Overview

In 2017, G2 Consulting Group (G2) was selected to complete a Ph I and Ph II ESA followed by a BEA and Due Care Plan for a commercial building in Ypsilanti Township, MI. At the time chlorinated solvent was detected in the ground, but levels were below levels of concern per local regulations.

At the beginning of 2021, G2’s client was interested in buying this same building and asked G2 to provide a PH I ESA and vapor intrusion studies once again. The vapor intrusion studies consisted of installing sub-slab vapor points and collecting air samples. Since the original environmental investigations had taken place, regulations had changed, and the chlorinated solvent detected in the ground was now deemed to exceed the levels permitted.

G2 worked with the client to design a minimally invasive, cost-effective vapor mitigation system to keep vapor levels below the requirement. The first step was to remove concrete in the vapor source areas, exposing the ground where the vapor mitigation system was to be installed.

Next, a four-inch slotted, PVC pipe was placed horizontally in the ground, surrounded by pea stone, and later the concrete was replaced. Vertical pipes that vented to the outside were then connected to each end of the horizonal pipe and fitted with manometers and motorized, electric fans.

The system allows vapors to enter the pipe in the ground through the slots, the fans then pulled the vapors up through the vertical pipes and pushed them out of the building through the vent. The manometers detect the pressure in the pipes allowing the clients to actively verify that the harmful vapors are being removed from the facility and ensure their staff are in a safe working environment.

Challenges/Solutions:

Harmful levels of chlorinated solvent were detected in the ground of a commercial building. A common solution to prevent vapors from coming up through the floor includes removing all the existing flooring, installing a vapor barrier the footprint of the building, and reinstalling the flooring. However, this solution is time consuming, expensive, and it is difficult to determine the effectiveness.

G2’s vapor mitigation design solution provided benefits that are threefold. The mitigation system was installed only at vapor source areas minimizing the amount of floor and concrete that needed to be excavated and reinstalled. This approach saved the client time and money. Additionally, the manometer allows the client to  easily verify that the vapor mitigation system is working at any given time.