Pollution

Long-term Durability Verification of Permeable Groundwater Purification Wall Construction Method “Multi Barrier ®” | 2021 | Taisei Corporation

Confirmation to maintain the purification function of contaminated groundwater and improve durability prediction accuracy

March 23, 2022
Dacheng Corporation

Taisei Corporation (President: Yoshiro Aikawa) is a type of volatile organic chlorine compounds (CVOCs).※1), a technology that prevents the spread of polluted groundwater, has proven the long-term durability of the permeable groundwater purification wall construction method “Multi Barrier” at application sites that have been installed for more than 15 years. The results confirmed that the purification effect is still continuing, and the purification function can be maintained for more than 10 years. In the future, we will increase the measured data of installing multiple barriers to improve the durability prediction accuracy.

To prevent the spread of CVOC-contaminated groundwater that is used to clean electronic parts and metal parts, groundwater is pumped underground, and clean, treated water that removes contaminants is discharged to the sewer. The “pumping barrier” technique has been widely used in the past. However, this technology suffers from huge operational and maintenance costs, as the pumped contaminated groundwater must be continuously purified and must be maintained on a daily basis.
Therefore, we developed “Multi Barrier” (see Figure 1 and Table 1) as a technology to purify contaminated groundwater by forming permeable walls underground using purification materials that adsorb and decompose pollutants.※2In 1997, prior to the above implementation, measures to prevent the spread of contaminated groundwater in electronic parts factories were applied for the first time in Japan. Since then, we have been implementing purification measures for groundwater contaminated with various substances, and have accumulated about 70 results so far.
By collecting and evaluating the special iron powder used in the multi-fence purification material of the above-mentioned structure that has been built for more than 15 years, a new understanding of the long-term durability of the multi-fence has been obtained. as follows. finished.

  1. 1

    Verify long-term durability and confirm further maintenance of decontamination (see Figure 1)
    The durability of the originally designed multi-channel barrier, according to long-term laboratory testing, is expected to maintain the purification function for about 20 years, but through this verification, even on the purification wall that has been completed for a longer time, pollutants will be adsorbed . For more than 15 years, it is confirmed that the decomposition performance is still sufficient, and the function of reducing the concentration of CVOCs to below the groundwater environmental standard is maintained. From this result, we can expect the purification function to be maintained for another 10 years or more.

  2. 2

    Improve durability prediction accuracy using application results
    So far, there is almost no measured data on the durability of the purification wall at home and abroad. In the previous multi-barrier design, the durability prediction results based on the compatibility test and long-term laboratory test of each target site have been used. From the long-term durability evaluation conducted this time, it is possible to grasp the functional maintenance status of the on-site purification wall after construction, and improve the durability prediction accuracy.

In the future, based on the data obtained from this follow-up survey, we will improve the prediction accuracy of long-term durability, and we will use many barrier technologies to prevent the spread of contaminated groundwater in addition to the maintenance technology that restores the purification function that has been developed. We will strive to further improve reliability.

Table 1 Comparison of treatment methods between multi-barrier and pumped-storage barriers

multiple barriers

pumping barrier

construction method

Build a permeable purification wall containing purification materials underground

Continuous Sewage Pumping Well Construction

purification method

Contaminated groundwater comes into contact with purification materials, adsorbing and decomposing pollutants

Removal of pumped contaminated water in water treatment facilities

maintenance management

Not required until the purification effect wears off

Requires continuous purification

Maintenance frequency Updated every 15 to 20 years every day

Countermeasure cost
(See Figure 2)

Since it is maintenance-free, operating costs are low and life cycle costs reverse in about 5 to 6 years. Since maintenance costs are accrued in perpetuity, operating costs increase and life cycle costs increase.
Fig. 1 Outline of construction method of permeable groundwater purification wall (multi-barrier)
Fig. 1 Outline of construction method of permeable groundwater purification wall (multi-barrier)
Figure 2 Life cycle cost comparison
Figure 2 Life cycle cost comparison
Figure 1. Sectional view of the reactant (special iron powder) recovered on site
Figure 1. Sectional view of the reactant (special iron powder) recovered on site
(Special iron powder recovered from the interior of the multi-layer barrier that has been in service for more than 15 years. In the cross-sectional image observed with an electron microscope, the white part is the unreacted area of ​​the special iron powder, and the surrounding area is the product of the decomposition reaction on the film. In this state, confirm that the desired reactivity is maintained.)
  1. ※1

    Volatile Organic Compounds:
    Abbreviation for chlorinated volatile organic compounds. It is a group of compounds represented by trichloroethylene and has a history of being industrially used as various solvents and cleaning agents, but has been designated as an environmentally controlled substance because its harmfulness has been confirmed.

  2. ※2

    Soil Pollution Countermeasures Act:
    The law, promulgated in February 2003, aims to protect people’s health by grasping the status of soil pollution and taking measures to prevent soil pollution from causing damage to human health.

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