CAUSE OF THE 1985 ROSS STORE The setting of the accident- an old-world Levantine market place a few miles from Hollywood; the famed tarry grave• EXPLOSION AND OTHER GAS yard of the sabre-toothed tigers; pillars of frre dancing in the VENTINGS, FAIRFAX DISTRICT, darkened streets - these biblical images attracted attention LOS ANGELES 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• Douglas H. Hamilton duction of Los Angeles' quirky environment. Outside of a Principal Geologist lawsuit that was settled quietly in 1990, the possibility that Earth Sciences Associates. Inc. the accident was caused by the knowing agency of Los An• 701 Welch Road geles' lesser known industry or that the official report of the Palo Alto. California 94304 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 !r~'1own to the public, as we shall Richard L. Meehan proceed to do here. Consulting Civil Engineer 70 I Welch Road Palo Alto. California 94304 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 INTRODUCTION isolated topographic high of the Baldwin Hills (Fig. I). The Late in the afternoon of March 24, 1985, methane gas that area drains via Ballona Creek. which cuts through Ballona had been accumulating ignited in an auxiliary room of the Gap to the coastal plain fringing Santa Monica Bay. The Ross Dress-For-Less Department Store located on Third Ross Store is in a neighborhood that has been attracting at• Street. in the Wilshire-Failiax District of Los Angeles. The tention since the mid-Pleistocene on account of its hydrocar- 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• Figure 1. Location and Regional Setting 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. 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 , .... ., . Approl
escaped from the reservoir and migrated toward the surface e Site of Gas Venting E.. nl (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 Figure 2. Wilshire-Fairfax area and the Salt Lake Oil Field ...... "'" " -eo... "'• ...... ,5 ......
Figure 3 Abandoned and Active Oil Welts in the Salt Lake Oil Field Source: C.D.O.G. Map 118
146 C.AUSE OF THE !985 ROSS STORE EXPLOSION AND OTHER GAS VEl\TTJJ--JGS. FAL~FAX DISTRICT. LOS Af--~GELES and the surface was established by drilling more than 450 heads of 43 wells which were slant-drilled to exploit several wells (Fig. 3). Nearly 50 million barrels of oil were brought lease biock hoidings over an an:a of about a square mile to the surface through these wells. Most was conveyed off• (Figs. J, 4), together with necessary equipment for separation site to markets, initially in tanks and thereafter mostly by of the well-head crude oil into oil, gas, and water com• pipeline, but some was ·spilled and left in sump basins that ponents. The gas was disposed of by injection back into the were then a standa...rd feature of the production system. By Gilmore block of the field between 1961 and 1971. Salt the 1930s, the urban development value of the land overlying water was initially disposed of by discharge into a local the Salt Lake oil field exceeded its value as a production site storm drain, but for environmental reasons was required to be for a declining oil field, and the field was largely abandoned. injected back into the field, also in the Gilmore block, since The legacies of a thirty-year oil boom included several large 1964 (Crowder and Johnson, 1963; California State Division family and corporate fortunes, a few square miles of land of Oil and Gas [C.D.O.G.], 1974). 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 AFTERMATH OF THE 1985 ROSS STORE by a partially depleied hydrocarbon reservoir. Following the EXPLOSION abandonment of most oil production, the area was rapidly covered by the homes, apartments, businesses and industrial After the flames subsided and the post-explosion exploration facilities that exist today (Fig. 2). The remaining and most and gas-control drilling was completed, a special Task Force notable hydrocarbon presence is manifest in that popular and was convened at the direction of the Los Angeles City Coun• scientifically important exhibit of the "La Brea Fossil Pits" cil. The Council wanted to know what had happened and and Page Museum in Hancock Park on Wilshire Boulevard how future accidents could be prevented. The Task Force near Fairfax Avenue. was made up of representatives from both City and State agencies and from industry, and it had available a Geologic Meanwhile, beneath this urban environment, t.~e underlying Technical Committee which included experts in engineering Salt Lake oil field was again tapped, in 1961, through skillful geology and other relevant disciplines. Concurrent with the application of modem oil drilling techniques and production deliberations of the Task Force, the Senate of the California technology. This time, however, the entire surface installa• State Legislature enacted SB1458, the Roberti Bill, which re• tion was contained in an unobtrusive, screened complex quired a study of the location of all abandoned oil and gas covering only one acre. This compact facility included the wells within the State of California. , .. I I I I I EXPLANATION IIOUUYAAD
• . • • • • Concllled fiUII
---- Surt.c.Dtceof ....u -~ L Jc...... ,.. I
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 < Oesplt~i~ s own initial interest in abandoned '>~tells as: a pocten· e~pl{))>lt"Yn, co~tduded l!:u
!48 CAUSE OF THE 1985 ROSS STORE EXPLOSION A.l\ffi OTHER GAS VENTINGS, FAIRFAX DISTRICT. LOS ANGELES
the character of the 1989 venting incident led the sub• "ABANDONED WElLS AS A SOURCE OF METHANE - sequently reconstituted Task Force to abandon the "rising The potential hazard imposed by old abandoned wells was water table" mechanism, but to otherwise leave as open ques• not considered in the 1985 report because the gas was tions where the methane actually comes from and the means believed to have formed within the shallow biogenic areas by which it is forcefully vented to the surface. above the production zone. However, the extent of chemical stripping of gas constituents and microbial alte;nations during migration probably could not occur within a gas TASK FORCE REPORT II - DISCUSSION bubble rising upward in a vertical shaft filled more or less with water or brine. These could. however. be the source of The Methane Gas Task Force was reestablished by the Los low-volume methane that mixes at the surface with ambient Angeles City Council three days after the second major gas gas at low pressures. However all available chemical and venting in the Fairfax District, which occurred on February isotopic information exonerates these abandoned wells as the 7, 1989. Its charge was again to report on the recent incident source of the higher-pressure methane events. (Underlining and "present recommendations necessary to protect health added for emphasis). and safety within the area". The revived Task Force began its work with less urgency than had existed in 1985, since no These wells are an entity to be considered in the future or as actual damage had occurred in connection with the 1989 they are uncovered by area construction. But, even if the venting, but with a larger and more confusing data set. wells could be located. reabandonment to modern standards Some of the data that had accumulated since 1985 were would be an expensive program." simply contradictory, mainly the two different gas-origin stu• dies. One indicated a shallow-source biogenic origin for the The writers do not understand how the isotopic information gas, the other indicated an oil field origin for the Fairfax gas, reported by Global Geochemistry (1986), which indicated the but the forceful ejection of gas, water, and mud during the Ross Store gas to be thermogenic, hence of oil field origin, 1989 venting clearly required a driving mechanism with in any way exonerates a potential conduit from the oil field more energy than a "rising water table". Faced with these to the surface such as an abandoned well. contradictions and uncertainties, the 1989 Task Force elected to, in effect, throw up its hands with the following paragraph. With regard to the possibility that the problem might be re• "CONCLUSION ON ORIGIN - Obviously, the origin of the lated to disposal by pressure injection back into the subsur• methane gas is complex and not clearly understood. Two face of salt water stripped from the crude oil currently being reputable firms with qualifications and experience seem to extracted from the field, the Task Force stated the following: have opposing opinions on the origin of the gas. But. if we intend to shield buildings or vent areas of probable methane "PRESSURE INJECTION OPERATIONS - Within the Salt gas seepage. the origin of the gas realiy does not matter. Lake field aboui 42 wells are curremly producing from the The most probable origin of the gas 'may' be a 'combination "C" and "D" Production Zones. According to production or thermogenic and shallow biogenic sources with the high• records of the Division of Oil and Gas. more fluids are being pressure events from thermogenic (deep) sources and the withdrawn than are returned to the production zones. The /ow-pressure background gas from a combination of biogenic type of injection used by McFarland Energy is a water dis• and thermogenic sources. So, in reality, the origin of the posal program that does not cause field repressurization. methane has its implications in the total understanding of the Current oil field operations within the Fairfax area, there• problem, but not in remediation or control. Methane gas fore, do not appear to have an adverse affect on the area produced within deep fields or in shallow marshes will not methane seepage." (Underlining added for emphasis). physically function nor react in the same manner. Both are capable of explosive conditions and both can be safely We address this latter conclusion in the discussions presented vented to the atmosphere." in following sections.
Before going on to its recommendations for dealing with the Although Task Force Report II explicitly "exonerated" past problem, by a 3-point program comprising venting by relief and present oil field operations from any role in the 1985 and wells, use of an area-wide monitoring survey team, and City 1989 gas ventings. it did, unlike the 1985 report, at least inspection for Code compliance, the 1989 Task Force paused mention them. But, even this was evidently regarded as to provide assurance that neither past nor present activities stepping outside of some kind of bounds by the Task Force related to exploitation of the underlying Salt Lake oil field member representing the C.D.O.G., since that member wrote had anything to do with the 1985 or 1989 gas venting inci• a letter providing comments regarding the second draft of the dents. · With regard to the possibility that the gas might have Task Force Report II which seemed to generally take his fel• escaped via one of the 400 plus abandoned wells that low members to task for even mentioning oil field operations formerly tapped that field, the Task Force stated the follow• (Baker, 1989). This letter was provided as an attachment to ing: Task Force Report II.
150 CAUSE OF THE 1985 ROSS STORE EXPLOSION AND OTHER GAS VENTINGS, FAIRFAX DISTRICT. LOS ANGELES At the same time, a contradictory view was set forth in time (Hill and others, 1979; Crook a.nd .Proctor in this another letter, this from Dr. James E. Slosson. fanner Cal• voluiT!e). Hill and others (1979) based on data provided ifornia State Geologist and Consultant to the Task Force in ti:tem by the City of Los Angeles Bureau of Engineering, and both 1985 and 1989. In this letter, Slosson (1989) details his following Grant and Sheppard (1939), studied the surface disagreement with virtually every point made in the Task subsidence in the region of the Santa Monica fault, including Force Report II that dissociates the 1985 and 1989 gas the Salt Lake oil field area. Although Hill and others (1979) venting incidents from the Salt Lake oil field. Unlike the let• viewed the results of analysis of recent micro-earthquake ac• ter from the C.D.O.G. member, Slosson's letter was not at• tivity as suggesting that subsurface faults in the Santa Mon• tached to or referenced in Task Force Report II, even though ica-Raymond fault zone are undergoing tectonic strain accu• it was dated six weeks earlier. mulation, the pattern of surface subsidence they mapped within a 5-mile wide zone along the inferred trace of this fault could be interpreted as indicating surface relaxation GEOLOGIC SETTING OF THE FAIRFAX rather than compression (as well as indicating response to AREA consolidation in the subsurface resulting from prior extraction The geology of the Ross Store area has been studied and de• of ground water). So it is not clear that the Santa Monica scribed in terms variously of surficial geology, emphasizing fault is contributing to any near-surface tectonic deformation the formation of the La Brea tar pits (Shaw and Quinn, in the area. Within the ground south of the Santa Monica 1986), hydrogeology (DWR, 1965), neotectonics (Richards, fault, the folds and faults that form the structural trap of the 1973; Hill and others, 1979), engineering geology (Converse, Salt Lake oil field are the principal local geologic structures. 1981; L.A. County Aood Control, 1977) and petroleum ge• This area is underlain by about a 200-foot thickness of Qua• ology (e.g., Hoots, 1931 ; Soper, 1943; Crowder and Johnson, ternary shallow marine and aiiuvial deposits, which overlie 1963; Wright, 1991). To summarize, the area is situated near late Miocene and Pliocene age Repetto and Pico Fonnations the northern edge of the Los Angeles Basin, and the central (undivided) and late Miocene Puente Fonnation. The Teni• axis of the Salt Lake oil field nearly parallels and lies about ary strata are both tightly folded and displaced by steeply in• 2 miles south of the Santa Monica fault. This fault forms the clined reverse faults, but the overlying Quaternary strata are local boundary between the Western Transverse Ranges and apparently undeformed (Fig. 5). Therefore, the tectonism the Los Angeles Basin. The Santa Monica fault is generally that formed the compressional structure of the Salt Lake oil represented as a steeply north-dipping reverse fault, which field therefore died out or has been quiescent since approxi• has been active at least as recently as during late Quaternary mately Plio-Pleistocene or at least early Pleistocene time.
Ul BI'N T•r PitS Lagoon A A'
0
300
100
1100 1200 }: 1500 I 1500 J 1100 1100 ~ 52100 2100
2400
2700
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3300
plot shows the gradual decline in oil production noted above. sures fourfold from 200 psi to 770 psi. The worlcover re• Of particular interest in the context of the present discussion, cord~ show that considerable effort was expended in the No. however, is the history the production (and disposal) of 9 conversion, including acid treatment with 5,000 gallons of water, brought to the surface along with the crude oil and gas hydrochloric acid and 2,500 gallons of hydrofluoric acid, in hydrocarbon fluids. · This is plotted separately in Fig. 7. January, 1985. The well was then tested by injecting back showing monthly production and injection back into the field into the C zone of the field at 475-500 psi. Thereafter, the of the salt water byproduct of oil production. The indicated C.D.O.G.-tabulated records of production for the Salt Lake pattern is one of steadily increasing water production as oil oil field show Gilmore No. 9 as a disposal well, but no injec• production decreased, Fig. 6, from the beginning of 1980 tion disposal is recorded for it prior to March, 1989. How• through mid-1984. Between mid-1984 and about mid-1985, ever the dramatic decrease in the quantity of water disposed however, reported water production declined precipitously of by injection into the original disposal well, Gilmore No. from around 14,000 to around 6,000 and less bbVmo, the low 16, coincided with the time Gilmore No. 9 was converted to being about 3,000 bbl in January 1986. A gradual upward a disposal well. Since the production of oil did not suffer a trend in water production was re-established in 1985, so that corresponding decrease, but instead actually increased by average water production had increased to about 8,000 3,000 to 4,000 bbl/mo. from early 1985, when the decrease bbVmo. by late 1988. in water disposal was most dramatic, to early 1986, the ex· planation for the pattern of water disposal must lie elsewhere. Taken at face value, the water production data shown in Figs. Given the generally constant (or at least only gradually 6 and 7 would seem to indicate either a radical change in the changing) ratio of oil to water for production from this field, oil-water ratio of the field's production, or a remarkably we suggest that the explanation may involve omission of data successful exercise in selective control of water production from the record rather than implausibly effective control of (for example, by shutting in certain wells or grouting off cer• water production. According to this scenario, by mid-1984 tain producing zones). In fact, however, well records on file water production would have exceeded the injection capacity with the C.D.O.G. show no evidence that anything like this of the only disposal well in the field, Gilmore No. 16, so occurred. What did happen, however, was that a second work was begun to convert a second well, Gilmore No. 9, well, Gilmore No. 9, was reconditioned and converted from a complete.d in the same lease and zone as No. 16, to function production to an injection disposal well, in 1984. Meanwhile as a second disposal well; this was initiaUy accomplished by the operator, McFarland Energy, Inc., sought and received late 1984, and an increasing percentage of the field's water permission from C.D.O.G. to raise well head in 'ection res- production was diverted into the new disposal weU through
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