Last week’s column on the replacement of the Commercial Street Bridge described an impressive local engineering project; this week we would like to discuss another equally impressive project, the ALCOSAN Combined Sewer Remediation Project. This project has a much broader significance; cleaning up the Ohio River affects millions of people downstream. It is also significant to the folks who will be footing the (estimated!) two billion dollars bill to pay for it – all of us ALCOSAN customers.
ALCOSAN is the acronym for the Allegheny County Sanitary Authority, an organization with eighty-three customers – the city of Pittsburgh and eighty-two other municipalities adjacent to it, including the boroughs and townships in the Chartiers Creek Valley. These municipalities have a. population of about 900,000 persons. To serve these customers, ALCOSAN maintains a system of ninety miles of interceptor sewers that transport sewage from the individual municipal systems to the wastewater treatment plant at Woods Run, close to the McKees Rocks Bridge. This facility has the capability of treating 250 million gallons of sewage per day, significantly more than is normally produced by the domestic, commercial, and industrial customers in ALCOSAN’s service area. Unfortunately, a series of historical developments have created a situation, the combined sewer overflow problem, that overloads the facility many times a year.
To understand this problem, we must consider its history. At the turn of the twentieth century the disposition of domestic sewage was the responsibility of individual homeowners, who solved it primarily by the installation of outhouses. Once we became more sophisticated, our municipalities installed extensive networks of sewers which efficiently moved our domestic wastes from our homes to the nearest creek; in Bridgeville, either to McLaughlin Run or Chartiers Creek, both of which were already so polluted with acid mine drainage that this addition was hardly noted. This worked well in the suburbs; the densely populated neighborhoods in the city had an additional problem – stormwater runoff. In the suburbs most of the rainfall was intercepted by trees, lawns, and gardens. In the city it was a different story – there was so much runoff that it had to be collected and transported to the rivers by large storm sewers. Instead of running small domestic sewage pipes in parallel with the large storm sewers, the City of Pittsburgh elected to combine the two. After all, they both had the same destination.
In the middle of the twentieth century we realized that polluting the rivers was a bad idea and decided to intercept the domestic sewage and transport it to a modern wastewater treatment plant where it could be cleaned up before being discharged into the Ohio River. We established ALCOSAN and charged them with the responsibility of intercepting the flow just before it was dumped into the rivers and streams. The result was the current system, which works well in dry weather. However, when we have a significant rainfall the total volume of the stormwater runoff and domestic sewage exceeds the capacity of the treatment plant. On those occasions the excess flow is diverted into the rivers. At this time, it appears that this occurs in Allegheny County every time we get about half an inch of rain, perhaps fifty times a year. When this occurs, ALCOSAN issues warnings restricting recreational use of the river.
A few years after ALCOSAN was established, restrictive legislation, including the Clean Water Act of 1972, was passed to ensure that the overall objective of cleaning up our streams would be achieved. The Environmental Protection Agency, empowered to enforce it, began to attack the combined sewer overflow problem by negotiating Compliance Agreements with all the cities where it existed. The one applicable to ALCOSAN requires them to initiate an ambitious program which includes increasing the capacity of their treatment plant to 600 million gallons per day and installing massive underground storage capacity (120 million gallons) to accumulate excess runoff and meter it out at a rate consistent with the upgraded facility’s capability.
The storage capacity will be achieved by drilling sixteen miles of eighteen-foot diameter tunnel in bedrock one hundred and fifty feet below the level of the rivers. This will be accomplished by a tunnel boring machine (TBM) in three successive phases. The first phase will be along the Ohio River from the treatment plant to a location on the North Shore near the Point. Next will be one paralleling the Allegheny River, followed by one paralleling the Monongahela River. The expansion work at the Woods Run treatment plant is progressing already and should be completed well before the tunnels. The combination of all these phases will add 470 million gallons per day of capacity to the system and reduce the number of overflows each year to perhaps five or six times a year. The quantity released each time will be small enough to have a minimal effect on the quality of water in the Ohio River.
The current total cost forecast for this project is about two billion dollars. It will be financed by user fees on all of the ALCOSAN customers (four or five thousand dollars per household over perhaps ten years, if the estimate is correct). These customers are already seeing a significant increase in their monthly bills. Despite the burden this puts on households already struggling with inflated costs, it does seem to be a worthwhile thing to do. Clean water is perhaps the most valuable resource in southwestern Pennsylvania; it behooves us to maintain it.
P. S. This Day In History (September 10, 1953) The United States Army announced that it finally had reached “the bottom of the barrel” with the enlistment of draftee John F. Oyler, serial number US 52314746. Fortunately, the Army survived and I survived and two years later I returned to civilian life. The Army has raised its enlistment standards to ensure that such a travesty would not be repeated.