (green), Anoka County Riverfront Park, Fridley, Minnesota

Tables

1. Borehole constructions for injection and observation wells at the Anoka County Riverfront Park, Fridley, Minnesota

5. Estimates of changes in attenuation and total dissolved solids for selected anomalies in zero-offset radar data

Suggested citation:
Lane, J.W. Jr., Day-Lewis, F.D., Johnson, C.D., Joesten, P.K., and Kochiss, C.S., 2007, Borehole geophysical monitoring of amendment emplacement and geochemical changes during vegetable oil biostimulation, Anoka County Riverfront Park, Fridley, Minnesota: U.S. Geological Survey Scientific Investigations Report 2006–5199, 54 p. ONLINE ONLY

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