The trail starts where Marginal Way - which technically becomes Sewage Plant Road as it crosses under the Washington Avenue overpasses - ends. At a small parking area, the Back Bay trail enters from the left and the Eastern Prom Wilderness Trail (paved for both hikers and cyclists) heads straight ahead, between the sewage treatment plant and the bay.
Many wilderness trails take visitors to the splendors of our rivers and estuaries, and the Eastern Prom Wilderness Trail is no different. This sewage treatment plant, run by the Portland Water District, is the mouth of a huge man-made watershed that runs from Sebago Lake in Standish to the outlet pipe here in Casco Bay.
Like many coastal estuaries, the plant filters out contaminants from the watershed before emptying into the bay. This plant typically treats about 20 million gallons of sewage a day (a similar amount of water flows through the mouth of the Stroudwater River). During storms, when rain and melting snow washes off all the flotsam of city streets and parking lots into storm sewers, the plant handles as much as 80 million gallons daily. Often, it's not enough, and stormwater, mixed with sewage and whatever garbage was washed from the streets, flows untreated into the Bay.
Still, before the plant opened in 1979, all of Portland's sewage got dumped into Casco Bay.
Heading east, the trail passes several excellent signs from the Water District that describe each step of the treatment process. Heading west to east, as the Wilderness Trail does, follows the process in reverse: this is a picture of the last sign the trail passes, at the plant's Process Building.
Past the plant, the trail descends toward the waterfront and gains the open fields of the Eastern Prom park. Here there are fine views of the harbor, including the landmark that will be the subject of next week's trail report: the East End Beach.