Underground Gasoline Storage Tanks Research Articles

Divergent dual C-H isotopic fractionation pattern during anaerobic biodegradation of toluene within Aromatoleum species under nitrate-reducing conditions

Toluene is a pollutant frequently detected in contaminated groundwater, mostly due to leakage from underground gasoline storage tanks and pipeline ruptures. Multi-element compound-specific isotope analysis provides a framework to understand transformation processes and design efficient remediation strategies. In this study, we enriched an anaerobic bacterial culture derived from a BTEX-contaminated aquifer that couples toluene and phenol oxidation with nitrate reduction and the concomitant production of carbon dioxide and biomass. The 16S rRNA gene amplicon data indicated that the toluene-degrading consortium was dominated by an Aromatoleum population (87 ± 2 % relative abundance), and metagenome sequencing confirmed that the genome of this Aromatoleum sp. encoded glycyl-radical enzyme benzylsuccinate synthase (BssABC) and phenylphospate synthase (PpsA1BC) homologous genes involved in the first step of toluene and phenol transformation, respectively. Carbon and hydrogen isotopic fractionation were εbulk, C = - 3.5 ± 0.6 ‰ and εrp, H = - 85 ± 11 ‰, respectively, leading to a dual C-H isotope slope of ΛH/C = 26 ± 2. This value fits with a previously reported value for a consortium dominated by an Azoarcus species (ΛH/C = 19 ± 5) but differs from that reported for Aromatoleum aromaticum (ΛH/C = 14 ± 1), both of which grow with toluene under nitrate-reducing conditions. Overall, this suggests the existence of different BssABC enzymes with different mechanistic motifs even within the same Aromatoleum genus.

Determining a Bioventing Scale-Up Factor

Bioventing is an increasingly popular means of removing hazardous petroleum products from sites contaminated by industry and underground gasoline storage tanks. A mesoscale bioventing reactor system was used to determine the rate of bioremediation and compared to previous work completed on smaller scale reactors. Ten 4kg reactors with two different soil types were spiked with synthetic gasoline to an initial concentration of 4000mg/kg soil. Vacuum was then applied at a rate of 1mL/min, with sufficient water levels monitored and maintained to induce bioventing conditions. Gas chromatography was used to determine concentrations of synthetic gasoline in soil every two days for each soil type. Results indicate a smaller scale up factor for sandy soils (Delhi), than for clayey soils (Elora). Furthermore it was observed that slower decay rates exist as reactor size increases, suggesting that conservative estimates are needed when transferring lab results to the field.

A re-evaluation of the taste and odour of methyl tertiary butyl ether (MTBE) in drinking water

Methyl tertiary butyl ether (MTBE) is a gasoline additive that has been found in groundwater when an underground gasoline storage tank leaks. Although dependent on the clean-up standards that are applied, clean-up costs have been estimated in the US alone to be in the billions of dollars. MTBE is considered primarily a taste and odour concern and not a toxicity issue at concentrations found in drinking water. Thus, the clean-up of MTBE problems is controlled by the MTBE odour threshold concentration (OTC). The level of clean-up and associated differential of millions of dollars is a matter of concern for water purveyors and well owners. A 1993 study of nine OTC studies showed the OTC of MTBE in water to be between 0.04 and 0.06 microg/L, a level over two orders of magnitude less than eight other studies. This 1993 study was repeated at the original laboratory in 2004 and is reported in this paper. The laboratory's quality control programme and ability to repeat one of the eight other studies indicated the laboratory was qualified to repeat its original OTC study. The flavour and odour detection threshold range in the 1993 study, however, could not be confirmed by trained assessors repeating the original study in 2004. The inconsistencies in the data and the high detection on water blanks indicate that the dilution series of the test solutions for the 1993 study were mainly at subthreshold levels. Therefore, the original study of 1993 is not a valid OTC study for MTBE and should not be used to develop drinking water and clean-up standards. The OTC of MTBE is over 15 microg/L for the eight valid studies.

Vapor Intrusion in Homes over Gasoline‐Contaminated Ground Water in Stafford, New Jersey

AbstractThe potential for chemical vapor intrusion from contaminated ground water to the interior of homes was investigated at a site with a leaking underground gasoline storage tank in Stafford Township, New Jersey. This location exhibited conditions favorable to vapor intrusion, with sand soil and a water table depth of 3.3 m. Concentrations of volatile organic chemicals in the ground water were as high as 82 mg/L for total benzene, toluene, ethylbenzene, and xylene (BTEX) and up to 590 mg/L for methyl‐t‐butyl ether (MTBE). Soil vapor samples at multiple depths were taken adjacent to several homes. Inside the homes, air samples were taken on the main floor, in the basement, and under the foundation slab. Despite high ground water concentrations, only one home had measurable impacts to indoor air quality attributable to some of the ground water contaminants. In this house, the BTEX chemicals were not detected in the basement, indicating a lack of indoor air impacts from the ground water for these chemicals. Oxygen measurements suggested that degradation attenuated these chemicals as they diffused through the vadose zone. However, MTBE, 2,2,4‐trimethylpentane (isooctane), and cyclohexane were found in the indoor air. The first two of these chemicals served as gasoline‐specific tracers and indicated that vapor intrusion was occurring. Attenuation factors (the ratio of the indoor air concentration to a source soil vapor concentration) for the BTEX chemicals between the ground water and the indoor air were <1 × 10−5, and for MTBE was 1.2 × 10−5. Attenuation factors between the deep‐soil vapor and the basement air were as follows: BTEX compounds, <1 × 10−5; MTBE, 2.2 × 10−5; 2,2,4‐trimethylpentane, 3.6 × 10−4; and cyclohexane, 1.2 × 10−4. Attenuation factors between the subslab vapor and the basement air were 7 to 8 × 10−3.

English

More than two hundred homes in Hazleton, Pa. were found to have benzene vapors (a known carcinogen) from one of the largest underground gasoline storage tank spills in PA history. Remediating this site became the number one priority of USEPA Region III (EPA). A relic underground coal mine situated along a 3000 ft long plunging syncline beneath the Laurel Gardens neighborhood complicated site geology. The U.S. Army Corps of Engineers (USACE) determined if air filled mine voids existed and contained gasoline and gasoline vapors. The plan called for four study phases: Determining the mine location, Visualizing the geology and water table, Modeling mine pool effects on plume behaviors, and Field sampling to verify study results. Mine Location: GIS was used to georeference and compare a 19 th century mine map of unknown datum and coordinate system with old aerial photos, boreholes data and microgravity survey results. Extremely accurate location of the mine was critical for locating potential gas filled voids. Visualization: A three dimensional geologic model was constructed from the GIS data and available site data depicting the relationship between site geology, the mine void, the mine pool elevation and the surrounding groundwater table. This predicted air filled mine voids in the upper areas of the syncline. Modeling: A finite element groundwater model (FEMWATER) was developed to study mine pool effects on gasoline plume movements. Two different approaches were compared for modeling the mine pool. In one approach the mine void was modeled as high conductivity aquifer. In the adopted approach, it was modeled as an interior boundary with assigned heads. The model showed dissolved gasoline contaminants migrating to the mine. Field Sampling: Using the gravity data and 3 dimensional mine model, several target areas for drilling were identified. Gas vapor explosion was a concern during drilling. The drilling plan incorporating the use of on-demand nitrogen gas connected to a drill rig. A gas filled mine void was encountered and an aqueous sample confirmed gasoline contamination in the mine.

REMOTE SENSING, VISUALIZATION AND MODELING OF THE DIAMOND COAL MINE IN HAZLETON, PA

Abstract: More than two hundred homes in Hazleton, Pa. were found to have benzene vapors (a known carcinogen) from one of the largest underground gasoline storage tank spills in PA history. Remediating this site became the number one priority of USEPA Region III (EPA). A relic underground coal mine situated along a 3000 ft long plunging syncline beneath the Laurel Gardens neighborhood complicated site geology. The U.S. Army Corps of Engineers (USACE) determined if air filled mine voids existed and contained gasoline and gasoline vapors. The plan called for four study phases: Determining the mine location, Visualizing the geology and water table, Modeling mine pool effects on plume behaviors, and Field sampling to verify study results. Mine Location: GIS was used to georeference and compare a 19th century mine map of unknown datum and coordinate system with old aerial photos, boreholes data and microgravity survey results. Extremely accurate location of the mine was critical for locating potential gas filled voids. Visualization: A three dimensional geologic model was constructed from the GIS data and available site data depicting the relationship between site geology, the mine void, the mine pool elevation and the surrounding groundwater table. This predicted air filled mine voids in the upper areas of the syncline. Modeling: A finite element groundwater model (FEMWATER) was developed to study mine pool effects on gasoline plume movements. Two different approaches were compared for modeling the mine pool. In one approach the mine void was modeled as high conductivity aquifer. In the adopted approach, it was modeled as an interior boundary with assigned heads. The model showed dissolved gasoline contaminants migrating to the mine. Field Sampling: Using the gravity data and 3 dimensional mine model, several target areas for drilling were identified. Gas vapor explosion was a concern during drilling. The drilling plan incorporating the use of on-demand nitrogen gas connected to a drill rig. A gas filled mine void was encountered and an aqueous sample confirmed gasoline contamination in the mine.

MTBE in California's Drinking Water: A Comparison of Groundwater Versus Surface Water Sources

During the last decade, the fuel oxygenate methyl tertiary butyl ether (MTBE) has received widespread attention as a potential threat to water quality, primarily due to leaking underground gasoline storage tanks and watercraft with two-stroke engines. In this article, we examine the annual detection frequency, number of new source detections, and concentration of MTBE detected in California's public drinking water groundwater and surface water sources from 1995 to 2002. This work builds on our previous evaluations of California's water quality monitoring database. However, it is unique in that it includes separate evaluations for groundwater and surface water sources that are of greatest concern to regulators, and which are likely being used for current public consumption. Our evaluations also include full-year data for 2002 (which have not been published previously) and an analysis of how the sampling and reported detections of MTBE vary by geographic location. We find that MTBE was generally detected (at any level) in approximately 0.5-0.9% and 0.2-0.4% of all groundwater sources assuming a one-detection and two-detection criterion, respectively. The overall detection frequency for MTBE in surface water sources is significantly higher than for groundwater sources, although these surface water detections appear to have substantially declined since 1996 (e.g., 7-9% for all surface water sources during 1996 to 1999 and 4% for all surface water sources during 2000 to 2002, assuming a one-detection criterion). The detection frequency of MTBE concentrations at or above the state drinking water standards in all drinking water sources (both groundwater and surface water sources) and the subset of drinking water sources that are likely to currently be delivered to consumers is markedly lower (and often zero). Despite the significant increase in water sampling over time, the number of new drinking water sources found to contain MTBE in California has not increased at the same rate and appears to have remained relatively stable or to have decreased since 1998. The data also show that nearly all of the 58 counties in California have routinely sampled at least some of their groundwater and surface water sources for MTBE over the last 8 years. Geographical evaluations show that MTBE has been detected (at least once) in groundwater sources in 34 counties and in surface water sources in 18 counties but has only been detected routinely (i.e., for 3 or more years) in 16 and 7 counties, respectively. Detected concentrations of MTBE are also generally below state drinking water standards, particularly for surface water sources. In short: (1) MTBE is rarely found in California groundwater or surface water sources that are of greatest concern to regulators or the public, and (2) drinking water detections of MTBE are expected to decline in the future due to the pending phase-out of MTBE and recent regulatory programs aimed at controlling gasoline releases from underground storage tanks and two-stroke-engine watercraft.

Sorption and permeability of gasoline hydrocarbons in organobentonite porous media

We investigate the use of organobentonites as liners for underground gasoline storage tanks to reduce the risk of subsurface contamination. A series of permeability measurements were conducted on two types of organobentonites: benzyltriethylammonium-bentonite (BTEA-bentonite) and hexadecyltrimethylammonium-bentonite (HDTMA-bentonite). Both water and commercial unleaded gasoline were used as the permeant liquids. Results of these measurements indicate that the intrinsic permeability of the organobentonite decreases by one to two orders of magnitude when the permeant liquid is changed from water to gasoline. Results of batch sorption measurements reveal that benzene sorption to both organobentonites from water is greater than benzene sorption to conventional bentonite. The magnitude of benzene sorption is related to the loading of the organic quaternary ammonium cation on the clay. As the HDTMA cation loading increases from 25% of cation exchange capacity (CEC) to 120% of CEC, benzene sorption increases. However, as the BTEA cation loading increases from 40 to 120% of CEC, benzene sorption decreases. Collectively, these results suggest that organobentonites can be used effectively to reduce hydrocarbon migration rates beneath leaking underground gasoline storage tanks, and that the optimal organic cation loading with respect to pollutant sorption may be less than 50% of cation exchange capacity for some organobentonite–solute combinations.

Development of permeable barriers for groundwater remediation: Air stripping of methyl tertiary‐butyl ether (MTBE)

Physical barriers constructed in a contaminated groundwater system that intercept and degrade or remove soluble pollutants yet allow groundwater to flow through are called permeable barriers. They may be constructed as trenches placed down gradient from a leak or spill, and the trench backfilled with media which intercepts the solutes and removes them from solution. This project investigated the feasibility of using trench based air stripping to remove volatile hydrocarbons from groundwater contaminated with gasoline components, specifically methyl tertiary‐butyl ether (MTBE). Based on theoretical calculations and previous laboratory research a 9 m long trench‐based air stripping/biodegradation barrier was constructed at a site contaminated from a leaking underground gasoline storage tank. Monitoring data show the trench removed approximately 100% of the MTBE reaching it by natural groundwater flow, even at a relatively low air‐to‐liquid flow ratio. The total construction cost of the barrier was less than $5000, including the installation of a monitoring well, and annual operating costs were found to be about $180/year. Guidelines for succesful application of the permeable barrier concept to groundwater remediation are presented based on the experience from this project.

Implications of MTBE for Intrinsic Remediation of Underground Fuel Tank Sites

AbstractMTBE in groundwater has been shown to travel over 1,000 feet downgradient from its source in several comprehensive field studies conducted across North America. The biodegradability of MTBE is examined by summarizing all the significant literature on the subject and by detailing the findings of recent field investigations of MTBE transport. In Orange County, California, the persistence of MTBE is analyzed and statistical representations of source variability are presented. Regional and far field transport of MTBE in groundwater sourced from underground gasoline storage tanks are summarized in comprehensive tables of frequency and plume length. Estimates of source mass and duration allow for comparison of associated plume size. The conclusion reached after reviewing all the available literature on MTBE is that its biodegradability seems slight and the size of the plumes are surprisingly large. Intrinsic or natural attenuation remedies for MTBE merit close scrutiny.

Bioremediation of gasoline‐contaminated soil using poultry litter

Abstract Contaminated soil, excavated from around a leaking underground gasoline storage tank, is commonly subjected to thermal degradation to remove the gasoline. Bioremediation as an alternative treatment technology is now becoming popular. The important hydrocarbon‐degrading bacteria include Pseudomonas, Arthrobacter, and Flavobacterium. Poultry litter contains a large number of microorganisms, including Pseudomonas, as well as many inorganic nutrients and organic biomass that may assist in biodegrading gasoline in contaminated soil. During bioremediation of contaminated soil, microbial densities are known to increase by 2–3 orders of magnitude. However, bioremediation may result in an increase in the toxic characteristics of the soil due to the production of potentially toxic degradation intermediates. The objective of this research was to study the influence of the addition of poultry litter on the bioremediation of gasoline‐contaminated soil by quantifying the changes in the densities of microorgani...

Toxicity of gasoline aqueous‐leachate through sand‐clay columns

Abstract The objective of this study was to understand the effect clay type and clay concentration may exert on the toxicity of the percolating water around a leaking underground gasoline storage tank. This situation in the laboratory was simulated using sand‐clay columns. The experiment was conducted with two types of clays (kaolinite and illite) and three clay concentrations (0, 5 or 10%). The gasoline (0, 0.2, 0.5 or 0.8 mL) was injected through a hole in the middle of the column. After 24 hours of gasoline injection 100 mL of deionized water was added to the column and the leachate was tested for toxicity (E0) using the marine luminescent bacteria (Photobacterium phosphoreum). Leachate from the pure sand column was less toxic than the control but was more toxic than from the columns with clay. The addition of clay significantly reduced both the toxicity and the hydraulic conductivity. The toxicity increased significantly with the increase in gasoline concentration up to 0.5 mL but decreased with 0.8 m...

Sampling of VOCs with the BAT Ground Water Sampling System

AbstractIn the BAT ground water sampling system, a stainless steel probe with a porous filter element is pushed vertically to the desired sampling depth. An evacuated glass sampling tube is then lowered down the penetration rods where it makes contact with the filter via a hypodermic needle and draws a pore fluid sample.An investigation of the system was carried out at a number of sites contaminated by leaking underground gasoline storage tanks. Ground water samples obtained using the BAT system and adjacent monitoring wells were analyzed for volatile organic compounds (VOCs).Because the BAT system is an in situ penetration device with a small filter length, it is possible to determine variations in contaminant concentration with depth. BAT samples in general exhibited higher recovery of VOCs than did bailer samples from adjacent monitoring wells screened over large intervals.Much higher levels of VOCs were recovered when the probe was used with its 316 stainless steel filter than when using the high‐density polyethylene (HDPE) filter. Significant sorption apparently occurred on the latter filter.Because the BAT sample tubes are sealed and remain a closed system, the in situ water pressure is maintained. No significant loss of VOCs was found in sampling tubes containing headspace. Samples from the upper tube in the cascaded setup with headspace recovered levels of VOCs as high, or in a few cases higher, than the lower, no‐headspace tubes.

Gasoline Leak Not Sudden

In 1981, R.W. Harp and Sons Inc. installed underground gasoline storage tanks, pumps, and lines at a newly constructed convenience store in South Carolina. On June 6, 1983, a telephone crew notified the state that a manhole about 30 yards from the store smelled like gasoline. A leak was found in a pipe union connecting the underground pump and tank to the dispensing pump; 4,321 gallons of gasoline had leaked into the ground. The state ordered the store to take cleanup measures and to reimburse the state for its expenses. Total cost to the store was nearly $183,000. The store sought reimbursement from Harp. Harp was insured by Harleysville Mutual Insurance Company under a multiperil insurance policy that excluded pollution damage except for sudden and accidental discharges. The insurer sought a declaration that it was not responsible for the cleanup expenses. The trial court ruled for the insurer.

Evaluation of worker exposure to benzene.

estimated 2-3 million workers are potentially exposed to benzene (ATSDR 1989). It is important to have cancer risk factors available for the evaluation of worker exposures in various settings. The risk factors for benzene published by the EPA are designed to evaluate general population exposure (not worker exposure) and do not include the results of recent studies. In this paper, risk factors are derived for the evaluation of worker cancer risk due to the inhalation and ingestion of benzene. These cancer risk factors are characterized by route, species, strain, sex, dose, dose rate/kg, and fraction of lifetime exposed. Such characterization facilitates the matching of a risk factor to any exposure situation. Example applications of the risk factors are presented. These examples concern OSHA's permissible exposure limit (PEL) for benzene, inhalation exposure at leaking underground gasoline storage tank sites (LUSTs), and ingestion of contaminated soil. MATERIALS AND METHODS Cancer risk factors are usually derived from experimental studies in units of excess risk/(mg/m 3) or excess risk/(mg/kg/day). Experimental studies can be animal or epidemiologic. In order to obtain a risk factor, it is first necessary to compute excess risk and equivalent human dose from an experimental study. Excess risk is the frequency of response in the exposed group corrected for the control group response. The equivalent human dose from an animal or epidemiology study is a function of the following variables: pharmacokinetics; body weight (or surface area); exposure concentration; daily Send reprint requests to W. Hallenbeck at the above address.

Gasoline Hydrocarbons: Groundwater Pollution Potential in Metropolitan São Paulo

The municipality of São Paulo currently faces a potential groundwater threat from thousands of underground gasoline storage tanks. This study presents data to demonstrate the reality and size of this threat and provides technical guidance on how to assess and remediate gasoline releases from underground storage tanks.

Benzene Exposure Assessment of Underground Storage Tank Contractors

Abstract Benzene and total hydrocarbon (as hexane) exposures were measured during removal, cleaning, pumping, and testing of underground gasoline storage tanks at five gasoline retail outlets in New Jersey during 1988. Personal air samples were collected using 3M 3500 Organic Vapor Monitors with sampling times ranging from 15 minutes to 6.5 hours. Benzene exposures to the observer ranged from 0.12 to 0.43 ppm (sampling times ranging from 4.75 to 6.5 hours). Benzene exposures to laborers during tank removal (including cutting and cleaning) ranged from 0.43 to 3.84 ppm (sampling times ranging from 1.5 to 6 hours). The highest short-term benzene exposure was 9.14 ppm (sampling time 15 minutes) for a tank cleaning assistant. Benzene exposures during tank cutting ranged from 2.16 to 4.57 ppm (sampling times ranged from 0.5 to 3 hours). Benzene exposure to a tank tester was 0.23 ppm (sampling time of 4.75 hours). Total hydrocarbons as hexane were also determined. The mean ratio of benezene to total hydrocarbon concentrations was 0.028 (n = 21, S.D. 0.02). Gasoline tanks were not purged of vapors prior to being removed, cut open, and cleaned. This raises a safety issue (flammable/combustible vapor hazard) in addition to changing the time, duration, and magnitude of benzene exposure during the tank removal process. Dermal exposure to gasoline was frequent.

EVALUATION OF THE ACCURACY OF VOLUMETRIC LEAK DETECTION METHODS FOR UNDERGROUND STORAGE TANKS CONTAINING GASOLINE1

ABSTRACT A United States Environmental Protection Agency (EPA) research program evaluated the current performance of commercially available volumetric test methods for the detection of small leaks in underground gasoline storage tanks. The evaluations were performed at the EPA Risk Reduction Engineering Laboratory's Underground Storage Tank Test Apparatus in Edison, New Jersey. The methodology used for evaluation made it possible to determine and resolve most of the technological and engineering issues associated with volumetric leak detection, as well as to define the current practice of commercially available test methods. The approach used (1) experimentally validated models of the important sources of ambient noise that affect volume changes in nonleaking and leaking tanks, (2) a large data base of product-temperature changes that result from the delivery of product to a tank at a different temperature than the product in the tank, and (3) a mathematical model of each test method to estimate the performance of that method. The test-method model includes the instrumentation noise, the configuration of the sensors, the test protocol, the data analysis algorithms, and the detection criterion. Twenty-five commercially available volumetric leak detection systems were evaluated. The leak rate measurable by these systems ranged from 0.26 to 6.78 L/h (0.07 to 1.79 gal/h), with a probability of detection of 0.95 and a probability of false alarm of 0.05. Five methods achieved a performance between 0.19 L/h (0.05 gal/h) and 0.57 L/h (0.15 gal/h). Only one method was able to detect leaks less than 0.57 L/h (0.15 gal/h) if the probability of detection was increased to 0.99 and the probability of false alarm was decreased to 0.01. The measurable leak rates ranged from 0.45 to 12.94 L/h (0.12 to 3.42 gal/h) with these more stringent detection and false alarm parameters. The performance of the methods evaluated was primarily limited by test protocol, operational sensor configuration, data analysis, and calibration, rather than by hardware. The experimental analysis and model calculations suggested that substantial performance improvements can be realized by making procedural changes. With modifications, it is estimated that more than 60 percent of the methods should be able to achieve a probability of detection of 0.99 and a probability of false alarm of 0.01 for leak rates between 0.19 L/h (0.05 gal/h) and 0.56 L/h (0.15 gal/h), and 100 percent should be able to achieve this performance for leak rates of approximately 0.76 L/h (0.20 gal/h).

LIMITATIONS ON UNDERGROUND STORAGE TANK LEAK DETECTION SYSTEMS

ABSTRACT This paper discusses the limitations imposed on internal volumetric leak detection systems for underground gasoline storage tanks by uncertainty in the value of the thermal expansion coefficient for gasoline and uncertainties in measurements of the temperature of the gasoline. For leak detection or level sensing systems that are used to infer or measure volumetric leak rates, correction must be made to account for the expansion or contraction of the gasoline. An analysis is made of experimental determinations, in other work, of the density of samples of gasoline and calculated values of the thermal expansion coefficient. The data are divided according to three categories of gasoline: regular, unleaded, and premium. In each of these categories the estimate of the standard deviation of the thermal expansion coefficient is approximately 3 percent of the mean value. Examples are given of the magnitude of the apparent leak rate or error in leak rate due to uncertainties in the thermal expansion coefficient. In order to correct for expansion or contraction of the gasoline, the mean temperature of the entire quantity of the gasoline must be known. An error in mean temperature will result in an apparent leak rate or an error in leak rate. Examples are given of the magnitude of the apparent leak rate or error in leak rate.

A Graphical Approach to Prediction of Groundwater Pollutant Movement

Important to any analysis of a potential or actual groundwater pollution problem is the ability to predict when and where any pollutant may interface with the biologic realm. It is also necessary to know the amounts that may appear at an outflow boundary over a period of time. Thus a geography-time distribution and a geography-quantity distribution can assist decision-makers in evaluating and comparing different waste disposal schemes. A graphical procedure based upon flow net analysis coupled with vector analysis permits estimation of pollutant arrival times at an outflow boundary. The procedure also aids in determination of variations of pollutant concentrations across the outflow boundary with time and in space. The technique utilizes contour maps and simple graphs. Intraformational (macroscale) and interformational (megascale) aspects of groundwater pollution can be analyzed with the technique. Examples of applications to which the technique can be applied are potential groundwater contamination from a sanitary landfill leachate, the case of a leaky waste-holding pond, and the pattern of contamination from a leaky underground gasoline storage tank. The technique also can be applied in reconnaissance studies for hazardous waste site evaluation using available hydrogeologic data. Detailed site evaluation can be guided through use of the approach. It can be utilized relatively inexpensively to predict longterm, downstream effects of pollutant leakage from a disposal site.