Sat 26 May 2012
Washington DC, like hundreds of other cities in the U.S., has a dirty water problem. The problem goes by the name of combined sewer overflow (CSO). CSO is a fancy way of saying when it rains a lot, our shit and piss go straight into the river untreated.
This foul condition is caused by sewer systems that combine sewage flows (from toilets and drains) with stormwater flows (from lots and streets). Seven hundred and seventy-two cities in the U.S. have these antiquated systems that overflow when it rains a lot. Cities that were built after 1900-1910 solved the problem by building separate systems for sewage and stormwater.
Washington DC is under a court order to fix the problem. The original court-ordered plan is a multidecade, multibillion-dollar program of installing giant water storage tunnels. It would reduce raw sewage discharges by 98 percent and would be paid for by doubling water bills over a 20-year period.
In August 2011, the DC Water and Sewer Authority proposed a test of low-impact development (LID) in order to reduce its costs and construction requirements. LID is a set of stormwater management practices that directs runoff to places where it can soak into the ground: swales, rain gardens, trenches, porous pavement, etc. If we put stormwater into the ground instead of sewer pipes, says DC Water, the pipes will overflow less often.
But local environmental groups are wondering just how feasible the DC Water proposal is. They are objecting to it — in particular, the proposed eight-year delay in tunnel construction and potential reductions in tunnel capacity. While proven cleanup techniques are delayed, DC Water will experiment with LID techniques that may or may not provide significant reductions of stormwater runoff. Washington Post columnist Mike DeBonis describes the situation:
Problem is, the environmental advocates on the other side of the tunnel agreement remain skeptical of the low impact development plan. They are understandably hesitant to give up the guaranteed prevention of sewage outflows for a speculative reduction in runoff that would require years of delay.
Leaders of 16 environmental groups signed a letter late last month saying, essentially, that low impact development is a good idea and all, but they’re not convinced it’s a proven way to handle a serious sewage problem. Just today, Earthjustice — the legal group behind the lawsuit that forced the tunnel deal — told the Environmental Protection Agency it will “strongly oppose” any attempt to change the agreement to swap tunnel capacity for green infrastructure.
– “Can green development cut your D.C. Water bill?” Washington Post, May 24, 2012
EPA Stormwater Regulations to Clean Up the Chesapeake Bay
In addition to the court-ordered consent decree to clean up its CSO problem, DC must contend with EPA regulations written to clean up the Chesapeake Bay. These regulations took effect in 2011 and address water quality impacts from polluted stormwater runoff. When stormwater flows over buildings and lots, and across streets and parking lots, it picks up pollutants that eventually end up in the Chesapeake Bay.
Although this is a separate issue from CSO cleanup, the EPA regulations also specify that DC should use LID to reduce water pollution. Can LID do double duty for both programs — can the same installations fix the CSO problem and clean the Chesapeake Bay? Is there any coordination between the two programs?
Proof of LID
More generally, is there any evidence LID works at large scales? I know that LID has been tested and proven at the level of individual sites. And I know that EPA regulations and other regulations are based on models that assume those results will scale up to the city, county, and watershed scale.
That’s not what I am asking about. I’d like to find empirical evidence that LID improves water quality at scales larger than the site. The ward, district, city, county, regional or watershed scale, for example.
We know that centralized storage and treatment methods work, because the results are evident. In Paris, the Seine River has been heavily polluted for many decades, partly because of its CSO system. Now the cleanup effort has progressed to the point that 28 fish species have returned, including migratory Atlantic salmon. In Copenhagen, the harbor used to be an industrial waste dump. Now it is clean enough for people to swim in. Both of those cities have densely developed waterfronts that are extremely popular. Cleanup has been accomplished by installing centralized water treatment plants and stormwater tunnels and reservoirs.
What similar successes has LID demonstrated?
Maybe LID has not yet been implemented at large enough scales to produce measurable effects on any major water bodies. But LID is being mandated in more and more jurisdictions, with the expectation that it will be effective at large scales. This seems backward. The effectiveness of LID at large scales should be empirically demonstrated before it is accepted as an alternative to conventional, proven methods of controlling water pollution at large scales.
What happens if cities and counties mandate LID across their entire jurisdiction, and subsequently the overall water quality of the watershed shows little improvement? How long should they wait for results? Is there a backup plan?
Additional quotes and links below the fold.