n Environmental Expedition and their seven Nepali sherpa guides reached the 8,848-metre peak at different times between 09.00 a.m. and 12.35 p.m. The ministry said they all used the standard southeast ridge route, pioneered by Sir Edmund Hillary in May 1953. The Americans are expected to pick up trash on their descent from Everest. The trash will be shipped to the United States. "This is the first time we are making a concerted effort to clean the mountain," Hoffman had told Reuters in April in Kathmandu before starting the ascent. The plan is to pick up empty oxygen bottles, gas cylinders, plastic cans and other garbage dumped along the route to the summit since 1953. Estimates put the amount of garbage below the South Col - the site for the final camp enroute to the summit - at 16,000 kg. Wally Berg of Copper Mountain, Colorado, leading a different 1998 American Everest Expedition, also reached the peak at about the same time as the environmental expedition, the ministry said. Berg led a scientific expedition that planned to install a Global Positioning System (GPS) on the summit as well as conduct research on the physical condition of climbers. It was not known if Berg was able to conduct his research. Four Iranians and two Sherpa guides also climbed the mountain along the same route on Wednesday. The four Iranians became that nation`s first climbers to conquer Everest. Everest was first conquered by Hillary of New Zealand and Nepal`s Tenzing Norgay Sherpa in May 1953. It has now been climbed 547 times from the Nepali side. The mountain can also be climbed from the Tibetan side.