Transcript
CAUSE OF THE 1985 ROSS STORE
EXPLOSION AND OTHER GAS
VENTINGS, FAIRFAX DISTRICT,
LOS ANGELES
Douglas H. Hamilton
Principal Geologist
Earth Sciences Associates. Inc.
701 Welch Road
Palo Alto. California 94304
Richard L. Meehan
Consulting Civil Engineer
70 I Welch Road
Palo Alto. California 94304
INTRODUCTION
Late in the afternoon of March 24, 1985, methane gas that
had been accumulating ignited in an auxiliary room of the
Ross Dress-For-Less Department Store located on Third
Street. in the Wilshire-Failiax District of Los Angeles. The
resulting explosion blew out the windows and pa;tially col-
lapsed the roof of the structure, reduced the store interior to a
heap of twisted metal and resulted in injuries requiring hospi-
tal treatment of twenty-three people. Police closed off four
blocks around an eerie scene of spouting gas flames that con-
tinued through the night.
In the following days, a drill rig brought to the site was used
to test for possible gas accumulations in the alluvial soil
beneath the store. A "pocket" of pressurized gas was en-
countered at a depth of 42 feet beneath the parking lot be-
tween the store building and Third Street. Gas was also en-
countered in several other borings at the site in smaller quan-
tities and at lower pressures. Pressure gauges, control valves,
and. on the hole where the high pressure pocket was en-
countered. a valved flare pipe, were installed. Following a
brief period during which gas was flared and bled off into
the air, the anomalous gas condition at the Ross Store site
gradually declined to the norma! gas concentrations charac-
teristic of the local area. In 1989 another venting incident
occurred. this time at several sites on the north side of Third
Street. This second venting fortunately was detected in time,
and did not ignite. In this case, water and silt were ejected
from outdoor vents along with the gas, in addition to accu-
mulation of dangerous levels of gas in several buildings. A
blow-out crater several feet deep, from which din and small
stones were ejected several feet into the air was formed
during this episode which lasted about 24 hours.
The setting of the accident- an old-world Levantine market
place a few miles from Hollywood; the famed tarry grave-
yard of the sabre-toothed tigers; pillars of frre dancing in the
darkened streets - these biblical images attracted attention
of the press, the bar, and local politicians. And yet, three
months later when a hastily convened panel of experts an-
nounced that the event was caused by digestive rumblings of
an ancient and invisible swamp the whole thing had been
mostly forgotten, the explanation accepted as yet another pro-
duction of Los Angeles' quirky environment. Outside of a
lawsuit that was settled quietly in 1990, the possibility that
the accident was caused by the knowing agency of Los An-
geles' lesser known industry or that the official report of the
experts, rather than being a serious statement of the scientific
community, was a heavily edited script with a happily blame-
less ending, was not made to the public, as we shall
proceed to do here.
THE SETTING - TAR PITS AND OIL
FIELDS IN THE URBAN ENVIRONMENT
The vicinity of the gas ventings lies within a sloping plain
between the easternmost Santa Monica Mountains and the
isolated topographic high of the Baldwin Hills (Fig. I). The
area drains via Ballona Creek. which cuts through Ballona
Gap to the coastal plain fringing Santa Monica Bay. The
Ross Store is in a neighborhood that has been attracting at-
tention since the mid-Pleistocene on account of its hydrocar-
Figure 1. Location and Regional Setting
bon wealth; the La Brea tar pits are about two blocks to the
south.
The old Salt Lake oil field, once the biggest producing field
in California, directly underlies and extends west and east of
the i..--nmediate neighborhood (Fig. 2). Methane gas has been
a ubiquitous feature of this area so that urban engineering for
both public and private facilities has required consideration
of the hazards of flammable gas present in the soil. Ex-
amples include the excavation for the L.A. County Flood
Control Pan Pacific storm runoff basin and park, the storm
drain along Third Street, and the (formerly planned but since
relocated) L.A. Metro subway along Fairfax Avenue.
Before the Ross Store explosion in 1985, there was general
acceptance of the view that the hydrocarbon presence in the
surface and shallow subsurface environment had its source iii.
the underlying reservoir of the Salt Lake oil field. Upward
migration of oil from parts of this reser"'oii was thought to
be the source of the "breas" or tar accumulations that had
happed many of the Pleistocene residents of the area (Shaw
and Quinn, 1986). Gas known to be present at shallow depth
within the alluvial soil was likewise considered to have
escaped from the reservoir and migrated toward the surface
(Converse et al., 1981). The surface accumulation of the re-
sidual bitumin "breas" (Spanish for pitch) led to the dis-
covery of the once-prolific Salt Lake oil field in 1902. As
the field developed, mairJy before 1917, furt .... "ter conl .. Taunica-
tion between the confmed oil, gas, and water in the reservoir
Source: C.D.O.G. Map 118
, .... ., .
r ) Approl!>ro>rimate Alea nf Poa·1 9$1 Oil Fleld
e Site of Gas Venting E .. nl
Figure 2. Wilshire-Fairfax area and the Salt Lake Oil Field
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Figure 3 Abandoned and Active Oil Welts
in the Salt Lake Oil Field
146 C.AUSE OF THE !985 ROSS STORE EXPLOSION AND OTHER GAS VEl\TTJJ--JGS. DISTRICT. LOS
and the surface was established by drilling more than 450
wells (Fig. 3). Nearly 50 million barrels of oil were brought
to the surface through these wells. Most was conveyed off-
site to markets, initially in tanks and thereafter mostly by
pipeline, but some was ·spilled and left in sump basins that
were then a standa...rd feature of the production system. By
the 1930s, the urban development value of the land overlying
the Salt Lake oil field exceeded its value as a production site
for a declining oil field, and the field was largely abandoned.
The legacies of a thirty-year oil boom included several large
family and corporate fortunes, a few square miles of land
where the natural upward hydrocarbon migration was compli-
cated by the presence of hundreds of abandoned wells plus
numerous filled sumps and covered-over spills, all underlain
by a partially depleied hydrocarbon reservoir. Following the
abandonment of most oil production, the area was rapidly
covered by the homes, apartments, businesses and industrial
facilities that exist today (Fig. 2). The remaining and most
notable hydrocarbon presence is manifest in that popular and
scientifically important exhibit of the "La Brea Fossil Pits"
and Page Museum in Hancock Park on Wilshire Boulevard
near Fairfax Avenue.
Meanwhile, beneath this urban environment, t . ~ e underlying
Salt Lake oil field was again tapped, in 1961, through skillful
application of modem oil drilling techniques and production
technology. This time, however, the entire surface installa-
tion was contained in an unobtrusive, screened complex
covering only one acre. This compact facility included the
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..
,
I
I
I
I
I
heads of 43 wells which were slant-drilled to exploit several
lease biock hoidings over an an:a of about a square mile
(Figs. J, 4), together with necessary equipment for separation
of the well-head crude oil into oil, gas, and water com-
ponents. The gas was disposed of by injection back into the
Gilmore block of the field between 1961 and 1971. Salt
water was initially disposed of by discharge into a local
storm drain, but for environmental reasons was required to be
injected back into the field, also in the Gilmore block, since
1964 (Crowder and Johnson, 1963; California State Division
of Oil and Gas [C.D.O.G.], 1974).
AFTERMATH OF THE 1985 ROSS STORE
EXPLOSION
After the flames subsided and the post-explosion exploration
and gas-control drilling was completed, a special Task Force
was convened at the direction of the Los Angeles City Coun-
cil. The Council wanted to know what had happened and
how future accidents could be prevented. The Task Force
was made up of representatives from both City and State
agencies and from industry, and it had available a Geologic
Technical Committee which included experts in engineering
geology and other relevant disciplines. Concurrent with the
deliberations of the Task Force, the Senate of the California
State Legislature enacted SB1458, the Roberti Bill, which re-
quired a study of the location of all abandoned oil and gas
wells within the State of California.
IIOUUYAAD
EXPLANATION
• . • • • • Concllled fiUII
---- Surt.c.Dtceof
.... u
L Jc... ....... , ..
ecJUI..EVAIIIp
Figure 4. Surface plan of wells, faults and gas ventings, vicinity of Ross Store S1te
CAUSE OF THE 1985 ROSS STORE EXPLOSION AND OTHER GAS VENTINGS. FAIRFAX DISTRICT. LOS ANGELES 147
< own initial interest in abandoned as: a pocten·
tial source of the gas and the mandated purpose of the
Roberti Bill to study such wells, the Task Force's surprising
conclusion was that neither the existence of dozens of such
abandoned wells, nor even the presence of the underlying oil
and gas field which had been venting to the surface for a
hundred millennia, had anything to do with the gas venting
accidents. In fact, the oil field operation was not even men-
tioned as a possible agent in the Task Force report. Instead,
a chemical analysis of a sample of the venting gas led the
Task Force to conclude that the gas was of "biogenic" origin,
presumably derived from near surface decaying of organic
matter in the alluvial soil, rather than being of petrogenic or
thermogenic origin, i.e., derived from rock-source hydrocar-
bon (oil fieid type) accumulations. The Task Force then
went on to present a scenario of shallow "biogenic" methane
being displaced and pressurized by a rising water table in the
perched fresh-water aquifer beneath the Ross Store. It was
an imaginative explanation: what school child is not aware
of that primordial scene of mastodons thrashing about in a
gassy swamp (as is artfully represented at full scale in the
Hancock Park exhibit, only two blocks from the Ross Store).
Troublesome legal issues were eliminated by this conclusion,
the impiication being that the methane hazard could exist vir-
tually anywhere, so no human agency was at fault for its
workings. The presence of the abandoned wells, the filled
sumps, or anything else having to do with the past and cur-
rent exploitation of the Salt Lake oil field evidently was con-
sidered no more than coincidence.
About a year after the issuance of the Task Force report, the
results of two separate studies of the composition and indi-
cated origin of near smface gas samples both at the Ross
Store and elsewhere in the Los Angeles Basin, became avail-
able. One report was prepared under contract to the
C.D.O.G., in response to the Roberti Bill (Geoscience Ana-
lytical, Inc., 1986). It presented the results of a study of
eight selected urban areas sited over oil and gas fieids where
there were wells abandoned prior to 1930, and where there
was a history of oil and/or gas seepage. This report con-
cluded that with few exceptions. the methane present in these
areas was, as at the site of the Ross Store building, of bio-
genic origin and thus unrelated to the underlying oil and gas
accumulations. In their opinion it was essentially swamp
gas. This remarkable conclusion was all the more interesting
since it turned out that most of the areas sampled are local
topographic highs. In any case, the resujts of this massive
study assured the public the hazardous conditions identified
by the Task Force as existing at the Ross Store, as well as
"the vast majority of the high concentration gas samples"
taken from the surface areas overlying oil and gas deposits
throughout the Los Angeles basin, were also of purely natural
swamp gas origin unrelated to human activities or oil field
presence.
The other study, based on isotopic analysis of samples of gas
at the Ross Store building escaping on the day following the
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