A field blank, laboratory blank, and spiked
a strip chart recorder. Concentrations were estab-
duplicate sample or calibration check standard
lished by comparison of sample peak heights to
aqueous standard peak heights. Combined stan-
were analyzed with every group of six VOC or
dards (TCE and PCE) were prepared using chro-
TPH samples. All field and laboratory blanks were
matography grade reagents and serial dilution
below the PQL. Calibration check standard con-
centrations remained within two times the
techniques.
TPH samples were collected in the 2-L Pyrex
standard deviation of the calibration standard
separatory funnels used for analysis, acidified with
ranges, i.e., within accepted analytical standards
HCl to pH 2 within 30 minutes and analyzed
(APHA 1992). Duplicate VOC samples were col-
within 4 hours of collection. TPH concentration
lected during trials 5 and 9 for the purpose of
was determined by fluorocarbon-113 solvent ex-
spiking them with aliquots of standards. During
traction followed by infrared spectrophotometer
TPH sampling and analysis, known additional
analysis (EPA Method 418.1, U.S. EPA 1978). In-
samples were created during trials 5, 6 and 9 by
frared analysis was performed with a Foxboro
adding a known mass of diesel fuel to 1 L of
Company (East Bridgewater, Mass.) MIRAN-1FF
ultrafiltered water. The percentage of spiked stan-
dard or known addition recovered indicated the
infrared spectrophotometer absorbance measure-
ments were at a fixed wavelength of 3.48 m.
relative analytical precision and verified the ab-
sence of matrix effects. All percentage recoveries
TPH concentrations were established by com-
were within the 70120% acceptance limits estab-
paring sample absorbances to standard absor-
lished by APHA (1992).
bances. Diesel fuel was used as the TPH standard
since GC/MS analysis indicated the majority of
hydrocarbons to be in this range. A stock stan-
Analysis of hydrocarbons
dard was prepared by pipetting a known mass of
in air stripper off-gas
diesel fuel into a known volume of spectral-grade
Real-time measurements of total hydrocarbons
fluorocarbon-113. Working standards were pre-
in the air stripper off-gas were made during trials
pared by serial dilution of the stock standard with
36. Analysis was made with a model 51 Total
spectral-grade fluorocarbon-113. The 1-L samples
Hydrocarbon Analyzer (Thermo Environmental
were extracted with 100 mL of solvent, resulting
Instruments, Inc., Franklin, Massachusetts) fitted
in a sample concentration factor of 10. TPH con-
with a heated flame-ionization detector (FID). A
centrations were calculated with this formula:
brass sampling tube was fitted into the off-gas
stack, and a heated sample line conducted flow
RD
TPH (ppm) =
from the sampling tube to the analyzer. The
(1)
V
sample line and analyzer were heated to ≥200C
(≥392F) to prevent condensation of the 100% hu-
where R = concentration of TPH as determined
midity off-gas. The detector signal was recorded
from calibration curve
on a strip chart. The analyzer was calibrated ac-
D = extract dilution factor (0.1)
cording to the manufacturer's specifications us-
V = volume of sample.
ing a 100-ppm TCE calibration gas standard. To-
Method detection limit and accuracy were greatly
tal off-gas hydrocarbons were therefore measured
"as TCE" because TCE made up ≥ 75% of the liq-
enhanced by preparing sample extracts that were
10 times the actual sample concentration, and by
uid hydrocarbons entering the stripper. The model
collecting samples directly into the separatory fun-
51 detects concentrations on a volume per vol-
nels used for extraction.
ume basis; therefore the data were converted to
mass per volume as follows:
Analytical precision and accuracy
A
Method detection limits (MDLs) were deter-
g L
Hydrocarbons 3 = 3 TCE
m m
mined according to APHA (1992). Practical
quantitation limits (PQLs) were also used so that
results could be directly compared to results pro-
1 mole TCEB
duced by different laboratories. PQLs were calcu-
24.5 L
lated as five times the respective MDLs and rep-
resent practical and routinely achievable detection
131g TCEC
limits with a relatively good certainty that any
(2)
1 mole TCE
reported value is reliable (APHA 1992).
6
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