What’s Your Poison?

Effluent sampling

Environmental scientist holding colorimetric filter paper for effluent sampling

It’s poisonous, corrosive, and invisible. Volcanoes spew it. Swamps burp it up.

But you don’t have to be on Gilligan’s Island to encounter hydrogen sulfide. You can find it in right in your neighborhood…in the sewers. Highly toxic and potentially corrosive, this compound has a characteristic rotten egg odor (althought there is no odor at the most dangerous concentrations). It can build up in sewer lines, particularly when the effluent is stagnant in pipelines between sewer pumping cycles. Utility providers need to know when it’s there in order to protect their facilities.

Understandably, testing sewer systems for hydrogen sulfide requires precautions. The sampler wears a Tyvek suit, two pairs of gloves, and eye protection. Special equipment is used to test for explosive and poisonous gases in the atmosphere around the manhole. If that is clear, gas levels can then be measured in the manhole. If gas levels are high, then masks and ventilators may also be required. To prevent a fall into the sewer manhole (never a good time), the sampler uses a fall arrest system with a body harness and a self-arresting retractable lanyard, shown on the environmental scientist in the photo above. If he were to fall wearing this safety gear, he would hang high and dry (whew…) and then climb out by ladder. He also brings shaving equipment along in case he needs to wear a respirator, to ensure a good seal.

The effluent sampling is decidedly unsophisticated and basically involves collecting effluent from the base of the manhole using a plastic cup attached to a rod. The sewage is then placed in a container with colorimetric filter paper and effervescence tablets (aka Alka Seltzer!). The filter paper is then compared to a color chart and hydrogen sulfide concentrations can be determined.

The result? The utility provider now has the data to determine whether there is a problem, how serious the problem is, and what the next step should be.