Safety works are being carried out at Fort Darnet, near Hoo, in Kent, before plans are finalised.
wHoo Cares supports more than 500 vulnerable people across the Hoo Peninsula.
Objections to the plans include affecting air quality, biodiversity and burdening local services.
The building, which is on River Medway near Hoo, was built in the 19th Century.
Fort Darnet, built in the 19th Century as a naval defence, is on the market for £50,000.
Medway Council has approved the expansion to the Syntech Biofuel facility near Hoo.
Southern Water says the blockage was caused by items which should not be flushed down the drains.
Sarah Haddock, 42, sets a Guinness World Record after running the London Marathon dressed as a fish.
A decision will be made on the 134-home development in Hoo on Wednesday.
