The three-story building at 1098 Manhattan Avenue in Greenpoint is slated to become a six-story apartment building, and before that happens the developer plans to dig out and truck away roughly 355 tons of contaminated soil. That’s according to a city Voluntary Cleanup Program fact sheet issued July 10 by the New York City Office of Environmental Remediation, the agency that supervises cleanups of low- to mid-level polluted land it calls “brownfields.”