..- - .

-. I.. .~ -. .

USE OF THERMAL-DESORPTION/GAS CHROMATOGRAPHY AS A PERFORMANCE-BASED SCREENING METHOD FOR PETROLEUM HYDROCARBONS

-_ - ~ .“a Lon Dawson r - . $ - -a -= Paula J. Slavin KarinCrandall __- I

GRAM, Inc./SNL, Brown and Root Environmental Sandia National Labohtones * Org. 7582, MS-1147 - 2300-Buena-VistaSE -- - . Org. 7582, MS-1147 t9,, 88 J

Albuquerque, New Mexico 87185 Albuquerque, KwWexico 37106 Albuquerque, New Mdico. 871 85 - ~

(505) 284-2496

Richard Kottenstette Q - - n, (505)284-2552 O d d i,

(505) 247-4933

Michael Wade

(505) 845-3270 (505) 284-2579

ABSTRACT

Thermai desorptiordgas chromatography (TD/GC) was used to screen soil samples on site for total petroleum hydrocarbon (TPH) content during a RCRA Facility Investigation (RFI). It proved to be a rapid, cost-effective tool for detecting non-aromatic mineral oil in soil. The on-site TD/GC results correlated well with those generated at an off-site laboratory for samples analyzed in accordance with EPA Method 4 18.1.

I. INTRODUCTION

The Sandia National LaboratoriesMew Mexico (SNL/NM) Environmental Restoration (ER) Project has been characterizing and remediating inactive waste sites as part of the requirements under the Resource Conservation and Recovery Act (RCRA). A RCRA Facility Investigation (RFI) was conducted within two of SNL/NM’s Technical Areas (TA-I11 and -V) at sites that were identified as potential contaminant release sites. One of these, the High Energy Radiation Megavolt Source (HERMES) I1 Site, exhibited mineral oil spills related to underground storage tanks (USTs). A screening tool for detecting mineral oil in soil was developed during the investigation of this site.

11. SITE HISTORY

From 1968 until December 1989, the H E W S I1 Facility (located in Building 6596, Figure 1) was used for radiation-effects testing operations in which mineral oil was used as an electrical insulating medium. The oil was stored in five 35,000-gallon, 1 5 4 diameter USTs and was pumped in a circulating system between the buildings and tanks. Under normal operating conditions, the oil remained in the system and did not come in contact with outside sources of contamination. There are no reported occurrences of off-normal conditions.

Oil spills commonly occurred during high-volume, unregulated pumping of oil from inside the facility to the USTs through 8-in-diameter discharge pipes. This unregulated pumping often resulted in overflow through the tank vents before the load could be distributed evenly throughout the series of tanks. These spills typically were not reported, and their frequency and volume are not known. Approximately one acre of soil was impacted by the mineral oil spills, including the former tanks’ location and the associated runoff area.

Subsequent to removal of the USTs, six boreholes were drilled within, and adjacent to, the backfilled UST excavation in late 1991 to assess the extent of petroleum hydrocarbons in the shallow subsurface soil underlying

DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty. express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or use- fulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any spe- cific commercial product, process, or service by trade name, trademark, manufac-. turer, or otherwise does not necessarily constitute or imply its endorsement, ream- mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

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_, . .

Building 6596

Legend 36.WQl

i E R M E W / 0 1995 RFI Borehole L o d i o n o 1991 Borehole Location

Fiu re 1. Location of 1991 and 1995 Boreholes at HERMES Site, SNL/NM

the former UST site (Figure 1). The first borehole (HERMES-C) was drilled to a depth of 280 ft, which was the lower extent of soil contamination based on field screening with the Hanby Method (a carbon tetrachloride- based Friedel-Crafts alkylation colorimetric method). The borehole was abandoned prior to receipt of off-site laboratory analytical results which indicated TPH concentrations in excess of the state regulatory standard of 100 mgikg at 280 fi. The horizontal extent of the mineral oil was defined in all but the southwest direction by the remaining four boreholes, each drilled to a depth of 280 ft. The southwest borehole exhibited elevated TPH at depths from 30 to 230 ft. As a result of this experience, and that of other investigations, the Hanby Method was demonstrated to be an inadequate field-screening method for non-aromatic mineral oil because it consistently underestimated the concentrations of contamination by two or more orders of magnitude.

Based on the results.of the initial investigation, the site required further characterization to determine the horizontal extent of mineral oil to the southwest as well as the vertical extent of oil beneath borehole H E W S - C . Therefore, drilling was conducted at the site during the

----I_*L .--l-_l___f_^__

RFI. ----. ---__ ~ - - - . - .

111. RFI FIELD ACTIVITIES

Two deep boreholes were drilled in February-March 1995 in the vicinity of the former HERMES tanks to define the vertical and horizontal extent of oil in soil identified during the 1991 invesrigation (Figure 1). One borehole was drilled adjacent to the HERMES-C borehole to a total depth of 340 ft to define the verticai extenr: of TPH contamination. The second borehole was drilled southwest of Building 6596 to a total depth of 320 ft to define the horizontal extent of HERMES oil. Soil samples were collected at 10- to 2 0 4 intervals to more closely define the vertical extent of contamination beneath the site. Soil samples were split for on-site field screening using TDIGC and for off-site TPH analysis by EPAMethod418.1.

IV. MINERAL OIL DETECTION .

I

.--

The transformer oil used at the HERMES I1 facility is primarily a mixture of aliphatic and alicyclic hydrocarbons, and contains no EPA-regulated h k d o u s constituents as manufactured (e.g., polychlorinated

-biphenyls -[PCBs] -- or --volatile - organic -compounds _ - - - - . f - - _ I _ - . ~ . ~ __ . . . _. .-.

SLAV /d 2

--- -.- .- ._._. - .--- -_ -... ~

[VOCS] j. ---Indeid,%iii ~~pE5ia6le-&iount 5 f VOCS-iii‘ .-l the mineral oil would have significantly altered the insulating properties of the oil. The boiling point for the mineral oil ranges from about 120°C to 365OC; its relatively low volatility makes it undetectable by real- time field monitoring instruments such as photoioniz2tion and flame ionization detectors (PIDs and FIDs) -which rely on volatilization of contaminants at ambient conditions.

HERIVES oil (25 to. 500 m m g bn a soil basis) in‘toluene. The calibration curve was linear with a correlation coefficient of r’= 0.998 (Figure 2). TPH in soil was quantified by “pattern recognition” using the total area under the distinctive mineral oil chromatogram. An internal standard (dodecane) was added to determine sample matrix interference and injection efficacy. Quality assurance samples included replicate analyses for every 10 samples and a mid-range calibration check standard prior to daily sample analyses, after every 20

--samples, or at the end of a 12-hour sample analysis penod. The continuing calibration verification (CCV) traditionally used for this analysis, was avfiilable-off-site-- .--. - - -

-xas-within.20% for the runs. Blank samples were run but was not developed on site because of EPAXncerns -periodically to ensure a contaminant-free TD/GC system. about using Freonm-l 13 with this method, SNLMM ER

EPA Method 418.1, which is an infrared-procedure---. - -

personnel conducted an investigation of available technologies to locate an alternative heavy-end TPH field-screening technique that was more reliable than the Hanby Nethod, --W.eit-eld- .

screening using immunoassay kits (EPA Draft Method 4030) was effective because neither is sensitive to the non-aromatic H E M S oil. Because these screening methods proved ineffective, a technique was developed that employs direct thermal desorption of the oil onto a gas chromatograph column. This technique proved to be a rapid way to quantify mineral oil in soil.

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TD/GC has been used recently to characterize fuel- contaminated soils (i.e., those containing volatile and/or semivolatile constituents) as well as soils containing PCBs.’ The technique utilizes the direct injection of organic contaminants from soil onto a GC column, avoiding the use of costly and environmentally harmful solvents.

TD/GC analyses were performed using an SRI Model 861G gas chromarograph equipped with a thermal desorption oven and manual sampling valve (VICWalco 10-port). The system was equipped with a FID, which was used for the detection and quantitation of the HERMES mineral oil after it had passed through the TD/GC sequence. In accordance with the GC manufacturer’s suggestion, an aliquot of soil (approximately 0.5 g) was placed in the desorption chamber for one minute at 325°C to vaporize organic constituents. (A temperature of 325°C was chosen because it was above the boiling point, and was high enough to volatilize the organic constituents, yet not so high as to lead fo sample degradation.) The vapors were then swept onto the GC column for separation. A relatively non-polar megabore capillary column (J&W Scientific, DB-5, 8 m x 0.53 mm) was used for constituent separation. A five-point calibration curve was

The method detection limit (MDL) achieved for the H E W S oil was 10 m a g . The low MDL was a result of direct sample analysis without potential dilution problems associated -with sample -preparation. -Method accuracy was also enhanced by-analysis of-the soil sample within hours of field collection, which minimized storage loss and cross-contamination. The normal run time for a TD/GC analysis of TPH was 20 minutes.

V. RESULTS

Results of the soil sampling conducted in the vicinity of the HERMES site are summarized in Table 1 and are provided graphically in Figures 3 and 4. The table includes only those samples split for both TD/GC and EPA 418.1 analyses; the figures present all data, including samples analyzed only by TD/GC and those analyzed only by EPA Method 418.1. For graphing purposes, the non-detects and estimated (“J”) values were set equal to their respective MDLs. For TD/GC, the MDL is 10 me/kg; the MDL is 20 mEAg for the EPA 418.1 analysis. Figure 3 illustrates the distribution of data for samples from Borehole 36-BH-01 (where higher TPH concentrations existed); Figure 4 presents the data for samples from Borehole 36-BH-02 (where low to non- detect TPH concentrations were noted). Precision data for the TD/GC method generated an average relative percent difference (RPD) of 12%; the RPD for EPA Method418.1 was 14%.

A comparison of the results generated by S N L M M ’ s on-site laboratory with the results from two separate off- site laboratories revealed good agreement between the TD/GC technique and EPA Method 418.1. A general correlation within similar soil types is seen for the high concentrations of TPH (Figure 3). All are .within the same order of magnitude, and many results are within 2,000 mgkg of each other. The aliquot size was reduced

3

2000

m m 0

4 1600 -2

9 n

0

;no0

5 800 0 0 u) G

400 ln

d

Borehole Sample Depth (fi)

Borehole 80 36-BH-0 1 280

300

0

TPH by TPH by Thermal Desorption EPA Method 41 8.1

(m@,o) (m@,o) 17,600 22,000

38 NDGO 40 33

0 50 100 150 200 250 300 350 400 450 500

Concentration of Mineral Oil (mgikg)

36-BH-02

Figure 2. Thermal DesorptionlGas Chromatography Calibration Curve for Mineral Oil

80 13 NDGO 90 45 NDGO 100 21 21 120 35 NDGO

Table 1 Comparison of TD/GC and EPA Method 418.1

120 (Dup) 200

200 (DUD)

31 NDGO 18 NDGO 15 NDGO

nd40 NDGO

340 22 27

260 280 300

Borehole I 70 I

13 NDGO 10 . NDGO

N D 4 0 NDGO

15 1 NDGO

320 35 NDGO

1240-- 23 1 NDGO

Dup - Duplicate sample.

30,000

25,000 n EIl

3 3 E 20,000 v E 0 .- c 2 15,000 E 0 0 E 6 10,000

5,000 E

0

100

I

0 ! x TPH oTPH 1 -- I by TD/GC by 418.11

1 xTPH oTPH I by TD/GC by 418.1

TD/GC MDL = 10 mgkg 418.1 MDL=20mgkg

TD/GC Error = +I- 12% 418.1 Error=+/- 14%

v

0 50 100 150 200 250 300 350 Sample Depth (ft)

Figure 3. Comparison of TPH Concentrations by TD/GC and EPA 418.1 for Borehole 36-BH-01

got , O t

TDIGC MDL = 10 m-ag 418.1 MDL = 20 m-ag

TDIGC Error = -J- 11% 418.1 Error=+/- 14%

X

X

0 50 100 150 200 250 300 350 Sample Depth (ft)

Figure 4. Comparison of TPH Concentrations by TD/GC and EPA 418.1 for Borehole 36-BH-02

maintain the GC response within the linear range of the calibration.

The correlation is extremely good for the !ramples with low TPH concentrations (Figure 4). Most of the non- detect values match up very well. In many cases, the TD/GC was biased toward the high end -.. it revealed slight TPH concentrations where EPA Method 418.1 indicated a non-detect. Thus, the problem inherent in the Hanby Method (Le,, underestimating actual contamination at low concentrations) was solved with the TD/GC method.

VI. SUMMARY AND CONCLUSIONS

TD/GC can be used on a wide variety of cantaminants. Typical applications include fuel-contaminated (&.soline, naphtha and diesels) and PCB-contamiinated soils. TD/GC has particular advantages for non-aromatic oils like the HERMES mineral oil because theset oils do not elicit an accurate response froin current imnxnoassay or Hanby-based field tests for TPH.

For applications in the SNL/NM ER Pmject, where ready access to on-site infrared analysis by €?PA Method 418.1 is limited, the TDIGC technique app1:ars to be a low-cost and viable option for quick, on-i;ite analysis during soil sampling activities, particularly those associated with drilling. The procedure retiuces costly dri lhg down-time (as much as two to three days) typically required when waiting for off-sit: laboratory anaIyses to determine whether the extent of contamination has been adequately defined. The added costs associated with sample management activities, sample shipment to an off-site laboratory, and the customary 100% surcharge levied for 24-hour turnaround

analyses are eIiminated. Approximately 10-20 samples per day can be run on a technician-supervised system for a cost of about 15% of that currently charged by some off-site laboratories; fidly automated systems could increase this production rate, allowing unattended analysis, and perhaps hrther reducing the cost per sample. TD/GC also has the potential for reducing the use of solvents (Le., FreonTM) typically associated with the traditional EPA Method 418.1 TPH analysis. In addition to the elevated cost of FreonTh’ and other chlorinated solvents, their use in laboratory methods is being discouraged by the EPA because of environmental concern.

TD/GC proved to be an extremely useful screening technique for detecting the non-hazardous mineral oil found in soil at the HERMES site. The method detected TPH at concentrations as low as 10 mg/kg, one-tenth of the New Mexico State action level of 100 mg/kg, and half the minimum concentration of 20 mgkg detected by EPA Method 418.1. Thus, the method is capable of detecting TPH at concentrations well below those needed for site characterization purposes.

REERENCES

1. Goldsmith, H., 1994. Thermal Soil Desorption for Total Petroleum Hydrocarbon Testing on Gas Chromatographs, American Association for Health of Soils, Long Beach, CA.

ACKNOWLEDGMENTS

This work was supported by the United States Department of Energy under contract DE-ACO4- 94AL85000.