OTTAWA- Two companies are on the hook for looking after a mercury-contaminated site near Ontario’s Grassy Narrows First Nation, the Supreme Court of Canada has ruled. The 4-3 decision Friday brought some clarity to a long-running dispute over one element of the legacy of environmental poisoning that has caused significant health problems for many residents. Eight years ago, the Ontario government ordered Weyerhaeuser Co. and a firm that later became Resolute Forest Products to care for a mercury waste-disposal site in Dryden, Ont., where toxic material from a pulp-and-paper mill’s operations entered the English-Wabigoon River system in the 1960s. The order obligated the two companies to repair site erosion, do water testing, file annual reports, prevent any leaks and give the Ontario Environment Ministry $273,063 as financial assurance with respect…