Monitored Natural Attenuation (MNA) is a remediation method that relies on natural processes to decrease contamination in the soil or groundwater. It is a popular method of remediation since it tends to involve less equipment and labor and therefore, less cleanup costs.
Scientists typically monitor the contamination at a site to ensure that it is attenuating properly and within a reasonable time period. According to New Jersey’s MNA guidance, the applicability of MNA must be demonstrated by lines of evidence directly or indirectly indicate that natural attenuation processes are occurring. With TS-CHEM, it is simple to establish a clear line of evidence that demonstrates natural attenuation is occurring at your site.
This blog post will cover the second Example Application in the TS-CHEM Example Application series: Natural Source Flushing with MNA. To follow along and review the model files, you can download this example application HERE.
In this scenario, there has been a gasoline release from the dispenser island at a service station. While the leak is repaired shortly after the release, regulators and residents are worried about the release of benzene to the ground considering a residential development is located 1,200 feet to the east where shallow domestic wells are located. An initial on-site investigation reveals the following information:
|Figure 1. Site map showing the distance from the benzene source at the dispenser island to the residential area.|
|Figure 2. Site map showing model observation points located in between the dispenser island and the residential area.|
|Figure 3. The C v t chart in TS-CHEM displaying benzene concentrations near the source at MW-1 (dark blue), 600 ft from the source (aqua), and 1000 ft from the source (red).|
The contour plot shows that the plume reaches its maximum extent of about 875 feet after 7 years and does not extend into the residential development. The calculated plume at the 7-year time point encompasses an area of 88,350 ft2.
|Figure 6. The C v t chart in TS-CHEM displaying benzene concentrations at the three set observation points.|
|Figure 7. The contour chart in TS-CHEM set to year 6 highlighting its shorter plume extent compared to the previous analysis.|
|Figure 8. The TS-CHEM C v t chart showing benzene concentrations in the three set observation points. In this analysis, benzene isn't detected at the latter two observation points.|
|Figure 9. A greatly reduced benzene plume seen in TS-CHEM's contour chart following the increase of plume and source degradation rates.|