|
' Thrifty Oil Co
<br /> Station # 172
<br /> 2.2 Previous Site Assessments/Remedial Action
<br />' From May 23 thru June 6, 1991, SSB Environmental Consultants, Inc installed four groundwater
<br /> monitoring wells (MW-1, MW-2, MW-3, and MW4) (Figure 2) Two monitoring wells located
<br /> adjacent to the UST's and two monitoring wells near the pump island. The monitoring wells were
<br />' installed to a depth of 76 to 80 feet, and groundwater was encountered at 58 feet below surface
<br /> grade Laboratory analysis of soil samples collected from the bonng/well B-2/MW-2 at a depth of
<br /> 20 feet indicated the highest reading of TPH and benzene of 380 mg/kg and 33 mg/kg, respectively
<br />' Laboratory analysis of groundwater samples collected ranged from 36 4 ug/L to 5,270 ug/L benzene
<br /> in wells MW4 and MW-2 (SSB, 199 1)
<br /> On April 22, 1994, Thrifty Oil Co installed three vapor wells (VWA, VWB, and VWC) to depths
<br /> of 35 feet, 48 feet, and 45 feet below surface grade Thrifty also installed two groundwater
<br />' monitoring wells MW-7 and MW-8 to 56 feet and 58 feet,respectively (Figure 2), and groundwater
<br /> was encountered at about 50 feet below surface grade Laboratory analysis of soil samples detected
<br /> TPH concentrations from ND to 21,000 mg/kg, and detected benzene concentrations from ND to 36
<br /> mg/kg Laboratory analysis of groundwater samples detected 5,500 ug/L TPH and 830 ug/L benzene
<br />' in MW-7,and 130,000 ug/L TPH and 7,200 ug/L benzene in MW-8 (Thrifty Site Assessment, 1994)
<br /> On July 11, 1995,three vadose wells (VWA, VWB, and VWC) and three groundwater monitoring
<br /> wells (MW-1, MW-2, and MW-8) were properly abandoned prior to station remodeling activities
<br /> (Thrifty, 1995)
<br /> On July 25, 1995, five single-walled, steel underground storage tanks were removed from the site
<br /> and disposed of by Erickson Richmond of California. Approximately 1500 cubic yards of soil was
<br /> removed from the UST excavation and transported to Forward Incorporated, of Stockton, California
<br /> for disposal Nine soil samples were collected beneath the five UST's after excavation and seven
<br />' soil samples were collected at a depth of 2 to 4 feet beneath the product lines TPH and benzene was
<br /> detected in soil samples collected from beneath the UST's at concentrations ranging up to 12,000
<br /> mg/kg TPH and 33 mg/kg benzene, respectively (Alisto, 1995)
<br />' On May 28 thru 30, 1996 wells VW-2, VW-4, VW-5, VW-6, MW-10NW-1 and MW-1 I/VW-3
<br /> were installed onsite to depths ranging from 16 5 to 58 5 feet bgs (Figure 3), (monitoring wells
<br />' MW-10/VW-1, and MW-11/VW-3 were installed as nested wells) Monitoring well permits were
<br /> obtained from the SJCEHD prior to the installation of the groundwater and vadose zone monitoring
<br /> wells Well VW-2 was completed as a dual-completion vadose zone monitoring well Wells VW-4,
<br />' VW-5, and VW-6 were completed as tnple-completion vadose zone monitoring wells Wells MW-
<br /> 10/VW-i and MW-11/VW-3 were completed as dual-completion groundwater/vadose zone
<br /> monitoring wells (Thrifty, Additional Site Assessment Report, 1997)
<br /> 5
<br />
|