The subsurface pollution due to hazardous chemicals like organochlorines has been a great environmental issue in Japan as well in Europe and America. Basically hazardous chemicals are long persistent to biodegradation in subsurface environment and tend to stay there for many years. They should be removed or decomposed, otherwise, subsurface environment is faced to lose the natural functions as food production and drinking water. In this context, various sorts of remediation technologies are designed and applied to in-situ environment polluted with hazardous chemicals. The paper describes the present state and future aspect of remediation technology development for subsurface environment. Key Words: subsurface pollution, volatile organochroines, remediation technologies, cost efficiency

View full abstract

The relative fine particles sometimes behave like a semipermeable bed against the volatile organic chlorinated compounds or such that are undiluted solution (DNAPL: Dense Non-Aqueous Phase Liquid) that is intruding into coarse-grained sediments such as sand layers which have a high permeability (Schwille,1998). In our experiment, a highly concentrated contamination zone of DNAPL Pool (apool of volatile organic chlorinated compounds or such that are undiluted solution) was found in a range of saturation zones comprising coarse sands of pebble matter.
In this paper, it is confirmed that the highly concentrated contamination zone exists above places in which many fine particles are closely each other, and it is explained that the pattern and behavior of volatile organic chlorinated compounds in coarse-grained sediments. In addition, a remediation experiment was conducted and established with a new method combining Air-Sparging/Pump-and-Treat systems (patent registration number: 2663235) with a tube for air injection and pumping and the soil gas absorption method, which could keep remediation efficiency higher than the usual method (a combined method of Air-Sparging method and soil gas injection method only).
The granularity analysis (the Hirosaki University method based particle analysis device was used) of The samples collected from drilling from the highly concentrated contamination zone and another six zone above and below it was conducted. In consequence, the sand in the experiment site could be classified into two types: (A) relatively well sorted, few fine grains; and (B) relatively poor sorted, many fine grains. The high concentration contamination zone and another one on this zone belong to the type A, and the low concentration zone which exists under the highly concentrated contamination zone belongs to the type B. In the classification, it was found that the sand layer of the type B acts as a semipermeable bed against volatile organic chlorinated compounds in a state of undiluted solution.
In this remediation experiment, three types of operations were carried out; the operation of Air-Sparging only (type A); the operation of pumping only (type B); and the operation of Air Sparging and pumping (type C). As a result, the amount of withdrawal per unit time became the biggest when type C was operated.

View full abstract

The air sparging coupled with the soil vapor extraction as the physical remediation technologies has been applied to a site contaminated with volatile substances like tetrachloroethylene. The air sparging technology facilitates the contaminant volatilization with air injected into saturated zone and the soil vapor extraction technology extracts the contaminant in soil gas and injected air. Therefore, in order to implement these technologies, it is indispensable to understand the mechanism of air migration injected in groundwater and the change of groundwater concentration. In this paper, we presented the results of full scale field experiment implemented to estimate the recovery of water quality by air injected in groundwater. The summery was follows. It was clarified that injected air spread sufficiently in an experimental site when the pulsed operation for air injection was carried out. The concentration in injected air, which was calculated by the observed data like extracted gas concentration, showed the possibility that there would be the denser-than-water non-aqueous phase liquid in an aquifer. And also, it has been removed with the substances dissolved in groundwater by air injection.

View full abstract

Advective-dispersive analysis is performed to establish an engineering approach that would allow effective in-situ bioremediation of groundwater contaminated with organic matter. The principal consideration involved in the design of in-situ bioremediation is twofold: 1) to understand the biodegradability conditions; 2) to make sure that the contaminated groundwater to be cleaned up should be mixed with the stimulated microbes based on the hydraulic and transport characteristics specific to the site. This study reviews methods of mixing a number of substances to enhance the microbial co-oxidation activity in an in-situ aquifer, which is to be efficient for trichloroethyene contaminanted groundwater. It then proposes a method of evaluating the key elements in dealing with mixture in an aquifer bioremediation, that is characteristics such as degree of dispersion. Advection-dispersion analyses are carried out, assuming various substances injected into the aquifer through a well during the treatment process. In so doing, this study presents the basic design principles of in-situ bioremediation.

View full abstract

We developed a model to simulate the performance of permeable groundwater treatment wall using zero-valent iron for groundwater remediation. In the model, we assumed that the reaction rate of chlorinated organic compounds and powdery iron is initially fast at fresh condition, and later is becoming slow by the generation of oxide film.
Simulation results showed a good agreement with the results of series of laboratory experiments in which an aqueous solution of trichloroethylene (TCE) was passed through columns packed with mixed quartz sand-powdery iron and TCE concentration of the effluent was monitored. With the parameters estimated from laboratory experiments, the model would give useful information on the design of permeable groundwater treatment walls.

View full abstract

Some approaches have been conducted to regenerate and to conserve soil environments contaminated by toxic substances. However, sites requiring remediation are usually inside plants in operation and it is difficult to place remediation equipment, including wells, there. This is one obstacle to soil environment regeneration.
Horizontal wells are installed at the required depth by boring from ground surfaces. Using this method, it is possible to install contaminated soil and groundwater remediation wells right under plants and tanks from the outside into contaminated zones without stopping production lines.
Using a gas-pipeline drilling technique, the horizontal well was installed for remediation volatile organic compounds. The problems of constructing the horizontal well and the effects of remediation were examined.
There was concern that contaminants are included in water used for boring and muddy water when a drilling head passes through a contaminated section during the construction, and these water and muddy water diffuse towards the surroundings.
Influenced areas of soil vapor extraction are more than a radius of 4.9 m horizontally and a radius of 3.9 m vertically. Because a long screen can be placed horizontally in this well, it is expected that the well is effective in the remediation of horizontally spread contaminants.

View full abstract

The contaminated area is located in Yamagata Prefecture, and it has appeared significantly in 1991. Our task is initiated in 1993, and the purpose of this research is to constitute a simulation code available for recovery and improvement of these polluted areas.
The former part in this paper describes the survey on this polluted area. The extent is two km long in east-west direction, one km long in south-north direction, then one hundred meter in depth. The area is deeply contaminated by Trichloroethylene and slightly by Tetrachloroethylene. Not only present wells but also shut-in wells might be influential to propagation of pollution both horizontally and vertically. Sources of pollution might be of surface spill of raw TCE and distilled TCE in re-cycled system.
The latter part describes the constitution and the test-run of the simulation code which is composed of equivalent both particle- and fluids phase (two-phase) from the practical point of view in unsteady-state three-dimensional system. Consequently emission of pollution over impermeable layers carried through shut-in wells is simulated in addition to the infiltration of polluted water to free ground water table.

View full abstract

In general, a natural aquifer has a hydrogeologically non-uniform structure. The movement of pollutant in groundwater is affected by such structural properties while it is transported by local advection and microscopic dispersion. The macroscopic dispersion grows linearly with respect to the travel distance or the travel time at the initial stage after the pollutant is released, and then, asymptotically converges to a constant value through the transient stage. It is important for the practical applications to know how such macroscopic dispersion grows when the prediction of pollutant spread is required in the transient stage.
In the present study, a method for judging the convergency of macroscopic dispersion is discussed for the analytical and observed average concentration by the numerical simulation. The χ²-test for convergency in the macroscopic dispersivity is applied. Besides, an evaluation procedure for the auto-regressive parameters in the generating model of the random field of permeability is proposed, for the case in which the macroscopic dispersion is estimated to be still in the growing stage. The characteristics of the proposed method is examined through the applications to synthetically generated random fields of permeability.

View full abstract

Informations for well and hydrology in Japan are collected and constructed a database by Hydrogeology Section at Geological Survey of Japan. The database have following data;
1) Geographical data (owner, address, longitude, latitude etc. )
2) Groundwater data (water temperature, water quality etc. )
3) Well data (screen depth, diameter, pumping ratio etc. )
4) Geological data (geology and its depth etc. )
This report opened the format of the database, and the two bite code used for Japanese characters will be useful for all languages, so that our database will be able to correspond to the demand of making database from anywhere of the world. Weliking Dictionary which is a original developed handling software for the database, is reported, simultaneously. This software works on PC, and see mapping of wells, detail data of each well, and log data.

View full abstract

Recently, it is noticed that the measurement method of soil water content from the dielectric constant of soil, and TDR (time domain reflectometry) method and FDR (frequency domain reflectometry) method are frequently utilized. However, these methods have some problems of cost and of their complex automatic measuring system. ADR (amplitude domain reflectometry) method which measures the dielectric constant of soil at low cost using a simplified impedance measuring technique has been developed to solve these problems and has a similar performance to TDR method and FDR method. In the measurement by the ADR sensor, the amplitude of the voltage standing wave produced on the transmission line is outputted as direct current voltage from the ADR sensor, and θ is calculated from the voltage. ADR method is very effective for measuring soil water content because of the easiness of automatic or multiplexing monitoring and the possibility of the use in deep underground.
In this study, calibrations with the soil moisture sensor based on ADR method were carried out by laboratory experiments and field measurements, and the applicability of the ADR sensor to the measurement of soil water content was examined.
The calibration curves with the ADR sensor were obtained applying the theory that the relationship between the volumetric water content θ and the square root of dielectric constant √ε can be approximated by a linear equation, and these calibration characteristics can be obtained easily with only two parameters, i. e., the slope and the intercept of the curve. The calibration characteristics between√εand θ obtained in this study are almost matched to that obtained for mineral soil by Miller & Gaskin (1996) and that obtained by White et al. (1994).

View full abstract