JSHCE_submission_poi.. - John S. Horvath Consulting Engineer

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New York City v. Con Ed (P.A.G.E.)
Submission Points Relative to NTSB Causation Report
This document provides supporting evidence (given in red text) for talking points (given in black
text) that are based on documents provided to or generated by the NTSB that were reviewed by Dr.
Horvath.
Talking points that reflect the professional-engineering opinion of Dr. Horvath are so indicated.
Talking points that are grayed out are not addressed in this document.
DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
Background Information: Areal Structural Geology and Seismology
1. The geology of the incident site and its immediate vicinity plays a fundamental role in a wide
variety of conditions observed in the present so a basic understanding of this geology is
essential.
2. The incident site lies just north of the trace (theoretical surface outcrop) of the 125th Street
(a.k.a. Manhattanville) Fault. This is the largest known geologic brittle fault on Manhattan Island
and has exhibited predominantly strike-slip (right-lateral) displacement throughout its
existence that is estimated to be of the order of hundreds of millions of years.
3. This fault trace is estimated to intersect Park Avenue just south of the incident site, at about
East 114th Street.
4. A relatively recent seismic event associated with this fault occurred on the morning of 17
January 2001. It was epicentered just south of the incident site, at approximately Park Avenue
and East 102nd Street, with a relatively shallow focal depth of approximately 4 miles. It had an
estimated 'Richter' magnitude = +2.4 so would have readily both been felt and heard by people
in the area.
5. Because of the size and age of this fault it has had a profound effect on shaping the natural
topography and geology of this portion of Manhattan Island across its entire width.
6. The geology in the vicinity of the incident site is dominated by bedrock conditions associated
with Mount Morris (named Slang Berg (in Dutch) or Snake Hill in the colonial era), a locallysignificant topographical feature that is a geological klippe protruding above the Harlem Valley,
and the once-surrounding hills (now largely leveled as a consequence of human development)
referred to as the Ronde Gebergte (in Dutch) or Round Hills. Historical maps indicate that the
incident site lies along the southeast edge of this cluster of hills.
7. Available information suggests that the bedrock underlying the incident site is a combination of
schist and gneiss, types of metamorphic rock, most likely that of the Manhattan Formation. The
rocks associated with this formation are noteworthy for their relative durability and as such
define most of the higher ground and rock outcrops found on Manhattan Island.
8. A boring drilled in 2007 as part of the required geotechnical site investigation for the current
building that occupies the 1642 Park Avenue building lot indicates that hard, sound gneiss
bedrock was encountered at approximately el. -2.5' (Manhattan NYC-DOB datum) which is
approximately 36 feet below the current sidewalk level in front of this building. This boring
indicated 13.5 feet of fill material (consisting of soil mixed in with demolition debris) associated
with demolition of the previous building at this location that was underlain by 20.5 feet of
natural soil associated with the most-recent glacial events that ended about 20,000 years ago.
Although this natural soil is overall coarse-grain in nature (predominantly sand), it is significant
to note that the upper 5 feet or so is a relatively soft mixture of silt and clay.
>>> The referenced boring and survey information was contained in the 2007 geotechnicalengineering report prepared by Tectonic Engineering & Surveying Consultants P.C. that was in
the NYC-DOB digital file titled "scanned docs1.pdf".
-1DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
Background Information: Areal Hydrogeology
9. At the present time, the incident site is slightly more than 30 feet above Mean Sea Level.
>>> This is based on site-survey information contained in the NYC-DOB digital file titled
"scanned docs2.pdf".
10. Rock types associated with the Manhattan Formation in their sound condition are inherently
impermeable to fluids, e.g. water. Consequently, groundwater within this formation can exist
only in the natural discontinuities (e.g. joints or fractures, brittle faults) that occur within the
rock.
11. Independent of a 'true' groundwater level within the bedrock there can be a 'perched' or 'false'
groundwater level within the more-permeable granular materials (natural soil as well as fill
materials from human activity) overlying bedrock.
12. Given all the human development (discussed subsequently) that has occurred in the vicinity of
the incident site, combined with the generally impervious nature of the underlying bedrock, it is
difficult to say with certainty what the natural groundwater level(s) was/were originally in the
area. There may well have been a perched groundwater table in the generally coarse-grain soil
overlying bedrock that was found in the aforementioned 2007 site investigation at the 1642
Park Avenue lot and a true groundwater table within the discontinuities of the underlying
bedrock.
>>> This is based in part on the boring information contained in the 2007 geotechnicalengineering report prepared by Tectonic Engineering & Surveying Consultants P.C. that was in
the NYC-DOB digital file titled "scanned docs1.pdf".
13. A groundwater-level observation well installed at the time of the aforementioned 2007 site
investigation at 1642 Park Avenue indicated a groundwater level approximately 25 feet below
the surface or el. +7' (Manhattan NYC-DOB datum). This is within the natural soil overlying
bedrock and may reflect a perched condition controlled by factors that are discussed
subsequently.
>>> This is based on information contained in the 2007 geotechnical-engineering report
prepared by Tectonic Engineering & Surveying Consultants P.C. that was in the NYC-DOB digital
file titled "scanned docs1.pdf".
-2DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
Background Information: Human Development
14. The area around and including the incident site is one of the oldest on Manhattan Island with
regard to human occupation and development related to both Native Americans as well as the
first European settlement of the early 17th century. The area was part of Nieuw Haarlem (later
Village of Harlem) that was settled and developed contemporaneously but separately from
Nieuw Amsterdam (later City of New York) in the early 1600s.
15. Brick sewer and cast-iron water mains...the very same ones in existence at the time of the
incident...were constructed along the west side of Park Avenue through the incident site circa1887. A cast-iron gas main was also placed during the same timeframe but a portion of this
main had been replaced by polyethylene (PE) piping circa 2011-2012. This utility installation in
the late 19th century was done to keep pace with increased real-estate speculation and
concomitant residential development brought on by construction of the Second and Third
Avenue elevated-railroad lines several blocks east of the incident site.
>>> The ages of the utility lines are discussed in both drafts of the NTSB fact reports. The ages
of the sewer and water mains are also contained in the NYC-DEP digital file labeled "DEP
Records 1. pdf".
16. However, the very first railroad on Manhattan Island and one of the first in the U.S. was built
directly in front of the incident site along Park (then Fourth) Avenue in 1837 to connect the
population centers of the City of New York with the Village of Harlem which at that time were
separate political entities. This railroad line, named the New York and Harlem Railroad, went
through three distinct stages of development in the immediate vicinity of the incident site:

the initial two-track line of 1837 that would have been at-grade or perhaps in a shallow cut
(excavation);

a four-track line constructed circa-1870s in a wider cut with stone retaining walls that may
still be buried beneath the present streetscape;

a four-track line constructed circa-1890s that was elevated and exists in more or less the
same form to the present.
17. A noteworthy consequence of the circa-1890s railroad construction to elevate the railroad
through this area (done, it should be noted, after the aforementioned gas, sewer, and water
mains were constructed) is that Park Avenue through the incident site was reportedly closed
completely temporarily with construction activities occupying the full width of the street and
even overhanging the sidewalks on either side. These activities, which apparently generated
significant litigation at the time for the perceived temporary and permanent 'nuisances' they
created, are matters of public record for several locations in the area and specifically for 1642
Park Avenue.
-3DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
Background Information: Combined Impacts of Site Geology and Human Development
18. The original natural topography and landscape in the vicinity of the incident site have been
significantly impacted and altered by the almost 400 years of human development since
European colonization began. Most of this alteration has taken place with little or no known
permanent documentation relative to current standards and practices. The net result has been
to produce a complex set of subsurface conditions that likely vary significantly over relatively
short horizontal distances and about which little is known in the present.
19. Although the original topography within the Round Hills area surrounding and including the
incident site has been flattened to a significant extent to create streets and building lots there
are still significant variations in topography over relatively short horizontal distances. This is
evidenced by the localized topographic high that exists at present at the intersection of Park
Avenue and East 116th Street, and the approximately 10 feet of elevation decrease going
northward on Park Avenue from East 116th to East 117th Streets past the incident site.
>>> This described topography is depicted on the WPA 'rock data map' location plan provided
by the NYC-DDC. This Depression-era plan also shows some of the few remaining rock outcrops
that remained in this area from the prior extensive rock outcroppings that existed prior to
human development of the area.
20. When utility (gas, sewer, water) mains were constructed through this area circa 1887, the gas
and water mains, which operate under positive pressure, were able to follow the varying
topography with more or less uniform burial depths. However, the combined sewers of the era,
which were designed to function under gravity conditions, had to be placed at set elevations.
>>> The relationship between topography and sewer inverts is illustrated on the original
sewer-profile drawing for the incident site and surrounding areas that was contained in the
NYC-DEP digital file titled "DEP Records 1.pdf" (Page 95).
>>> The relationship between topography and inverts of the gas and water mains as well as the
sewer along Park Avenue through the incident site are shown on several NYC-DEP and Con
Edison drawings prepared subsequent to the incident.
21. This latter requirement resulted in a relatively deep excavation for the sewer main along the
west (current southbound) side of Park Avenue in the vicinity of East 116th Street and for some
distance north and south of there that includes the incident site. It is estimated that the
excavation depth for this sewer main may have been close to 30 feet at the intersection of Park
Avenue and East 116th Street and only a few feet less in the vicinity of the incident site.
>>> This is reflected in the previously-referenced NYC-DEP sewer-profile drawing and NYCDEP and Con Edison post-incident drawings.
22. Excavation for this sewer main would likely have been in the form of a continuous trench along
Park Avenue that extended to a depth somewhat below the final invert of the sewer and several
feet wider than the maximum width of the sewer to allow masons room to work placing the
bricks for the sewer wall.
23. Indications are that the relatively deep excavation for the sewer line encountered the
aforementioned schist/gneiss bedrock in at least some places within the vicinity of the incident
site that required removal of hard, sound rock.
>>> This is reflected in the previously-referenced NYC-DEP sewer-profile drawing that shows
the apparent top-of-rock relative to the sewer invert.
-4DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
24. Given the technology available at the time, this rock excavation was most likely done using
controlled blasting which tends to produce rock fragments in a wide range of sizes that, at least
to some extent, cannot be controlled. Thus relatively large boulder-size (defined as more than
one foot in minimum dimension) pieces of rock fragments, referred to colloquially as 'shotrock', would likely have been produced during the rock-removal process.
25. Based on test pits and other excavations made within the incident site subsequent to the
incident, it appears that this shot-rock was reused to backfill around and over the sewer main.
This was, and sometimes still is, a common, standard practice, especially in New York City, for
reasons of construction economics as is minimizes the costs of both disposing of excavated
materials and importing materials to replace them.
>>> The presence of shot rock within the two test pits excavated under the direction of the
NYC-DEP subsequent to the incident to locate the sewer main is documented in photos
contained in the DVD labeled "DEP test pits (Sep 12 2014)".
>>> The general occurrence of shot-rock beneath the water main within the incident site is
documented in photos contained in both drafts of the NTSB fact report as well as numerous
photos taken by NYC-DEP and FDNY.
26. In addition to the large size range of shot-rock, another feature of using shot-rock as fill
material, especially at the time this sewer was constructed in the late 19th century, is that within
a relatively confined space such as a utility-line excavation there is no reasonable way to
compact the pieces of rock to fit close together to minimize the spaces ('voids') between pieces.
Thus the shot-rock is typically placed in a relative loose, open state with significant voids
between pieces of rock in some places. This is simply accepted as an inherent consequence of
reusing this material as opposed to disposing of it off-site and importing soil fill that can be
compacted, even within the confines of a relatively narrow utility excavation.
>>> The presence of significant voids between the pieces of shot-rock is documented in photos
in both drafts of the NTSB fact report as well as NYC-DEP and FDNY photos.
27. In addition to the substantial excavation associated with construction of the sewer main, there
would also have been relatively deep excavations for every sewer lateral ('house connection')
that was ever constructed to connect a building to the sewer main. This was true in the past and
remains true to the present. It is quite likely that these excavations were backfilled with the
excavated material, including shot-rock.
>>> The necessity of a relatively deep excavation to construct the sewer lateral to 1642 Park
Avenue is supported by several pieces of information:
 The depth of the sewer main is documented on several NYC-DEP and Con Edison drawings
prepared subsequent to the incident as well as NYC-DEP test pits excavated subsequent to
the incident.
 The depth of the 'wye fitting' connection to the plumbing inside the building is shown on
drawings in NYC-DOB files (see the as-built version of drawing No. P-270 on the digital file
named "scanned docs2.pdf").
 The testimony of the 'outside' plumber (Murdocca) to the NTSB in 2014.
28. With specific regard to 1642 Park Avenue, there is video evidence of three such sewer laterals
that were constructed for this property prior to the one for the current building that occupies
this site. Thus within the approximately 25-foot lot width for 1642 Park Avenue there appears
to have been a total of four excavations for sewer laterals between the late 19th century and the
present. As discussed subsequently, the reuse of shot-rock to backfill at least a portion of the
-5DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
excavation for the most-recent (2011) sewer-lateral constructed at 1642 Park Avenue was
confirmed by a post-incident test pit.
>>> Sewer videos performed in 2006 and 2011 prior to the incident and in 2014 post-incident
clearly show three 6" sewer laterals within the frontage limits of the 1642 Park Avenue lot that
were apparently associated with prior building construction on this lot.
29. In summary, it is expected that along the west (current southbound) side of Park Avenue
for some distance north and south of East 116 th Street for well over 100 years the street
surface has been underlain by varying thicknesses of shot-rock as a consequence of sewerrelated construction circa 1887. Thus such conditions, which were encountered in the
vicinity of 1642/1644/1646 Park Avenue, would not be expected to be unique to those
building locations. Furthermore, such conditions with shot-rock underlying street surfaces
is a not-uncommon reality of many parts of New York City in general and the Borough of
Manhattan in particular. Thus the subsurface conditions found at the incident site are not
in the least unusual or atypical for the City of New York or Borough of Manhattan.
-6DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
Technical Issue: Defect in Sewer Main
30. As noted previously, the underlying schist/gneiss bedrock in the vicinity of the incident site is
relatively impervious to water. Therefore, natural groundwater flows would tend to be
primarily via a perched groundwater table located within the relatively coarse soil directly
overlying bedrock and follow the topography of the soil-rock interface.
31. The aforementioned deep sewer-related excavations along Park Avenue in the vicinity of East
116th Street would have artificially and locally depressed the soil-rock interface due to the
aforementioned rock excavation required for sewer construction. These artificial depressions in
the bedrock surface created 'bathtubs' around the sewer lines where perched groundwater
would naturally flow and collect under gravity. Therefore, in the vicinity of the incident site the
perched groundwater table is likely artificially controlled by the existence of the sewer main.
The groundwater levels observed during the 2007 geotechnical investigation at the 1642 Park
Avenue site are consistent with this.
>>> The 2007 geotechnical engineering report by Tectonic is in the NYC-DOB digital file labeled
"scanned docs1.pdf". At the time of this investigation they measured the groundwater table to
be at approximately el. +7 feet relative to the Manhattan NYC-DOB datum. Available information
from a 2006 site survey of the 1642 Park Avenue lot (in NYC-DOB digital file "scanned
docs2.pdf") as well as from NYC-DEP and Con Edison drawings produced post-incident (note
that elevations on the latter are relative to the NAVD88 datum so must be corrected to the
Manhattan NYC-DOB datum) indicate that the invert of the sewer main in the vicinity of 1642
Park Avenue is at approximately el. +9 relative to the Manhattan NYC-DOB datum.
32. From the 1930s (and probably decades earlier than that as there are historical indications that
the use of stones as a road-paving material on Manhattan Island dated back to the Dutch
colonization of the mid-17th century) to at least the early 1960s photographic and video
evidence indicates that Park Avenue in front of the incident site was paved with 'Belgian block'
(locally and colloquially called 'cobblestone') and the sidewalks were paved with thin slabs of
natural rock colloquially called 'bluestone', both of which were common paving materials of an
older era throughout New York City in general and the Borough of Manhattan in particular.
33. Cobblestone pavements are not water-tight and some amount of rainfall and snowmelt from not
only the roadway but also the elevated rail line above (which dumps stormwater directly on the
roadway surface) would have infiltrated the pavement and into the underlying ground. This
surface-water-turned-groundwater would have flowed downward under gravity through the
underlying fill materials (including shot-rock) and natural soil until it reached the
aforementioned perched groundwater table.
34. This process of water flow through the fill materials and natural soil underlying Park Avenue
went on for many decades, quite possibly the better part of 100 years. Nevertheless, photos
from the 1930s and early 1960s do not indicate any depression(s) in Park Avenue within the
incident site as a result of this. The implication is that even though surface water was
continuously infiltrating the subsurface and flowing as groundwater through the shot-rock fill
materials there was no visually-apparent adverse outcome from this in terms of roadway (or
sidewalk) settlement and surficial depressions.
35. At some point in time after the early 1960s, Park Avenue in the vicinity of the incident site was
repaved using what is technically known as Portland-cement concrete (colloquially 'concrete')
-7DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
that appears, in this case, to have been unreinforced. At some time later still the concrete
pavement was overlain with what is variously referred to as asphalt-cement concrete
(ACC)/asphalt concrete (AC)/hot-mix asphalt (HMA) or, colloquially, 'asphalt'.
>>> The Park Avenue pavement conditions at the time of the incident are documented in
numerous photos of post-incident excavations and test pits that were contained in both drafts
of the NTSB fact report (the second/revised one in particular) as well as photos taken by NYCDEP and FDNY. Pavement thickness at selected excavation locations are also depicted on
several NYC-DEP and Con Edison drawings produced post-incident.
36. At some time prior to 2006 (the date of the earliest sewer-inspection video available), a defect
developed in the wall of the sewer main at approximately the property line between 1644 and
1646 Park Avenue. This is approximately 25 feet north of and downhill (and thus downgradient with respect to natural surface water and groundwater flow due to gravity) from the
north property line of 1642 Park Avenue. This defect was just above the sewer invert on the
east side, i.e. the side closer to the Metro-North viaduct and away from these buildings. The
cause of this defect is unknown at the present time.
>>> The existence of this defect is documented in sewer-inspection videos performed prior to
the incident in 2006 and 2011 and is noted in both drafts of the NTSB fact report.
37. This defect would have allowed groundwater flow from the uphill direction (i.e. toward East
116th Street) to concentrate at this location because it could readily discharge into the sewer,
carrying smaller soil and rock particles with it.
38. There is evidence from both photos and written records that this sewer defect caused a
localized depression in the roadway surface but only more or less directly above the defect, i.e.
within the traffic lane of Park Avenue more or less directly opposite the 1644/1646 Park
Avenue property line. The NYC-DOT repeatedly placed asphalt overlays in the area of the
depression in an effort to maintain the geometry of the roadway surface.
>>> Both drafts of the NTSB fact report discuss this issue and summarize NYC-DOT records
concerning patch-paving of this roadway depression. Pavement thicknesses at select locations
within post-incident test pits and excavations are also documented on NYC-DEP and Con Ed
drawings and are visible in numerous photos taken by the NYC-DEP and FDNY.
39. However, all available evidence indicates that the sewer defect had a noticeable effect only on a
relatively limited portion of the Park Avenue roadway that did not extend to the portion in front
of 1642 Park Avenue. Furthermore, there is no evidence that the sewer defect caused
settlement of the sidewalks anywhere within the incident site or caused a malfunction of the
gas, sewer, or water services to any of the buildings within the incident site.
>>> The information presented in both drafts of the NTSB fact report as well as on NYC-DEP
and Con Edison drawings and in NYC-DEP and FDNY photos does not provide any evidence that
the roadway depression above the sewer defect extended to or in front of the 1642 Park Avenue
building lot.
40. That green-dyed water was found to enter the sewer defect during a test made post-incident
proves absolutely nothing. As discussed in detail previously, the entire incident area (and
almost certainly beyond) is underlain by a thick layer of shot-rock fill material that is inherently
highly pervious to water flow. The fact that dyed water was introduced into the ground at a
higher elevation and flowed naturally under gravity downhill and found its way into the sewer
main through a defect proves nothing.
-8DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
>>> Post-incident photos taken by NYC-DEP and FDNY within test pits and other excavations
indicate that the roadway areas within the incident site are underlain by a more or less
horizontally-continuous layer of shot-rock. The NYC-DEP test pit photos and logs in particular
document that this shot-rock extends down to the sewer main. Collectively, this factual
information means that water introduced anywhere within the layer of shot-rock will simply
flow downward both vertically and horizontally under gravity. The known defect in the wall of
the sewer main simply provided a ready place of ingress for water.
41. It is also worth noting that available information suggests that the sewer defect was made
worse by the 2014 incident, both directly and indirectly. Comparing videos made pre-incident
in 2006 and 2011 indicates no significant change in appearance in the defect in terms of missing
bricks during the intervening five years whereas the video made shortly after the incident in
2014 indicates additional missing bricks (possibly from the ground-shock of the explosion) and
evidence of more soil washing into the sewer than previously (most likely from the significant
volume of water used to suppress the post-explosion fire and possibly the aforementioned dye
test itself).
>>> This is self-evident from a careful comparison of pre-incident sewer videos from 2006 and
2011 (that show essentially the same condition of the sewer defect in terms of the locations of
missing bricks and the external soil and rock material washing into the sewer) to the postincident sewer video in March 2014 that shows additional missing brick(s) and soil/rock
material washing into the sewer.
42. In summary and conclusion, this sewer defect had a very localized effect in terms of
roadway-pavement subsidence and is not believed to have had any causal influence or
effect on the 2014 incident.
>>> This is a logical and self-evident conclusion based on all the factual information available to
the NTSB, whether or not they chose to include it in their draft fact reports.
-9DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
Technical Issue: Water-Main Rupture
43. There is no indication from either leak-detection surveys by the NYC-DEP or documented
civilian complaints that the water main at the incident site in the vicinity of the 1642/1644 Park
Avenue property line was leaking at any time prior to the incident.
>>> There is no evidence presented in either draft of the NTSB fact report or from documents
supplied by the NYC-DEP that the water main at the location of the rupture on the day of the
incident was leaking at any time prior to the incident.
44. Post-incident excavations made in the vicinity of 1642 Park Avenue do not show any visual
evidence of utility and/or sidewalk undermining that would be consistent with leakage of a 12inch water main prior to the incident.
>>> The emergency excavation and backfilling performed on the day of the incident that were
made to first locate the source of the water-main leak and then stabilize the area for emergency
operations disturbed the ground in the immediate vicinity of the rupture. This makes forensic
assessment of uncontaminated soil conditions around the water main at the location of the
rupture inherently impossible. However, areas to the south of the rupture directly in front of
1642 Park Avenue were not affected by these emergency operations. Photos taken by the NYCDEP and FDNY during post-incident exhumation and investigation of utility lines within these
previously-undisturbed areas do not indicate any evidence of soil erosion and concomitant
undermining of utility lines and/or sidewalk slabs that would be consistent with a chronic
water-main leak that had been ongoing for some period of time.
45. The NYC-OEM manager at the incident site during the initial hours of the incident was first
informed of a water leak approximately five hours after the incident occurred. It is also relevant
to note that the FDNY had no reported water-pressure issues for fire-fighting purposes after the
incident occurred that would have been indicative of a pre-incident water-main leak.
>>> The timeline here is very important. Given the size of the water main and the fact that the
largest opening of the rupture was pointed directly upward there would have been ample
physical evidence of a leak on the ground surface. This was indeed the case but it came several
hours after the incident occurred, not before.
46. The observed fracture pattern in the water main clearly indicates that the mode of failure was
flexural (bending) in nature due to what is called a 'hogging' pattern of pipe displacement. This
means the portions of the pipe adjacent to the point of rupture displaced downward relative to
the point of rupture. Alternatively, the point of rupture displaced upward relative to the pipe on
either side of the rupture. This hogging mode of displacement caused a negative bending
moment, i.e. the crown of the pipe was in tension whereas the invert was in compression. As
cast iron is typically considerably weaker in tension compared to compression (a distinct
difference from steel which essentially has the same strength in tension and compression) it
fractured preferentially where there was tension, i.e. at the crown as observed.
>>> The observed mode of failure is obvious to one versed in the art as is the fact that the
tensile and compressive strengths of cast iron are substantially different. In view of this, it is
surprising that the NTSB Draft #2 report on the cast-iron water main does not appear to include
the results of any tests performed to measure the tensile and compressive strength of test
specimens prepared from samples cut from the failed section of the water main that was
retrieved. Furthermore, given the focus the NTSB gives to 'graphitic corrosion' in the area of the
rupture it is surprising that they did not present the results of any examination of the section of
water main that included both the service connection to 1642 Park Avenue and a joint between
- 10 DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
that service connection and the point of rupture that was also exhumed and retrieved postincident. This section of main did not fail and it would be relevant and of significant interest to
see if it suffered graphitic corrosion to the extent found within the ruptured section. The point
being made here is not to dispute the existence of graphitic corrosion but to point out that it
may have had absolutely nothing to do with why the water main ruptured at the place it did.
Graphitic corrosion may be a red herring with respect to the rupture of the water main.
47. Based on the available evidence that indicates the water main ruptured after the incident, the
only logical conclusion is that the rupture was due to the incident. Note, however, that this does
not preclude the potential existence of pre-incident factors that contributed to the rupture
occurring at the specific place it did. The explosion that occurred would have sent significant
stress waves through the ground. These stress waves produced displacements in the ground
that caused displacement of the water main. Because the water main at the point of rupture
happened to be resting directly on a boulder-size piece shot-rock this would have created a
'hard spot' that caused hogging displacement and concomitant negative bending moment in the
water main.
>>> The timeline that documents that the water-main rupture occurred post-incident is
irrefutable based on documents produced by the NYC-DEP. Both drafts of the NTSB fact report
as well as numerous photos taken by NYC-DEP and FDNY and video segments by NYC-DEP
place great emphasis on the fact that the water main was resting on a boulder-size piece of
shot-rock exactly at the point of rupture. Yet there is no attempt in the NTSB fact report to
relate the mode of failure to the fact that the water main was resting on a boulder at the
location where failure occurred. There is much more emphasis on the voids found beneath the
water main at that point. As noted previously, such voids were not unique to that specific
location but were actually found throughout the entire incident site.
48. It is relevant to note that the location of the water-main rupture was within a few feet of the
area that had been excavated and significantly disturbed in 2011-2012 by the aforementioned
deep excavation for the new sewer lateral to 1642 Park Avenue (discussed in additional detail
subsequently). Thus the location of the water-main rupture was close to a section of the water
main that had lost all soil support and was temporarily supported over an open excavation for
some period of time, and had subsequently been placed on a restored subgrade that likely had a
support stiffness that differed from both the original stiffness as well as the undisturbed
subgrade stiffness beneath the section of the water main that ruptured.
>>> The location of the water-main rupture relative to various relevant features and
construction activities at 1642 Park Avenue can be deduced from numerous post-incident
photos taken by the NYC-DEP and FDNY as well as from post-incident drawings produced by
NYC-DEP and Con Edison.
>>> The nature of the deep excavation to construct the sewer lateral to 1642 Park Avenue and
the fact that the support integrity of both the cast-iron water and gas mains were compromised
for an extended period of time by this activity were discussed in the testimony that the 'outside'
plumber (Murdocca) gave to the NTSB.
49. It is also relevant to note that the location of the water-main rupture was adjacent to a section
of the 8-inch cast-iron gas main that had been replaced as a result of the loss of integrity of its
subgrade support due to the aforementioned sewer-lateral construction (the cast-iron gas main
had presumably been suspended over the open excavation for the sewer lateral in the same
manner as the water main). Not only were the original and replacement gas mains in very close
proximity of the water main but photographic evidence indicates that there was a butt-joint in
the new polyethylene (PE) gas main adjacent to the location of the water-main rupture. If this
- 11 DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
butt joint was made within the excavation the connection process could have disturbed the
support for the water main in some fashion.
>>> The vertical and horizontal proximity of the water and gas mains within the area in which
the rupture of the water main occurred is well documented in photos in both drafts of the NTSB
fact report; photos and videos from the NYC-DEP; and photos from the FDNY. The fact that a
butt-joint in the new PE gas main occurred adjacent to the point at which the water main
ruptured is also visually obvious from this same material.
50. The combined utility-construction activities of 2011-2012 could have compromised the support
conditions for the water main which, it should be noted, had apparently performed
satisfactorily and without incident for over 125 years at that point in time.
>>> NYC-DEP records indicate that the section of the water main within which the rupture
occurred had performed satisfactorily for approximately 127 years up until the date of the
incident. During that time numerous significant construction activities had occurred both above
and below the water main without compromising its performance:
 at least two different pavement systems (the concrete overlain with asphalt is considered
one single system) were installed;
 at least three sewer laterals to the 1642 Park Avenue lot and two laterals to the 1644 Park
Avenue lot had been installed, all of which would have involved relatively deep excavations
similar to what was done in 2011 for the sewer lateral to the current building at 1642 Park
Avenue, i.e. the water main would have been locally and temporarily undermined;
 an unknown number of taps were installed to provide water service to buildings at 1642
and 1644 Park Avenue;
 an unknown number of taps to the adjacent cast-iron gas main were installed to provide gas
service to buildings at 1642 and 1644 Park Avenue;
 the nearby four-track rail line was changed from below-grade to above-grade, all while
maintaining traffic on the line. This would have included the placement of heavyconstruction equipment within the Park Avenue right-of-way and presumably directly
above the water main.
Note that all of these activities occurred while the water main was presumably resting on the
same boulder-size piece of shot-rock found post-incident. Yet none of these activities caused the
water main to rupture.
51. In summary and conclusion, all available evidence indicates that the water main ruptured
as a consequence of the incident, not a cause. Furthermore, it is quite possible that
construction activities related to the new building at 1642 Park Avenue a few years prior to
the incident degraded the support conditions for the water main that had performed
satisfactorily for more than 125 years at the time of the incident.
>>> The timeline presented in NYC-DEP documents is clear that the water-main rupture
occurred hours after the incident. Thus the break was an effect, not a cause, of the incident.
Furthermore, while the main was resting on a boulder-size piece of shot-rock at the location of
the rupture the fact is that it had apparently been doing so, without problem, for approximately
127 years despite numerous and varied episodes of construction activity over and around that
location. This suggests that the construction activities related to the new sewer lateral to the
1642 Park Avenue lot and the replacement of the adjacent gas main during 2011-2012 may
have synergistically degraded the overall support for that section of the water main so that the
ground-borne shock wave associated with the incident caused a pattern of displacement and
bending in the water main that caused a material rupture due to an overstress situation.
- 12 DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
Technical Issue: Voids Beneath Sidewalk at 1642 and 1644 Park Avenue
52. Post-incident observations indicated that voids existed beneath the Portland-cement-concrete
sidewalk slabs immediately in front of both 1642 and 1644 Park Avenue where these two
building lots meet.
>>> This is highlighted in both drafts of the NTSB fact report. In addition, post-incident photos
from the FDNY (in particular) and NYC-DEP both show these conditions.
53. The voids in front of 1642 Park Avenue were apparently limited to the area immediately in
front of the building as post-incident exhumation of the shutoff valve for the gas service line to
this building, which was located within the sidewalk approximately 3 feet in from the curb (i.e.
approximately 12 feet out from the face of the building), did not indicate any voids beneath the
sidewalk in that area.
>>> Post-incident photos from the NYC-DEP and FDNY support this.
54. The voids in front of 1642 Park Avenue may have been related to either or both of two preexisting conditions in front of this building. One was the use of a soldier-pile-and-lagging wall
for temporary excavation support for the current building on this lot. This wall was indicated to
be located approximately 3 feet out from the face of the building and was likely abandoned in
place at the conclusion of construction.
>>> The planned use of a soldier-pile-and-lagging wall as part of the basement/cellar
excavation and foundation-construction plan for the current building on the 1642 Park Avenue
building lot is shown on the construction plans for this structure contained within the NYC-DOB
documents.
55. The other pre-existing condition relative to 1642 Park Avenue was the likely existence of an
abandoned sidewalk 'vault' associated with the prior building on this lot. This vault, which was
a street-ward extension of the basement/cellar of this building beyond the legal building lot, is
estimated to have extended out approximately one-half the width of the sidewalk (15 feet),
including the thickness of the exterior wall below sidewalk level. Presumably this vault was
filled in with demolition debris similar in composition to what was found within the building lot
when the prior building was demolished and the existing below-grade area was filled in to level
the lot. There is no indication on the construction plans for the existing building on this lot that
this vault was removed as part of the new construction.
56. The voids in front of 1644 Park Avenue may also have been related to a pre-existing condition
involving the sidewalk vault associated with this building. It appears that the vault associated
with the 1644 Park Avenue lot was comparable to that associated with the 1642 Park Avenue
lot, i.e. it extended out approximately one-half the width of the sidewalk. For some currentlyunknown reason approximately one-half of the vault associated with the 1644 Park Avenue lot
(the more-southerly half adjacent to the 1642 Park Avenue lot) was abandoned at some time in
the past and presumably filled in.
>>> The vault details for 1644 Park Avenue can be seen clearly in the photos and Panoscan
images taken by the FDNY.
57. For the sake of completeness, it should be noted that the building at 1646 Park Avenue, which
appears to have been more or less identical in design and constructed at the same time as 1644
Park Avenue (there are indications that at one time the basements/cellars of these two
buildings were accessible to each other through an opening in the below-grade party (common)
- 13 DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
wall that they shared), also had a sidewalk vault. This vault, which also appears to have
extended outward approximately one-half the width of the sidewalk, was unmodified at the
time of the incident.
>>> The vault details for 1646 Park Avenue can be seen clearly in the photos and Panoscan
images taken by the FDNY.
58. In summary and conclusion, there is ample evidence that vaults formerly or currently
existed in front of both the 1642 and 1644 Park Avenue buildings at the time of the
incident. In addition, there is ample evidence that a temporary excavation wall associated
with the current 1642 Park Avenue building also existed at the time of the incident.
Individually and collectively these pre-existing features likely contributed to the voids
observed post-incident beneath the sidewalk slabs in the vicinity of the 1642/1644 Park
Avenue property line.
>>> The presence of this prior construction beneath the sidewalk areas in front of all three
buildings at the incident site is supported by NYC-DOB drawings and FDNY photos yet is not
mentioned in either draft of the NTSB fact report nor is it accurately represented on either NYCDEP or Con Edison drawings. The failure to note this pre-existing below-sidewalk construction
is significant given the emphasis placed on the existence of the sidewalk voids in both drafts of
the NTSB fact report.
- 14 DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
Technical Issue: Utility Installations to 1642 Park Avenue
59. As noted previously, the conditions within the incident site required unusually deep
excavations for construction of sewer laterals (house connections). For the new building at
1642 Park Avenue this meant an excavation of the order of 20 feet deep at the point of
connection between the new lateral and main. The 'outside' plumber (Murdocca) who
performed this work testified to the NTSB that a relatively substantial excavation
approximately 8 feet by 8 feet in plan view was required in the vicinity of the connection
between the sewer main and new lateral to this building.
>>> This is supported by extensive documentation including NYC-DEP and Con Edison
drawings plus a post-incident NYC-DEP test pit documenting the depth of the sewer main.
60. There is now irrefutable evidence that the NTSB testimony of Murdocca was incorrect in that
the new sewer lateral to 1642 Park Avenue was installed more or less horizontally from its
connection with the main as opposed to utilizing a 'drop connection' at the main as Murdocca
testified. This meant that a trench excavation relatively deep (close to 20 feet in depth) and
several feet in width (Murdocca stated 5 feet in his testimony) would have extended all the way
from the sewer main to where the sewer lateral made a connection with the 'inside' plumbing
at the 1642 Park Avenue building property line, a horizontal distance of approximately 25 feet.
This is because as-built drawings for the 1642 Park Avenue building on record with the NYCDOB indicate that the new sewer lateral made connection with the plumbing inside the building
via a 'wye' connection at the property line that was placed at el. +18.33 feet (Manhattan NYCDOB datum) or approximately 16 feet below sidewalk level in front of the building.
>>> The NYC-DEP test pit at the location of the connection between the sewer main and lateral
to the existing building at 1642 Park Avenue, as documented in photos and drawings, clearly
indicates that a drop connection was not used and that the sewer lateral extended toward the
building more or less horizontally from its connection to the main.
>>> The depth of the connection between the sewer lateral and interior plumbing is clearly
shown on drawings in the NYC-DOB files.
61. There is now evidence that Murdocca's NTSB testimony that this extensive excavation for both
the connection of the new sewer lateral with the main and the approximately 25-foot horizontal
distance from sewer main to the wye connection with inside plumbing at the property line was
backfilled with recycled material with soil-size particles (defined as 3 inches or less per ASTM)
was also incorrect. A test pit performed subsequent to the incident by the NYC-DEP revealed
that the area over the sewer lateral was backfilled with shot-rock up to a depth of
approximately 6 feet below sidewalk level. As noted previously, it is not possible within the
relatively narrow confines of a utility trench to compact shot-rock. Therefore, it would be
expected that this shot-rock was in a relatively loose and unconsolidated state with significant
voids between pieces prior to the incident.
>>> The test pit performed by the NYC-DEP, as documented in photos and drawings, provides
conclusive evidence that the excavation to install the sewer lateral to the existing building at
1642 Park Avenue was not backfilled in accordance with Murdocca's testimony to the NTSB.
62. There is further photographic proof from this post-incident NYC-DEP test pit that the sewer
lateral was placed directly on the relatively soft natural silt and clay soil. There is no indication
that the sewer lateral was placed on any crushed stone or other bedding material.
>>> Photographs taken during execution of the NYC-DEP test pit to document the connection
between the sewer main and lateral to the existing building at 1642 Park Avenue clearly show
- 15 DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
the piping of the sewer lateral resting in brown fine-grain soil that is quite wet and soft. This
material and the depth at which it was encountered in the test pit are in complete agreement
with subsurface conditions found in the boring drilled in 2007 as part of Tectonic's geotechnical
investigation of the 1642 Park Avenue building lot.
63. This extensive excavation for the sewer lateral would have temporarily removed all support for
the other, shallower utility lines through the area such as the gas and water mains as well as
electrical conduits and any telecommunications (telephone, cable) conduits. Although the gas
main was replaced subsequent to construction of the sewer lateral (reportedly precisely for the
reason that its support had been compromised by construction of the sewer lateral) the water
main and, apparently, other conduits were not replaced. Therefore, there is a question as to the
adequacy of the support for the utility lines that were not replaced after the excavation for the
sewer lateral was backfilled.
>>> That the utility lines in question were undermined and would have had to span the
excavation made to install the sewer lateral to the existing building at 1642 Park Avenue is
obvious based on the relative depths of the various lines involved. This is also consistent with
Murdocca's testimony to the NTSB. In addition, photos taken of the NYC-DEP test pit made to
investigate the connection between the sewer main and lateral to this building show that this
was also done at that time as well.
64. Although the gas main within the area disturbed by utility construction related to 1642 Park
Avenue was replaced, due to the aforementioned proximity of the water main to the new gas
main it is questionable how adequate the bedding beneath and around the new gas main was in
terms of placement and compaction to Con Ed standards and specifications.
>>> The close proximity of the gas and water mains in the vicinity of 1642 Park Avenue are
obvious from photos in both drafts of the NTSB fact report as well as numerous NYC-DEP and
FDNY photos.
65. Although the gas main was replaced the water main was not so there is a question as to the
adequate the bedding under and around the water main was after being removed and disturbed
by installation of both the sewer lateral and new gas main. This point was made previously as it
relates to the rupture of the water main subsequent to the 2014 incident.
>>> This is professional opinion based on the close proximity of the gas and water mains as
shown in numerous NYC-DEP and FDNY photos.
66. There is a further concern that the fill soil used to backfill the uppermost several feet of the
utility excavation around not only the new gas main but also the new gas and water service
lines to 1642 Park Avenue was not adequately prevented from being washed down into the
voids of the underlying shot-rock by means of a separation or filter layer of any kind, e.g. soil of
appropriate gradation and/or a geotextile.
>>> This is professional opinion based on basic soil-mechanics knowledge that relates soilparticle sizes necessary to prevent loss of soil due to 'piping'.
67. In summary and conclusion, the construction of the sewer lateral (house connection) to
1642 Park Avenue in 2011-2012 resulted in a volume of ground approximately 25 feet long
(from property line to sewer main); up to 20 feet deep; and 5 or more feet wide that was
considerably disturbed by construction and then backfilled with approximately 6 feet of
soil resting directly on a layer of relatively loose shot-rock up to 14 feet thick underlain by
relatively soft natural silt and clay that had been disturbed by construction. This volume of
ground, which would have been susceptible to compression and settlement from self- 16 DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
weight, was also used to support the relatively shallow gas and water service lines, each of
which was approximately 20 feet long, that were installed between the mains in Park
Avenue to the building property line.
>>> This is supported by factual information from NYC-DOB records; NYC-DEP photos, videos,
and test-pit logs; and FDNY photos yet has not received adequate attention in either draft of the
NTSB fact report.
Prepared by John S. Horvath, Ph.D., P.E. d/b/a John S. Horvath Consulting Engineer
16 February 2015
- 17 DRAFT - 16 February 2015
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