Flow and Containment of Injected Wastes

Proper design, construction, testing and maintenance of Class 1 (hazardous waste) injection wells can guarantee that all waste is delivered to the injection zone. To assess the effects of waste injection, analytical models were developed which predict waste movement and pressure increases within the injection zone, and describe upward permeation through confining layers.
A basic plume model was used to track waste from several injection wells with varied injection history at DuPont's Victoria Texas site. To determine the maxi-mum distance that any portion of the waste might travel, special purpose models were employed to account for (1) density differences between the waste and the native formation brine, and (2) layered permeability variation within the injection zone. The results were generalized to a "multiplying factor concept," which facilitates development of a worst-case scenario.
A pressure distribution model based on the Theis (1935) equation for radial flow was applied to the Victoria site, with modifications to account for multiple wells, injection history and geological complexities.
Permeation into an intact confining layer was investigated by a new technique based on the Hantush and Jacob (1955) "leaky aquifer" theory. The model defines the maximum permeation distance, taking into account post-injection pressure decay.
Defects within confining layers, such as faults, fractures and abandoned wells, have been considered. Studies to evaluate their detailed characteristics are continuing. Initial results indicate that faults and fractures are not likely to provide conductive pathways in Gulf Coast settings, and site-specific evaluations are required to assess the impact of abandoned wells.     

Chemical Fate of Injected Wastes

The chemical fate of wastes put into disposal wells can be determined using standard chemical engineering techniques. The concentration of hazardous constituents is typically reduced by reactions within the waste itself or by reactions with the injection zone material, thus reducing any potential impact on the environment. Such reactions include neutralization, hydrolysis, ion exchange, adsorption, precipitation, co-precipitation and microbial degradation.
Extensive research was done to quantify these phenomena, so they could be used in a predictive model.
Neutralization, hydrolysis and precipitation were modeled using data from the open literature: reaction rates and equilibrium constants for the dominant reactions were incorporated into a sophisticated computer simulation that calculates solid-liquid equilibria of aqueous electrolyte solutions.
The model predicted the fate of two waste streams: (1) high-pH, cyanide-containing waste injected into sandstone is made less hazardous by hydrolysis and sand dissolution, and (2) FeCl₃-FeCl₂ HCl-H₂ O waste is made non-hazardous by reaction with dolomite. Experiments are planned to confirm certain model predictions. Further development and public access of the model are planned.     

Evaluation of Hydrogeo-chemical Conditions for Development of Nuclear Criticality in Low-Level Waste Disposal Facilities

The under ground disposal of fissile isotope-bearing wastes poses some unique issues. Specifically, radionuclides such as ²³⁵U disposed in low-level waste facilities, if present in the correct concentration and geometry, can create a nuclear criticality event that releases radioactivity to ground water. This paper reports the results of a study of the potential for ²³⁵U to be transported by ground water within low-level waste facilities and to concentrate to form a critical mass. Coupled hydrologic and geochemical modeling was used to investigate two possible mechanisms for concentrating mobile uranium: sorption on high capacity sites and precipitation in a reducing zone. The hydrogeochemical modeling showed that (1) it is difficult to mobilize uranium from sorption sites then re-deposit it; (2) if uranium is already in solution it can accumulate in zones of high sorption, and (3) reducing zones can accumulate sufficient uranium in the presence of oxygenated ground water. Site-specific disposal practices, such as the commingling of large quantities of depleted (nonfissile) uranium and the difficulty of bringing sufficient mass together in the correct geometry, limit the potential for criticality safety concerns. In order to determine appropriate disposal practices, hydrogeochemical modeling can be used to study the future mobility and accumulation of the waste.     

A Comparison of Ground Water Monitoring Data from CERCLA and RCRA Sites

Ground water quality data generated during the investigation of 334 hazardous waste disposal sites were used to contrast the Resource Conservation and Recovery Act (RCRA) and Comprehensive Emergency Response, Compensation and Liability Act (CERCLA) monitoring. programs. The minimum RCRA-required network of four wells was equaled or exceeded at 94 percent of the 156 RCRA sites and 70 percent of the 178 CERCLA sites in the data base. A sampling frequency of four events per year or more was used at 60 percent of the RCRA sites compared to only 24 percent at the CERCLA sites. CERCLA records compiled to date indicate that 480 compounds have been detected and another 220 compounds have been tentatively identified in ground water in the vicinity of hazardous waste disposal sites. However, the composite data from 123 RCRA site monitoring programs only indicates the presence of 100 chemical substances. The most significant discrepancy in the RCRA detection monitoring program is that it only generates data on three of the 20 organic contaminants that have been most frequently detected during the CERCLA hazardous waste disposal site investigations. Modification of the current RCRA program to include routine analysis for volatile organic compounds would correct this weakness.     

Recovery of Phosphate Sludge as Concrete Supplementary Material

The automotive industry plays a major role in the worldwide economy and represents an opportunity to increase the performance of the Turkish economy. Phosphating units in the automotive manufacturing plants generate phosphate sludge as waste, which is classified as hazardous waste in the European Waste Catalogue. Phosphate sludge must be disposed of in licensed disposal plants according to the current environmental regulations. Solidification/stabilization (S/S) is a widely used treatment technology for the disposal of hazardous wastes. Portland cement is used for the solidification and stabilization processes to immobilize Ni and Zn in the phosphate sludge as well as to create construction material to be used as cobble stone for pavement. Examination of products obtained by S/S processes is performed for two points: to determine the quality and to assess the environmental impacts. The phosphate sludge samples are subjected to chemical characterization and a size distribution analysis leaching test. Concrete for cobble stone was produced by the S/S process with the addition of phosphate sludge to replace sand. Tests for the quality of the product were carried out to determine compressive strength, permeability, and elasticity. At the end of the leaching test, elution concentrations of Zn and Ni while using water with pH values of 4.0, 5.4, and 9.0 were determined to be under the limit of inert material properties. Use of phosphate sludge should be considered as a sand replacement in the proportion of 1% of phosphate sludge to cement in concrete production, such as for cobble stone for pavement, without any adverse environmental impacts.     

Pre‐treatment of Waste Foundry Sand Via Solidification/Stabilization

This study was performed to propose a suitable treatment for waste foundry sand (WFS) before persistent disposal. It was observed that solidification/stabilization (S/S), which is the common pre‐treatment method because of its comparatively easy and inexpensive applicability, can treat WFS including dissolved organic carbon (DOC) above hazardous landfilling limits. Regular sand was partially replaced with WFS with a ratio of 0–90 wt% in order to prepare three different kinds of mortar samples, where Portland limestone cement (PLC) alone, calcium lime (CL) alone, and PLC together with CL were contained as binders. Leaching behaviors of all S/S products were analyzed according to the TS EN 12457‐4 leaching test. The treatment efficiency was assessed to reduce the DOC content to the levels under the European landfill acceptance criteria. Furthermore, heavy metals (Ni, Zn, Cr), fluoride (F^?), total dissolved solids leachability, and total organic carbon content were analyzed in order to investigate the pre‐treatment ability and to determine whether S/S products can be disposed of in a landfill site with municipal wastes or in a separate landfill site. The results showed that S/S of WFS is an efficient pre‐treatment technique before its disposal in a landfill and provides economical advantages compared to hazardous waste landfilling.     

Subsurface Disposal of Liquid Low-Level Radioactive Wastes at Oak Ridge, Tennessee

Liquid low-level radioactive wastes have been disposed of by subsurface injection at Oak Ridge, Tennessee, for the last two decades. The process entails mixing the wastes with cement and other additives, then pumping the slurry under pressure into a highly impermeable shale; the pressure is sufficient to create bedding plane fractures in which the grout, containing the wastes, sets. Research is being conducted to develop an understanding of the hydrology of the site and monitoring methods. The present regulatory climate regarding injection wells has created an uncertain future for this technique.     

Investigation of Failure Mechanisms and Migration of Organic Chemicals at Wilsonville, Illinois

Ground water contamination was discovered in 1981 in a monitoring well at the Earthline disposal facility near Wilsonville, Illinois. Organic chemicals had migrated at a rate 100 to 1000 times greater than predicted when the site received its permit to operate in 1978. Postulated failure mechanisms included migration through previously unmapped permeable zones, subsidence of an underground mine, organic-chemical and clay-mineral interactions, acid-mine drainage and clay interactions, trench-cover settlement, and erosion.
In this investigation, the Illinois State Geological Survey found the primary reason for the rapid migration: the presence of previously undetermined fractures and joints in glacial till. The inaccurate predictions of hydraulic conductivity were based on laboratory-determined values that did not adequately measure the effects of fractures and joints on the transit time calculations. Field-measured hydraulic conductivity values were generally 10 to 1000 times greater than their laboratory-measured counterparts, thus largely accounting for the discrepancy between predicted and actual migration rates in the transit time calculations. The problem was compounded, however, by the burial of liquid wastes and by trench covers that allowed excess surface runoff to enter the trenches. Organic-chemical and clay-mineral interactions may also have exacerbated the problem in areas where liquid organic wastes were buried.     

An Analysis of Nitrate-Nitrogen in Ground Water Beneath Unsewered Subdivisions

Water samples from private water supply wells in five unsewered subdivisions were tested for nitrate-nitrogen to determine the possible impact of septic systems on ground water quality. Three subdivisions are located in Eau Claire County and two in LaCrosse County, Wisconsin.
The nitrate-nitrogen concentrations in the wells were analyzed in relation to ground water flow direction, the location of septic systems within the subdivision, and the hydrogeologic and physical characteristics of the subdivisions. A comparison of three nitrogen mass balance models helped to identify the possible sources of nitrate-nitrogen in the wells.
The results indicate that nitrogen from septic systems and lawn fertilizer cause nitrate-nitrogen to increase in the ground water beneath the downgradient side of the subdivisions. In three of the five subdivisions the highest nitrate-nitrogen value exceeds the drinking water standard of 10 mg/L.     

Identifying Potential Pollutant Point Sources in an Area of High Ground Water Consumption

The Commonwealth of Pennsylvania relies heavily upon its ground water resources for drinking water. The U.S. Environmental Protection Agency, Region III, is responsible for regulating the discharge of waste to the subsurface through injection wells within Pennsylvania. To facilitate identification of industrial facilities unregulated by EPA that may be contaminating ground water through industrial water and waste water discharge wells, a screening procedure was devised utilizing a Geographic Information System (GIS). This procedure involved cross-referencing locations of industrial sites to maps of municipal sewer systems. The effectiveness of this GIS screening procedure was investigated in seven counties in southeastern Pennsylvania. Facilities identified by the procedure were inspected for possible violations of Underground Injection Control (UIC) program regulations. As a result of these inspections, many facilities were found to be illegally discharging waste into ground water. In addition, other EPA program violations were identified. The project demonstrated that the GIS screening procedure can be an effective tool to locate sources of pollution of ground water.     

Deep Injection of Waste Water in the Western Canada Sedimentary Basin

Injection of wastes into the deep subsurface has become a contentious issue, particularly in emerging regions of oil and gas production. Experience in other regions suggests that injection is an effective waste management practice and that widespread environmental damage is unlikely. Over the past several decades, 23 km³ of water has been injected into the Western Canada Sedimentary Basin (WCSB). The oil and gas industry has injected most of this water but large amounts of injection are associated with mining activities. The amount of water injected into this basin during the past century is 2 to 3 orders magnitude greater than natural recharge to deep formations in the WCSB. Despite this large‐scale disturbance to the hydrogeological system, there have been few documented cases of environmental problems related to injection wells. Deep injection of waste appears to be a low risk activity based on this experience but monitoring efforts are insufficient to make definitive statements. Serious uncharacterized legacy issues could be present. Initiating more comprehensive monitoring and research programs on the effects of injection in the WCSB could provide insight into the risks associated with injection in less developed sedimentary basins.     

Frequency Domain Electromagnetic Induction Sounding Surveys for Landfill Site Characterization Studies

A frequency domain electromagnetic induction sounding survey (FDEM) was conducted on a landfill in northern Illinois to determine the depth of fill, locate areas of drum disposal, and locate areas of heavy metal sludge disposal. Sketchy information obtained from interviews of the site personnel identified specific exploration targets and areas of concern. The results of the geophysical survey verified much of the reported disposal history and identified areas suspected to contain hazardous waste.
Based on the results of the survey, the thickness of fill was estimated and two areas with highly conductive fill were located. These areas could represent leachate pockets or sludge disposal areas. An area in which the fill appears to be thicker than expected was identified. This area is thought to represent industrial sludge disposal in trenches excavated into the existing fill and underlying soils. An area with several linear in-phase, quadrature, and conductivity highs was detected. A subsequent magnetometer survey detected linear magnetic anomalies that are believed to be caused by parallel trenches filled with steel drums. This area is believed to be a previously unreported hazardous waste drum disposal cell excavated into the native soil.
As of this writing, the results of this survey have not been verified by traditional intrusive methods. When these investigations begin, we expect that information provided by the FDEM survey will reduce project costs by directing subsequent investigations, thereby reducing the number of borings and test pits required to characterize the site. While there is an unavoidable margin of error and uncertainty in remote sensing methods, the subsurface coverage provided by this geophysical survey could not have been reproduced by traditional methods without substantial expense. This paper presents the results of the survey and discusses application of the FDEM method on landfills.     

Design of Lysimeter Leak Detector Networks for Surface Impoundments and Landfills

Sampling of soil pore moisture in the vadose zone underneath land disposal facilities (landfills and surface impoundments) for hazardous waste has been suggested as an "early warning system" to detect leakage from these facilities. Some states require vadose zone moisture sampling at such sites. Given a leak of a particular size, mathematical models can estimate the necessary moisture sample volume collection times and lysimeter spacings to guarantee detection of the leak in a homogeneous medium. Examination of 47 hazardous waste sites existing in 1984 indicated the most were located in areas with water tables too shallow to permit vadose zone detection monitoring. Several of the 47 sites had soils that could be described as loamy sand, silt loam or silty clay. Using these three soils as examples, the process of lysimeter leak-detector network design has been illustrated. For a particular loamy sand with a saturates hydraulic conductivity of 10^-6 cm/ sec, the maximum ceramic lysimeter spacing is 15.5 feet at a depth of 30 feet to collec a moisture sample of 10 mL in one week from a 1 ft2 leak. For a silt loam, maximum lysimeter spacing would be 17 feet at depth of 15 feet. For silty clays, the maximum lysimeter spacing is 7 feet at a depth of 2 feet; maximum emplacement depth is about 9 feet. Calculations show that in some soils, suction lysimeters will not be able to collect usable moisture samples. Since soil properties vary widely and lysimeter spacing is strongly dependent on soil-moisture characteristics appropriate soil measurements and modeling must be performed at each disposal facility to estimate lysimete performance and to select locations for emplacement.     

Long-Term Confidence in Ground Water Monitoring Systems

State-of-the-art analytical techniques are capable of detecting contamination In the part per billion (ppb) range or lower. At these levels, a truly representative ground water sample Is essential to precisely evaluate ground water quality. The design specifications of a ground water monitoring system are critical in ensuring the collection of representative samples, particularly throughout the long-term monitoring period.
The potential interfaces from commonly used synthetic well casings require a thorough assessment of site, hydrogeology and the geochemical properties of ground water. Once designed, the monitoring system must be installed following guidelines that ensure adequate seals to prevent contaminant migration during the installation process or at some time in the future. Additionally, maintaining the system so the wells are in hydraulic connection with the monitored zone as well as periodically Inspecting the physical integrity of the system can prolong the usefulness of the wells for ground water quality. When ground water quality data become suspect due to potential interferences from existing monitoring wells, an appropriate abandonment technique must be employed to adequately remove or destroy the well while completely sealing the borehole.
The results of an inspection of a monitoring system comprised of six 4-inch diameter PVC monitoring wells at a hazardous well facility Indicated that the wells were improperly installed and in some cases provided a pathway for contamination. Subsequent down hole television inspections confirmed inaccuracies between construction logs and the existing system as well as identified defects in casing materials. An abandonment program was designed which destroyed the well casings in place while simultaneously providing a competent seal of the re-drilled borehole.     

Assessment of Water Quality After 10 Years of Reclaimed Water Injection: The Nardò Fractured Aquifer (Southern Italy)

Experimental studies have been carried out in a fractured coastal aquifer of the Salento region (Nardò, Italy), which has been subjected to 12,000 m³/day of treated municipal waste water injected into a natural sinkhole since 1991. The analytical parameters of ground water sampled in 30 monitoring wells in the area down gradient from the sinkhole, taking into account the direction of ground water flow, have been compared before and after injection. The water table mound (1.5 m), the reduction of sea water extent (2 km), and the spreading of injected pollutants were evaluated by means of a mathematical model. The predicted values in the monitoring wells were adjusted to inorganic nitrogen biodegradation using transformation rates developed in laboratory tests. After 10 years, the injection has increased the volume of the available resource for agricultural and drinking water use, without any notable decrease in the preexisting ground water quality. Moreover, to preserve water resources from pollution, the mathematical model allowed the maximum constituent concentrations (standards) in waste water reclamation for recharge to be identified. A precautionary area around the sinkhole was also defined so that withdrawal prohibition could be implemented to avoid risks to human health.     

The Application of Television Borehole Logging to Ground Water Monitoring Programs

Borehole television has been successfully utilized to gather in situ information on boreholes and wells in several ground water monitoring programs. Borehole television surveys are proposed as a viable alternative to other downhole instruments in the subsurface investigation stages of a ground water monitoring program.
The borehole television camera used by the authors was originally developed for use in the examination of nuclear reactor cores; the camera has since been modified for use in borehole investigations. The lens attachments are capable of looking sideward or downward and include built-in lighting assemblies. Use of the camera, lenses and various support equipment are discussed.
The in situ characterization of fractures that can provide pathways for contaminant migration poses a significant challenge. Borehole television inspection can provide information on the frequency, size and orientation of these fractures. Vertical correlations of rock cores in areas where voids are present (i.e. deep mining or karst topography) can also be simplified by this technique. In addition, borehole television can also be used to check monitoring well integrity. Casing inspections are especially useful where construction details are not known. Well screens may be inspected in place to determine if rusting has enlarged the screen openings or if screens have been damaged during emplacement or well development operations (i.e. surge block, air jetting, etc.). This information may prove to be very valuable in the decision to decommission a well. Examples of these successful applications in ground water monitoring programs at several Superfund hazardous waste sites are presented.     

Investigation of Possible Contamination of Shallow Ground Water by Deeply Injected Liquid Industrial Wastes

The objective of this study was to assess the possible impact of deep well disposal operations, conducted between 1958 and 1974, on the ground water quality in a shallow fresh water aquifer beneath Sarnia, Ontario, Canada. Because of the breakout of formation fluids in Sarnia and Port Huron, Michigan, in the early 1970s, it had been hypothesized that liquid waste from the disposal zone in bedrock had leaked through numerous abandoned oil, gas, and salt wells in the area up to the shallow fresh water aquifer and from there to the surface.
A monitoring well network of 29 5cm (2 inch) diameter piezometers was established in the thin sand and shale aquifer system, which exists between 30 and 70m (100 and 230 feet) below ground surface. In addition, a 300m (1000 foot) deep borehole was drilled and instrumented with a Westbay multilevel casing, which permitted sampling of the disposal zone.
Ground water samples from the shallow monitoring wells and the Westbay multilevel casing were analyzed for volatiles by GC/MS. Those volatile aromatics that were conspicuously present in the deep disposal zone, e.g., ethyl toluenes and trimethyl benzene, were not detected in the shallow monitoring wells. Thus, if contaminants from the disposal zone did indeed migrate to the shallow aquifer, contamination was not widespread and probably consisted mostly of displaced chloride-rich formation waters.     

Effect of natural advection on stabilization of contaminant plume in natural traps at underground disposal of liquid wastes

The migration of a contaminant from a zone of injection disposal of hazardous liquid waste in a deep-seated aquifer is considered. Because of its higher density, the polluted groundwater will accumulate under the effect of gravity in aquifer dips (depressions). A 2D-model of variable-density groundwater flow is used to determine the conditions under which the gravity force will prevent polluted groundwater from leaving depressions driven by regional current. As the result, such depressions can serve as natural traps for polluted waters. The required conditions are based on simple analytical relationships, derived from the analysis of a theoretical model of variable-density groundwater flow in an inclined confined aquifer. The obtained technique is used to estimate the efficiency of such a trap at the site of injection disposal of liquid radioactive waste from Mining and Chemical Combine in Krasnoyarsk region. The analytical estimates of the trap with the use of the proposed technique are shown to be in good agreement with the results of numerical simulation of contaminant migration.     

Statistical Comparison of Leachate from Hazardous, Codisposal, and Municipal Solid Waste Landfills

There has been considerable debate regarding the chemical characterization of landfill leachate in general and the comparison of various types of landfill leachate (e.g., hazardous, codisposal, and municipal) in particular. For example, the preamble to the U.S. EPA Subtitle D regulation (40 CFR Parts 257 and 258) suggests that there are no significant differences between the number and concentration of toxic constituents in hazardous versus municipal solid waste landfill leachate. The purpose of this paper is to statistically test this hypothesis in a large leachate database comprising 1490 leachate samples from 283 sample points (i.e., monitoring location such as a leachate sump) in 93 landfill waste cells (i.e., a section of a facility that took a specific waste slream or collection of similar waste streams) from 48 sites with municipal, codisposal, or hazardous waste site histories. Results of the analysis reveal clear differention between landfill leachate types, both in terms of constituents detected and their concentrations. The result of the analysis is a classification function that can estimate the probability that new leachate or ground water sample was produced by the disposal of municipal, codisposal, or hazardous waste. This type of computation is illustrated, and applications of the model to Superfund cost-allocation problems are discussed.     

Nitrate Source Identification Using δ15N in a Ground Water Plume Near an Intensive Swine Operation

Nitrate-contaminated ground water beneath and adjacent to an intensive swine ( Sus scrofa domesticus ) production facility in the Middle Coastal Plain of North Carolina was analyzed for δ¹⁵N of nitrate (δ¹⁵N-NO₃). Results show that the isotopic signal of animal waste nitrogen is readily identifiable and traceable in nitrate in this ground water. The widespread land application of animal wastes from intensive livestock operations constitutes a potential source of nitrogen contamination to natural water throughout large regions of the United States and other countries. The site of the present study has been suspected as a nitrate contamination source to nearby domestic supply wells and has been monitored for several years by government and private water quality investigators through sampling of observation wells, ditches, and streams. δ¹⁵N of nitrate allowed direct identification of animal waste-produced nitrate in 11 of 14 wells sampled in this study, as well as recognition of nitrate contributions from non-animal waste agricultural sources in remaining wells.