HomeMy WebLinkAbout[Untitled]_2017012011174374_4-6Former Garriot Crop Dusting - 2 - 10 February 2016
Bakersfield, Kern County
Closure Summary'
The BFD issued an Unauthorized Release (Leak) Report, on 25 May 2001, and requested an
investigation to determine the extent of the release in soil and the potential for groundwater
impact. The case was referred to the Central Valley Regional Water Quality Control Board
(Central Valley Water Board) UST Unit by letter dated 22 August 2002.
The Central Valley Water Board Cleanup Unit staff has oversight of a separate onsite release of
pesticides, at the address 2010 South Union Avenue, case number SLT5FQ013.
Soil Investigation
Six soil borings were advanced to between 50 - 70 feet bgs during June 2014, to define the
vertical and lateral extent of gasoline constituents. Forty samples were selected for laboratory
analysis for TPHg and TPHav by EPA Method 8015M; and benzene, toluene, ethylbenzene and
xylenes (BTEX), MTBE and naphthalene by EPA Method 8260B. Samples from 2.5, 5.0, and
7.5 feet bgs or 2.5 and 7.5 feet bgs were analyzed to determine whether or not the State Water
Resources Control Board Low - Threat Underground Storage Tank Case Closure Policy (Policy)
Direct Contact and Outdoor Air Exposure Criteria were satisfied.
TPHg was detected beneath the former dispenser island from 87 - 1,600 milligrams per
kilogram (mg /kg) in samples from 7.5, 40 and 50 feet bgs, and at less than 1 mg /kg in the other
samples. TPHav was detected up to190 mg /kg to 50 feet bgs. TPHg was detected up to
8,100 mg /kg in samples from two borings beneath the northern ends of the former USTs, and
concentrations below 50 feet bgs were usually less than one mg /kg or not detected. Low
concentrations of TPHav were also reported. Benzene was usually less than 1 mg /kg or
between minimum detection and reporting limits, but was greater than 1 mg /kg in four samples,
all below 15 feet bgs. MTBE was not detected, and naphthalene was reported up to 140 mg /kg
in some of the samples. Naphthalene was detected to a maximum of 27 mg /kg in samples
collected from 10 feet bgs or shallower. Gasoline constituents were not detected or detected at
less than 1 mg /kg with a few exceptions, in samples from the outer borings, drilled to delineate
lateral extent of the release.
The consultant concluded that hydrocarbons extended vertically in soil to less than 65 feet bgs,
and laterally less than 30 feet from the former USTs and dispenser island. As much as
24,000 pounds of hydrocarbons may remain. The UST release did not migrate to groundwater,
which is greater than 200 feet bgs. The extent of soil affected by the release was adequately
defined, and benzene, ethylbenzene and naphthalene concentrations detected in shallow soil to
10 feet bgs did not exceed screening level criteria contained in the Policy for Direct Contact and
Outdoor Air Exposure.
Soil Remediation
Excavation and disposal, soil vapor extraction (SVE) and bioremediation by natural attenuation
were evaluated as alternatives to. reduce the hydrocarbon source mass in soil in a September
2014 Corrective Action Plan. Excavation was not feasible due to the proximity of onsite
buildings, and the depth of contamination. The cost of soil vapor extraction (SVE) was relatively
high compared to the benefits derived. Bioremediation by natural attenuation was
recommended as a feasible, low cost remedial alternative, since free phase petroleum product
was absent, and site use was not expected to change during the long time period required,
provided that the Policy criteria to evaluate health risk from Petroleum Vapor Intrusion to Indoor
Air were satisfied, since occupied buildings are within 30 feet of contaminated soil. Previous
investigation had confirmed that health risk from Direct Contact and Outdoor Air Exposure were
satisfied.