Thoughts on Flint, Michigan

The water crisis in Flint, Michigan had once again highlighted the fact that water distribution systems, including the portion within individual buildings (which are generally the responsibility of property owners), are not inert.  In the US, water utilities are obliged to produce water that is acceptable for drinking (and other uses) at the consumers taps

Without getting into the politics, as someone who has done a lot of work in water treatment, and water chemistry, I have a number of questions:

  1. A basic measure of the stability of water is the corrosion (or stability) index.  I have not seen basic data on the raw water basic chemistry of the Flint River, nor the chemistry of the major species (alkalinity, hardness, pH, sulfate, chlorides) after treatment.  General Motors apparently went off the Flint Water supply due to high chloride levels (http://www.freep.com/story/news/local/michigan/2015/10/10/missed-opportunities-flint-water-crisis/73688428/).  For quite some time, the concept of stability indices (Langelier, Ryznar, Larson Ratio, etc) have been well known as tools to assess the aggressiveness (corrosivity) of a water.  For example, see this paper from 1980 (Millette, James R., Arthur F. Hammonds, Michael F. Pansing, Edward C. Hansen, and Patrick J. Clark. 1980. “Aggressive Water: Assessing the Extent of the Problem”. Journal (american Water Works Association) 72 (5). American Water Works Association: 262–66. http://www.jstor.org/stable/41270478.)  There is no single universal tool as pointed out by Marc Edwards in his important review in 2001(McNeill, Laurie S., and Marc Edwards. 2001. “Iron Pipe Corrosion in Distribution Systems.”  Journal of the American Water Works Association 93 (7):88-100.) 
  2. It seems clear now that as early as March 2015, a consultants report was issued in which the addition of corrosion control chemicals was advised (http://www.freep.com/story/news/local/michigan/flint-water-crisis/2016/01/21/flint-red-flag-2015-report-urged-corrosion-control/79119240/).  

    The full report from Veolia is online and has a suite of important and prioritized recommendations to take.  The response of this in terms of decisions to take or not to take action will be interesting to watch. However the focus of this report was NOT corrosion control, as exemplified in this quote: 

    • “The primary focus of this study was to assure compliance with the TTHM limits. That is not the only problem facing the city and its customers though. Many people are frustrated and naturally concerned by the discoloration of the water with what primarily appears to be iron from the old unlined cast iron pipes. “

  3. In the absence of corrosion control, one would expect that the solubilization of iron would cause a decrease in the chlorine residual.  Rhodes Trussell reviews the important relationships between corrosion, residual, and disinfection byproduct formation (http://www.awwa.org/publications/journal-awwa/abstract/articleid/13992/issueid/33528176.aspx?getfile=/documents/dcdfiles/13992/waternet.0049164.pdf).  Either no action was taken if the chlorine residual sampled in the distribution system was noticed to drop from previous levels, or the chlorine dose was boosted, and potentially resulted in increased disinfection byproduct formation.  Given that Flint had apparent concerns about compliance with TTHM levels, they may have been reluctant to increase residual.  It would be interesting to see lab data sheets for chlorine residual measurements in the distribution system before and after the switchover to Flint River water.
  4. If the chlorine residual dropped, then microbial levels in the distribution system could have increased.  Some, but not many, utilities measure heterotrophic plate count bacteria (HPC) in the distribution system.  I would expect their levels to have increased with a drop in residual.
  5. While the connection between the elevation of the Legionella case count subsequent to the switchover is possible, a direct connection may never be known because of the absence of samples from many of the clinical cases.  Frequently a genetic match between clinical isolates and environmental isolates is deemed necessary to make a definitive connection.

I will post subsequent thoughts and comments as they develop.

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Code of Ethics and Sustainability

The ASCE Code of Ethics, Canon 1 states :

Engineers shall hold paramount the safety, health and welfare of the public and shall strive to comply with the principles of sustainable development in the performance of their professional duties.

Point f under this Canon states:

Engineers should be committed to improving the environment by adherence to the principles of sustainable development so as to enhance the quality of life of the general public.  

A classical definition of “sustainable development” is the Brundtland commission of 1987:

“Development that meets the needs of the present without compromising the ability of future generations to meet their own needs.”

It is an interesting to ask what is the obligation of a civil engineering professional who seeks to uphold Canon 1 and clause f given the definition.  I ask a number of rhetorical questions:

  • Is it unethical to accept a job in which there is an inordinate consumption of non-renewable resources when alternatives (perhaps in the short term more costly) are available?
  • Is there an affirmative ethical obligation to do a life cycle assessment of a project to determine what alternative(s) most closely meets the Brundtland definitions as operationalized? This may require excluding others (even requiring going beyond narrow requirements under particular RFQ’s or RFP’s of clients — making the problem bigger).
  • Do engineers have an affirmative obligation under Canon 1d (“Engineers who have knowledge or reason to believe that another person or firm may be in violation of any of the provisions of Canon 1 shall present such information to the proper authority in writing and shall cooperate with the proper authority in furnishing such further information or assistance as may be required.“) to report others who may not be considering the principles of sustainable development in the performance of their duties?

Costs and Benefits of Quarantine and Isolation

 

Clearly, at least in the US, ebolaphobia has been contagious.  But lets look at the concepts of quarantine and isolation.  According to CDC:

  • “Isolation separates sick people with a contagious disease from people who are not sick.
  • Quarantine separates and restricts the movement of people who were exposed to a contagious disease to see if they become sick.”

I want to focus on the concept of quarantine.  The operative phrase in the CDC definition is “who were exposed to a contagious disease”.  What precisely does that mean — is it that they are almost certain to progress to illness (i.e., the level of exposure was sufficiently high to give a near 100% probability), or that they were in circumstances where they could have received a dose (but they have perhaps a less, or much less probability of progressing to illness)?


There are clear costs and potential benefits to quarantine.  The obvious costs include the following:

  • lost wages for individuals unable to work during the quarantine period
  • room and board if the quarantine is not home quarantine
  • medical monitoring
  • costs associated with enforcement
  • there is the less tangible, but nonetheless real, cost of reducing civil liberties of the affected persons
  • for quarantine of health care workers after they have cared for patients (either in Africa or domestically) there is the cost that is also not well quantifiable in deterring others from giving such vital services in the future.

There are also potential benefits, which may be more difficult to calculate.  For the fraction of individuals who will succumb to disease, placing them in quarantine may reduce the spread of disease in others.  But to adequately quantify this one needs to employ a disease transmission model, which will require estimation of the underlying parameters, and also the underlying baseline disease prevalence.


Right now rather than such rational decision making, the mad rush towards quarantine seems to be political.  The general consensus seems to be that a signal early symptom of Ebola is a rapid onset of fever.  Therefore, if a person is deemed to be responsible (and presumably a default ought to be that health care workers are regarded as such), self monitoring and reporting is sufficient.


It seems to be unfortunate that decision making now has a strong element of science denial.

Engineers need to make problems broad to find good solutions

 

Sometimes It Pays to Make a Problem Bigger to Solve It

I have become more and more enamored of the quote from Dwight David Eisenhower:

Whenever I run into a problem I can’t solve, I always make it bigger. I can never solve it by trying to make it smaller, but if I make it big enough I can begin to see the outlines of a solution.”

I think this is a very important mindset for engineers. As I approach a new academic year with a number of seniors seeking to do senior design projects, I think this is a most important maxim. Unfortunately, too much engineering practice forestalls the ability to take this type of broader view.

Consider the following three problem statements:

  • A. I need to have a bigger bridge between point A and point B.
  • B. I need to have greater capacity for transport of people and things between point A and point B.
  • C. I need to have a better way for people who live in point A and whose employers are in B to work (and vice versa); I also need better supply routes of material to point A and point B.

Note the difference! Problem statement A admits only one type of solution (a bridge or bridge expansion or renovation). Problem statement B allows for other solutions (rail, an alternative routing, a tunnel, etc.). Problem statement C is the broadest (of the three) and allows for even further options (electronic transmission of work assignments and finished work, 3D printing, alternative suppliers and supply routes).

It may be that by over specifying a problem we do not allow ourselves to see what might be (particularly when multiple objectives are present) the entire robust set of alternative solutions.

Engineers should, in my opinion, be alert to such over specification of a problem and be sure that they express a problem in a broad fashion so as to see a larger set of alternative solutions.

Quantifying Ebola – I

With the ongoing Ebola outbreak, what seems to me missing in the discourse is some quantification.  There have been a number of detailed epidemiologic models in the literature and on the web.  For example:

http://monkeysuncle.stanford.edu/?p=1359

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2870608/

http://www.sciencedirect.com/science/article/pii/S0022519304001092

These models all use some version of the SEIR model, depicted in the graphic below 

 

SEIR

 

 

FROM:http://en.wikipedia.org/wiki/Compartmental_models_in_epidemiology#mediaviewer/File:SEIR.PNG

In this approach, a human population is considered to be either susceptible, exposed, infectious or recovered, with a progression as indicated by the arrows (with each arrow representing a rate of “flow” between one state and another.  There may be other paths as well (for example, conversion of some of the recovered to once again susceptible).

If we focus on the first two boxes, susceptible (S) and exposed (E), then using a deterministic form and homogenous populations, two differential equations for S and E can be written following Daley and Gani (1)

BasicEqns

 

 

 

 

 

 

The initial conversion to exposed is therefore the term “beta” x S x I, where “beta” is the rate at which new exposures occur from interactions between infectious (I) and susceptible (S) populations.

It seems to me that it is useful and interesting to regard “beta” as being the product of two terms:

beta = b1 x b2

where b1 is the frequency (#/unit time) of contacts between susceptible and infectious individuals and b2 is the probability that a single contact would result in conversion to an “exposed” state.  Note that in standard epidemiological parlance, the term “exposed” refers to an individual who will become but is not yet infectious.  The term b1 would presumably be driven principally by the nature and velocity of population mixing (which could be reduced by isolation of the exposed from the susceptible).

In this terminology, b2 is essentially the risk probability (frequently termed the probability of infection) which is widely used in quantitative microbial risk assessment (2).  To obtain b2, we essentially need two sets of information:

  • the average dose (d) of infectious agent transferred in the interaction between susceptible and infectious individuals during an interaction
  • a dose-response relationship giving the relation between dose and probability of infection.  the following two forms are widely used (see reference 2):

DoseResp

 

 
 

 

 

 

The first equation is the exponential dose response relationship (with an unknown parameter k) and the second is the approximate beta Poisson with unknown parameters N50 and alpha.  N50 is the median infectious dose.  As alpha in the second equation goes to infinity, the beta Poisson equation becomes the exponential.  

This analysis points to two types of data that are in need of quantification in the current Ebola outbreak.  First, what is the average dose transferred between an infectious person and a susceptible person during their contact?  This clearly will be a distribution depending on the nature and extent of contact.  Risk assessors are accustomed to incorporating and modeling various sources of uncertainty and variability (3).

Second, the dose response curve (parameters k or alpha and N50) need to be known.  I have not yet seen data (either in animal systems or humans) needed to construct such a curve, although we have many relationships for a variety of pathogens (4) .  In the context of weaponized aerosolized Ebola, an infectious dose (my interpretation of this is the median infectious dose) of 1-10 organisms is widely reported, e.g. (5), however the infectivity by what are thought to be the most relevant large droplet routes (6) (which might have different portals of entry) does not appear to have been established.

So it seems to me that there are two important research needs identified for quantification of the outbreak: (1) quantification or estimation of the transferred dose upon different types of contacts between infectious and susceptible individuals; and (2) estimation of the dose response parameters for the most important routes of exposure.

REFERENCES:

1.Daley, D. and J. Gani, Epidemic Modeling: An Introduction NY, New York1999: Cambridge University Press.

2.Haas, C.N., J.B. Rose and C.P. Gerba, Quantitative Microbial Risk Assessment. 2nd ed2014, New York: John Wiley.

3. http://www.fao.org/docrep/008/ae922e/ae922e08.htm

4. http://qmrawiki.msu.edu/index.php?title=Dose_Response

5. http://www.phac-aspc.gc.ca/lab-bio/res/psds-ftss/ebola-eng.php

6. http://virologydownunder.blogspot.com/2014/08/ebola-virus-may-be-spread-by-droplets.html 

 

 

Musings on Resiliency of Cities – More than Just Recovery to Ex Ante

I have just gotten back to the office after a day and a half conference on cities.  One topic discussed was resiliency.  A graphic used was similar to the one below:

NewImage

(Source: https://www.e-education.psu.edu/geog030/node/327)

The concept is that given a shock — a natural or manmade disaster, resilience is a property wherein the ex ante state can be re-attained.

 

But I have started to wonder whether we should explicitly acknowledge that in fact this type of resilience is settling for second best.  Perhaps a highly surpra-resilient system can take advantage of a shock to recover to an even better ex-post state. 

Perhaps the concept of chemical activation energy is more apt.

NewImage

(Source: http://en.wikipedia.org/wiki/Transition_state_theory)

In this figure a low energy is considered more favorable.  But it is only the shock of a disruption that permits the system to attain a more favorable (lower energy) state due to the barrier.

So by looking merely to return to ex ante conditions, we are ignoring opportunities for improvement (e.g., more sustainability, more equity, etc.).

Thoughts?

France Going Down a Different Route with #Fracking, #Nuclear, #Solar and #Renewables

I was fascinated to read of the upholding of an absolute ban on fracking in France.  This appears to be coupled with plans to enact a 
carbon based tax on other fuels, and a tax on nuclear, with proceeds to go towards promotion of renewables.

NewImage

There have also been a recent number of papers, for example here,  that indicate when the total social costs are properly considered, renewables emerge as a favored alternative (possibly with nuclear) ahead of conventional or new fossil alternatives.  Of course, as technology advances (and our understanding of the best way to valorize consequences evolves), this perspective might change.

But the picture emerging is that conventional economic analysis, which ignores “externalities” may not be up to the task of correctly informing decision making in the energy sector.

Vive La France.