Treatment of polluted soil(As)②

Successful on-site processing without spoiling the scenery of beautiful rice fields

Emergence of a problem

We received an inquiry after a local newspaper wrote an article about AMRON’s technology for dealing with heavy metal pollution.
We were told that arsenic level exceeding the standard level was detected from the discharged soil from a construction site during the repair work of an irrigation canal near the rice fields.
As there were nearby rice fields where crops were grown, effects on the rice fields were unacceptable, not to mention the nonproliferation of pollutants.

Diagnosis

First, we went to the field to see the on-site situation. Rice fields surrounded the site, while minimum space and equipment were used to suppress the influence on the rice fields. The repair work had already been started, and the deadline for completing the project could not be extended. It was necessary to take quick action for processing the contaminated soil.

After asking more about the specifics of the case, it became clear that the customer needed to avoid the delay in construction and spend as little money as possible.

Validation

We had been assuming that the contaminated soil was piled up in one place until we went to see the site; however, the soil at the bottom of the irrigation canal was actually the object to be processed.

After selecting the materials and validating the amount to be used on soil samples from the field, we started to devise a technical countermeasure method.

The initial idea of the customer was to remove the contaminated soil by scraping and bring it to a disposal site, and so, at first, we hesitated to propose on-site insolubilization. After considering the situations on the ground and of the target object, and the risk occurring as a result of the processing, we proposed a plan that had considerably higher merit compared with the method of taking it out.

Planning

In certain situations, such as the one mentioned above, the method of removing the contaminated soil off site has a drawback in that it is difficult to both scrape the contaminated soil from the bottom of the canal and transport the material containing a large amount of water. A further complication is that a dehydration process would be required. There would not only be the expense of taking over the disposal site but also a preprocessing expense that would be incurred. Furthermore, it is necessary to safely perform the processing and disposal of the water generated by dehydration.

The water squeezed out from the soil containing arsenic would be fluid and would, present a high risk.

To avoid this, AMEC proposed a construction method where the contaminated soil at the bottom is left as it is and an insolubilization material is sprayed on it.

In this method, it is possible to minimize the time and expense incurred because the process consists only of spraying and mixing the soil and insolubilization material. A small amount of additive water and the water contained in the target material act together as a dispersant to achieve a homogeneous mixture, thus allowing us to incur the minimum necessary expense.

More importantly, the process is completed by using neutral insolubilization materials that do not affect rice fields; this minimizes proliferation risks without transferring contaminated soil and without increasing environmental load.

Solution to the problem

After our proposal, these on-site measures were adopted safely. The construction measures were completed safely without trouble during the construction or after completion of the project, and without spoiling the scenery of the beautiful rice fields.

Comments from the person in charge

We proposed a method different from what the customer had envisioned. The key reasons that the customer agreed to adopt AMEC’s proposal were not only the construction schedule and expense but also the consideration for environmental load and risk of diffusion to the surrounding environment.

AMEC proposes the best measures for both people and environment by considering the on-site situation, the state of the processing target, and the surrounding environmental situation.