South Tucson’s pension system for police officers and firefighters is breaking under the weight of dwindling assets and the ever-increasing cost of benefits. The strain of keeping its financial promise to retirees or their surviving spouses is costing the 1.2-square-mile city an estimated $520,000 a year, with pensioners outnumbering employees paying into the retirement programs. To keep the police pension checks going out, the city is using general funds to cover 72 percent of the program. That’s more than three times the statewide average of 20 percent of general funds being used in municipal pension plans. It gets worse. Of South Tucson’s nearly $8 million in estimated police pension liabilities over the next two decades, it has $176,000 invested — 2.2 percent of what it will need. As a rule of thumb, an agency should have roughly 80 percent of its pension liabilities in some type of investment assets, said Michael Bond, a senior lecturer of the University of Arizona’s Eller College of Management. For South Tucson’s police pension, that would be roughly $6.4 million. South Tucson’s Fire Department pension program has fared better, with $1.4 million in assets and an estimated $2 million in liabilities over the next 20 years. “Both of these (pensions) are really underfunded, and the police plan is incredibly underfunded,” Bond said. The police plan, he said, is the most financially precarious he has seen in his nearly 40 years in the financial industry. Bond said the projected return on investments, calculated at 7.5 percent, is also optimistic. “It is not impossible, but it is probably unlikely they will see that,” Bond said. If the pension fund fails to meet its projected investment rate, he said, the city will have to make up that money from somewhere — likely by taking more from the city’s general fund.