New York City v. Con Ed (P.A.G.E.)
Historical Documents Relative to NTSB Causation Report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text) that are based on historical documents researched and reviewed by Dr.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.
>>> This is based on professional opinion as discussed in the following paper by Dr. Horvath:
 "Foundation Challenges in the New York City Metropolitan Area Caused by Nature, Humans,
and Their Interactions" that was presented at the American Society of Civil Engineers
Metropolitan Section/Geo-Institute Chapter seminar titled "Foundation Challenges in Urban
Environments" on 16 May 2013.
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.
>>> This is based on numerous papers dealing with regional structural geology and seismology
such as:
 Lynn R. Sykes, John G. Armbruster, Won-Young Kim, and Leonardo Seeber, "Observations
and Tectonic Setting of Historic and Instrumentally Located Earthquakes in the Greater New
York City–Philadelphia Area", Bulletin of the Seismological Society of America, Vol. 98, No. 4,
pp. 1696–1719, August 2008, doi: 10.1785/0120070167
 Charles Merguerian, "Stratigraphy, Structural Geology, and Ductile- and Brittle Faults of the
New York City Area", pp. 49-56 in Hanson, G. N., chm., Geology of Long Island and
Metropolitan New York, 23 April 1994, State University of New York at Stony Brook, NY,
Long Island Geologists Program with Abstracts, 165 p.
 Charles Merguerian, "Brittle Fault Chronology of New York City (NYC)", Geological Society of
America Abstracts with Programs, v. 36, no. 2, p. 73, 2004.
3. This fault trace is estimated to intersect Park Avenue just south of the incident site, at about
East 114th Street.
>>> This is based on visual inspection and interpretation of several historical maps in the book
titled "Manhattan in Maps; 1527-2014" by Robert T. Augustyn and Paul E. Cohen (Dover
Publications, 2014). Of particular use and value were the Randel Farm Maps of 1818-1820 that
can be found in digital form on the Web at <www.mcny.org/content/randel-farm-maps> and
the Colton map of 1836 that can be found in digital form on the Web at <tinyurl.com/ovw5vvs>.
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.
>>> This is based on information found on the Web from the Lamont-Doherty Earth
Observatory of Columbia University <tinyurl.com/ndftb5m> and Dr. Charles Merguerian
<tinyurl.com/n58k3l6>.
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.
>>> This is based on visual inspection of the previously-referenced Randel Farm and Colton
maps.
-1DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
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.
>>> This is based on textual material in the books:
 "Harlem (City of New York): Its Origin and Early Annals" by James Riker (self-published,
1881)
 "The History of Harlem" by Col. A. B. Caldwell (Small Talk Publishing Company, 1882)
 "Revised History of Harlem (City of New York): Its Origin and Early Annals" by James Riker
(New Harlem Publishing Company, 1904)
that are all available online through Google Books.
>>> This is also based on a visual inspection of:
 the previously-referenced Randel Farm and Colton maps;
 the Viele map of 1864-1865 (which can be found on the Web at
<watercourses.typepad.com/watercourses/>; and
 maps found on the Web in a blog on the colonial history of New York City
<earlymanhattan.tumblr.com/>.
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.
>>> This is based on the regional geology as discussed in numerous papers and other
documents such as:
 C. A. Baskerville and Charles Merguerian, "Stratigraphic Differentiation in the Manhattan
Schist, New York City", in Geological Society of America Abstracts with Programs, v. 15, no. 3,
p. 169, 1983.
 Charles Merguerian and C. A. Baskerville, "The Geology of Manhattan Island and the Bronx,
New York City, New York" in Roy, D.C., ed., Northeastern Section of the Geological Society of
America, Centennial Fieldguide, p. 137-140, 1987.
together with local information relative to Mount Morris as found in the latter publication.
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 mixes 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.
-2DRAFT - 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.
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.
>>> This is basic rock-mechanics knowledge known to one versed in the art.
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.
>>> This is basic soil-mechanics knowledge known to one versed in the art.
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.
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.
-3DRAFT - 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.
>>> This is based on textual material in the previously-referenced books dealing with the
history of Harlem as well as textual material in the book "Manhattan in Maps; 1527-2014" by
Robert T. Augustyn and Paul E. Cohen (Dover Publications, 2014).
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.
>>> A discussion of the development history of the East Harlem neighborhood can be found on
the Web at several websites:
<www.east-harlem.com/index.php/history/>
<forgotten-ny.com/2009/05/mt-morris-park-manhattan/>
>>> A depiction of what the vicinity of the incident site looked like on the cusp of development
can be seen in this photo available from the Museum of the City of New York
<tinyurl.com/m44oy8n>.
>>> The history and developmental timeline of the two noted elevated railroads can be found
on the Web at these sites:
<en.wikipedia.org/wiki/IRT_Second_Avenue_Line>
<en.wikipedia.org/wiki/IRT_Third_Avenue_Line>
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 overall history of the New York and Harlem Railroad can be found on the Web at
<en.wikipedia.org/wiki/New_York_and_Harlem_Railroad>.

the initial two-track line of 1837 that would have been at-grade or perhaps in a shallow cut
(excavation);
>>> A depiction of this initial rail line as it existed at-grade between East 115th and East
116th Streets just south of the incident site can be seen in this pencil sketch available from
the Museum of the City of New York <tinyurl.com/ml7thmw>.

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 discussion of the construction of this improved line can be found in issues of
"Scientific American" between 1874-5, portions of which have been reproduced on the Web
here <www.columbia.edu/~brennan/beach/chapter13.html>. A depiction of this rail line in
-4DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
a cut with retaining walls can be seen in this image available from the New York Public
Library Digital Collection <tinyurl.com/m5sfu3f>. This view is from the 125th Street Station
looking south toward the incident site which would be in the distant-right portion of the
image.

a four-track line constructed circa-1890s that was elevated and exists in more or less the
same form to the present.
>>> This photo <tinyurl.com/p92bk6d> from the Museum of the City of New York shows
construction of the steel trestle for the elevated rail line being constructed within the
confines of the existing line that was depressed within a cut.
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.
>>> A description of the legal complaint and answer with specific regard to the property at
1642 Park Avenue can be found on the Web here <tinyurl.com/lkbadjo>.
-5DRAFT - 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.
>>> This is obvious based on a comparison of the topography shown on the previouslyreferenced historical maps and the current landscape.
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.
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.
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.
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.
>>> This reflects typical construction techniques of the era for sewers in New York City as
reflected in this photo from the Museum of the City of New York <tinyurl.com/n3l5pbu>.
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.
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.
>>> This is based on professional opinion and general knowledge of rock-excavation practices
in New York City.
-6DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
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.
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.
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.
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
excavation for the most-recent (2011) sewer-lateral constructed at 1642 Park Avenue was
confirmed by a post-incident test pit.
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.
>>> This is opinion based on a logical assessment of items discussed in this section combined
with professional experience.
-7DRAFT - 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.
>>> This is professional opinion based on basic soil-mechanics knowledge.
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.
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.
>>> The historical use of cobblestone street pavements and 'bluestone' sidewalks is addressed
in various websites such as the following:
<forgotten-ny.com/category/cobblestones/>
<en.wikipedia.org/wiki/Stone_Street_(Manhattan)>
>>> The specific use of cobblestone street pavements in the vicinity of the incident site can be
seen in several photos from the 1930s that are in the Municipal Archives of the City of New
York:
<tinyurl.com/p65lyhb> [shows the 1642/1644/1646 Park Avenue buildings directly]
<tinyurl.com/lt9ktfr> [the incident site is on the right in this view]
<tinyurl.com/ogulhxa> [the incident site is on the left in this view]
<tinyurl.com/p2bhgql>
>>> The prior building occupying the 1642 Park Avenue lot was used as the primary setting for
the 1964 film "The Pawnbroker". This film was reportedly shot in late 1963 and various still
photos found on the Web at this site <onthesetofnewyork.com/thepawnbroker.html> clearly
show the street (cobblestone) and sidewalk (bluestone) paving materials in existence at that
time. Additional views can be seen by viewing the entire film which is available on YouTube
<tinyurl.com/m6t9y7c>.
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.
-8DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
>>> The individual nature of Belgian blocks (cobblestones) as used in New York City as a roadpavement material is shown in this 1930s photo <tinyurl.com/jwf8ton> from the Municipal
Archives of the City of New York that was taken at the intersection of Park Avenue and East
116th Street, not far from the incident site.
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.
>>> The lack of any visual depression(s) in the roadway or sidewalk pavements within the
incident site is obvious in this previously-referenced 1930s photo <tinyurl.com/p65lyhb> from
the Municipal Archives that shows the entire incident site. An identical conclusion can be drawn
from viewing the street scenes shot in 1963 for "The Pawnbroker", both in still photos
<onthesetofnewyork.com/thepawnbroker.html> and the film itself <tinyurl.com/m6t9y7c>.
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')
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'.
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.
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.
>>> Professional opinion based on basic concepts of hydrogeology.
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.
>>> The horizontal limits of pavement patching can be visualized and estimated from historical
Google Street Views of the incident site that go back to September 2007.
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.
-9DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
>>> This is supported by the previously-referenced historical Google Street Views that clearly
show the limits of patch-paving within Park Avenue by NYC-DOT and also show no obvious
signs of sidewalk depressions.
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.
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).
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.
>>> The Google Street Views dating back to 2007 provide useful additional factual information
concerning the extent of the roadway-pavement subsidence within the incident site.
- 10 DRAFT - 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.
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.
45. The NYC-OEM manager at the incident site 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.
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.
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.
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.
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
- 11 DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
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
butt joint was made within the excavation the process could have disturbed the support for the
water main in some fashion.
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.
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.
- 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.
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.
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.
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.
>>> The existence of a sidewalk vault in front of the former building at the 1642 Park Avenue
lot is inferred from the appearance of steel entrance doors set flush with the sidewalk surface in
the previously-referenced "The Pawnbroker" film and website with still photos. Such doors are
signature details of sidewalk vaults for older low-rise buildings in New York City. The presence
of a sidewalk vault at the 1642 Park Avenue site is also consistent with the known presence of
vaults at 1644 and 1646 Park Avenue.
>>> There is every reason to believe that when the prior building on the 1642 Park Avenue lot
was demolished and the basement/cellar portion of that building simply filled in with soil
mixed with demolition debris (as confirmed by the boring drilled on this lot in 2007 as part of
the geotechnical-engineering investigation by Tectonic) that the sidewalk vault was abandoned
in place and similarly filled in.
>>> The construction plans for the current building at 1642 Park Avenue make no mention of
this presumed abandoned vault so there is every reason to believe that this vault, filled in with
some mixture of soil and demolition debris, existed beneath the sidewalk at the time of the
incident and still exists at present.
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
- 13 DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
(the more-southerly half adjacent to the 1642 Park Avenue lot) was abandoned at some time in
the past and presumably filled in.
>>> Additional evidence of a sidewalk vault in front of the 1644 Park Avenue building can be
seen in historical Google Street Views as well as the previously-referenced "The Pawnbroker"
film and associated website with still photos.
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)
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.
>>> Additional evidence of a sidewalk vault in front of the 1646 Park Avenue building can be
seen in historical Google Street Views as well as the previously-referenced "The Pawnbroker"
film and associated website with still photos.
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 historical information discussed above is essential evidence to support the fact that a
sidewalk vault existed with the previous building on the 1642 Park Avenue lot.
- 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.
>>> Google Street Views from the past support the size of the excavation required at the point
where the new sewer lateral connected with 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
in the 1642 Park Avenue building, a horizontal distance of approximately 25 feet. This is
because as-built drawings for the 1642 Park Avenue building on record with the NYC-DOB
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 NYC-DOB
datum) or approximately 16 feet below sidewalk level in front of the building.
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.
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.
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.
- 15 DRAFT - 16 February 2015
John S. Horvath Consulting Engineer
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.
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.
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.
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 selfweight, 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.
Prepared by John S. Horvath, Ph.D., P.E. d/b/a John S. Horvath Consulting Engineer
16 February 2015
- 16 DRAFT - 16 February 2015