HomeMy WebLinkAbout[Untitled]_4-6Former Phoenix & Son Garage & Storage - 2 20 September 2016
Bakersfield, Kern County
Closure Summary
(MTBE) was detected at concentrations less than 1 mg /kg in some samples.
Following resolution of issues related to the responsible party, during 2014 the Central Valley
Water. Board staff requested additional investigation. Two deep soil borings were advanced to
75 - 80 feet bgs to verify the vertical extent of petroleum. hydrocarbons in the former USTs and
dispenser areas. The borings were adjacent to borings advanced during the previous
investigation.. Soil samples were collected at five foot intervals, beginning five feet below the
maximum depths of the previous borings. Another deep boring was advanced to 60 feet bgs
within the shop building, to determine the western extent of hydrocarbons in the dispenser area.
The vertical extent of petroleum hydrocarbons in soil beneath the former USTs and diesel
dispenser area was confirmed to be less than 60 feet bgs and 75 feet bgs, respectively, by the
absence or low, concentrations of TPHg and TPHd in at least two consecutive samples from the
bottoms of the borings. TPHd was detected at 6 milligrams per kilogram (mg /kg) in one sample
and naphthalene was. detected at 5.1 mg /kg in one sample from the deep borings. The western
extent of hydrocarbons beneath the shop building was defined.
During 2014, soil samples were ,also collected at 2.5, 5.0, 7.5 and 10.0 feet bgs in four shallow
borings and one of the deep borings. The borings were advanced in the former fuel dispenser
and product piping area areas,. and adjacent to the former USTs, to determine whether or not the
State :Water Board's Low - Threat Underground Storage Tank Case Closure Policy (Po,licy)
screening level criteria for Direct Contact and Outdoor Air Exposure were met. Ethylbenzene
was detected up to 7,24 mg /kg`in the shallow soil samples and naphthalene was detected up to
18.8 mg /kg. Benzene was 'detected at concentrations up to 3.08 mg /kg, Analytes were not
detected in two of.the borings. The 'Policy's Commercial /Industrial screening level criteria for
Direct Contact and Outdoor Air .Exposure were not exceeded.
The consultant estimated that as much as 290,000 pounds (lbs.) of hydrocarbons remained in
soil in the 1ormer UST area, and as much as 79,000 lbs. remained in soil beneath the former fuel
dispenser area. Most of the estimates were of diesel range hydrocarbons, based on TPHd
concentrations detected in soil samples collected during multiple phases of site investigation.
Soil Vapor Investigation
Soil -gas sampling was. conducted during 2015. One temporary sampling well was installed west
of the former dispensers, adjacent to the eastern wall of the. shop building, and a second was
installed east of the`dispensers; adjacent to the west wall of the office building. Each well, was
constructed with a porous, sampling tip set at five feet bgs. Benzene was detected up to 70,000
micrograms per cubic meter (pg /m), ethlylbenzene was detected up to 6,100 pg /m3, and
naphthalene was not detected at .a Reporting Limit of 400 pg /m3 in the sample and duplicate
collected from S.G -1. Benzene; ethylbenzene and naphthalene were not detected at Reporting
Limits of 100 Ng /m3 (benzene and naphthalene), and 400 pg /m3 (ethylbenzene) in SG-2. The
Policy's Commercial /Industrial screening level criteria for Vapor Intrusion to Indoor Air (Vapor..
Intrusion), without a bioattenuation zone, were exceeded.
Permanent soil -gas sampling wells installed near the eastern wall of the shop building and within
the shop building, were initially sampled during 2015. Benzene, ethylbenzene and naphthalene
were not detected in the soil -gas samples at reporting limits of 80, 400 and 80 micrograms per
cubic meter pg /m3 respectively. Oxygen was detected from 3.7 —.9.4 percent.
Additional shallow soil samples were collected at 2.5 and. 5.0 feet bgs during the permanent soil -
gas well installations. TPHg was detected at 5:5 milligrams per kilogram (mg /kg) in one sample
at 2.5 feet below bgs. TPHd was detected in the same sample at 7,030. mg /kg and at 35.1 mg /kg
at 5 feet bgs. Benzene, ethylbenzene and naphthalene were detected at 2.5 feet bgs at 6.34,
2.28, and 46 mg /kg, respectively. Naphthalene was also detected in a sample from 5.0 feet bgs
at 13.1 mg /kg. The consultant concluded that a petroleum vapor bioattenuation zone, as defined