Which of the following is an environmental hazard that may be encountered when excavating or laying drains?

Sewer gas is indeed an environmental hazard frequently encountered during excavation or drain laying. This gas is a mix of various gases that can include methane, hydrogen sulfide, and ammonia, all of which can be produced from the decomposition of organic matter in sewage systems. When working in areas where sewage lines are present, there is a risk of these gases being released, particularly when the integrity of the sewer pipes is compromised. Exposure to sewer gas can pose serious health risks, including respiratory issues, dizziness, headaches, or even unconsciousness in high concentrations, making it essential for workers to be aware of this hazard and to use appropriate safety measures, such as ventilated workspaces and personal protective equipment.

In contrast, while abrasive dust, high voltage wires, and radiation exposure are indeed hazards that workers may face in various contexts, they are not directly related to the specific activities involved in excavating and laying drains. Abrasive dust primarily occurs in construction or demolition environments where materials are ground down or cut. High voltage wires are a concern in many construction sites but are not specific to drainage work. Radiation exposure is more relevant in specific industries like construction near nuclear facilities or specific types of waste management, rather than typical drainlaying activities. Thus, sewer gas most