A Greenwich developer is proposing an expansion of outdoor storage at a contaminated warehouse site on 15 acres near the Danbury-Bethel border. Plans include cleaning up illegal dumping and adding a 66,000-square-foot paved storage area. The site has environmental restrictions due to hazardous waste under the warehouse slab, which will remain capped unless the building is demolished. The proposal also includes filling some wetlands while creating more to improve flood protection. Danbury’s wetlands commission is reviewing the plans, with a site walk scheduled for this Wednesday.