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2, Previous Investigations
<br /> A summary of previous investigations performed by others is presented below. Historical groundwater
<br /> elevation, analytical data tables, groundwater gradient, and monitoring well construction details are provided as
<br /> Tables 2, 3, 4, and 5, respectively.
<br /> 2.1 Unauthorized Releases
<br /> Five spills have been documented at the site. The first surface spill occurred on June 9, 1984 near the transmix
<br /> tank and consisted of 13,000 gallons of gasoline, diesel, and heating oil. Soil was excavated immediately in the
<br /> spill area until no subjective evidence of hydrocarbons remained. The second spill occurred in August of 1990
<br /> and consisted of a tank overflow of approximately 300 gallons of gasoline. The third spill occurred in August of
<br /> 1998 when an unknown volume of gasoline was released due to an overfill of tank T-137. The fourth spill
<br /> occurred in November of 1999 when an unknown quantity of red dye diesel was released from a tanker overfill
<br /> at the loading racks. The fifth spill occurred on December 28, 2001 when a flange on a piping manifold, near
<br /> MW-15A, failed and released less than 10 gallons of red dye diesel(SECOR, 2002a).
<br /> 2.2 Assessment Activities
<br /> Between December 1983 and July 2005, 72 wells (including 66 monitoring wells and six remediation wells)
<br /> were installed at the site. During this time period, wells T-2, MW-2, MW-8, MW-10, MW-11, MW-14, MW-
<br /> 16, MW-17, MW-20, MW-21, MW-53A MW-57A, MW-58A, and MW-59A were destroyed; and well MW-9
<br /> has not be located since 1997, following demolition and rough grading of the former onsite Keylock facility. As
<br /> of the fourth quarter 2005 (4Q05) Groundwater Monitoring event, 45 existing monitoring wells are used to
<br /> monitor groundwater quality at the site, including 38 wells screening the shallow water-bearing zones (Upper A
<br /> zone and A zone) at depths ranging between 15 to 30 feet bgs. The remaining seven wells (MW-12B, MW-1313,
<br /> MW-2213, MW-2313, MW-5013, MW-64B, and MW-65B) are used to monitor the B zone at depths ranging
<br /> between 55 to 65 feet bgs (SECOR, 2005c). A profile of existing monitoring well screen intervals is included as
<br /> Figure 10.
<br /> The following is a brief chronology of past site assessment activities performed at the facility:
<br /> ' • In December 1983, groundwater monitoring wells MW-1 through MW-7 were installed in the vicinity
<br /> of the ASTs and pump islands (Pacific Environmental Group [PEG], 1995).
<br /> • In November 1984, wells T-1 through T-3 were installed in the area of an underground diesel storage
<br /> tank (PEG, 1995). Monitoring wells T-1 and T-3 were subsequently renamed MW-34UA and MW-
<br /> 35UA, respectively, and T-2 was destroyed.
<br /> • In October 1988, groundwater monitoring wells MW-8 through MW-11 were installed on the periphery
<br /> of the property boundaries(PEG, 1995).
<br /> • During November 1988, shallow exploratory soil borings B-1 through B-9 were advanced along the
<br /> . northern property boundary (PEG, 1995).
<br /> BLASLAND, BOUCK &LEE, INC.
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