NRG Energy began demolition of the 400-foot Encina Power Station stack this week. The apparatus mounted around the top of the stack, known as the Mende Spider, is equipped with a jackhammer that breaks the concrete in a cylindrical pattern; the pieces of the stack fall through the center of the stack and are recovered from the bottom. NRG estimates the device will remove the stack about 10 feet per day. At this rate, NRG anticipates removing the top 350 feet of the Encina stack by the end of April. The remaining 50 feet will be removed from the ground by an excavator.