Get ready – Allegheny County is about to go through the largest public works project in its history. An estimated 2-3 billion dollars will be spent to update our region’s sewer system.

At first it may seem that there are more exciting, more tangible, projects to direct our attention to. However, by the project’s end in 2026, that occasional curious smell by our river fronts, that opaque brown tone of the water, will be gone.

Why make changes to our sewers?

As it stands, an estimated 9 billion gallons of untreated wastewater annually enter Pittsburgh area rivers, streams and creeks during a heavy rains. This ‘untreated’ water includes runoff from our streets and raw sewage from our homes. (http://www.post-gazette.com/stories/local/region/alcosan-asked-to-adopt-green-plan-to-cut-sewage-spills-658285/). Since 1905, various laws have attempted to prohibit dumping of sewage into rivers, but the problem is simply a result of how our area’s sewer system constructed. Some sewage lines are 50-100 years old, and are comprised of CSO’s (combined sewer overflows) which direct sewage and runoff to overflow into our rivers after a heavy rainfall.

The resulting water toxicity levels are unacceptable by the requirements of the Federal Clean Water Act. The Environmental Protection Agency and the PA Department of Environmental Protection have therefore required CSO based systems, including our local sewer authority, ALCOSAN, to eliminate this pollution through issuance of a consent decree.

The Pittsburgh area is not alone in this issue. Over 700 municipalities around the country, from Cleveland to San Diego, utilize CSOs and will all require updating in the coming years. For example, it is estimated that 20 billion dollars will be spent to remedy the issues in the Great Lakes region alone.(http://www.americanwaterintel.com/archive/2/2/general/consent-decrees-whos-next.html)

When are the rivers safe?

Most days it is safe to use Pittsburgh’s rivers for recreation. However, after a rain event, Allegheny County recommends that the rivers and streams not be used for any recreational purpose. As the river’s current carries sewer pollution downstream, the rivers are typically flushed with cleaner water within a 72 hour period after a heavy rains. (http://3r2n.collinsandgoto.com/river-research/pittsburgh-pool/swimming-river-city/swimming-the-river-city-BEN-LEDEWITZ.pdf)

Starting this past May, at 30 sites along Pittsburgh rivers, you will can see an orange “CSO” flag when the river is considered to be unsafe. For further information, contact this number or check the following sites (http://www.achd.net/pr/pubs/2013release/051313_cso.html) 412-687-ACHD (2243), visiting www.achd.net, http://www.3riverswetweather.org/

What’s the project status?

The EPA Consent decree was issued to ALCOSAN in 01/2008. (http://www.alcosan.org/WetWeatherIssues/ALCOSANDraftWetWeatherPlan/tabid/175/Default.aspx) Last July, ALCOSAN released a plan to meet these requirements. Beginning in 2013, the plan has been in public commentary period. The project is currently scheduled to be completed by 2026.

How is the CSO problem fixed?

‘Graywater’ solution 1 – the most common design solution: Expand tunnel capacity, i.e. – make tunnels that flow into sewage treatment plans bigger, so they will not overflow.

‘Graywater’ solution 2 – less common design solution: A city can segregate disposal systems for water and sewage (ie.– road pollution still enters the river during overflows).

Green Infrastructure solution: A city can implement green infrastructure and/or reduce the amount of pervious pavement, implement constructed wetlands/bioswales, etc. The city of Cleveland and Cincinnati provide examples of combined Green + Greywater solutions. (http://www.epa.gov/sciencematters/april2012/overflows.htm)

New Technology solution: A city can add inflatable dams. (http://www.nytimes.com/interactive/2012/09/16/nyregion/inflatable-dams.html?_r=0)



Article by Tonya Markiewicz, VDC Engineer

tmarkiewicz@massarocorporation.com