If you live east of Twin Peaks, the contents of your toilet have probably passed through the custody of Andrew Clark. He works as a senior stationary engineer at the Southeast Water Pollution Control Plant, the city's largest sewage-treatment facility. It's a job in which he takes pride, toiling amid the fumes of sodium hypochlorite and human waste so that the rest of us — "on the outside," in sewage-plant argot — can enjoy the hygienic living conditions we expect. "Because of what we're doing, our clients — people on the outside — aren't getting sick," the stocky, silver-haired engineer says.

Clark's job isn't easy, but it pays pretty well: about $99,000 a year including overtime. Add to that the retirement and health benefits typical of the public sector, and you're looking at a decent employment package. But there's another source of income into which Clark can tap, which boosts his annual pay into six figures. It's a bonus, albeit one of a sort that might be unfamiliar to workers in the private sector.

Clark receives an additional 7.5 percent of his salary for holding certifications for special skills, such as hazardous-materials management or training from the Federal Emergency Management Agency (FEMA) in disaster preparedness. What's odd is that such licenses are a normal part — actually, a necessary part — of his job. All wastewater operations staff are required by the San Francisco Public Utilities Commission to receive FEMA training, as well as certification in the federal Hazardous Waste Operations and Emergency Response standards.

Compensation of this sort is called premium pay, and it amounts to a lot of money in San Francisco. Last year, as the city faced a $575 million budget deficit, public employees earned a combined $66.4 million in premium bonuses on top of regular pay and overtime, according to records obtained from the Office of the Controller by SF Weekly. In fiscal year 2009, the figure was $70.6 million. The extra pay is given to public employees based on the type, rather than the amount, of work performed.

In some cases, they don't actually have to work at all. In fiscal 2010, the top 10 earners of premium pay in city government all received bonuses — in individual amounts ranging from $43,000 to $65,000 — for "standby" hours, in which they were away from the job but subject to recall if needed. City departments pay employees as much as half of their normal wages for such hours, and up to 1.5 times their normal pay when called back. (The above dollar figures include both types of compensation; city records on standby pay do not distinguish between them.)

Some kinds of premium pay are more easily justifiable than others. Nurses in the Department of Public Health, for instance, are awarded a bonus for working undesirable shifts on nights and weekends; the payment is intended as an incentive to make sure hospital wards are staffed around the clock. It can be argued that particularly hazardous or dangerous work also warrants a cash incentive. But other premiums seem redundant with basic job requirements and raise questions about government waste in a time of economic crisis.

Firefighters, for example, earn premiums for driving fire engines, despite the fact that every employee of the San Francisco Fire Department is trained to do so. They also earn premium pay for time spent working as emergency medical technicians, even though holding EMT certification is a condition of their employment. Members of the Teamsters receive premium pay whenever they're behind the wheel of one of no fewer than 20 different types of "specialty" vehicles, including tractor-trailers, street sweepers, and storm-drain cleaners.

In what many acknowledge as one of the more puzzling varieties of premium pay, city clerical workers until 2007 received a bonus for proficiency in computer word-processing software. A word-processing premium is still paid to some employees of the San Francisco Superior Court, which is funded by the state of California.

Despite the substantial burden premium pay represents for San Francisco, it has not been the object of public scrutiny, even as other forms of extra compensation, such as overtime, have come under fire. Last year, the city's overtime expenses totaled $123.8 million; premium pay still costs more than half as much.

But premium pay has started to draw attention, as some call for a reassessment of the bonuses in light of the city's financial straits. Halfway through the 2011 fiscal year, which began at the end of June, the city had already paid out $29.5 million in premium pay. Meanwhile, bus routes and community centers were shut down to help offset another half-billion-dollar budget deficit.

In September, the Board of Supervisors' Budget and Legislative Analyst's office proposed a sweeping audit of premium pay, examining how it has grown over time, its impact on pension costs, and whether the city's premium-pay practices are in line with those of other municipalities. Supervisors authorized the office to proceed with an audit, in modified form, last month. The report is expected to be released this spring.

"Some of [the premiums], it's just not warranted," Severin Campbell, audit manager for the Budget and Legislative Analyst, tells SF Weekly. "We think it's gotten pretty distorted in the city, and it also allows room for people to game the system."

Campbell, who has wavy brown hair and a gentle voice appropriate to her former profession — she used to be a nurse and union representative — appeared before the Board of Supervisors' Government Audit and Oversight Committee on Sept. 23. On the agenda was a list of potential audits on a range of topics, including policies for permitting advertising on public property and the success of Healthy San Francisco, the city's landmark health care-access law. But it was one item — a proposed audit of premium pay — that took up most of the discussion.

"I think it's a very important topic," Campbell told the committee. "There's very much that's happened in the structure of various pay practices in the city that I believe the Board needs to look at and address."