Formatted Title
ERH Remediation of a High Mass Site in a Residential Area
Background/Objectives
A decommissioned industrial site that is now in the middle of a residential neighborhood in Sao Paulo, Brazil had a significant amount of CVOC contamination. Residential houses have been built directly next to the contaminated source area. A MIP investigation was conducted to map the source areas and subslab vapor monitoring points were installed to assess possible risks to the neighboring community. High CVOC source zones were identified and concentrations in subslab vapor were above the permissible risk assessed residential value. A fast action solution was required to be implemented to mitigate this risk.
Approach/Activities
A communication plan to talk to the neighbors was defined and an emergency SVE barrier was installed while the source area remedy was being designed. Due to the high mass source zones and proximity to the neighbors, electrical resistance heating (ERH) was implemented to remove the maximum amount of mass as quickly as possible. Ninety-eight electrodes were installed to treat five different source zones, the remediation was split in two phases due to electrical power restrictions in the area. An average of 900 kW was applied to the ground during operations. During the remediation, many safety actions needed to be taken to guarantee safety to the residents which include: daily ambient air monitoring and monthly suma cannister samples sent to the lab for analysis, subslab monitoring and sampling, daily voltage surveys, and periodic structural surveys at the walls and inside one of the houses.
Results/Lessons Learned
The thermal remediation system removed 4,536 kg of CVOCs over a period of 267 days (~ 133 days per phase), this total was 137% of the total estimated in the project design. All site-specific target levels (SSTLs) for indoor inhalation were reached faster than initially predicted. Additionally, in some areas, final concentrations were very close to minimum concentration levels (MCLs) of CETESB (São Paulo State Environmental Agency).