THE PROBLEM

Confirming odor levels during deep excavation can be challenging. Although significant time and preparation are devoted to designing mitigation systems for anticipated odors, actual conditions may reveal higher concentrations or additional compounds. Understanding the surrounding geology is therefore critical. During deep tunneling for the Westside Subway Extension Project (Westside), construction occurred near the La Brea Tar Pits, where elevated hydrogen sulfide (H₂S) levels were anticipated. Once drilling commenced, additional noxious odors were encountered, requiring enhanced air treatment measures to be taken by the City to maintain safe working conditions.