Archive, Infrastructure

Clean Water Agenda: LTCP vs LID

I shared the podium yesterday with Bob Perciasepe, the Deputy Administrator of the USEPA, at the National Environmental Policy Forum hosted by the National Association of Clean Water Agencies (NACWA). Although we did not plan our presentations together in advance, our messages are remarkably similar. The similarity flows from an understanding that we live at a moment in time when a series of critical issues pertaining to water are at the forefront of our national agenda. For my part, I acknowledged to the crowd that I am still very new to the field of running a large water and wastewater utility – at that I have very, very much to learn. Yet I see six issues facing us in this business – three pertaining to water policy, and three to water management.

A. Water Policy.
1. LTCP and LID.
2. Cardin and Cummings and the Future of CWA
3. Age and Rates.
B. Management.
1. Communication and Customers
2. Consolidation and Markets
3. Competition and Innovation.
Over the next several weeks I will publish posts that delve into each of these areas in some detail. Today, I will start with LTCP and LID.
LTCP vs. LID. This polyglot of letters pertains to the current debate over the role and relevance of the two fundamental solutions to combined sewer overflows (CSOs). For those who don’t know – sewer systems in most older cities were built to handle both sanitary flows (water used by people in homes and businesses) and stormwater flows (the water that flows to a storm drain on your street in a rainstorm). This system works very well when the rain is light, because the pipes can handle the combined flow and deliver this mix to a treatment plant before it goes to a River. Unfortunately, ever y pipe can only handle so much flow – and once filled with the mixture it can handle no more.
Historically, there have been two solutions to this challenge: sanitary or storm water can flow back to where it came from (flooding our basements or streets), or it can be released directly into a nearby waterbody. The second option was the appropriate choice of the two because of the catastrophic health and structural consequences of sewage in homes and flooded streets. The alternative is not great either though, because the overflows to our Rivers contain a mixture of sewage and stormwater — called, not surprisingly, a combined sewer overflow.
Under the authority of the Clean Water Act, the USEPA has been working with cities to resolve this problem – usually in conjunction with a legal case filed due to violations of CWA requirements cause by the overflows. To date, the option selected to resolve this major problem has been termed the LTCP for a system – short for Long Term Control Plan. In almost all cities facing this issue, the LTCP has been a combination of three components: i) improvements to the system to reduce the amount of water in the pipe (tide gates to reduce inflow, pipe improvements to limit infiltration, etc.); ii) separation of combined systems into distinct stormwater and sanitary pipes; and III) building of large underground tunnels to hold the mixture during the storm event – to be pumped back into the existing pipes when flows recede.
The great benefit of this approach is that its performance can be engineered and measured very specifically, and the maintenance requirements are well understood and can be priced and managed. The great disadvantage is that LTCP programs are usually very costly and also largely unseen by the public. For example, the LTCP for Washington DC, which includes elements of all three components –although the tunnels drive the line share of the cost – is currently estimated to cost $2.6 billion dollars. And while the public will see improvement to the water quality of the waterways of the nation’s capital – they won’t understand why or how it is happening – since almost all will be deep in the ground, with no impact on our lives at the surface.
An alternative strategy that has come to the forefront in the most recent years is to reduce the amount of stormwater entering the system in the first place. This solution is known by the acronym LID – which stands for Low Impact Development. LID is an assortment of strategies that enables landowners to retain water on-site – for example, rain gardens, bioswales, rain barrels and cisterns, green roofs, pervious roads, walkways and parking lots and expanded tree canopies that rely on redesigned roads to channel water to tree boxes. LID has the advantage that it captures the rainwater before it hits the pipes and adds a range of quality of life benefits – reduced energy use, expanded ground level habitat, reduction of heat islands, improvements to the developed landscape. The disadvantage is that LID relies on more speculative performance metrics (how much rains does a tree really hold in its canopy, or absorb in its roots?), and relies on a decentralized maintenance system that is ongoing and intensive. Philadelphia, which has a CSO problem three times the size of DC, has proposed a LTCP almost entirely made up of LID at almost half the cost. The proposal is visionary, could help transform the landscape of cities, but is also almost entirely based on speculation about long term performance.
For the District of Columbia, I foresee a hybrid solution. DC’s LTCP currently includes major capture tunnels for the Anacostia (which is belabored by about 2 billion gallons of CSOs a year) and separate tunnels for the Rock Creek and Potomac (which together suffer about 1 billion gallons of CSOs). All these tunnels will be designed to capture flows that ultimately are treated at the Blue Plains Advanced Wastewater Treatment Plant (BPAWTP). The Anacostia Tunnel will be built first, and has the advantage of also enabling the BPAWTP to meet the next round of stringent nutrient reduction limits to benefit the Chesapeake Bay. (Achieving these goals with a joint solution actually saves hundreds of millions of dollars over resolving them separately.) Because the tunnels for the Potomac and Rock Creek are farther away from BPAWTP – the cost is quite high, and the performance improvements are significantly less. Moreover, this component of the solution is not planned until the second phase of the program – not to start until 2018.
The phased approach of the DC LTCP gives us the opportunity to devise, test and them implement an LID alternative. The biggest challenge is to quantify the performance metrics – and we will propose a pilot, scale implementation program in a smallish subwatershed on the Rock Creek to gain real performance numbers and operational maintenance experience. Based on the pilot, we can devise an LID program to scale for a large swath of the Rock Creek and Potomac “CSO-sheds” and carefully quantify how much we can downscale the size of the tunnels, or maybe eliminate them entirely. In Bob Perciasepe’s words, this approach would reduce the stormwater hydrograph that is behind the design of the tunnel system.
One added issue that Bob also discussed is the current expansion of the MS4 (municipal separate storm sewer system) permit program for urban districts. MS4’s govern those systems that are not combined – which have the advantage of not allowing sanitary flows into the River, but suffer from allowing stormwater to flow virtually untreated to our waterways at all times right from our storm drains. I negotiated an implementation system for the prior MS4 permit for DC in the summer of 2007, which at the time was the nation’s most stringent. Unlike any other permit I have worked on over the years, the MS4 scheme includes requirements that touch on many of the operations of a city – tree planting, street cleaning, illicit discharge enforcement, development standards for post-development stormwater retention and much more.
USEPA just released the proposed new MS4 permit for the District last week, which I must say I think is overly stringent. (A topic of a separate post will be the concern that if we are too stringent on urban permits, development will be driven back to green fields by market costs – since stormwater can always be managed easier on larger parcels in the hinterlands then in heavily developed cityscapes. This is an outcome we do not want to encourage!). Bob’s point, though, is that these two programs should be coordinated – MS4 permit requirements are designed to reduce CSO flows and therefore become part of the LTCP itself. We look forward to engaging USEPA on this opportunity in the days ahead.
So the conclusion of this analysis is that the issue is not LTCP vs, LID, but the development of an exciting road ahead to incorporate LID into the LTCP in a way that can generate the performance we seek, maintain it over time, and improve our daily lives at the same time.


  • I was at the NACWA event and posted about this in a different blog. As mentioned in that other comment, it was a great speech and you (George)mentioned the Gowanas Canal in Brooklyn as an example of a CSO problem area in the context of the debate between LID vs. traditional storage to deal with the CSO problem. Please see the 2007 study in Landscape and Urban Planning titled, "Rapid Assessment of the Cost-effetiveness of Low Impact Development for CSO Control" – this speaks to both topics, and the results show a mix of both may be required. Interesting stuff as DC WASA moves forward with the Rock Creek experiment.

  • I was at the NACWA event as well as I was responsible for setting our agenda. On that note, thank you for attending despite your busy schedule that day. I can say our members greatly appreciated your remarks. Also, we have a bill that would provide greater emphasis and funding for LID solutions. It is H.R. 4202, the Green Infrastructure for Clean Water Grant Act of 2009. Sponsor is Donna Edwards (D-Md) and we are building support for the bill every day. More help is always welcome…


    John Krohn

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