WORCESTER - A lawsuit filed by a group of Southborough residents who allege improprieties among town officials and a developer during the approval process for a large housing project near a problematic Rte. 9 intersection is slated to begin Wednesday in Worcester Superior Court. A group of about 20 plaintiffs filed suit against the developer, William Depietri, and members of the town’s Zoning Board of Appeals in 2016 seeking to halt the project. The project, which would go in under the state’s 40B affordable housing law and has yet to be built, would include 180 condominium units on a 101-acre parcel not far from the Cumberland Farms before the Interstate-495 North ramp.