Preliminary Investigation of Paleochannels and Groundwater Specific Conductance using Direct-Current Resistivity and Surface-Wave Seismic Geophysical Surveys at the Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, Delaware, 2008

Abstract

For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprodTo order this and other USGS information products, visit http://store.usgs.gov Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report.Suggested citation: Degnan, J.R., and Brayton, M.J., 2010, Preliminary investigation of paleochannels and groundwater specific conductance using direct-current resistivity and surface-wave seismic geophysical surveys at the Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, Delaware, 2008: U.S. Geological Survey Open-File Report 2010-1058, 27 p., at http://pubs.usgs.gov/of/2010/1058/. iii AcknowledgmentsThe authors of this report would like to recognize the work and dedication of Bernice Pasquini Altitude, as used in this report, refers to distance above the vertical datum.Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 25°C).Resistivity is given in Ohm meters. ACRONYMS USED IN AbstractThe U.S. Geological Survey (USGS), in cooperation with Region III of the U.S. Environmental Protection Agency (USEPA) and the State of Delaware, is conducting an ongoing study of the water-quality and hydrogeologic properties of the Columbia and Potomac aquifers and the extent of cross-aquifer contamination with benzene; chlorobenzene; 1,2-dichlorobenzene; 1,4-dichlorobenzene; and hydrogen chloride (hydrochloric acid when dissolved in water) in the vicinity of the Standard Chlorine of Delaware, Inc. (SCD), Superfund Site, Delaware City, Delaware. Surface geophysical surveys and well data were used to identify and correlate low-permeability units (clays) across the site and to search for sand and gravel filled paleochannels that are potential conduits and receptors of contaminated groundwater and (or) Dense Non-Aqueous Phase Liquid (DNAPL) contaminants. The combined surveys and well data were also used to characterize areas of the site that have groundwater with elevated (greater than 1,000 microsiemens per centimeter) specific conductance (SC) as a result of contamination.The most electrically conductive features measured with direct-current (DC) resistivity at the SCD site are relatively impermeable clays and permeable sediment that are associated with elevated SC in groundwater. Many of the resistive features include paleochannel deposits consisting of coarse-grained sediments that are unsaturated, have low (less than 200 microsiemens per centimeter) SC pore water, or are cemented. Groundwater in uncontaminated parts of the Columbia aquifer and of the Potomac aquifer ...

Surface geophysics and porewater evaluation at the Lower Darby Creek Area Superfund Site, Philadelphia, Pennsylvania, 2013

“…The methodology for the DC-resistivity surveys conducted for this report is adapted from Degnan and Brayton (2010) and Degnan and Harte (2013). DC is induced in the ground using two current electrodes, while the voltage is measured across two potential electrodes.…”

Hydrogeologic framework, hydrology, and refined conceptual model of groundwater flow for Coastal Plain aquifers at the Standard Chlorine of Delaware, Inc. Superfund Site, New Castle County, Delaware, 2005-12

“…Natural gamma logs were collected for selected wells in 2006, prior to barrier wall installation and for each new boring location during 2007-10. Electrical and seismic surface-geophysical methods were used at the site beginning in 2008 (Degnan and Brayton, 2010), with additional data collection and interpretation currently ongoing (2014). Natural gamma radiation borehole geophysical logs were collected at selected wells to differentiate fine-grained from coarse-grained sediment.…”

“…Descriptions of standard boreholegeophysical logging methods and interpretation can be found in Keys (1990). Direct current (DC) resistivity measurements taken from core that was collected and preserved during drilling has assisted in the interpretation of data from surface DC resistivity surveys, enabling features to be verified at specific depths (Degnan and Brayton, 2010). An analysis of boring logs from drilling, in combination with DC resistivity data, has furthered the understanding of how the flow system varies laterally and with depth.…”

“…The exact thickness of Merchantville confining beds was determined at borehole locations. DC resistivity surveys (Degnan and Brayton, 2010) were used to interpolate between boreholes and identify geologic contacts, although in many cases, a thin Merchantville unit was broadly interpreted as lumped together with silts and clay of the upper Potomac Formation because of the similar electrical conductivity response ( fig. 8).…”

Hydrogeologic characterization and assessment of bioremediation of chlorinated benzenes and benzene in wetland areas, Standard Chlorine of Delaware, Inc. Superfund Site, New Castle County, Delaware, 2009-12

“…The extremely high estimated cost of a thermal remedy and the recognition of advances in bioremediation since 1993 (Black & Veatch, 2003;HydroGeoLogic, Inc., 2009) led to the decision to reinvestigate the potential of bioremediation for the SCD wetland areas. In cooperation with EPA, the U.S. Geological Survey (USGS) expanded its ongoing Potomac aquifer investigation at the site (Degnan and Brayton, 2010) and began a preliminary investigation in June 2009 of the feasibility of monitored natural attenuation or of combined natural attenuation and enhanced bioremediation as remedial strategies for the contaminated wetland areas.…”