AMHERST – A fourth medical marijuana facility will be asking the Select Board for a letter of support at its meeting Monday. Happy Valley Ventures of Newton, which last month withdrew its application with the state Department of Public Health to locate a marijuana cultivation and production facility in Ludlow, is asking for support for a site at University Drive and Amity Street. The Zoning Board of Appeals, meanwhile, will hold a public hearing June 30 for Mass Alternative Care, Inc., which is requesting a special permit for its proposed 55 University Drive site. The state recently granted a provisional certificate of registration for that Springfield-based company. The ZBA held the first public hearing for GTI-Massachusetts NP Corp. but that company recently submitted its siting profile to the state, a step before a certificate is issued. The company wants to open a facility in the former Kimball Auction & Estate Services on Meadow Street. Senior Planner Jeff Bagg wrote in an email that the board continued the hearing to allow the applicant to continue in the public health process and secure the provisional certificate of registration . Mass Modicum, the Easton-based non-profit, which also sought Select Board support, has not yet filed a siting plan with the state or requested a special permit with the ZBA. That company filed a request to locate at 85 University Drive. Temporary Town Manager Peter Hechenbleikner said that based on estimates, medical marijuana could generate about $10 million in annual sales in total, no matter how many facilities were located in town. Based on that, the town would earn about $250,000 in revenue. Currently, New England Treatment Access in Northampton, which opened last fall, is the only treatment facility in Hampshire County.