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The Geological Society of America (GSA) released a Critical Issues Paper on induced seismicity

David R. Wunsch, Delaware’s State Geologist and Director of the Delaware Geological Survey, is a member of the GSA Public Policy Committee and lead author and chairman of the committee tasked with preparing the critical issues paper. A link to the paper, available on the GSA website, is: http://www.geosociety.org/criticalissues/Induced_Seismicity/index.asp

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Delaware Geological Survey Issues Report on Groundwater Monitoring and Water-Quality Impacts of Rapid Infiltration Basin Systems

The Delaware Geological Survey released a new technical report entitled “Groundwater Quality and Monitoring of Rapid Infiltration Basin Systems, Theory and Field Experiments at Cape Henlopen State Park, Delaware” which was prepared by A. Scott Andres and Changming He of the Delaware Geological Survey, Edward Walther of the South Water Management District, Florida, Müserref Türkmen of the Izmir Water and Sewerage Administration, Turkey, and Anastasia Chirnside and William Ritter of the University of Delaware. DGS Bulletin 21C documents the results of a detailed study of groundwater quality at a rapid infiltration basin system.

B21C Groundwater Quality and Monitoring of Rapid Infiltration Basin Systems (RIBS), Theory and Field Experiments at Cape Henlopen State Park, Delaware

B21C Groundwater Quality and Monitoring of Rapid Infiltration Basin Systems (RIBS), Theory and Field Experiments at Cape Henlopen State Park, Delaware

A rapid infiltration basin system (RIBS) consists of several simple and relatively standard technologies; collection and conveyance of wastewater, treatment, and discharge to an unlined excavated or constructed basin. By design, the effluent quickly infiltrates through the unsaturated or vadose zone to the water table. During infiltration, some contaminants may be treated by biological and/or geochemical processes and diluted by dispersion and diffusion. The combination of contaminant attenuation and dilution processes that may occur during infiltration and flow through the aquifer are termed soil-aquifer-treatment, or SAT. In the past decade, RIBS have been proposed more frequently for use in Delaware because they stop the direct discharge of treated effluent to surface water, can accommodate significant flow volumes typical of residential subdivisions, yet require much less land than options such as spray irrigation or sub-surface disposal systems.

Decades of research on the shallow Columbia aquifer of the Delmarva Peninsula have clearly identified the high susceptibility of the aquifer from land- and water-use practices, and the processes that control the fate and transport of contaminants from their origin at or near land surface to points of discharge in creeks, estuaries, and wells. The risk of aquifer contamination is great because it is highly permeable, has little organic matter in the aquifer matrix, and the depth to groundwater is very commonly less than 10 ft below land surface. USEPA guidance documents and several engineering texts that cover RIBS design clearly identify these same factors as increasing risk for groundwater contamination but do not provide much information on means to monitor and mitigate those risks. Further, design criteria are based on a small group of experiments conducted in the 1970s prior to development of current understanding of the processes that control groundwater contaminant transport.

Field and laboratory experiments to characterize the physical, chemical, and biological controls and processes associated with the rapid infiltration of treated sewage effluent through infiltration beds and the vadose zone were undertaken at a RIBS located at Cape Henlopen State Park (CHSP), Delaware. Field experiments to understand the geochemical effects of the long-term operation of a RIBS on ground and surface waters, and to evaluate monitoring systems were also conducted at the site. The CHSP RIBS has been in operation since the early 1980s.

Significant concentrations of nitrogen and phosphorus occur in groundwater from the point of effluent entry at the water table to distances greater than 150 ft from the infiltration beds. The high hydraulic, nitrogen (N), phosporus (P), and organic loading rates associated with the operation of RIBS overwhelm natural attenuation (e.g., sorption and precipitation) processes. Data are not sufficient to indicate whether denitrification is occurring. If there is denitrification, the rate is insufficient to remediate RIBS effluent at the site — despite a 25-ft thick vadose zone, an effluent with enough organic carbon to facilitate anaerobic conditions that permit abiotic denitrification and feed microorganism-driven denitrification processes, and hypoxic to anoxic groundwater.

Significant horizontal and vertical variability of contaminant concentrations were observed within the portion of the aquifer most impacted by effluent disposal. Despite the relatively small spatial extent of the disposal area in our study area, identification of the preferential flow zone and characterization of the vertical and temporal variability in the concentrations of contaminants required a multi-phase subsurface investigation program that included an analysis of data from samples collected at bi-monthly intervals from dozens of monitoring points and high frequency temperature monitoring in several wells. A well-designed monitoring system should be based on experimentally determined site specific evidence collected under conditions that duplicate the flow rates that are expected during full-scale operation of the RIBS. Conservative tracers should be used to determine if the monitoring wells are in locations that intercept flow from the infiltration beds.

Delaware Geological Survey Issues Report on Hydrogeologic Impacts of Rapid Infiltration Basin Systems

The Delaware Geological Survey released a new technical report entitled “Hydrogeology of a Rapid Infiltration Basin Systems at Cape Henlopen State Park, Delaware” which was prepared by A. Scott Andres and Changming He of the Delaware Geological Survey, Edward Walther of the South Water Management District, Florida, and Müserref Türkmen of the Izmir Water and Sewerage Administration, Turkey, and DGS Bulletin 21B documents the results of a detailed study of groundwater and hydrogeology at a rapid infiltration basin system.

B21B Hydrogeology of a Rapid Infiltration Basin System (RIBS) at Cape Henlopen State Park, Delaware

B21B Hydrogeology of a Rapid Infiltration Basin System (RIBS) at Cape Henlopen State Park, Delaware

The hydrogeologic framework of Cape Henlopen State Park (CHSP), Delaware was characterized to document the hydrologic effects of treated wastewater disposal on a rapid infiltration basin system (RIBS). Characterization efforts included installation of test borings and monitoring wells; collection of core samples, geophysical logs, hydraulic test data, groundwater levels and temperatures; testing of grain size distribution; and interpretation of stratigraphic lithofacies, hydraulic test data, groundwater levels, and temperature data. This work was part of a larger effort to assess the potential benefits and risks of using RIBS in Delaware.

The infiltration basins at CHSP are constructed on the Great Dune, an aeolian dune feature composed of relatively uniform, medium-grained quartz sand. The age of the dune, determined by carbon-14 dating of woody material in swamp deposits under the dune, is less than 800 years. Underlying the dune deposits are relatively heterogeneous, areally continuous, coarse-grained spit deposits of the proto-Cape Henlopen spit with interbedded and relatively fine-grained, discontinuous swamp and marsh deposits, and beneath, relatively fine-grained, continuous, near-shore marine deposits. The dune deposits can be 45 ft thick under the crest of the dune and nonexistent at the surface. Spit deposits range from 5 to 15 ft thick. Test drilling determined that the near-shore marine deposits are at least 10 ft thick in the vicinity of the infiltration basins. The complete thickness of these deposits was not determined in this study.

Hydraulic testing and grain-size data indicate that the dune and spit deposits are relatively permeable, with average hydraulic conductivities of 140 ft/day and that the swamp and marsh deposits are more than one order of magnitude less permeable, with average hydraulic conductivity of 25 to 10 ft/day. The water-table aquifer is present in the sandier dune and spit deposits. The swamp, marsh, and near-shore marine deposits form a leaky confining unit. The water-table aquifer is 15 to 20 ft thick under the thickest section of the Great Dune and nonexistent where the dune deposits are absent. The vadose zone is greater than 25 ft thick under the infiltration basins.

High-frequency groundwater level and temperature monitoring during periods of maximum wastewater disposal rates indicates that wastewater disposal causes increases in water-table elevations on the order of 1 ft. Groundwater elevations indicate that the water-table elevation is greatest under the infiltration basins and that most flow is directed southward toward a swampy discharge area.

Maximum disposal rates typically occur in summer months when the numbers of park users and water use are greatest. Coincident with greater disposal rates are higher wastewater temperatures. These higher wastewater temperatures are observed in groundwater and provide a means to track the flow of water from beneath the infiltration beds towards a nearby discharge area. Tracking of the warmer groundwater and modeling two-dimensional particle tracking both indicate that wastewater discharged to the infiltration basins reaches the nearby discharge area within 180 days.

Delaware Geological Survey Issues Report on Wastewater Treatment used for Rapid Infiltration Basin Systems

The Delaware Geological Survey released a new technical report entitled “Evaluation Of Wastewater Treatment Options Used In Rapid Infiltration Basin Systems (RIBS)” which was prepared by Müserref Türkmen of the Izmir Water and Sewearge Administration, Turkey, A. Scott Andres of the Delaware Geological Survey, Edward Walther of the South Water Management District, Florida, and William Ritter and Anastasia Chirnside of the University’s College of Agriculture and Natural Resources. DGS Bulletin 21A documents the results of a detailed study of wastewater treatment plant technologies and effectiveness of treatment types that are used to treat wastewater prior to disposal into the ground by rapid infiltration basin systems.

Delaware Geological Survey issues report on groundwater modeling in eastern Sussex County

The Delaware Geological Survey (DGS) has released a new technical report titled Simulation of Groundwater Flow and Contaminant Transport in Eastern Sussex County, Delaware with Emphasis on Impacts of Spray Irrigation of Treated Wastewater, which was prepared by Changming He and A. Scott Andres of DGS.

DGS Report of Investigations No. 79 documents development of a detailed study of subsurface hydrogeology, interactions between aquifers and streams, and the effects of spray irrigation of treated wastewater on groundwater beneath southern eastern Sussex County.

RI79 Simulation of Groundwater Flow and Contaminant Transport in Eastern Sussex County, Delaware With Emphasis on Impacts of Spray Irrigation of Treated Wastewater

Simulation of Groundwater Flow and Contaminant Transport in Eastern Sussex County, Delaware With Emphasis on Impacts of Spray Irrigation of Treated Wastewater

This report presents a conceptual model of groundwater flow and the effects of nitrate (NO3-) loading and transport on shallow groundwater quality in a portion of the Indian River watershed, eastern Sussex County, Delaware. Three-dimensional, numerical simulations of groundwater flow, particle tracking, and contaminant transport were constructed and tested against data collected in previous hydrogeological and water-quality studies.

The simulations show a bimodal distribution of groundwater residence time in the study area, with the largest grouping at less than 10 years, the second largest grouping at more than 100 years, and a median of approximately 29 years.

Historically, the principal source of nitrate to the shallow groundwater in the study area has been from the chemical- and manure-based fertilizers used in agriculture. A total mass of NO3- -nitrogen (N) of about 169 kg/day is currently simulated to discharge to surface water. As the result of improved N-management practices, after 45 years a 20 percent decrease in the mass of NO3- -N reaching the water table would result in an approximately 4 percent decrease in the mass of simulated N discharge to streams. The disproportionally smaller decrease in N discharge reflects the large mass of N in the aquifer coupled with long groundwater residence times.

Currently, there are two large wastewater spray irrigation facilities located in the study domain: the Mountaire Wastewater Treatment Facility and Inland Bays Wastewater Facility. The effects of wastewater application through spray irrigation were simulated with a two-step process. First, under different operations and soil conditions, evaporation and water flux, NO3- -N uptake by plants, and NO3- -N leaching were simulated using an unsaturated flow model, Hydrus-1D. Next, the range of simulated NO3- -N loads were input into the flow and transport model to study the impacts on groundwater elevation and NO3- -N conditions.

Over the long term, the spray irrigation of wastewater may increase water-table elevations up to 2.5m and impact large volumes of groundwater with NO3-. Reducing the concentration of NO3- in effluent and increasing the irrigation rate may reduce the volumes of water impacted by high concentrations of NO3-, but may facilitate the lateral and vertical migration of NO3-. Simulations indicate that NO3- will eventually impact deeper aquifers. An optimal practice of wastewater irrigation can be achieved by adjusting irrigation rate and effluent concentration. Further work is needed to determine these optimum application rates and concentrations.

Assessing Potential Impacts of a Wastewater Rapid Infiltration Basin System on Groundwater Quality: A Delaware Case Study

DGS staff member A. Scott Andres along with J. Thomas Sims of the University’s Department of Plant and Soil Science have had a paper “Assessing Potential Impacts of a Wastewater Rapid Infiltration Basin System on Groundwater Quality: A Delaware Case Study” published in the Journal of Environmental Quality. This paper is the latest technical report from a DGS-led project “Evaluation of Rapid Infiltration Basin Systems (RIBS).” Four additional reports on this project are nearing release in the DGS bulletin series. Information about this project can be found at: http://www.dgs.udel.edu/projects/evaluation-rapid-infiltration-basin-systems-ribs

Presentation on RIBS at Fall 2012 AGU meeting

A poster "Modeling Engineered Approaches to Enhance Denitrification under Rapid Infiltration Basins" resulting from a collaborative research project between Paul Imhoff, Maryam Akhavan (UD Civil&Environmental Engineering), A. Scott Andres (DGS), and Stefan Finsterle (Lawrence Berkley National Lab) was presented at the Fall 2012 AGU meeting in San Francisco, CA on Dec. 3.

“Application of a Coupled Overland Flow–Vadose Zone Model to Rapid Infiltration Basin Systems”

Maryam Akhvan

Department of Civil and Environmental Engineering/DGS/Water Resources Center Research Fellow Maryam Akhavan authors paper on Rapid Infiltration Basins.

Land application of wastewater in Delaware - Results of research on RIBS, spray irrigation, and reuse

Scott Andres of Delaware Geological Survey did a presentation titled "Land application of wastewater in Delaware - Results of research on RIBS, spray irrigation, and reuse" at Delaware Onsite Wastewater Recycling Association annual conference, Oct 11, Dover DE.

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Source Water Assessment and Protection Program

Two Delaware Geological Survey staff members attended the Source Water Assessment and Protection Program meeting held Sept. 14 in Dover, Del. Scott Andres made a presentation titled "Results of Field and Lab Experiments on High Rate Land Application of Wastewater" and John Callahan made a presentation titled "Web-Delivered Application for Hydrogeologic Data."

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Delaware Geological Survey releases new geologic map of Harbeson area

The Delaware Geological Survey (DGS) has published a new geologic map of the area east of Georgetown in Sussex County entitled Geologic Map of the Harbeson Quadrangle, Delaware. Geologic Map 17 presents the results of research by Kelvin W. Ramsey and Jaime L. Tomlinson of the DGS.

The map shows and describes the geologic units found at the land surface and in the shallow subsurface in the map area. The map includes cross sections that show stratigraphic units that lie beneath the surficial units and detailed descriptions and ages of all units presented on the map.

DGS honors retiring director, state geologist Talley

Talley is retiring after 38 years of service

John Talley joined the Delaware Geological Survey as a project geologist in 1972, became a senior scientist and hydrogeologist by 1986, and rose to director and state geologist by 2004. He’s consulted with dozens of university, state, and federal governments and groups and amassed a list of more than 50 publications and reports.

Scott Andres made a presentation at the Center for the Inland Bays

Scott Andres of the Delaware Geological Survey made a presentation titled "Results of Field and Lab Experiments on High Rate Land Application of Wastewater -- RIBS -- Update on Current Research," at the Center for the Inland Bays, Scientific and Technical Advisory Committee, May 6, Lewes, Del.

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DNREC raises capital request - Sixfold hike includes beach, water projects

More money would go to projects that make Delaware cleaner, greener and safer under a mostly no-growth budget outlined Monday by the Department of Natural Resources and Environmental Control. Agency Secretary Collin P. O'Mara asked the Office of Management and Budget for about $35.2 million in general funds for the fiscal year that begins July 1, with health care costs accounting for most of the nearly $2 million increase from the current year.

Sewage disposal battle shapes up - Citizen groups warn of threat to Inland Bays

This news story discusses RIBS project.

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Wastewater Reuse: Benefits and Risk Assessment in Inland Bays Indian River Basin

Study domain
Project Contact(s):

The goal of this project is to develop a three-dimensional (3D) numerical groundwater flow model to evaluate the potential impacts to surface- and groundwater resulting from the disposal of treated wastewater in a portion of the Inland Bays drainage basin.

By developing a sub-regional, fresh, groundwater flow model and analyzing results, several issues will be addressed that are related to state policy, regulation revision, and proposed projects associated with land-based wastewater disposal (LBWD) in Sussex County.

A GIS screening tool for assessing suitability of land for RIBS

Scott Andres and Edward Walther, of the Delaware Geological Survey, presented "Development and Application of a GIS Screening Tool for Assessing Suitability of Land for Rapid Infiltration Basin Systems" at the National Ground Water Association Summit, Denver, April 12-15. Andres also participated in a panel discussion co-sponsored by the U.S. Subcommittee on Groundwater, "National Groundwater Monitoring Network: Listening Session."

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