Arizona Republic: Salt River Project customers will begin paying about $6 more on their monthly bills this spring, most of which will pay for a new $1 billion coal-fired power plant near Springerville in northern Arizona. Unit 4 at the Springerville Generating Station began commercial operations in December and has been running at full throttle since then, burning about 60 rail cars’ worth of coal a day from the Powder River Basin in Wyoming. The plant supplies low-cost electricity to the …