TITLE
Recommendation to receive and file the report, "Elevation Changes in the City of Long Beach, November 2007 through April 2008." (Citywide)
DISCUSSION
The City of Long Beach (City), through the Long Beach Gas and Oil Department (LBGO), supervises oil production and subsidence control operations in the Wilmington Oil Field. LBGO conducts elevation surveys every six months to monitor elevation changes in the oil fields and adjacent City areas. This report focuses on elevation changes that have occurred from November 2007 through April 2008. The LBGO survey includes the following areas: Civic Center, Central City, Alamitos Bay, Naples, Harbor District, and an offshore area encompassing the four offshore oil islands.
The results of the six-month survey show that elevations were stable in the Civic Center, Central City, Alamitos Bay, Naples, and offshore areas. Harbor District elevations were stable except in one small area where an elevation loss of up to 0.070 feet (0.840 inches) was observed overlying parts of Piers A and S, adjacent to the Cerritos Channel. There is no reason for concern as this area had minor elevation changes due to waterflood adjustments corresponding to oil field development programs. LBGO is mitigating the elevation change in the area by increasing and realigning water injection.
The LBGO survey uses a series of bench marks to determine elevation changes. Studies by the Department's engineers and geologists show that the bench marks may rise and fall in such a manner as to make a survey either optimistic (slightly up in elevation) or pessimistic (slightly down in elevation). These changes in elevations may be associated with tidal cycles, temperature changes, and/or deep earth tectonic changes or repressuring operations. Surface elevations in a rebounded area can be expected to fluctuate under changing water flood conditions.
Principal Deputy City Attorney Charles Parkin reviewed this item on August 19, 2008.
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