EPA 510-R-92-802
                        DRAFT FINAL REPORT

                    BACKGROUND HYDROCARBON
                   VAPOR CONCENTRATION STUDY
             FOR UNDERGROUND FUEL STORAGE TANKS

                  U.S. EPA CONTRACT NO. 68-03-3409
                           February 29, 1988
                             Prepared for:

                     MR. PHILIP B. DURGIN, PhD

              U.S. ENVIRONMENTAL PROTECTION AGENCY
               Environmental Monitoring Systems Laboratory
                           Las Vegas, Nevada

                             Prepared by:

                  GEOSCIENCE CONSULTANTS, LTD.

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                                                             Printed on Recycled Paper

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          DRAFT FINAL REPORT

      BACKGROUND HYDROCARBON
      VAPOR CONCENTRATION STUDY
FOR UNDERGROUND FUEL STORAGE TANKS

     U.S. EPA CONTRACT NO. 68-03-3409
              February 29. 1988




               Prepared for:

        MR. PHILIP B. DURGIN, PhD

 U.S. ENVIRONMENTAL PROTECTION AGENCY
  Environmental Monitoring Systems Laboratory
             Las Vegas. Nevada

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                  . .  --   DRAFT FINAL REPORT

                    BACKGROUND HYDROCARBON
                   VAPOR CONCENTRATION STUDY
              FOR UNDERGROUND FUEL STORAGE TANKS

                  U.S. EPA CONTRACT NO. 68-03-3409
SUBMITTED
GCU Program Kftna
GCL Project Director  d
                                   DATE:

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                                 TABLE OF CONTENTS

         •                             :                   se
 1.0  EXECUTIVE SUMMARY ..........                              ,
                                            •••••ป••.	     i

?2.0  PURPOSE OF:STUDY  ......                 '                  -  r
                 ••-	ซซซซซ••.......     o

C3.JO  SITE SELECTION  ...  .  .  ...  .                               '   ,
     "3.1  LOCATIONS	            '  '  '	     4
      3.2  SERVICE STATIONS  .	'.'.'.'.'.'.'.'.'.'.I'.'.'.'.     8

-4iO  GEOLOGY, HYDROLOGY AND CLIMATE  .....                           q
     r4.a  AUSTIN, TEXAS	.!!.'.*.'!"'*'     q
          -•4.1.1   Geology and  Hydrology	]	     q
          4.1.2   Climate 	 .....            .......     y
      4.2  LONG ISLAND SOUND AREA,  NEW YORK, RHODE*ISLAND  "	
           AND CONNECTICUT  .... 	  .....              IQ
           i'H   5eoJฐgy and  Hydrology - Long  Island, *New*York  !  !  !    10
           4.2.2   Geology and  Hydrology - Providence,  Rhode  Island   .    11
           4.2.3   Geology and  Hydrology - Storrs,  Connecticut  ....    11
           4.2.4   Climate	                            n
      4.3  SAN DIEGO REGION, CALIFORNIA ....!!!!!!!''*'    12
           4.3.1   Geology and  Hydrology ......          .....
           4.3.2   Climate ........ ....!!!  i!!!  i  i  ]    {3

5.0  FIELD METHODS	                                    1A
      5.1  SAMPLING  STRATEGY	'.'.'.	*  *  '  '    };
      5.2  SAMPLING  METHODS		    iซi
      5.3  ANALYTICAL PROCEDURES	-1  !!!!!!'!!!!!    16

6.0  QUALITY  ASSURANCE AND QUALITY CONTROL ...                        17
      6.1   QA  OBJECTIVES  FOR MEASUREMENT DATA (QAPP SECTION 3.1)" .'  '    17
           6.1.1   Gas  Chromatograph Analyses  	          17
           6.1.2   Soil Moisture Content Analyses   ....      '          19
      6.2   SAMPLING  PROCEDURES (QAPP SECTION 3.2)  ....      *  ' '  '    19
      6.3   SAMPLE  CUSTODY  (QAPP SECTION 3.3)  .....     	   21
      6.4   CALIBRATION PROCEDURES AND FREQUENCY           	
           (QAPP SECTION 3.4)	                         ?1
      6.5  ANALYTICAL  PROCEDURES (QAPP SECTION 3.5) . .*	   22
      6.6  DATA REDUCTION, VALIDATION AND REPORTING       	
           (QAPP SECTION 3.6)  .	                         22
      6.7   INTERNAL QUALITY CONTROL CHECKS (QAPP SECTION'3!7)  '  ' *  '   23
      6.8  PERFORMANCE AND SYSTEM AUDITS (QAPP SECTION 3.8              23
      6.9  PREVENTIVE MAINTENANCE (QAPP SECTION 3.9)  .     	   23
     6.10 ASSESSMENT OF DATA PRECISION, ACCURACY AND       	
          COMPLETENESS (QAPP SECTION 3.10)  ........             24
„    6.11 CORRECTIVE ACTIONS (QAPP SECTION 3.11) ....      "  ' '  '   ?5
     6.12 QUALITY ASSURANCE REPORTS TO MANAGEMENT          	
          (QAPP SECTION 3.12)   .  	                   25

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7.0  REPORTING METHODS	   26
     7.1  DETERMINATION OF TOTAL HYDROCARBON CONCENTRATIONS
          IN MICROGRAHS PER LITER  .	•   26
          7.1.1  Gas.Chromatograph and Flame lonization Detector
                 'Operation	't	   27
          7.1.2  Calculation of Total Hydrocarbons as Benzene  ...   28
          "7.1.1:. Calculation of Total Hydrocarbon Concentrations
                 Using Average Response Factors  ...........   29
     7.2  DETERMINATION OF TOTAL HYDROCARBON CONCENTRATIONS IN
      -   PARTS PER MILLION  	 ........   32

8.0  RESULTS .	   36
     8.1  SOIL GAS DATA	   36
    .8.2  CONTAMINATED SITE DATA	   36
     8.3  EXPANDED AUSTIN STUDY	   40
     8.4  CHARACTERIZATION OF BACKFILL MATERIAL	   46
     8.4  U-TUBE SAMPLING  	 	 .....   46
     8.6  GROUND WATER SAMPLING	   51

9.0  UST REGULATIONS..	   53
     9.1  AUSTIN, TEXAS	   53
     9.2  SUFFOLK COUNTY, NEW YORK	   53
     9.3  SAN DIEGO, CALIFORNIA	   54

10.0  TANK TIGHTNESS TESTING RECORDS	   56

11.0 DATA ANALYSIS	   61
     11.1 EMPIRICAL DISTRIBUTION OF TOTAL HYDROCARBON
          CONCENTRATIONS (LESS METHANE) FOR NON-CONTAMINATED
          SITES	   63
     11.2 EMPIRICAL DISTRIBUTION OF TOTAL HYDROCARBON
          CONCENTRATIONS (INCLUDING METHANE) OF NON-
          CONTAMINATED SITES . .	   68
     11.3 COMPARISON OF TOTAL HYDROCARBON CONCENTRATIONS FOR NON-
          CONTAMINATED SITE AND CONTAMINATED SITE DATA SETS  ....   71
     11.4 NON-PARAMETRIC STATISTICAL TESTING 	   78
          11.4.1  The Risks Associated with Hypothesis Testing ...   79
          11.4.2  Comparison of Non-Contaminated Site and
                  Contaminated Site Data Distributions 	   81
          11.4.3  Non-Parametric Testing for Data Patterns Within
                  the Non-Contaminated Data  	   82
               11.4.3.1  Location  . . ........... . ...   83
               H.4.3.2  Sample Depth	   84
               11.4.3.3  Conclusions from Non-Parametric Tests
                         Within the Non-Contaminated Data  	   91
     11.5 RESULTS AND CONCLUSIONS OF DATA ANALYSIS .... 	   92

12.0  CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER STUDY  ......   96
     12.1  CONCLUSIONS . . .	   96
     12.2  RECOMMENDATIONS FOR FURTHER STUDY 	   96

13.0  REFERENCES CITED ....... 	 ....   98

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                               LIST OF TABLES
 TABLE 6-1   RESULTS OF REPLICATE ANALYSES FOR SOIL MOISTURE
             CONTENT	- j .                 20
 TABLE 7-1   MAJOR COMPONENTS OF API PS-6 GASOLINE  .     •••••••   ">
 TABLE 8-1   MAXIMUM CONCENTRATIONS AT AUSTIN, TEXAS  .!'*'**'   37
 TABLE 8-2   MAXIMUM CONCENTRATIONS LONG ISLAND SOUND COASTAL AREA* '   38
 TABLE 8-3   MAXIMUM CONCENTRATIONS AT SAN DIEGO, CALIFORNIA  . .       39
 TABLE 8-4   DESCRIPTION OF CONTAMINATED SITES  ......         '   4?
 TABLE 8-5   MAXIMUM. CONCENTRATION DATA AT CONTAMINATED         ' ' '
             SITES	                   42
 TABLE 8-6   MOISTURE RANGES OF SOIL AND BACKFILL SAMPLES .""!!'*'   47
 TABLE 8-7   U-TUBE VAPOR SAMPLES                                  . '
             SUFFOLK COUNTY, NEW YORK .......;.;.             50
 TABLE 8-8   HYDROCARBON CONCENTRATIONS FROM GROUNDWATER            '
             SAMPLES	                     52
 TABLE 10-1  TANK TIGHTNESS TEST RESULTS		   57
 TABLE 11-1  DISTRIBUTION OF NON-CONTAMINATED SITE DATA   	
             FOR TOTAL HYDROCARBONS (LESS METHANE)  ........     65
 TABLE 11-2  DISTRIBUTION OF NON-CONTAMINATED SITE DATA
             FOR TOTAL HYDROCARBONS (LESS METHANE)
             (PARTS PER MILLION BY VOLUME)  .........            66
 TABLE 11-3  TOTAL HYDROCARBON CONCENTRATIONS LESS METHANE   •   "  ' '
             GREATER THAN 100,000 MICROGRAMS PER LITER  	     67
 TABLE 11-4  COMPARISON OF TOTAL HYDROCARBONS INCLUDING METHANE
             AND LESS METHANE AT NON-CONTAMINATED SITES
             (MICROGRAMS PER LITER) 	                69
 TABLE 11-5  COMPARISON OF TOTAL HYDROCARBONS INCLUDING METHANE "
             AND LESS METHANE AT NON-CONTAMINATED SITES
             (PARTS PER MILLION BY VOLUME)	                70
 TABLE 11-6  DISTRIBUTION OF CONTAMINATED SITE DATA FOR     	
             TOTAL HYDROCARBONS LESS METHANE	                  73
 TABLE 11-7  COMPARISON OF NON-CONTAMINATED AND CONTAMINATED	
             SITE DATA DISTRIBUTIONS FOR HYDROCARBONS
             LESS METHANE 	                74
 TABLE 11-8  RESULTS OF KRUSKAL-WALLIS TESTS FOR LOCATIONS WITH '  '  '
             STEEL TANK SYSTEMS USING NON-CONTAMINATED
             DATA	              85
 TABLE 11-9  RESULTS OF KRUKSAL-WALLIS TESTS FOR LOCATIONS WITH '  '  "
             WITH FIBERGLASS TANK SYSTEMS USING NON-CONTAMINATED
             DATA ...........  	      86
 TABLE 11-10 RESULTS OF PAGE L FOR DIFFERENCES IN DATA
             ACCORDING TO SAMPLE DEPTH  	                89
 TABLE 11-11 RESULTS OF WILCOXON TESTS FOR DIFFERENCES IN    	
             DATA ACCORDING TO SAMPLE DEPTH 	          90
 TABLE 11-12 DESCRIPTIVE STATISTICS FOR TOTAL HYDROCARBON  LESS
             METHANE CONCENTRATIONS IN STEEL TANK SYSTEMS  AT
             DIFFERENT LOCATIONS AND SAMPLE DEPTHS (MICROGRAMS
             PER LITER) .	                93
TABLE 11-13 DESCRIPTIVE STATISTICS FOR TOTAL HYDROCARBON  LESS*  *  '  '
             METHANE CONCENTRATIONS IN FIBERGLASS TANK SYSTEMS
             AT DIFFERENT DEPTHS (MICROGRAMS PER LITER)  	      94

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                             LIST OF FIGURES
FIGURE 2-1
FIGURE 7-1

FIGURE 8-1 -

FIGURE 8-2
FIGURE 8-3
FIGURE 11-1
FIGURE 11-2
             TYPICAL UST ARRANGEMENT ........;	     6
             RATIO OF BTEX TO TOTAL HYDROCARBON CONCENTRATIONS
             VERSOS CUMULATIVE NUMBER OF SAMPLES 	   31
            .AUSTIN #6 (FRESH SPILL) MEDIAN TOTAL HYDRO-
             CARBON DATA .......	   43
             AUStlN #6 (FRESH SPILL) MEDIAN C4 - C6 DATA    	   44
             U-TUBE LEAK DETECTION SYSTEM
48
             NON-CONTAMINATED SITE DATA DISTRIBUTION 	    76
             CONTAMINATED SITE DATA DISTRIBUTION
77
                            LIST OF APPENDICES

APPENDIX A  TANK SUMMARY
APPENDIX B  SUMMARY OF FIELD NOTES AND CONDITIONS
APPENDIX C  WEATHER DATA
APPENDIX D  SOIL GAS DATA AND SITE MAPS
            SOIL MOISTURE AND SIEVE ANALYSIS DATA
            INDIVIDUAL GC-FID DATA
            QUALITY ASSURANCE PROJECT PLAN
            RESPONSE FACTORS AREA COUNTS, AIR ANALYSES AND NITROGEN
            BLANKS - DATA FOR QUALITY ASSURANCE
APPENDIX I  QA/QC AUDIT - LETTER RESPONSE
APPENDIX J  SUPPORTING DOCUMENTATION FOR REPORTING METHODS EVALUATION
APPENDIX K  CONTAMINATED SITE DATA
APPENDIX L  TANK TESTING RECORDS
APPENDIX M  CALCULATIONS FOR STATISTICAL TESTS
APPENDIX E
APPENDIX F
APPENDIX G
APPENDIX H

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1.1)  EXECUTIVE SUMMARY
The  Environmental  Monitoring  Systems .Laboratory  (EMSL)  of  the  USEPA
awarded  Contract  No:  68-03-3409  to  Camp,  Dresser  and McKee  (COM)  to
conduct-a study to determine the  background hydrocarbon-concentrations  In
soil, vapor  1n  the backfill  of representative  underground fuel  storage
tank   (UST)   sites  across  the  country.    COM  designated   Geoscience
Consultants.,  Ltd.  (GCL)  to  select  sampling  sites,  prepare  sampling
strategies,  review data collection*, analyze the data and prepare  a  final
report.   Field data oh""clean  UST sites were collected  from September  14
to  December 13,  1987.   Data on  UST sites with documented releases were
obtained  from Tracer  Research Corporation files.

Since  no database  for  soil  vapor information at  non-contaminated under-
ground storage tank 'sites was known  to  exist,  a field sampling  program
was  undertaken  to establish  a baseline  data set  of  hydrocarbon  vapor
concentrations.    Data  were collected  from 27 gasoline service  stations
selected  as non-contaminated  sites in three diverse  geographic  regions:
Central   Texas  (Austin,  Texas);     areas  surrounding  Long Island  Sound
 (Suffolk  County,  New   York;     Providence,  Rhode   Island;     Storrs,
Connecticut); and  Southern California (San Diego, California).  The three
regions  were   selected  for  their   active  underground   storage  tank
regulatory programs, as well  as their differences  in geology, hydrology
 and climate.   The non-contaminated database  consists of  279  soil  vapor
 samples  from 25  service stations.  At the other  two stations,  observed
 or suspected leaks  prevented their  data  from being  used  in  the non-
 contaminated database.

 At each  location,  soil  was sampled at varying  distances  and depths from
 UST  appurtenances (such  as submersible pumps,  vents and  product flow
 lines) to determine  1f a particular pattern of hydrocarbon concentration
 existed.  Samples were collected by  driving  a  hollow  steel probe Into  the
 ground,  and evacuating  5 to  10 liters of soil vapors with a vacuum pump.
 Volatile hydrocarbon species were  identified and  quantified at the  site

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 by  utilizing  gas  chromatograph/flame   lonization  detection   (GC/FID)
•equipment.   Ten  to fifteen samples were  collected and analyzed at  each
 site.
                                                    /      -•
                                                    >
 Hydrocarbon "'vapor  concentrations from the  non-contaminated sites range
 from detection  limit  levels of 0.02  micrograms per  liter  (ug/1)  to
 maximum values  of 870,000 ug/1  of-methane,  110,000  ug/1  of  benzene,
 160,000 ug/1 of toluene.,  25,000 ug/1  of ethyl benzene, and 110,000 ug/1  of
 xylenes.   The maximum concentratftuv of total  hydrocarbons (less  methane)
 is 1,000,000  ug/1.   Determination  of total  hydrocarbon concentrations
 exclude  methane   peaks   in  order  to  elevate   the  compounds   most
 representative of  gasoline.   Additionally,  subtraction  of the methane
 peaks   precludes   the   inclusion  of  methane  concentrations   caused  by
 naturally-occurring organic decomposition.

 The  statistical   distribution   of  total  hydrocarbons   (less   methane)
 indicates  that a  majority of the concentration  values  are in the lower
 concentration ranges.   The  relative  frequency  distribution  shows  53.2
 percent of  the samples  below 1,500  ug/1  (500 ppm by  volume)  and  93.1
 percent below  100,000 ug/1  (27,000 ppm  by  volme).   The  median is  800
 ug/1  and the mean is 23,300 ug/1.

 Contaminated site  data  were  obtained from Tracer  Research  Corporation's
 historical  records.  The  contaminated site data consists of 60 soil  vapor
 samples  taken  from  nine sites   having known   contamination   from  a
 petroleum  fuel  leak  or  spill.   These  sites were  all  active  gasoline
 service stations or fueling facilities.   The  contaminated site data  also
 shows  much   variability.    The   statistical  distribution  of   total
 hydrocarbons (less methane)  shows a  majority  of sample values  to be in
 the lower  concentration  ranges.   The  relative frequency  distribution
 shows 35 percent of the samples below 1,500  ug/1  (500  ppm by volume) and
 66.7 percent  below 100,000  ug/1(27,000  ppm by  volume).   The median is
 9,000 ug/1  and the mean Is 160,000 ug/1.

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 Although  much ^variability  exists  in  both  the  non-contaminated  and
 contaminated site  data,  significant differences can be  seen between the
 two distributions.  -A .-ten-fold difference  exists between the  means and
 the medians *of ซeach   dat.a  set.   This ten-fold  difference also  exists
 between -the' numbers  of.samples  with concentrations  above 10,000  ug/1
 (3,000 ppmv) for  the  two data  sets."  For  example; 29.6 percent  of the
 non-contaminated samples occurred in the range of  10,000 ug/1  to 100,000
 ug/1   while 33.3   percent  of  the  contaminated  samples  concentrations
 occurred in the range  of 100,000 ug/1  to  1,000,000 ug/1.      '  "  -

 Statistical data patterns associated with site location  and  sample depth
 were  delineated using  non-parametric statistical methods.   Statistically
 significant differences were found  to  exist between the total  hydrocarbon
 (less  methane)  vapor'concentrations among the five  locations studied for
 steel  tank systems, whereas  these  differences were not significant  for
 fiberglass  tank  systems.   Statistically  significant  differences  also
 occurred    between   the   total    hydrocarbon    (less    methane)  vapor
 concentrations  among the sample depths of 2, 6 and  10 feet for both steel
 and  fiberglass tank systems.    Higher  concentrations were  found at  the
 lower  depths.

 A  fresh spill  at  one  station  in  Austin  provided  an  opportunity to  add
 butane to the  list  of analytes under study.  The butane  concentration in
 15  soil gas  samples taken during the first  four days  after  the spill
 occurred ranged from 530 ug/1 to  300,000  ug/1.   Butane was  also sampled
 at  sites in  Storrs, Connecticut  and  Providence,  Rhode  Island  both  of
which  had  no evidence  of recent  leaks or  spills.   At  these two  sites,
 butane  concentrations   in  65  soil  gas samples  ranged from  the minimum
detection limit.of  0.02 ug/1  to 930 ug/1.   The large difference between
 the butane  concentrations  at  the fresh spill site in Austin  and  the  non-
contaminated sites  in  Connecticut and  Rhode Island suggests that  butane
may be a good indicator of a fresh spill or leak.

Because .there ,are  no  standard  procedures for calculating and reporting
total  hydrocarbon concentration  data,  GCL evaluated different calculation

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methods.    It  was  determined  that  the  best  approximation  of  total
hydrocarbon  (less  methane) concentrations, based  on available calibration
data, was  achieved using an  average  response factor calculated  from the
daily  response  factors  of  benzene,  toluene,  elhylbenzene  and  ortho-
xylene.-    -.._--

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 2.0  PURPOSE OF STUDY
 Proposed Federal  regulations to monitor ground  water contamination around
.underground  storage  tank   (UST)  systems  require;  the  development   of
-effective  external *and  internal  leak  detection 'methods.    Soil  gas
 sampling is  an-external  detection  method which  could prove  useful   in
 determining whether an underground storage tank  is leaking.

 In  order to  determine the effectiveness  of soil  gas surveys  in leak
 detection,  a study was designed with the following goals:

       -•  Collection of  soil gas data  from sites where  the tank  system
           was tested and  found to be tight,  providing  background soil gas
           data, and
       *•  Comparison "of these  background data to  soil gas data from sites
           known  to  be contaminated by  spills  or  leaks  in  order   to
           identify a data pattern which  may be indicative  of a  leaking
           system.

 To  fulfill  these  goals,  soil  gas  surveys were performed  at  27  active
 gasoline service  stations in three diverse geographic  regions.   Hydrocar-
 bon  vapor  concentrations in  the backfill  surrounding  the underground
 storage tanks were sampled and analyzed.

 The  term "soil,  gas"  refers to  vapors found  in  the  interstitial area
 between particles  of sand or gravel  (pores).   "Soil  gas" and "soil vapor"
 are used interchangeably  in this report.   These vapors, often loaded with
 hydrocarbons when  a  underground storage tank  is leaking,   escape into the
 gravel  or sand which  is  used  to surround  the tank during  installation.
 This surrounding tank medium is called  "backfill".  Typically pea  gravel
 is  used  for  bapkfill  around  fiberglass  tanks,  and sand  around steel
 tanks.   An overview of a typical UST arrangement is shown in Figure 2-1.

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 3.0  SITE SELECTION
.3.1  LOCATIONS                 e
 Soil-gas surveys were conducted-at the following locations:
                                                     >
          •''               .  •               •          >      -ซ
  --„.. -•  Austin, Texas
       -•  San Diego,  California
       -•  Long Island Sound area  *
      .:    -   Suffolk County,  New York                      '         '
           -   Providence,  Rhode Island
           -   Storrs,  Connecticut

Austin,  San  Diego and  Suffolk County,  New York were  originally  selected
as  the  locations  for the  study because  they  were recognized as  having
exemplary local underground  storage tank regulatory  programs,  and they
represented  different  geographical  situations.   Stations in  Providence
and Storrs were added  to provide a broader  data base  from the Long Island
Sound  area,  and to interact with the underground storage  tank  evaluation
program  at the University of  Connecticut.

Active regulatory  programs  were desired in order to assure that  accurate
information  would  be available for the  stations to be studied.  Since a
major purpose  of the  study  was to determine background soil vapor  levels
at  clean,  well-managed stations, it was necessary  to  determine  if leaks
or  spills  had  previously  occurred at the stations being tested.  Records
at  Austin, San Diego and Suffolk County were carefully reviewed and all
available  information was  obtained concerning  the  specific stations to be
studied.

Different geographical  locations were desired  for  the study  in order to
eliminate possible data bias  that  could  occur  if  sampling were done at
one location.   The selected locations represent a wide range of  tempera-
ture, humidity,  geology and topography.  Although  soil  gas samples were
taken primarily from the backfill  areas  of the tanks,'the  surrounding
geology  and  climatic conditions  can  affect  the concentration  of vapors
existing In the backfill material.  *
          —         *     •             7

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3.2  SERVICE STATIONS
Three oil companies  cooperated  in  the study by offering several of their
service stations as  candidates  for field testing.   Twenty-seven stations
                                                    t
were  selected  which represent  a variety  of. tank ages,  tank materials,
products  stored,  and  backfill   materials.    The stations  were selected
according to the following screening criteria:

     -•    The stations were  to  be  clean, well-managed businesses with no
          major environmental problems.
     *•    Existing tanks  were required to meet the appropriate operation
          specifications.
     •    The tanks  must  have been in the  ground  and operational for at
          least 6 months prior to the site sampling.
     •    The  stations  were required  to  have  relatively  large  total
          throughputs of  product since beginning operation and relatively
          large throughputs on a monthly basis.
     •    The stations were required to have good inventory control.

Twenty-seven service stations with ten to  fifteen  sample points at each
station were selected,  providing  a  broad data  base with a variety of
tanks, backfills and field  conditions.   There were a total of  100 under-
ground  storage  tanks Involved  in this  study,  of which  63 were made of
steel and 37 of fiberglass.   Tank installation dates ranged  from 1940 to
1984  for  steel  tanks, and 1978  to 1984 for fiberglass tanks.  A listing
of all of the tanks  1s shown  in Appendix A.
                                       8

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 4.0  GEOLOGY,  HYDROLOGY AND CLIMATE
 This  section  briefly  describes  the  geologic,  hydrologic  and  climatic
 characteristics  wMeh  may  effect hydrocarbon  sol]  gas., concentrations
 within  the  three study  regions.                    " '

4.1  AUSTIN, TEXAS
 4.1.1 -Geology and Hydrology     ~ •
 Bedrock in  the Austin area consists dominahtly of limestones, marls, and
 shales^ .all of Cretaceous age. ^Terrace deposits  and  aTluvium locally
 overlie the bedrock units  in the  present valley of.the Colorado River and
 on  terraces representing older Quaternary drainage levels.

 Station sites  AU-2,  AU-4,  AU-5,  and AU-6 all lie in outcrop areas of the
 Upper Cretaceous  Austin  Group,  which  consists  of  chalk,  limestone and
 marly limestone.   A very  thin  (less  than 5  feet) cover of sand and gravel
 terrace deposits may be present at site AU-4.  Site AU-5 lies within 100
 feet  of a fault which exposes Cretaceous clay at the land surface on the
 side  of the fault opposite the station.

 Sites AU-1  and AU-7 are  located  in areas  of alluvial  sand  and gravel
comprising  terrace deposits, but these deposits are probably  less than 10
 feet  thick  at  both sites.   The alluvium Is underlain by Lower Cretaceous
clay  of the Del  Rio  Formation,  a  pyritic,  gypsiferous  and  calcareous
shale unit  which may represent a  barrier to ground  water or  soil  gas
movement.

Site  AU-3   lies  within  a  small  exposure  of altered  volcanic  tuff  of
Cretaceous  age,  In  an   area  consisting  dominantly  of  Austin  Group
limestones.  A very  thin  cover of terrace deposits similar  to those at
AU-4  may also  be present  at AU-3.   As at site AU-5, a  Cretaceous  clay
unit crops out within 100  feet  of the AU-3 site, on the opposite side of
a fault passing near the station.

The  Edwards aquifer underlying  the  Austin  area  is  contained  within
limestones of  Cretaceous  age.  Depth to  water in  the  Edwards aquifer is

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 highly dependent on  topography,  ranging from the  land surface  In  river
^valleys to over 250 feet below It In upland areas.
 Elevation of  the  water table  varies by  as  much as  50 feet over  time,
 depending on  recharge  and-pumpage.   Local  zones of perched water  occur
 above the Edwards aquifer  in  areas where Impermeable lithologic units are
•present.   Ground water was encountered  at a  depth of 7  feet at sites AU-4
 and AU-6, at  a  depth  of 9 feet at site  AU-7, and at a depth of. 10 feet at
 site AU-5.                              .

 4.1.2  Climate
 The  climate  of Austin,  Texas  1s  humid subtropical  with  an  average
 rainfall, of  20 to  40  inches  per  year which  is  evenly  distributed
 throughout   the  year.    During the  first sampling  period, September  28
 through  October  2,  the  weather  was   partly  cloudy  to  clear   with
 temperatures ranging from  62'F to 92'F.  The  barometric  pressure during
 this period ranged from  29.49 Inches Hg  to  30.09 Inches  Hg.   The second
 sampling period was October 26 to October 30.   The  same weather patterns
 were seen  with temperatures  ranging from  70*F to  96*F  and  barometric
 pressures ranging from 29.84  inches  Hg to 30.12 Inches  Hg.   Appendix B
 contains a summary of the actual field conditions.

 4.2  LONG ISLAND SOUND AREA, NEW YORK, RHODE ISLAND
      AND CONNECTICUT
 4.2.1  Geology and Hydrology - Long Island, New York
 Long  Island  consists  domlnantly  of glacial  till  and  outwash  deposits
 representing  a terminal  moraine  formed during  the Quaternary Period.
 Cretaceous  and Tertiary  rocks crop out locally  in  western Suffolk County,
 but  are  not  areally  significant.   All  station sites  examined  for this
 project are located In areas of glacial till.

 Ground water  on  Long Island  1s contained  within  the glacial  till and
 local  alluvial  deposits of reworked glacial  material.   Depth  to  water
 varies from about 10 to 100 feet  on the Island.  At site NY-2, ground
                                       10

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 water 1s  about 22  feet below  the surface.   At  all  other  Long Island
 sites,  ground water Is between 60 and 90 feet below the surface.
                      •                      '         >
                 • ".          '                        *
*4.2.2  Geology and Hydrology - Providence, Rhode Island
 In the Providence area, Quaternary glacial  deposits  of varying thickness
-overlie bedrock  of Cambrian  and Precambrlan  age.  As on  Long  Island,
 ground  water  is found  at  depths up to about 50  feet in the Rhode Island
 glacial  deposits.   Ground-water conditions are not well  known  in  many
 areas because most public  water supply. 1s  derived from surface sources.
 The depth to water at the station sites is not known.

 4.2.3  Geology and Hydrology - Storrs, Connecticut
 In the  Storrs area, Quaternary  glacial deposits  of varying thickness, up
 to  about  100 feet,   overlie  crystalline  and  metamorphlc  bedrock  of
 Cambrian and  Ordovlclan age.    Limited  quantities of ground  water  are
 found in  the glacial  fill,  but water supply  wells  generally tap  more
 extensive reserves In  fractures of the Paleozoic rocks.   Depth to water
 at the  Connecticut station sites Is 10 feet.

 4.2.4  Climate
 The three Long Island  Sound locations Included  in  the  study have similar
 climatic conditions which  are Influenced by the continental  and  oceanic
 weather systems.   The  average rainfall for  these locations 1s from 40 to
 60  Inches   per year.    During  the  sampling  period,  September 22  to
 September 25  in Suffolk County,  the temperature ranged from 61'F to 75*F
 with the barometric pressure  ranging  from  29.70 Inches Hg  to 29.94 Inches
 Hg.  During the  sampling  visit  to Storrs,  Connecticut  from November 11 to
 November 13,  the  temperatures ranged  from  29*F to 51 *F with snow  and  rain
 occurring >W1  November  11  and  November 12.  The barometric pressure during
 this time rangad  from  29.65 Inches Hg to 29.99  Inches Hg.  The sampling
 visit to  Rhode Island during the period of December 9  to  December 11
 experienced one day of rain,  December 11, with  temperatures ranging from
 40'F to 58*F  and  the barometric pressure ranging from 29.32 Inches Hg to
 29.83  Inches  Hg.   Appendix  B contains  a  summary  of actual  field
 conditions at the time of  sampling.   Appendix C contains general weather
                                       11

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data  for the Long  Island  Sound  area for the months of September, October,
November-and December 1987.           '.
                                                     /
•4.3   SAN DIEGO  REGION,  CALIFORNIA
4.3,1  Geology  and Hydrology
The   San  Diego  area  -of   southern  'California  contains   two   distinct
physiographic sections,  a  coastal  plain section  and a mountain-valley
section.  "  The  coastal  plain  section  consists  of Tertiary marine
sediments,  1n  many parts of  which wave-cut terraces are   apparent,  and
'through which  alluvial valleys have been  cut  between Inland watersheds
and   the  sea.    The  mountain-valley  section  Includes alluvium-filled
valleys dissecting mountain ranges which are comprised of  a wide variety
of volcanic, sedimentary,  and Igneous rocks.

Station  sites  SD-1, SD-4,  and SD-6  are located  in   Quaternary  coastal
sediments overlain  by a  thin veneer of Recent  alluvium.   All  three of
these sites  are  at elevations within  a few feet above sea level.  Water
was  encountered  7 feet below the  land surface at site SD-1 and 12 feet
below the land surface at site SD-6.   Ground  water probably exists at a
shallow depth at site SD-4, but was not encountered during  the study.

Stations  SD-3  and SD-7 are on  a terrace of Tertiary sediments elevated
 about 200 feet'above sea level, and are located about 3 to 5 miles  Inland
 from the sea.  Depth to water at stations SD-3 and SD-7 Is not known.

 Sites SD-2  and SD-9 are located In  valleys near the  eastern margin  of the
 coastal  plain  section.    At  these locations alluvium of unknown  but
 probably  shallow depth overlies volcanic  or metamorphic  bedrock.  Ground
water was .encountered  at  a depth of 8 feet at site SD-2.   Depth to water
 at site SD-9 Is'  unknown.

 Sites  SD-5  and  SD-8  are  in a  broad valley  within  the mountain-valley
 physiographic  section. These sites are located on the residuum produced
 by in-situ  weathering  of  underlying  volcanic bedrock. Based on
                                       12

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 Information from wells  In  the  vicinity,  depth to water at sites SD-5 and
 SD-8 1s probably between 10 and .25 feet.                             :

-4.3.2  Climate                                     ~J
 The coastal location  of San Diego, California  tempers the climate  of this
 city.  Rainfall  In San Diego ranges  from  10  inches to 20 inches  per year,
 with 85%  of this .precipitation  occurring  during the months  of Novembec
.through  March.    During  the  sampling  period,  September  15  through
 September 24,  the  temperature ranged  from 70*F to  86*F  with one  day of
 slight rain (September  22).  The barometric pressure during the sampling
 period ranged  from  29.90  Inches  Hg  to 30.10  Inches Hg.    Appendix  B
 contains  a  summary of  actual  field  conditions at the  time of sampling.
 Appendix  C  contains general  weather data for  the  San Diego area for the
 months of September, October, November and December  1987.
                                       13

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 5.0  FIELD METHODS
 The field  Investigation consisted  of on-site  sampling  and analysis  of
.soil  gas at a total  of 27 service stations In  the ฃhree  regional  areas.
Tracer Research Corporation  (TRC) performed the soil-gas  sampling and the
 on-site analysis of the samples.  TRC also performed on-site  analysis  of
 backfill  'samples: for  each  site to determine soil  moisture  content.
 Geoscience Consultants, Ltd.  (GCL)  was responsible  for overall  sampling
 strategy and'data quality  assurance.

 The field work  began on September 14, 1987 in  San Diego,  California and
 was completed on December  13,  1987  in Rhode  Island.   The field  schedule
 was as follows:

      San Diego,  CA   '         9 Stations          Sept 14  - 24, 1987
      Suffolk County,  NY       5 Stations          Sept 21  - 25, 1987
      Austin, TX               4 Stations          Sept 28  - Oct 2,  1987
                               3 Stations          Oct 26 - Oct 30,  1987
      Storrs, CT               2 Stations          Nov 10-13,  1987
      Providence, RI           4 Stations          December 10 - 13, 1987

 5.1  SAMPLING STRATEGY
 The sampling  strategy  was designed  to determine  the range and spatial
 distribution  of  hydrocarbons  within  the  backfill   of  the  underground
 storage tanks.  The sampling points  were  very close  to the tanks because
 excavation  and  backfill   typically  extended  only   one  to  three  feet
 laterally from the edges of the tanks.

 Soil-gas samples were collected  only from the backfill areas of the tank
 excavations.  The  specific sample sites were  located at  varying distances
 from tank fill  ports, pump chambers, and  product and vent piping, all of
 which can iป  sources of leaks.   A  typical  sampling  grid consisted  of four
 or five  simple1 holes with samples  collected  at  depths  of 2, 6,  and 10
 feet  1n  each  hole.   Typically,  ten  to  fifteen samples were collected at
 each service station.   The locations of the sample points are Identified
 on the site naps of the stations  in  Appendix D.
                                       14

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Soil  samples  to determine moisture content of the backfill material  were
taken from  fifty  percent of  the  sample  points.   These  samples  were
analyzed on-site by IRC personnel utilizing a portable oven and  balance.
Two soil samples were collected at each station by 'GCL personnel.  These
samples  were sent  to an  independent  certified laboratory, Professional
Service" Industries, Inc., for  the  determination  of moisture content  and
particle .size  distribution  (sieve analysis).    The  results  of these
analyses are  included  in  Appendix E.

Some  additional" sampling other  than  for  soil  gas  was  performed  at 5
stations where  some unusual  conditions existed.   This  consisted of:   1)
vapor sampling  from U-Tube monitoring  systems at Stations  #4 and #6  in
Suffolk County,  New York, and  2) water  sampling  from shallow ground  water
at Stations  #1  and #2  in Storrs,  Connecticut, and Station #6 in Austin,
Texas.

5.2   SAMPLING METHODS
Soil-gas samples were collected by driving  a  hollow  probe into the ground
to an appropriate depth  and evacuating a  small  amount  of soil gas (five
to  ten liters)  using  a  vacuum  pump.   A  hydraulic  hammer was  used  to
assist in driving probes  past cobbles and through unusually hard soil.

Probes consisted of 7-foot lengths  of  3/4-inch diameter steel  pipe which
were  fitted with a detachable  drive point.   The above  ground end of  the
sampling probe  was fitted with a steel reducer,  a  silicone rubber  tube
and  polyethylene  tubing  leading  to  the  vacuum  pump.    Samples  were
collected in  a  syringe during  evacuation  by inserting the syringe needle
into  the silicone rubber evacuation line  and drawing  a  sample from  the
gas strean.     -

A  split spoon   device was  used  to collect  soil  samples of backfill
material utilizing  the probe holes that were  used to collect the soil  gas
samples.  The soil  samples  were stored in  sealed plastic  bags prior  to
analysis.
                                      15

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Promptly uponrtcompletlon  of the sampling program at each site, all holes
made  in  the  concrete or  asphalt  apron were  patched  to  restore  the
integrity of the-apron.        "                     ;     _
                                                    >
r.a • ANALYTICAL PROCEDURES
Tracer  Research  Corporation .used  a mobile  field laboratory  which  was
equipped  with gas chromatographs. and  computing  integrators.    A flame
ionization  detector (FID)  was used to  measure  methane,  butane,  isopen-
tane,  benzene,  toluene,  ethylbenzene,  xylenes  and  total  hydrocarbons.
The methane concentrations  measured in the. soil,gas represent a  total of
Cj to  Cs compounds  since it  was  difficult  to identify individual peaks
within  this range.   In instances when  butane and isopentane concentra-
tions  were  reported,  a variation in the  temperature  program in  the gas
chromatograph  was  used  to  help  clarify  these  peaks.    However,  some
interference in  peaks  was still  observed.

Typically,  three  samples  were  analyzed  from  each   sampling  point and
operator judgement  was  used  in  the  field  to  determine  which of the
various results  could  be   considered   as  reliable.    Mean  values were
calculated  in  the field based upon experienced  operator  judgement and
these  averages were considered to be  representative  of the actual  soil
gas  concentration at  the individual  sample locations.  This  type  of field
judgement  is  generally  used  in  soil  gas  surveys  because   of  the
variability of the soil  gas  analysis technique  and the  skill required  to
achieve reproducible results.  Means derived  in this  manner  were used  in
this study in order to provide data that  is  comparable to existing  soil
gas  data and  to  data  that can be expected  to be  obtained  in future  soil
gas  surveys.  The actual values  of each analysis, which may be useful  in
further statistical analyses, are provided in Appendix F.
                                       16

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 6.0  QUALITY ASSURANCE AND QUALITY CONTROL
 The quality  assurance/quality control  (QA/QC)  goals and  procedures for
;th1s .project-are described  1n  the "Quality  Assurance  Project  Plan for
-Background Vapor Value Study"  (QAPP) dated  August', 1987  (Appendix G).
 Tha majority  of-the  goals  for  accuracy, completeness  and validity  of
 data, as  listed In  ths QAPP,  were "attained  during field  sampling and
^analysis.   Because some.of the project activities were  modified,  during
 the course of the" field work,  to reflect goals  slightly  different from
 those  anticipated   In  the  original  Work  Plan,  certain  corresponding
 modifications were  necessary in the QA/QC procedures.

 Additionally, a  few field  procedures  were modified  because those outlined
 1n the QAPP  proved unworkable.   These modifications to  field methods were
 discussed  with  project  personnel  and approved  by the 6CL  QA  Officer  at
 the time of  the QA Field Audit, which was performed at  two sites  1n San
 Diego, California  on  September  17,  1987.    All modifications to  the
 original QAPP are discussed in Sections 6.1 through 6.12 of this report.

 6.1  QA OBJECTIVES  FOR MEASUREMENT DATA (QAPP SECTION 3.1)
 6.1.1  Gas Chromatograph Analyses          '
 The  gas  chromatograph  (GC)  was  calibrated  dally  by  measuring  the
 instrumental  area count for  each  analyte  against  the known concentration
 of  that  analyte In  a standard  gas  mixture.    The gases, which  were
 traceable  to those of the  U.S. National  Bureau of Standard, were obtained
 from Scott Specialty  Gases.   The  calibration procedure is described  in
 Section 6.4 of this report.

 Because calibration was performed directly  from the BTEX  gas standard,
 the  independent  accuracy  check  against  another standard  was  not
 feasible.   Accuracy  checks during the  field day were  performed against
 the  same  gas  standard used for  initial calibration.   These  accuracy
 checks, generally  two  or  three  per field  day, were  performed  at the
 discretion  of  the analyst.   They  were  consistently  performed  more
 frequently than the .goal  of once per  20 analyses  which   was  stated  in
 Section 3.4  of  the   QAPP.    Area counts  for all  calibration  runs and
                                       17

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accuracy  checks  are'tabulated  in  Appendix H.    All  response  factors
(RF's)  determined  by the  accuracy  checks were  within  ฑ30% of  .those
established  at  the .beginning'of the  field day,  so  no  recall brat ions
during .any-field day+were  required.   RF's used for  each" day/s work are
•artso-listed In Appendix H.

In order  to-  assess  analytical  precision,  all analyses performed for this
project were  done in  triplicate,  by injecting three separate aliquots of
the  sample into  the  GC.   In  a-few  cases, where one  of  the injections
clearly  produced anomalous results,  additional injections  were  made as
necessary to yield  three valid  analytical  runs.   For  each  set of three
analyses  for each  component  at each .sample point,  Tracer  determined a
mean value which 1s  presented in Appendix  D,  and a standard deviation,
which  is  presented  with the three  analytical  values  in Appendix F.  The
standard  deviation  exceeded 25%  of the mean value in  58  out of the 950
triplicate analyses  1n  which  all  three results  exceeded  the detection
limit, or 6.1% of such analyses.   This surpassed the goal,  stated  1n the
QAPP,  that the  standard deviation should  exceed  25% of the mean  in no
more  than  15%  of  the  triplicate analyses.  At  most  points  where the
standard   deviation  was  more   than   25%  of  the  mean   concentration
determined at a point, the analyte  was present at a relatively low con-
centration,  in which case analytical error 1s normally expected to be a
greater  percent of  the concentration than for  samples  in which a greater
quantity of  the analyte  is  present.

At  sites  where  low  total  hydrocarbon and  methane  concentrations were
encountered,  the detection limits for analytes of  interest  were  normally
less than 0.10 ug/1, and in many cases were less  than  0.05  ug/1,  the goal
stated In the  QAPP.   As anticipated,  detection limits for all  analytes
were much higher In locations where high hydrocarbon concentrations were
encountered.     Detection   limits  for   all  non-detected   compounds  are
reported in  the accompanying data sets.
                                      18

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 6.1.2  Soil  Moisture Content Analyses
 Due to sampling and analytical problems  encountered  in the field, Tracer
 reported fewer .soil moisture analytical  results  thap were anticipated in
-the QAPP.   Sample  splits,-and  in  some locations 'the majority  of soil
 samples, were  sealed in  air-tight containers  and  submitted  by GCL  to
 Professional  Service  Industries,  Inc.  (PSI)  in Albuquerque,  New Mexico
 for moisture  .content  analysis.    PSI  submitted  results  for  42  soil
 samples, and  Tracer  submitted  results  for  26  samples.    Because  of
 inconsistent  sample  identification,  particularly  in  New York and  Rhode
 Island,  1t was not always possible to  identify which Tracer samples were
 in  fact  splits of PSI  samples.

 Table  6-1  lists  and  compares  all  soil  moisture  replicate  analyses
 identified  in  a review of the  Tracer and PSI  data.   In most  cases,  the
 laboratory  values  agree  well  with  those  obtained  in  the  field,  but
 significant  discrepancies exist  for  the data  at  sites  AU'2  and  SD-2.
 There  is  good   internal  consistency  among  the  values  reported  for
 replicate samples  which were  both sent to the PSI lab.

 6.2  SAMPLING  PROCEDURES  (QAPP SECTION 3.2)
 Soil gas sampling was performed as  described  1n  the QAPP.  At the request
 of  EPA  EMSL,  sample points  were confined  to the  area  of the  backfill
 immediately adjacent to the USTs at  each  site, and  in a few cases to soil
 just outside  the  backfill.   There were  generally  no more than  6 sample
 points per  site,  and  samples were normally  taken  from 3 depths at  each
 point.

A total  of  78  soil  samples,  mostly backfill material, were analyzed  for
moisture content.   The samples were  not uniformly  distributed among  the
 sites  because  of  difficulties  encountered in obtaining  soil  samples  at
some locations and the realization  that moisture  content was  of little
utility  in others, such as sites where the  backfill  material consisted  of
pea gravel.  The values reported In this document represent only samples
that were properly packaged, transported  and  analyzed.        .
                                      19

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                   TABLE 6-1

RESULTS OF REPLICATE ANALYSES FOR SOIL MOISTURE
 •:••--            CONTENT           ;
                                     " >
  CALL  ANALYTICAL  VALUES  IN  PERCENT  BY WEIGHT)
SITE
AU-1 .
AU-2
SD-2
NY-2
NY-4
NY-5
NY-6
TRACER
SAMPLE NUMBER
870.9291807
8709300935
8709161636
NY2-SG4-10
NY4-SG4-10
NY5-SG4-10 '
NY6-SG2-10
PS I
- SAMPLE NUMBER
8709301819
8709301825
8709300940
8709300946
8709161637
8709231230
8709241545
8709241600
8709251310
8709251800
8709251830
TRACER
ANALYTICAL
VALUE
14.7
12.4
11.3
t
.10.0
5.0
6.9
5.7
PSI
ANALYTICAL
VALUE
13
11
4
3
20
7
3
,5
8
5
6
!
REMA'RKS
Erroneous date
on samples
delivered to
PSI. Two
replicates to
PSI.
Two replicates
to PSI.

Correlation
uncertain. Two
replicates to
PSI.
Correlation
uncertain.
Two replicates
to PSI.
                        20

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6.3   SAMPLE CUSTODY (QAPP SECTION 3.3)
Chain-of custody procedures described  in  the QAPP were followed  for  all
soil  samples  sent to PSI for moisture  content or  sleeve  analysis.   Chain-
.of-custody  forms -for these  samples ^are  on file  at the  GCL office  in
•Albuquerque.

6.4   CALIBRATION PROCEDURES AND FREQUENCY
      (QAPP SECTION  3.4)
The  GC  was  calibrated  daily,  using gas  standards  obtained from  Scott
Specialty Gases.   These  standards  are traceable to those  of the U.S.
National  Bureau  of  Standards.   Two  separate  three-point  calibration
curves  were  established, as described  in  Section  3.4 of the  QAPP,  one  for
methane (hydrocarbons Cj-Cs)  and  one for  the aromatic hydrocarbons Cs-Cg.
However,  the curve used to quantify hydrocarbons Cs-Cg was established
using the BTEX gas  standard  rather than  an aqueous standard.    It  was
found that  this procedure yielded accurate  and replicable  results,  while
the   aqueous  standard  produced  a  response  factor  (RF)  that  did  not
accurately  quantify  the  gaseous  BTEX  standard.   Additional  calibration
and  accuracy checks  were made  periodically during  each  field day,  and
RF's  were then  revised  as necessary.   Recalculation of RF's  during  the
field day was  not  found to be necessary  at  any  site.   Area  counts  and
response factors as reported  by Tracer  are shown  in Appendix H.

Isopentane  was  not  originally  Included  among  the   compounds   to   be
specifically  Isolated under the original  Work Plan  and QAPP.   However,
GCL   and  Tracer  were subsequently  requested  by the  EPA  to attempt  a
determination of Isopentane concentrations  at selected  locations.  Since
no .standard  for Isopentane had  been  provided in the  field,  Isopentane
values  were determined after  field  work was complete by  reanalyzing  the
chromatograms to Identify  the Isopentane peak.   A response factor (RF)
for  Isopentane was defined by comparison  with the known RF for benzene, a
gas which had been  Included among the standards available in the field.
                                      21

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To  assure  the  cleanliness of  sampling  equipment,  syringe  blanks and
.system  blanks  (air  samples) were  taken  and  analyzed each  morning and
periodically  during  the day, as  provided  In the QAPP;.
                                                    >
6.5  ANALYTICAL PROCEDURES  (QAPP SECTION  3.5)
Analytical  Procedures are described In Section 5.3 of this report.  All
soil  gas analyses for benzene,  toluene,  ethylbenzene and xylenes  (BTEX)
and  for total   hydrocarbons  were  performed  by  Tracer  personnel  In
accordance  with the procedures  described  1n Section 3.5 and Appendix B of
the QAPP, except for the treatment of samples yielding total hydrocarbon
values  greater than 500 ug/1.   .Experience during the first day of  field
work  Indicated  that reducing the  Injection size  for such  samples,  as
proposed In the QAPP, resulted  In  obscuration  of the chromatogram  peaks
for hydrocarbons Cg-Cg (gasoline  constituents),  while not significantly
Improving   the  accuracy  of methane measurements.    Since  the  use  of
smaller Injection sizes resulted  in a great loss  of data, the practice
was discontinued.
 6.6   DATA REDUCTION,  VALIDATION AND REPORTING
      (QAPP SECTION 3.6)
 Data presented to GCL by  Tracer were recorded and analyzed  as  described
 in  Section 3.6  of the QAPP.   The  results of the analyses performed  are
 described elsewhere In this report.

 Some  extreme  values  ("outliers")  Identified  in  the  original  data
 recorded on site were discarded from the data set by Tracer because  the
 on-slte chemist, based on  his  field experience,  believed them  not  to be
 representative  of  actual  hydrocarbon   concentrations   in   the   sample
 analyzed (see Section 6.10 of  this report).  Consequently,  GCL has made
 no  attempt, to identify or  explain  the few outliers remaining 1n the data
 set, which would require excessive time  and yield little Information.

 The   data presented  1n  this  report have been  subjected  to Tracer's
 Internal review*process,  and have been  spot-checked for  accuracy  by.GCL
 personnel.   Although a few minor  errors were detected arid  corrected
                                      22

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 during the GCL review,  and  a few others undoubtedly  remain  in the large
 data  set,  GCL  Is  confident that  such errors  represent  a  very  minor
 portion of the total body of data.                   ;
                      ••. •                             >      ~
 6."7-'INTERNAL QUALITY CONTROL CHECKS (QAPP SECTION 3.7)
 GC calibration procedures 'and frequency were described in  Section 6.4 of
 this report!'  As a  standard  part of .Tracer's  analytical procedure, daily
 "blanks" consisting ofjpjure.  nitrogen, of-a.fr,  and of  air drawn through a
 soil gas.probe and .adapter ("system blank") were  analyzed.  These blanks
 were repeated as necessary during  the field day,  and specifically after
 any event which was suspected may affect analytical results.

 Soil gas samples at each  point were analyzed  in  triplicate,  as described
 1n  Section  6.1.1.  of  this report,   and  duplicate   soil  samples  for
 moisture content analysis were taken  at selected  points, as described in
 Section  6.1.2.     Replicability   of  results  was   within  the  goals
 established by the QAPP.

 6.8  PERFORMANCE AND SYSTEM AUDITS  (QAPP SECTION 3.8)
 A  field  system  audit  and   evaluation of  operational   procedures  was
 performed  in San  Diego on  September  17,  1987  by the GCL  QA Officer.
 Minor  modifications  to field  sampling and  analytical procedures were
 discussed with project  field personnel  and  approved by the QA Officer at
 that  time.   A  letter report describing  the  results  of the field audit
 was  submitted to  CDM  FPC   on  September 18,  1987,  and  is  Included in
 Appendix I of this  report.

-6.9  PREVENTIVE MAINTENANCE  (QAPP SECTION 3.9)
 All equipment  was  maintained In operable condition during the field work.
 Spare  parts and  new equipment  were obtained  as necessary to  complete
 field work In a timely  manner.
                                       23

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6.10  ASSESSMENT OF DATA PRECISION, ACCURACY AND
      COMPLETENESS (QAPP SECTION 3.10)                               :  •
The  data presented  in :this report  are complete  in the sense  that all
values  believed to  represent  valid  analyses  have  been fncluded.   Gas
chTomatographic analysis -.ts a procedure 1s  subject  to Interpretation by
the  GC  operator,  who -'must  evaluate  each run,  on  the  basis  of his
experience, -to determine   Its  validity.    Volume  of  sample  Injection,
concentrations  of  the  analytes of Interest,- and possible residual  effects
of previous  sample runs must  be considered by the  operator in deciding
whether  to  accept the  concentrations  Indicated  for  any  given  sample
Injection.   Concentration values  which were clearly. 1n error were rejec-
ted  by  the GC  operator  in  the field,  and  are not  included in the data
set.  Some other  values which appear  to be "outliers" Inconsistent with
         "            f                .
the  rest of the data Set have been  included in the tabulated analytical
results  (Appendix  F),  but  were  not  used in determining the mean values
of  the   triplicate analyses reported  in Appendix  D.   In  some  of  these
cases, the outlying  values  were  excluded by Tracer in calculation of the
mean  concentration,  but  were Included 1n  calculation of the standard
deviation.   GCL and  Tracer have  attempted  to  Indicate such points  where
such  operator judgment was exercised.  These  undoubtedly represent far
less than 1% of the total data set.

During  the course of  the  project,  Tracer was asked  to recalculate the
total  hydrocarbon  concentrations  to  show them  relative  to  the BTEX
total,  rather than as benzene.   Consequently,  the mean values  used in  the
data  analysis (Section 11.0) for total  hydrocarbons (less  methane) differ
from  the  means of  the values  shown  in  Appendix  F  (Individual   GC-FID
injections).   The standard deviations  for  the total hydrocarbon data were
calculated   on  the  basis  of  the  values  reported  "as  benzene",  and
consequently should  not  be applied directly to  the total hydrocarbons
(less methane) data calculated  from  average  daily  response factors  for
BTEX.
                                      24

-------
 Concentration values  reported  in  micrograras per  liter for  analytes of
 interest in this report .are normally  given  to two significant figures if
 greater than 10 ug/1, .and to one significant figure ;if less  than  10  ug/1.
 As illustrated by the  standard deviations presented1 with  this  data set,
 and based  on  Tracer's  experience  in  soil  gas analyses,  instrumental
 precision does not normally justify greater precision  in the reporting of
 results.

 Further  information   regarding  analytical   accuracy,   precision   and
 replicability was  presented in Section 6.1 of this report.

*6.11   CORRECTIVE ACTIONS (QAPP SECTION 3.11)
 During  the  field  system audit,  the requirements  for  proper  chain-of-
 custody procedures were explained  to some site  personnel who were not
 fully  aware of them.   Samples  previously  taken  for  soil moisture content
 analysis had been  properly   handled,  but  the  QA  Officer  felt  that
 additional  explanation was necessary  to prevent the possibility of future
 problems.

 No other corrective actions were found to be necessary during field  work.
 Problems with Tracer's  handling procedure  of the  soil  moisture  samples
 were discovered  too late to be remedied by GCL personnel.

 6.12   QUALITY ASSURANCE REPORTS TO MANAGEMENT
       (QAPP SECTION 3.12)
 Monthly quality assurance reports  were  submitted  during  the  course of
 the project,  as  described in Section 3.12 of the QAPP.
                                      25

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 7.0  REPORTING METHODS
 One of the problems  encountered In this study concerned  the  calculation
.and reporting  of the total  hydrocarbon concentration  data.    Different
.practices In calculating .and reporting these data were  discovered within
'the environmental Industry and  among  those who collect and analyze soil
 gas data".  For example,  some leak'detection device's  were  found to report
 total  hydrocarbons In  parts  per million by volume (ppmv)  "as  hexane", and
 others 1n  ppmv "as  butane"  (Radian).   Additionally, laboratories  using
 gas  chromatograph,   flame ionization  detection  (GC/FID)-equipment  to
 analyze soil-gas,  report total hydrocarbon concentrations  in mlcrograms
 per  liter  (Tracer).    The   method  of  determining  total  hydrocarbon
 concentration  values using  a  GC/FID also  vary.    A GC/FID  must  use  a
 response factor based on  the calibration of a  known  gas to determine the
 concentration of an  unknown  gas.   This calibration gas, or "gas standard"
 may be benzene, toluene, or some other hydrocarbon compound.

 Because of these variations,  GCL  evaluated different calculation methods
 to determine the most appropriate method  for  reporting total  hydrocarbon
 concentrations.   In  this method  evaluation,  both the calculations and
 their accuracy were  examined.   Since these data may be used in developing
 threshold  limits  between  non-contaminated  and contaminated  sites, they
 must be comparable to soil gas data determined by different methods.

 The evaluation consisted  of two parts:

        ซ  Calculation  of total hydrocarbon concentrations In  mlcrograms
           per  liter  from the calibration of the  GC/FID,  reported both  "as
           benzene" and according  to an average response factor,  and
        ซ  Calculation  of total  hydrocarbon  concentrations in parts per
           •1111oh.
                t
 7.1  DETERMINATION OF TOTAL  HYDROCARBON CONCENTRATIONS
      IN HICROGRAHS PER LITER
 The  field  Investigation  phase  of  this  study  required that  soil gas
 samples  be  collected  and  analyzed  at  non-contaminated  sites.    These
 samples  were analyzed on-site  using  a  portable  Gas Chromatograph  with  a
                                       26

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  flame  ionlzatlon detector (GC/FID).  The results of these  analyses yield
  concentration  values in micrograms per  liter.   Section 7.1.1 contains  a
  brief  discussion on "the  function of a  GC/FID  and^he procedure used to
  calculate  the total  hydrocarbon concentrations  from the  GC/FID in the
  field. _ This  procedure  uses  benzene as  the calibration  gas.   Section
  7.1.2   discusses ~a  more  accurate  method   used  to  calculate  total
  hydrocarbon  concentrations in micrograms  per liter using  data  from alj
- the calibration  gases.         -

  7.1.1  Gas Chromatograph  and Flame  lonization Detector
        Operation
 A gas  chromatograph  is  (GC) an analytical  instrument that can be used to
  separate volatile  organic compounds for analysis  (EPA Methods 8000).   A
  GC  equipped  with  a flame  ionization  detector   (FID)  can  be   used  to
 generate a chromatogram that  consists of peaks corresponding to  different
 compounds.     The   complete   analytical  system   used  in  the  field
  Investigation of this study consisted of a chromatograph1c packed column
 containing  All tech  OV101, a   hydrogen  flame  lonization  detector,  an
 integrator-recorder, calibration gases and glass syringes (Tracer).

 Calibration  gases  were used  to  generate  a  chromatogram  that   formed  a
 base-line or  standard  of peaks  in  the chromatogram.  Response  factors,
 defined as the ratio of the mass of  each gas standard  to  the Integrated
 area of  the peak  produced by that mass,  were determined  for  each  gas
 standard.  Individual hydrocarbon compounds in the  soil  gas samples  were
 identified by a comparison  of  sample chromatograms   to  the  standard
 chromatogram.   Concentrations of  Individual  compounds were calculated
 from the response factors for  the corresponding gas standard.

 Concentrations 
-------
 sample,   and  consequently,  response  factors   and   concentrations  are
 measured 1n mass units (Tracer).
                                                     '
'The  calibration  gas  standards  -used  were  methane^,  benzene,  toluene,
'ethylbenzene,,  and  ortho-xylene.    Concentrations   of   each   of  these
 compounds ~1n each- sample  were  calculated directly using the corresponding
 calibration* gas response factor and the  sample  Injection  size.   However,
 concentrations for total hydrocarbons  (less methane)  were required to be
 approximated.

 7.1.2  Calculation of Total Hydrocarbons  as Benzene
 During  the   field   Investigation,   total  hydrocarbon   (less  methane)
 concentrations were  approximated  by  using the response factor  for benzene
 to  compute  the  concentrations.    During  the  data  analysis,  1t  was
 discovered  that  this approximation  yielded  a  low  estimate of  total
 hydrocarbons  (less methane)  concentrations.   This discovery was made by a
 comparison   of  the   combined   concentrations   of   benzene,   toluene,
 ethyl benzene  and  xylenes  (BTEX)  to  the  total  hydrocarbon concentration
 (less methane).  This  comparison  shown in Appendix J, Indicates that the
 concentration  of  BTEX  was greater  than  the  concentration  of  total
 hydrocarbons (less methane) In 30 percent of the samples.
                         ซ
 A possible cause  for the  discrepancy between  the concentrations of total
 hydrocarbons  (less  methane)  and  BTEX   could   have   been an  erroneous
 Interpretation  of the chromatogram peaks.  However,  a re-examination of
 the chromatograms showed that no  Interpretation errors had occurred.

'The  discrepancy was  determined   to  be  the result of using  the benzene
 response  factors  for the  approximation  of  total  hydrocarbon  (less
 methane)  concentrations.   By an  examination  of the response factors  for
 all  of the  gas standards  (Appendix D), It  was found that  the benzene
 response  factor was  usually lower when  compared to response factors  for
 toluene,  ethylbenzene and ortho-xylene.   In theory, response factors  for
 similar  hydrocarbon  compounds should  be similar.   However, in practice,
 response  factors  vary because of  chemical and Instrument  effects.
                                       28

-------
Because  of  the discrepancies between the  total  hydrocarbon  (less methane)
concentrations   and   the   combined   BTEX   concentrations,   a   better
approximation  of  total  hydrocarbon  (less  methane)  concentrations was
needed.  "This-was considered Important  because  these  valued obtained from
nor;-.contaminated  sites  may affect the development of threshold limits to
be used  to distinguish  Between contaminated and non-contaminated sites.

7.1.3  Calculation of Total Hydrocarbon  Concentrations
       Using Average Response Factors
The total hydrocarbon concentration  in  a soil gas sample is actually the
summation of all  the  hydrocarbon compounds that can be detected from the
GC/FID  analysis.    To  accurately  determine  this concentration   would
require  that a gas  standard be  analyzed in the GC/FID for every compound
that existed  in the soil  gas.   This comprehensive type of analysis was
considered  impractical  since an enormous  amount of  GC/FID calibration
work would  have  been necessary  to quantitatively analyze all.the peaks in
the soil gas samples.

The best approximation, based on the available  calibration data,  was to
determine  total   hydrocarbons  (less  methane) using  the average  of the
response   factors  for   all  the  calibration   gases  (less  methane).
Therefore,   total   hydrocarbon   (less   methane)   concentrations   were
calculated  from an average of   the  daily response  factors  for benzene,
toluene, ethyl benzene and  ortho-xylene.

This  approximation  resulted in new total  hydrocarbon  (less methane)
concentrations  that  were  generally  higher.    A  comparison   of   total
hydrocarbon  (less methane)  concentrations calculated .from average BTEX
response factors and "as benzene" 1s  shown below.
           •'   i    "                  •     .                 •
          TOTAL HYDROCARBON (LESS METHANE)          PERCENTAGE OF
                   CONCENTRATIONS                     SAMPLES
            As Benzene  > As BTEX Average               8.6%
            As Benzene  - As BTEX Average              15.1%
            As Benzene  < As BTEX Average              76.3%

                                      29

-------
In the case where the  new values (as BTEX average) were greater than the
old values  (as  benzene), these  new values ranged from  7%  to about 100%
higher,  ปA-comparison  of the old  values  and new values for^ each  sample Is
provided 1n Appendix 0.                                        •

The new  concentrations  also  result in values  that are  larger  than the
combined BTEX  concentrations which, indicates a  more reasonable approxi-
mation of total hydrocarbon, concentration. "A comparison of .the BTEX and
the  new. total  hydrocarbon  (less" methane). concentrations  are  shown  in
Appendix J.

The calculation  of total hydrocarbon (less methane) concentrations  using
the average BTEX response factors,-was found  to be a better  approximation
than when using  only'benzene, because it accounted  for  variations  in the
response factors.   However,  1t  1s understood  that some  error  still  exists
1n  this method  because several  peaks   in  the  chromatograms and  their
corresponding compounds  were not identified  and  quantified.

To  better  understand  the  extent that  compounds  other than  BTEX are
contained   in  total  hydrocarbons,  a comparison   of  the  combined  BTEX
concentrations   to  total  hydrocarbons   (less  methane)  concentrations
 (calculated from average BTEX response factors) was made.  These  results
are shown In Figure 7-1.  The  tabular data used  to generate this  figure
 Is  included  In  Appendix J.   The percentage of  samples where the BTEX
concentrations were  less  than  50  percent of  total  hydrocarbons (less
methane) was about  59 percent of the total samples.  This means  that  in
 about 59 percent  of the samples, compounds other  than  BTEX make  up the
 majority of Jthe total  hydrocarbon concentrations.

 The result that compounds  other than BTEX make  up  the majority  of the
 total hydrocarbon concentration In most  of  the  samples  is not  surprising
 when  the  composition of  gasoline is  considered.   A  typical gasoline
 contains several  hundred hydrocarbon compounds, each falling Into  one of
 four  chemical  groups:   paraffins,, olpfIns,  napthenes  or aromatlcs  (NM
 EID).   The aromatlcs, which  1nclude.s BTEX,  are considered most Important
                                       30

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O



I


O
m
I
P
       RATIO OF BTEX TO TOTAL HYDROCARBONS  VS
                      CUMULATIVE PERCENT OF SAMPLES
                            FIGURE 7-1

                      CUMULATIVE PERCENT OF SAMPLES
                                                          100

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because they  are relatively  soluble  In water,  and  therefore,  present  a
risk  of ground-water  -untamination.    Table 7-1  shows a  list of major
components of  an API PS-6 Gasoline,  some  of which can be expected to be
present 1n soil  gas.  These  compounds  represent 04-'to  CJQ molecules  (API-
1985). :-,..--

Some  selected  sample chromatograms from Suffolk County, NY,  San Diego, CA
and Austin, -TX were qualitatively analyzed for a wide range of compounds
where  BTEX  was  found to  represent  less  than  10 percent of  the total
hydrocarbon-concentration.   These qualitative  analyses  Identified some
additional compounds:   methane, butane, Isopentane,  2-methylhexane, iso-
octane, and octane.  These chromatograms are  shown in Appendix  J.

7.2  DETERMINATION OF TOTAL HYDROCARBON CONCENTRATIONS  IN
     PARTS PER MILLION
The concentration of extremely dilute solutions are  expressed In parts
per million  (ppm).   Typically,  liquid solutions are  expressed 1n parts
per million by weight (ppmw) and  gaseous  solutions  are expressed  In  parts
per million by volume (ppmv).   (Himmelblau)

Parts  per million by volume  (ppmv) Is  a measurement unit that  1s commonly
used   in   the   environmental   Industry   for  reporting   air  pollutant
concentrations '(Hark and  Warner).   Many leak  detection  systems report
hydrocarbon contamination  in soil gas  in  ppmv (Radian).   Therefore,  parts
per million  by volume was considered appropriate rather  than parts per
million by weight.

Ppmv 1s defined  as:
                "•-.-.                 :         '-..ซ'
               'ippmv-  1 volume  of  gaseous  pollutant          Equation!
                         106  volumes  of pollutant &  air
                                      32

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                                 TABLE 7-1

                   MAJOR COMPONENTS OF API PS-6 GASOLINE
                                                   ) •
                                        PERCENT WEIGHT
 2-Methylbutane                        a  7?
 M-Xylene                               5  66
 2,2,4-Trlmethylpentane                 5*22
 Toluene                                4*73
 2-Methylpentane                        3*93
 N-Butane                               333
 1,2,4-Trimethy!benzene                 3*26
 N-Pentane                              3*U
 2,3,4-Trimethylpentane                 2 99
 2,3,3-Trlmethylpentane                 2 85
 3-methylpentane                        2*36
 0-Xylene                               2*27
 Ethyl benzene        •                   2*00
 Benzene                               _7 Q*
 P-Xylene                               17?
 2,3-D1methylbutane                     } 66
 N-Hexane                               J'JQ
 1-Methyl, 3-Ethylbenzene               1*54
 1-Methyl, 4-Ethylbenzene               1*54
3-Methylhexane                         1.30
                                    33

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The  data  in micrograms  per  liter  can  be  converted  to  ppmv by  the
following equation:               .    :
               ppmv
                                     RT
                                  .P. (Mol Wt)
                                           Equation  2
                    where:
          ppmv
          ug/i
             R

             P
             T
        Nol  Wt
Parts Per Million by Volume
Micrograms Per Liter
Gas Constant - 0.08205.  atm liter

Pressure In Atmosphere
Temperature 1n *K
Molecular Weight of Hydrocarbon
This equation was derived from the Ideal gas equation:
               PV - nRT

                    where:
                              V
                              n
                              R
              Pressure
              Temperature
              Volume
              Moles
              Gas Constant
                                                               Equation 3
The derivation is shown in Appendix J  (Wark and Warner).


The temperature  and pressure used  in  these  calculations represented the
ambient conditions measured  in the field at each site.


The  assumption  of  an  ideal  gas  was  justified  by  examining  a mean
compressibility  factor.   The mean compressibility factor is a factor that
is  introduced into  the  ideal  gas  equation  to account for non-Ideal or
real gas relationships.  Therefore, the ideal gas equation  becomes:
               PV
ZmnRT

where:
                           Equation 4
                               Zm - mean  compressibility factor
                                      34

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 If calculations can  show that Zm  Is  approximately equal to  one  for the
 soil  gas mixtures, then the assumption that the  soil  gas samples in this
;study can be approximated to an-ideal  gas is  valid qne.   (Himmelblau)
          . -    •            .       .                  >     %.
 Twq_ cases were examined  in  testing this assumption..  Because  the  complete
 composition  of soil  gas  is not  known,  Case  1 assumed soil gas  contains
 80%  air  and  Case  2 . assumed soij.gas  contains  20%  air.    The  mean
 compressibility  factor was determined to be 0.99  for  Case. 1 and  0.85 for"
 Case  2.   Therefore,  the  ideal  gas assumption introduces about  1 to  15
 percent error  in  calculating hydrocarbon concentrations in soil  gas.
 This   small  deviation  (1  to  15%) from the  ideal  gas  assumption  is
 reasonable  since  the  pressure conditions are  low,  and  the hydrocarbons
 in  the mixture are similar In  their chemical nature.

 The conversion  calculations from micrograms per  liter to ppmv were  made
 for each  sample  and  each compound within  that  sample.   The molecular
 weight of each compound was used in the conversion calculation.  However,
 for total hydrocarbons  (less  methane), an average  molecular weight was
 used.   This  average molecular weight  was based on the average  of the BTEX
 concentrations at  each  sample.

 To  compute total  hydrocarbons  (with methane), the methane concentration
 was converted  to ppmv and then  added  to total hydrocarbons (less methane)
 in  ppmv.   In these calculations,  the  detection limits were divided  by  2
 to  approximate  the actual concentration.  A  sample calculation is  shown
 in Appendix J.

 The average  of the BTEX  concentrations was used to compute  the  average
 molecular weight of each  sample  since BTEX concentrations were known  at
 all  sample points.   It  is  recognized that  some  error  Is Introduced  by
 using  only BTEX concentrations.   However, this  1s  considered to be the
 best   approximation  possible  from   the available  data.     Reporting
 hydrocarbon  concentrations in parts per million  may  be  useful for  some
 purposes.  However, reporting  them 1n micrograms per liter provides  more
 accurate values based on  fewer assumptions.
                                      35

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8.0  RESULTS
8.1  SOIL GAS DATA
The .maximum soil gas  concentration  values determined  in  this study are
presented 1n Table  8-1 for the sites In Austin, Table 8-2, for the sites
in the  Long Island Sound  area and Table 8-3 for those In the San Diego
area.

Average  hydrocarbon vapor  concentration  data and  site maps  for  all 27
gasoline  service stations are  presented In  Appendix  D.    The  average
hydrocarbon vapor concentration data, in most cases  represent mean  values
for  each  set  of  three  gas  chromatograph/flame  ionization detection
(GC/FID)  analyses  for each  sample.    These data  are  presented  in  two
formats:  1) concentration values listed by sample number and depth, and
2} concentration values listed by depth  and sample number.   In the  second
format,  computed average concentrations for all samples at each depth are
shown.   Additionally,  each site map  contains  an average total hydrocarbon
concentration  computed  from  concentrations  at each depth  within  each
hole.    In  computing  these  average  concentrations,  the  concentrations
reported  at detection limits  were  divided  by two  to  approximate  the
actual concentration.

A  pipeline  was  accidentally  punctured  during  the  investigations at
Station  16  In  Austin,  Texas.   Data  were collected during  four consecutive
days  at  this   station  to  study  soil  gas  migration  under  dynamic
conditions.  These  data are also  Included  in Appendix D.

Data  in  Appendix D presented both in microgram per  liter and parts per
million by volume.                        ••---  —

8.2  CONTAHINATtD SITE DATA
Soil  gas surveys were previously conducted at  a  number of UST sites  in
which  product  spills  were known to  have occurred.  Data from 27 sites
were  examined  as candidates.   Of these  sites,  8  were selected as being
appropriate for  comparison purposes because site maps were available and
contamination was known to exist.  Data  collected from  Austin Station #6
                                      36

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                                                    TABLE  8-1 .

                                MAXIMUM CONCENTRATIONS AT AUSTIN, TEXAS

                                (All concentration values in micrograms per liter)


Station 1
Station 2
Station 3
Station 4
Station 5
Station 6
10/27/87
10/28/87
10/29/87
10/30/87
- METHANE
(AS METHANE1
.790.0001'
210,000 '
120,000
870.000
1.500,000

710,000
8,600
13,000
4.800
TOTAL" HYDRO-
~ BENZENE-
7,400
ie,ooo _;
3.300
97.000
24,000
*
110,000
27,000
<250
53,000
TOLUENE ETHYLBENZENE XYLENES
5,300 . <310
. 17,000 . 160
1.700 <63
85.000 <680
26.000 25.000

90.000 <220
83.000 <250
<290 <270
1.600 <20
2.300
21.000
410
83,000
8,200

<240
70.000
<260
<31
CARBONS TANK TIGHTNESS
(LESS METHANE1 TEST RESULTS
21.000
63,000
5.700
210.000
1.100,000

960,000
790.000
690,000
290.000
Tight
Tight
NR
NR
Tight





 Station 7         59,000         <42          <48


Notations:

NAZ - Not Analyzed.
NR  ซ No records available showing tank tightness results.


Notes:
                                                            <50
                                                                          <58
                                                                                       55.000
                                                                                                           Tight
(2)   Total hydrocarbons are ealcutated from average response factors for Benzene. Toluene. Ethyibenzene and Orthoxytene.
(4)   SpiH occurred at 8:00 AM on 10/27/B7. These data were collected after the spffl.

(5)   At stations where C^/Cg are not analyzed, the methane concentration represents CrC5 peaks.

(6)   Tight means petroUte test results were < 0.05 gaRons per hour.
                                                        37

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                                                  TABLE 8-2.

                    MAXIMUM CONCENTRATIONS LONG ISLAND SOUND COASTAL AREA

                              (All concentration values in micrograms per liter)

                METHANE                                                 >
                                                                                TOTAL HYDRO-

•
Station 1
Station 2
Station 4
Station 5
Station 6
Station 1
Station 2
Station 1
Station 2
Station 3
Station 4
1^-05)
. fAS METHANE)
<40
140
<24
4
15
25,000
11,000
8
72
9
2,800

- BENZENE .TOLUENE
2,700 11.000
<29 420
3.700 1.000
2,300 13,000
<.6 55
<10 840
<6 <6
<.1 110
23 230
<.08 0.8
670 1.400
CARBONS
ETHYLBENZENE XYLENES (LESS METHANE)
12.000 10.000 270,000
130 <41 2.100
<37 <42 . 69.000
2.900 91 110.000
<.7 
-------
t
^

V
Station 1
Station 2
Station 3
Station 4
Station 5
Station 6
Station 7
Station 8
Station 9
TABLE 8-3:
MAXIMUM CONCENTRATIONS AT SAN DIEGO, CAUFORNIA
(All concentration values in micrograms per liter)
-..';'.--. >
-" ^METHANE
(AS METHANE^
48.000
110,000
'22
420.000
55.000
33,000
390,000
21,000
280,000

BENZENE
<89
<89
ฐ
<90
<86
<83
<90
<91
<98
'•'_
TOLUENE
11.000
11.000
17
17.000
2,600
23.000
31.000
22.000
32.000

ETHYLBENZENE XYLENES
<120 4.900
<120 5.100
<.05 .8
<-1 1,800
<-1 1,600
<-1 10,000
<.1 8,800
<.1 8.600
<-1 8,200
TOTAL HYDRO-
CARBONS
(LESS METHANE)
31.000
77,000
62
110.000
7.700
58,000
210,000
120,000
110,000

TANK TIGHTNESS
TEST RESULTS
Leak
Tight
Leak
Tight
Tight
Tight
Tight
Tight
NR
 Notations:

 NAZ - Not Analyzed.
 NR  - No records available showing tank tightness results.
 Notes;
B>
(4)  At stations where C^Cg era not analyzed, the methane concentration represents CrC5 peaks.
(5)  Tight means tightness test results were <0.05 gafons per hour.
                                                           39

-------
was  Included  as Site 9  since data from this  station  represents a fresh
spill.
                     . ,                              /
Table  8-4  gives  a  brief description  of  these  'sites  and  Table  8-5
presents the  maximum concentration data for them.  These sites Include
active  service  stations'"or  fueling  facilities.    Site  maps  and  data.
arepresented  in Appendix K.   Specific sample locations  at  these sites
were selected  for  use in the  contaminated  site database because of their
close proximity to the  tanks or contamination source.   It was-desirable
to  use  sampling  points  close  to  the  tanks  so  that  the data  would be
comparable to  the  clean  site  data  collected from the tank backfill areas
under  this study.   A  summary of  the  soil   gas data  is  Included in
Appendix K.  Total  hydrocarbon  values  are  reported less methane, and "as
benzene*.

8.3  EXPANDED  AUSTIN  STUDY
A four-day study was conducted  at  Austin  Station #6 to take advantage of
a spill that  occurred when a product line was punctured during  the field
Investigations.   Soil gas samples were taken  from  the same holes each day
and  the  results  are included  in Appendix  D.    Figure  8-1  shows  the
concentration  of total  hydrocarbons for each  of the four days  at 2-foot
and  6-foot depths, and  Figure 8-2 shows the corresponding concentrations
of C4-C6 components.

This Intensified study provided the following  basic Information:

        •  Total   hydrocarbon   concentrations    Increased   Initially  to
          >100,000 ug/1    near  the spill  site and higher concentrations
          migrated Into  the entire backfill  area.
        •  Total 'hydrocarbon  concentrations  decreased  after  peaking one
          day after the  spill.
        •  High concentrations of C4-C6 components  were  found  to parallel
          the total  hydrocarbon concentrations.
        •  Since high concentrations of C4-C6  components were  not usually
          encountered in the  field sampling at clean stations, it may be
                                      40

-------
                              TABLE 8-4

                 .DESCRIPTION OF CONTAMINATED SITES

                                                ">
       tSite 1    New  Service Station.    Tanks  were  tested
                  tight,  but   found   floating  product   in
                 -ground water.   Ground-water depth - 8'.

        Site 2    Active Service Station.

        Site 3    Active Service  Station.   Floating  product
                  in  ground   water.    Ground-water  depth  -
                  15'  - 20'.

        Site 4    Active Fueling  Facility.   Pipeline  leak.
                  No  ground-water  contamination.     Ground-
                  water depth =  >20'.

        Site 5    Active  Fueling  Facility.    Ground-water
                  depth - 12'.

        Site 6    Active Service  Station.    No ground-water
                  contamination.   Ground-water depth -  15'.

        Site 7    Active Fueling  Facility.

        Site 8    Active Service Station.   Floating product
                  on  ground  water.    Ground-water depth -
                  25'  -  35'.

        Site 9   Active Service  Station  (Austin  #6).  Spill
                  resulting from product like  puncture.


f!fiig:  I1??56  /1tes were selected  from  Tracer  Research Corporation
       files  to  develop database of  hydrocarbon  vapor concentrations
       for  sites with known hydrocarbon contaminated.
                                 41

-------
                                                TABLE 8-5  ;

                         MAXIMUM CONCENTRATIONS AT CONTAMINATED SITES

                             (All concentration values in micrograms per liter)

Station
Station
Station
Station
Station
Station
Station
Station

1
2
3
4
5
6
7
8
METHANE
"- 
1,200,000
NAZ .
NAZ :
NAZ
NAZ
NAZ
NAZ
100,000
BENZENE
.100,000
: <1ฐ; : -'
:. NAZ
780
28,000
<230-
<55
60.000
TOLUENE
68.000
1,200
31.000
620
11.000
4.000
1,700
40.000
ETHYLBENZENE
61.000
120
NAZ -
50

-------
                   TOTAL HYDROCARBON CONG (ug/I)

                             (Thousands)
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-------
                       frfr
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q>

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                  C4-C6 CONG (ug/I)

                     (Thousands)
           o
           o
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                 o
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               o
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     I
     04
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f$$,, ,,.,,,,,„

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at
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-------
 possible to  use  C4-C6 concentrations,  as  compared to  those  of total
 hydrocarbons,  to detect fresh  leaking conditions.  More study is reauired
:to  confirm this preliminary indication.
                                      45

-------
8.4  CHARACTERIZATION OF BACKFILL MATERIAL
Soil  moisture  and  particle  size  of  the  backfill  materials  impacts
hydrocarbon vapor  concentrations  because of liquid/vapor partitioning and
porosity effects.   Consequently,  soil moistures  and  sieve  analyses were
performed  011  soil  samples  collected  from  the  backfill  of  the  non-
contaminated sites. •  A summary of the results  of these  sample analyses
are  presented  in  Table  8-6.     Laboratory  analyses  are  included  in
Appendix E.                       '                                      -
                      • •—a* - * •
Backfill' soil material at  steel tank installations included fine,  medium
and sllty sands while the  backfill  at fiberglass tank installations were
of  fine  gravel,   gravelly  sand   and coarse  sand  mixed  with  gravel.
Moisture contents  were  higher in  the sands than  in the  gravels  and the
porosities of the sands were less than those of the gravels.

Because gravel  1s more porous and less moist,  hydrocarbons  will  likely
move  more quickly  through  gravel  backfill  than through  sand.    Also,
moisture  will  tend  to  Inhibit  the  movement of hydrocarbons and  will
absorb hydrocarbons through liquid/vapor partitioning.

8.4  U-TUBE SAMPLING
Leak  detection methods  are classified  into  four groups:   Volumetric,
Nonvolumetric, • Inventory  Control,   and  Leak  Effects  methods  (EPA).
Methods within  the Leak Effects  classification  are those  that identify
leaks by examining the environmental  effects  of the leak.  Those methods
usually require the  Installation  of monitor wells and chemical analysis.

Since soil gas  contamination 1s an  environmental  effect  that can result
from  a  leaking 1)ST system,  then  soil gas sampling, as performed in the
field Investigation of this  study,  would be classified as a Leak Effects
method.

Another   method   for   monitoring   leaks   within   the   Leak  Effects
classification utilizes  a U-Tube  device.  The U-Tube consists of a four-
Inch diameter, schedule 40, PVC pipe  installed as  shown in Figure 8-3.
                                      46

-------
                                        TABLE 8-6
                   MOISTURE RANGES OF SOIL AND BACKFILL SAMPLES

              (Values in percent by weight.  Moisture content analyzed by PSI,
                                     'Albuquerque, NM)
                       TANK
 LOCATION/5TATIQM      TYPE
 AUSTIN/TEXAS
     AU1               Steel
     AU2       -       'Steel
     AU3               FRP
     AU4               FRP
     AU5               steel
     AU6               FRP
     AU7               FRP

 STORRS, CONNECTICUT
     CONN1             steel
     CONN2             steel

 PROVIDENCE, RHODE ISLAND
     RH                Steel
     RI2                steel
     RI3                steel
     Rlซ                Steel

 SUFFOLK COUNTY. NEW YORK
     NY1                FRP
     NY2           '     steel
     NY4                FRP
     NY5               steel
    NY6               FRP

SAN DIEGO COUNTY. CA
    SD1               steel
    S02               steel
    SD3    -          FRp
    SD4            ..  steel
    SD5               FRP
    SD8               FRP
    SD7               steel
    S06               steel
    SD9               steel
                                        MOISTURE CONTENT
                                    SAND
 11-13
 3-4
 4-13
           GRAVEL
                                                        NATIVE SOIL
           10
           11
           79 •'
5

1-15
 15
 10
 4
 4
8
54
15-17
7-8
8-7
3-10
                     11
                               SIEVE
                          ANALYSIS RESULTS
Sitty sand

Sandy gravel
Gravefly sand
Medium sand
Fine gravel
                          Fine sand
                          Medium sand with silt
                          Fine sand
                          Medium to fine sand
                          Fine sand



                          Fine sand with silt

                          Fine sand with silt

                          Crs sand with gravel
                          Medium sand with silt
                          Medhm sand with sift
                         SWy sand
NOTE:  All Sieve Analysis results from backfill samples.
                                                                          ^
    *•  Native Soil Sample taken from saturated zone in bottom of monitor well.
                                         47

-------
      FINISHED
     -GRADE —
              OVERFILL
              PREVENTION
              DEVICE WITH EXTRACTABLE
              TEE TO GRADE
                    \
OBSERVATION WELLS: WATERPROOF CAPS
                  CAPABLE OF BEING
                  SEALED
         EXTENSION OF
         MANWAY TO GRADE
         (OPTIONAL) -
            /
      4'TEE-*-
SEALED
CAP  —
                                                                 NOTE: ALL PIPING
                                                                       TO BE 4'
                                                                       SCHEDULE
                                                                 --90'SWEEP
Sourca:  EPA
                                       4' DIAMETER HALF SLOTTED PIPE
                                       WRAPPED WITH FILTER MATERIAL—1/4"
                                       FOOT PITCH TOWARDS SUMP.
                                       SLOT SIZE .060
                                                                 PER
                                  •SPACING AND FILL TO BE IN ACCORDANCE TO
                                   TANK MANUFACTURER SPECIFICATIONS
                                  FIGURE 8-3
                        U-TUBE LEAK DETECTION SYSTEM
                                       48

-------
 These tubes were  Installed  under each tank within  the backfall material
 at Stations 14 and #6 1n Suffolk County, New York.

 A comprehensive comparison  of  leak detection methods was  not  within the
 scope of this project.  However, two  stations  with  U-Tubes were Included
 in  the  study  in order  to  make  a  comparison  of  hydrocarbon  vapor
 concentrations from  U-Tubes versus hydrocarbon  vapor concentrations  in
 soil  gas.

 The method of collecting soil  gas samples  from the backfill  areas  was
 presented ,1n Section  5.2.   Briefly,  soil  gas  samples were  collected  by
 Inserting  a  hollow probe  into the backfill  and evacuating a soil  gas
 sample using  a  vacuum pump.   Vapor samples from the U-Tubes  were  also
 collected by  Inserting a hollow probe to the desired  depth 1n  the U-7ube
 and evacuating a  sample using  a vacuum pump.  Samples were collected near
 the bottom  of the U-Tubes to minimize  the effects  of dilution from  the
 outside air.

 Since  vapor samples from  the  U-Tubes were collected  near the  bottom  of
 the U-Tubes,  these data were compared to soil gas samples  collected  from
 the backfill   at  the  10-foot  depth.   The  U-Tube samples  and soil gas
 samples  (at 10 feet) are shown  in Table  8-7.

At  Station  #4 In  Suffolk  County, New York,  the U-Tube sample  contained
90,000  micrograms per  liter of total hydrocarbons  (less methane) while
the soil  gas  samples ranged from 42,000 to 69,000 micrograms per liter  of
total hydrocarbons (less methane).   Benzene and toluene were found  in
both the U-Tube  and soil  gas samples while methane, ethylbenzene  and the
xylenes were  not found at detection limits for either the U-Tubes  or soil
gas samples,   i

At  Station  16 1n Suffolk County, New  York, the U-Tube sample contained  47
micrograms per liter of total  hydrocarbons (less methane) while the  soil
gas sample contained 1,500 micrograms per liter of total hydrocarbons
                                      49

-------
Station *4
U-Tubft-11*
                                             TABLE 8-7  :

                                       U-TUBE VAPOR SAMPLES
                                    SUFFOLK COUNTY, NEW YORK

                                        (Micrograms Per Liter)
              METHANE
                           BENZENE    TOLUENE   ETHYLBENZENE  XYLENES
<24
2800
                                        950
                                                      <37
                                                                   <42
                                                           TOTAL HYDRO-
                                                             CARBONS
                                                           (LESS METHANE)
                                                              90,000
                                                               TANK TIGHTNESS
                                                                 TEST RESULTS
SQ1-10'
SQ2-10'
SQ3-10'
SQ4-10'
Station *S
U-Tube-14'
SQ2-10'
<24
<24
<24
<24

<0.02
<0.4
?730"
880
3300
1800

<0.03
<0.8
120
300 .
1000
930

2
55
<37
<37
<37
<37

<0.04
<0.7
<42
<42
<42
<42

<0.04
<0.8
42.000
42.000
69,000
58,000

47
1500
 Notations;

 NAZ • Not Analyzed.
 NB ซ No records avalable showing tank tightness results.
 jMoios:

 (1) Total hydrocalbons are cateuteted from the average response factors for BTX

 (2) <24 indications that the concentration is less than the detection In* of 24 mJcrogmms per Her.
                                                    50

-------
 (less methane).  Only  toluene was Identified 1n both the U-Tube  and  soil
 gas samples.

 These results  Indicate that the  composition  of hydrocarbon vapors found
:Tn_U-Tubes:_are .similar to  the vapors found  in soil gas.   However,  the
 magnitude of the vapor concentrations may differ.   Thase conclusions are
 preliminary, since  more sample data-is  required to  accurately delineate
 these differences.-                        -

.816,  GROUND WATER SAMPLING
 Shallow ground water was  encountered at several locations which prevented
 soil  gas samples from  being taken at the  10-foot levels.   In these  cases,
 samples  of the ground  water were taken and analyzed by the GC/FID using
 the same procedures "as were  used for  the soil  gas.  These  results  are
 shown in Table 8-8.
                                      51

-------
STATION  SAMPLE NUMBER
                                                        TABLE 8-8

                                         HYDROCARBON CONCENTRATIONS FROM
                                                 GROUNDWATER SAMPLES
                            DEPTH (FT)  METHANE BUTANE  ISOPENTANE  BENZENE  TOLUENE  ETHTt-BENZENE  XYLENES  TOTAL HYOROCARBQ
AUS
AUS
AUS
AUS
AUS
AUS
AUS
AUS
AUS
AUS .
AUS
AUS
AUS
COHH1
COHH2
COHH2
CONN2
HW/H28 _ -
W/H20/P
HW/H20
HV/H20/S
KW/H20
SG4/H20
SG5/H20
SG2/H20
HW/H20 '
HW/H20/P
HW/H20/S
HW/H20
HV/H20
GV-04
GV-04
GU-03
GU-05
10/29' "'
10/29'
10/30
10/29;.
10/i9
10/28
10/28
•ID/28
10/29
10/29
10/29
10/30
10/28
11/12
11/13
11/13
11/13
7.
8.
8.
8.
9."
10.
10.
10.
11.
11.
11.
11.
NA
10.
6.
10.
10.
4000
• 5400"'
•6700
. 6600
4200
' .2100...
' 4700
1800
9300
10000
13000
4200
8600
62
18
18
4400
5700.
5000.
8900.
6200.
4900.
4300.
'2400.
2100.
5700.
1000.
690.
2400.
8500.
<7.
<4.
<4.
1700.
NA
-NAT
NA
NA
~NA
NA
-. 'NA '
NA
NA
NA,
NA
NA
NA
<6
<4
<4
<6
77000.
52000.
' 50000.
71000.
67000.
27000.
. 5600.
5600.
67000'.
7300.
7500.
4500.
10000.
• <6.
<6.
<6.
<30.
150000.
130000.
16000.
18000.
120000.
83000.
10000.
15000.
160000. .
15000.
15000.
1300.
25000.
<8.
<6.
<6.
-31.
<140.
<140.
<49.
<140.
<140.
<25.
<12.
<49.
<140.
<140.
<140.
<49.
<250.
<4.
<7.
<8.
<37.
80000.
110000.
<79.
110000.
51000. -
70000.
12000.
17000.
93000.
17000.
<130.
<79.
21000.
<8
<10.

-------
 9.0  UST REGULATIONS
?9.1  AUSTIN, TEXAS
 Underground  storage  tanks iat  existing  facilities i* Austin  must have  a
jpermit to  operate and ,are required  to  be tested  or'monitored for leaks  on
*a regular  basis.   If tank testing  1s conducted,  a,precision tank test,  as
 defined in the -NFPA National  Fires Codes, Section  329,  is performed  on
 each tank according to the following schedule:

           Tank Age                   ......
        (A$ of 6/18/85)                       Test Frequency
         0 to 5 years                               0
         6 to 10 years              Within  12  months  of 6/18/85  and then
                                    every 2 years  until  over 10 years old.
         over 10 years              Annually,  beginning  within 12 months
                                    of 6/18/85.

The  Department of Environmental  Protection (DEP)  assumed  the underground
tank responsibility from the  fire department  on January 14, 1987.  At the
present time,  the  DEP  has  approved  seven  tests  for  tank  tightness
testing:    Petro-tite  (Kent-Moore),  Hunter,  Horner,  Acutest,  Massney,
Tanty-Tech, and Tank Auditor.   Companies  who perform  these tests  are
registered  by the  DEP.

Monitoring  wells may be used as  an  alternative  to precision tank testing
for  leak detection of  underground storage  tanks.   For existing facili-
ties,  leak detection  monitoring by  surface geophysical  methods  such  as
ground   penetrating   radar,    electromagnetic  induction,   resistivity,
magnetometers,  and  X-ray  fluorescence  or by tracer  analysis may  be
permitted-only  by  approval  from the  DEP.
          **:-•,.
9.2  SUFFOLK  COUNTY, NEW YORK
Suffolk County  began  regulating underground storage tanks In  1980 when  a
law was passed stating that all  new tank installations except underground
petroleum tanks had to be double-walled  with  leak detection  between the
walls.   The law further  stated  that  all tanks had  to  be replaced with
                                      53

-------
double-walled  tanks by  1990.   Underground petroleum  tanks  could remain
single-walled  up  to 1985 1n critical aquifer  recharge areas  at which  time
they  had to  be replaced  with double-walled  tanks; with  leak detection
between walls.  The main aquifer recharge area 1s Inland and encompasses
75/4 of  the  Island.  'The coastal  areas  do not  affect the recharge of the
aquifer  and ..tanks  1n  this area  can remain single-walled with external
leak detection.

Testing  of underground  storage  tanks  . 1s  performed by  county licensed
testing  companies.   Tests  are performed  every two  years on older tanks
and every 5 years  on newer tanks (since 1975).  The only test recognized
by the  county Is the Petro-Tlte  Tank Tester  (formerly Kent-Moore)  system.

9.3  SAN DIEGO, CALIFORNIA
California  state  law regarding the monitoring and testing of underground
storage  tanks  allows  for  Implementation of  these  regulations to be
carried  out  at the  local  level.   Counties  Implement  the regulations
through  the Issuance of permits to underground storage  tank owners.  A
city  may,   by  ordinance, assume  such   responsibilities within Us boun-
daries.

All owners  of existing underground  storage tanks  are required to Imple-
ment  a  visual' monitoring  or  alternative monitoring  system.   Visual
monitoring  should  be used  as  the  principal  leak  detection  monitoring
method,  where  feasible.    When  visual monitoring  Is not  possible, an
alternative method should  be  Implemented.   The alternative methods are:

        •  Underground Storage Tank Testing,
          "
                  r Other Vadose Zone  Monitoring and Ground  Water Monitor-
          Ing with Soil  Sampling,
          Vadose  Zone Monitoring, Soil Sampling, and  Underground  Storage
          Tank Testing,
          Ground  Water and Soil Testing,
          Inventory Reconciliation,  Underground Storage Tank  Testing, and
          Pipeline Leak Detectors,
                                      54

-------
       •   Inventory  Reconciliation,  Underground  Storage  Tank  Testing
           Pipeline Leak Detectors, Vadose Zone, or Ground Water  Monitor-
           ing and Soil  Testing,
       ป•   Underground Storage Tank Gauging and Testing,  and
       *ป   Interim Monitoring.

Most tank  owners select the first alternative - underground storage tank
testing method.   In  the past,  Initial  testing  was required on all tanks
within 12  months  but subsequent testing on  non-leaking tanks  less than 10
years  old  was authorized to  be done in 30  months rather than annually.
Following  the expiration of the 30 month period, all underground  storage
tanks  operating under  the  option  will  require  annual  testing.   The
specific  test  is  not  designated,  but  it  must  comply  with the  NFPA
National  Fire Codes,'Section 329.
                                     55

-------
 10.0  TANK TIGHTNESS TESTING RECORDS
Tank tightness test records  were  available for most of the  study sites.
 Two  commercially  available systems  were used  to test the  tanks -  the
 Petro-Tlte Tester -(formerly Kent-Moore)  and  the Hunter Leak Lokater.   The
 Petro-T1te- Tester  has  been ~a recognized  standard  for  accurate  tank
-testing •within the  Industry for  many years.   This  system works on  the
 principle  of  applying  a-hydraulic  pressure  head  to the  tank  by  an
 externally connected, graduated standplpe  which 1s  filled with product to
 approximately  four  feet  above ground  level.    Product  level  in  the
 standplpe Is monitored for rise and  fall and measured  amounts  of product
 are  added or removed.   Readings are taken every  fifteen minutes  for six
 hours.
                     *                     „
 The  Hunter Leak Lokater measures  tank leakage by sensing weight  changes
 1n  a sensor which  1s suspended in  the liquid  of the  tank.    Changes in
 weight are transmitted  to  a recorder  that  registers these changes  as
 leaks In or out.  The only station In this study to use the Hunter  Leak
 Lokater was RI-4.

 The  manufacturers  of the Petro-Tite  Tank Tester  and the  Hunter  Leak
 Lokater  both report  that  these systems  can  detect  leaks  as low  as  0.05
 gallons  per hour (gph)  In tanks and pipes.  The  accuracy of these  tests
 1s currently  be"1ng examined in other EPA-related  studies.  Both tests do
 not  have  the capability  of detecting spills.

 Some records of tank  tightness  tests were obtained  from the  oil  companies
 who  owned the various sites.   In addition,  San Diego County  provided test
 results  for several  of the San Diego sites (SD-1  and SD-3  through SD-7).
 A government  agency  provided  tightness data  for Conn-1.   All  records
 which were obtained are .Included  In  Appendix L.   These records have been
 modified   to  protect the confidentiality of  the  site  locations  and
 operators.

 Table 10-1 presents the Tank Tightness Test Results of the  study sites.
 Tanks with absolute leak  rates  of less than  0.05 gph are labeled  "TIGHT".
                                       56

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                                     TABLE 10-1
                                TANK TIGHTNESS TEST
                                     -RESULTS
SITE/STATION
AU-1
AU-2
AU-3
AU-4
AU-5
AU-6
AU-7
NY-1
NY-2
NY-4
NY-5
NY-6
TANK '
MATERIAL
Steel
FRP -
Steel
FRP
FRP
Steel'
FRP
FRP
FRP
Steel
FRP
Steel
FRP
NUMBER
OF
TANKS
3
-•-.: i
3
-4
4
3
4
4
3
6
3
3
3
TANK
INSTALLATION
DATE
- 1961
. 1981
1973
1984
1981
1984
1984
1984
1982
1968
1980
1972
1980
DATE OF
TEST
4/9/86
4/9/86
5/1/86
NT
NTl
4/15/86
NT*
NT
T
12/30/85
NT
NA
NT
TEST
RESULTS
TIGHT
TIGHT
TIGHT


TIGHT



TIGHT

NA

FRP - Fiberglass Reinforced Plastic
NA  - Not Available
NT  - Tank Tightness Tests Not Required
1  if80'19?7  "aintenance records  Indicate  station had  several  small  soills in
   dispensing areasr, and possibly some pipeline spills.                   P
2  Spill occurred 'from product line during testing.  Corrective action was taken.
                                        57

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                             TABLE 10-1 (CONTINUED)

                               TANK TIGHTNESS TEST
                                     RESULTS
„
• ff
SITE/STATION
RI-1
RI-2
RI-3
RI-4











CONN-1




CONN-2

•
-.- .TANK
MATERIAL -
Steel
Steel
Steel "'
Steel

Steel

Steel

Steel'

Steel

FRP

Steel
Steel
Steel
Steel
Steel
Steel
Steel
NUMBER
OF
TANKS
3
,3 *
6 ,
1

1

1

1

1

1
.
1
1
I
I
I
I
2
TANK
INSTALLATION
DATE
1973
1976
1965
. 1966

1966

1966

1966

1966

1984

1984
1966
1978
1966
1966
1985
1940
-
DATE OF
JISJ
NA
9/25/87
NA
1/22/86
(Hunter)
1/22/86
(Hunter)
1/22/86
(Hunter)
1/22/86
(Hunter)
1/22/86
(Hunter)
1/22/86
(Hunter)
1/22/87
1/21/87
1/21/87
1/21/87
1/21/87
NA
NA

TEST
. RESULTS
NA
TIGHT
NA
LEAK1

TIGHT
A
LEAK2

TIGHT

TIGHT

TIGHT

TIGHT
TIGHT
TIGHT
LEAK3
TIGHT
NA4
NA
FRP - Fiberglass Reinforced Plastic
NA  - Not Available

1  Failed tightness test  on 1/22/86 due to a leak in system line.   No  records  on
   further testing.

2  Failed tightness* test on 1/22/86.  No records on further testing.

3  Failed tightness  test on 1/21/87  due to leak  in  suction  piping under   pump.
   Tank has been out of service since 1/87.

4  Hฃ0 was discovered in super unleaded tank in 1/85.   Tank was excavated
   and replaced with new steel tank.
                                        58

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                             TABLE  10-1  (CONCLUDED)

                               TANK TIGHTNESS TEST
                                     RESULTS
SITE/STATION

   SD-1
   SD-2.
   SD-3

   SD-4
   SD-5
   SD-6
   SD-7
   SD-8
   SD-9
 "TANK
MATERIAL

 Steel
 Steel
 FRP

 Steel
 FRP
 FRP
 Steel
 FRP
 FRP
 Steel
 Steel'
 Steel
 Steel
 Steel
NUMBER
  OF
TANKS

  2
  1
  1   ,

  3
  2
  1
  4
  3
  3
  1
  1
  1
  4
  3
    TANK   '
INSTALLATION
    DATE

    1971
    1971
    1978

    1972
    1982
    1982
    1965
    1983
    1983
    1972
    1965
    1965
    1965
    1967
DATE OF
TEST
11/11/86
11/21/86
11/21/86
6/17/87
12/10/86
12/22/86
11/5/86
5/7/86
5/18/87
4/16/86
4/16/86
4/17/86
1/21/86
.NA
TEST
RESULTS
TIGHT
TIGHT!
TIGHT2
TIGHT
TIGHT
TIGHT3
TIGHT
TIGHT
TIGHT
TIGHT
TIGHT
TIGHT
TIGHT
NA
FRP - Fiberglass Reinforced Plastic
NA  - Not Available
1  Failed tightness test on  11/11/86  due  to a leak in diesel vent line.
   on 11/21/86 and passed.

2  Failed tightness test  on  11/11/86  due to tank leak of -0.5 gph.
   on 11/21/86 and passed.

3  Failed tightness test on 12/10/86 due to leak in the vapor line.
   Retested on 12/22/86 and passed.
                                                         Retested
                                                         Retested
                                     59

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Tanks with  leak rates greater than 0.05  gph  are labeled  "LEAK"  and an
explanation,of the leak and the  surrounding circumstances Is provided In
-the accompanying .footnote.   Several sites had no  available records or had
•not been tested due  to recent tank  Installations and are labeled  "MA" and
"NT", respectively, In'the table...

There 'are ปa total of 100 underground  storage  tanks at  the 27 gasoline
stations that were 'studied.  0,f  this total, 63 tanks are fabricated from
steel and were Installed  between 1940 and  1984.   The  remaining  37 are
made of  fiberglass reinforced plastic  (FRP) and  were .Installed between
1978 and 1984.

Of the 63 steel  tanks, 42 were  determined tight In recent tests.  Three
steel tanks,  two  from RI-4 and  one  from  CONN-1, were found to be leaking.
No further  records  are  available  to  Indicate  repair  and/or subsequent
testing of these tanks.   No  tank tightness test records are available on
the remaining 18 steel tanks.

Tank tightness  tests were conducted on 12 of the FRP  tanks; all tested
tight.   Tests on  the remaining  25 were  not required  by the regulating
government agency due to the relatively new age  of the tanks.

Seven gas stations had histories of leaks:  AU-4 & 6;  RI-4; CONN-1 & 2;
and  SD-1  &  3.  Maintenance  records from AU-4 for the  period of 1980 to
 1987 Indicate that numerous  surface spills  occurred from vandalized split
hoses and dispensers.  Records  also exist of  low  or slow  flow which might
Indicate pipeline  leaks.   AU-4  was  removed from the database as a  clean
site because  of Its  history  of high maintenance  and Its unusually  high
soil gas  concentrations.   AU-6  was also  removed from the database because
of a known  spill  that occurred  from a product line  break.  The five other
stations remained  1n the database  as  background data because the soil  gas
concentrations were not excessive.
                                       60

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 11.0 DATA ANALYSIS
 Geoscience Consultants,  Ltd.  investigated  hydrocarbon vapor  concentra-
 tions in the backfill of underground storage tanks ;(UST)  In  two phases:
^a field investigation phase and  a data  analysis  phase.

 Since no.database for soil gas information  in non-contaminated  UST  sites
 was  known to exist,  it  was necessary to conduct field  investigations  to
 establish  a  baseline of  hydrocarbon  vapor concentrations.    Data were
 collected  from twenty-seven gasoline service stations  selected as non-
 contaminated  sites.    Selection  criteria  (Section  3.0)  were  used   to
 develop a data   set which   Included  a  variety  of   tank  ages,  tank
 materials,  stored  products  and  backfill   materials.    The  underground
 storage tanks selected were believed to be non-leaking, or "tight."  UST
 systems were  considered  to  be  tight  if:

        •   Tightness  testing Within the previous two  years Indicated the
           system  to be without leaks, or
        •   In  cases where  test records  were not available,  the  environ-
          mental  and  maintenance personnel of  the  oil  company had   no
           knowledge of contamination due to  leakage at the site.

Two  stations  sampled  (Stations #6 and  #4 In Austin,  Texas)  were deter-
mined  to be  inappropriate  as non-contaminated  sites,  and their data were
not  Included  in the data set.   Station #6 had a fresh gasoline  spill from
a  product line  puncture that occurred during  the  field investigation.
Station  #4 had  a history of frequent product  line  and  dispenser problems,
according to maintenance records,  and no test records were available.

The  non-contaminated  site  data,  therefore, consisted  of 279  soil gas
samples taken from twenty-five service stations.

Contaminated  site data  were  obtained  from Tracer Research  Corporation
historical records.   The contaminated site  data was  selected from  sixty
soil gas samples  taken from nine  sites  having  known contamination from a
petroleum  fuel  leak  or spill.    These sites were  all  active gasoline
service stations or fueling facilities.
                                      61

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The strategy for data  analysis  was determined by the fact that no usable
data for  non-contaminated sites were known to  exist.   Therefore,  analyses
were  employed ปwhieH~  could delineate  patterns  In;  the  data,   if  they
existed,  and -which could prove  useful  in  establishing contamination
thresholds."   ~-

Data analysis was broken down Into three parts:

       -•  Analysis  of  total  hydrocarbon concentrations  ("less*methane"
          and'"Including  methane") in soil  gas at non-contaminated sites
        •  with  the objective of establishing  a  descriptive statistical
          baseline.
       •  Comparison of the non-contaminated  site baseline information to
          data  from sites where petroleum fuel contamination  was  known to
        •  exist.     This   comparison  examined  the  appropriateness  of
          establishing  an  upper  limit  for  total  hydrocarbon  (less
          methane)   vapor concentrations at  non-contaminated sites that
          could  provide  a "threshold"  concentration value  between non-
          contaminated and contaminated sites.
       •  Non-parametric   statistical  testing  of  each  data set  (non-
          contaminated  and  contaminated)   in  order   to   substantiate
          observed  differences  and  Identify  significant trends  among
          total hydrocarbon vapor concentrations, sample  depth,  location,
          'backfill  materials, tank age and tank material.

Analyses  focused  on concentrations  of  total  hydrocarbons (less methane)
in  soil  gas,  as  the  presence  of  total  hydrocarbons   1s Indicative of
contamination  from a petroleum  leak or spill.  Methane was excluded from
the reported concentrations In  order to present  a  profile of compounds
similar to  that of gasoline, and to exclude methane concentrations which
may have  been present due to naturally-occurring decomposition of organic
matter.

The  use   of  total   hydrocarbon  concentrations   in   soil   gas  as   a
contamination  index is consistent with current EPA ground water  and  soil
monitoring  proposals.   An analysis  of total  hydrocarbon  data (including
methane)  is presented  (Section  11.2) to  show  how  these  data are
                                      62

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 distributed  as  compared  to  total   hydrocarbon   concentrations  (less
 methane).   This comparison may be useful  in  evaluating  total  hydrocarbon
 concentrations from leak detection devices which include methane.

 Accuracy In the data  analysis was essential  because the results may  be
 used  to provide "direction for  future leak  detection  methods.    Towards
-this  goal,-the soil gas  data were-reported  1n mlcrograms  per  liter (ug/l)_
 because this  provided ,a  better approximation  of  the total  hydrocarbon
 vapor concentrations  than parts "per million by  volume  (ppmv)  (Section
 7.0).   'Also, three gas chromatograph/flame ionization detection  (GC/FID)
 analyses were generally performed on  each sample,  and the arithmetic mean
 of the usable samples, as judged by the GC/FID  operator,  was  used in the
 analyses.    The  repllcablHty  of  analytical  results  were  within  25
 percent of  the average concentration  value for each  sample.

 11.1  EMPIRICAL DISTRIBUTION OF TOTAL  HYDROCARBON
      CONCENTRATIONS (LESS METHANE) FOR NON-CONTAMINATED
      SITES
 An empirical distribution  of the  total hydrocarbon  (less methane)  vapor
 concentrations 1n  soil  gas  surrounding non-contaminated UST systems  1s
 useful  for  two reasons:

        • It shows what concentrations can be considered  as  "background"
          concentrations 1n a UST  system,  and
        • The   distribution  can  be  compared  to  similar  concentration
          distributions from  contaminated  sites.

 Even  at sites with no known  contamination, a level  of  total  hydrocarbon
 vapor concentrations  is  present resulting from surface spills or  small
 undetected  leaks of .petroleum fuels.   These  concentrations are defined  as
 the total hydrocarbon  background level  of  the soil gas at the  site.

 The  best   way  to describe  the  distribution  of total   hydrocarbon
 concentration  data 1s  by using the relative frequency distribution.
 The relative frequency distribution's  obtained by  grouping the data Into

                                      63

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concentration classes  and determining the proportion of  samples in each
of the classes.   This distribution -for  total  hydrocarbon (less methane)
concentrations Is shown  In  Table 11-1  in microgramsj per liter (ug/1) and
In Table 11-2 1n parts per milIon by volume (ppmv).

The  classes  in  these  distributions  were  chosen  to  show the  overall
distribution of samples,  as  well  as the  percentage of samples below 1500
ug/1  (approximately 500  ppmv).   The  1500  ug/1 concentration  class was
chosen because  proposed  EPA regulations concerning  leaking  UST systems
have considered 500 ppmv as a possible  threshold  value to differentiate
non-contaminated  from   contaminated  sites.     The.  relative  frequency
distribution  shows  that  53.2 percent of  the  samples were below 1500  ug/1.
The overall  distribution shows that 93.1 percent of the samples  were less
than 100,000 ug/1.

There are  nineteen  samples  (6.8 percent  of the total)  that have average
concentration values greater  than  100,000  ug/1.   Site  and  sample data
were examined to  explore causes for these high values. Table 11-3 shows
the site  and sample location  of the data points.   The nineteen samples
came from  seven service  stations studied.  Tightness test results showed
the UST  systems  at four of these  stations  to be tight,  while no test
records were  available for the other three.

A   possible  source  for  the  high  total   hydrocarbon  (less  methane)
concentrations  at the seven sites  Is  from  surface  spills.    Interviews
with  the  participating  oil  companies   revealed  that  underground fuel
storage  tanks  are  occasionally  overfilled   by the  transporter.    Since
there is no system  for monitoring these  surface spills, the frequency of
this event is unknown.,  .  ,.                  ...              -       .
               t
Another possible  source for the  high  concentrations could be related to
the  age  of  the tanks.    Six  of  the   stations  contained  steel   tanks
Installed  between the years  1965 and 1971.  One station contained a
                                      64

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                                             TABLE li-1

                           DISTRIBUTION OF NON-CONTAMINATED SITE DATA
                              FOR TOTAL HYDROCARBONS LESS METHANE
                                                                             CUMULATIVE
     Not Detected    -             65                 '•••?* 2
           < 150ฐ    "             84       -  *         ]?) o                       ll'l
      1501 - 5000  •-,-       -      17                    ? n                     - *3'2
      5000 - 10,000             ';12                    43                       5?'2
    10,000 - 50,000               56      ^            20 0                       S3'5
    50,000 -. 100,000   -          27                    96                       ?3'5
   100,000-270,000              18                    *A                       93'1
       l.JOO.OOO               _   ,                    ซ"J                      ^
Mean         23,300
Median          800
Upper
 Quartile    33,000
                                           65

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   ;          .                            TABLE 11-12

                         DISTRIBUTION OF NON-CONTAMINATED SITE DATA
                             FOR TOTAL HYDROCARBONS LESS METHANE

                                (Parts Per Million by Volume)

          ,   %    -    .                                                     CUMULATIVE
          vPPnป)                  •---                                          RELATIVE
CONCENTRATION RANGES          NUMBER OF     '    RELATIVE FREQUENCY         FREQUENCY (%)
(Hicroorams Per Liter         SAMPLES            DISTRIBUTION t%)            DISTRIBUTION

    Not Detected "        "        65                    23.2                      23.2
        < 500                    88                    31.4              -        54.6
    501 - 1,350                  14           .          5.0                      59.6
  1,351 - 2,700                  11                     3.9                      63.5
  2,701 - 13,500                 57                    20.4                      83.9
 •13,501 - 27,000                 27                     9.6                      93.5
 27,001 - 72,900                 17                     6.1                      99.6
     > 72,900                     1                   	JL                     100.0
                                280                   100.0
Mean          7,200
Median          220
Upper
 Quartile     9,200
                                          66

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                                          TABLE 11-3

                 1TOTAL HYDROCARBON CONCENTRATIONS LESS METHANE
                      GREATER THAN 100,000 MICROGRAMS PER LITER
 STATION

 Austin. Tx
  Station #5
 Suffolk County. NY
  Station *1  (1)


  Station t5

 San Dleao. C/\
  Station 4>4
  Station #7 (1)
 Station #8 (2)


 Station *9 (1)
 TANKAGE
    AND
 MATERIAL
                      1971-Stee)
 PETROTITE
 TEST RESULTS
                Tight
1   9 ' 8   2
Fiberglass

1972-Sted
1965-Steel
1965-Steel
1965-Steel
1967-Stee)
NR
NR
Tight
Tight
               Tight
                                    NR
                                SAMPLE NUMBER-nFPTH
 SQ1 -2
 SQ1 -6
 SQ1 -10
 SQ2-6
 SQ3-2
 SG4-2

 SQ2-2
 SG2-6
 SG2-8
 SG4-10
SQ4-2
SG1 -10
SQ2-2
SQ2-6
SQ2-10
SQ2-10
SQ3-10
SQ4-10
SG2-6
                       TOTAL HYDROCARBONS
                       CONCENTRATION LESS
                       METHANE
                       (Mlcroorams Per Liter)
  150,000
  110,000
1.100,000
  120.000
  190,000
  140,000

  170.000
  210,000
  270,000
  110,000
 110.000
 120.000
 120,000
 130,000
 210.000
 110.000
 104,000
 120.000
 110.000
NOTES: (1) SQ2 is located near a tank ซ cap.
       (2) Station ซ to an inactive service station.
                                            67

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fiber-glass tank Installed  1n  1982.   The possibility of undetected leaks
could be greater 1n older tanks.
11.2 EMPIRICAL DISTRIBUTION OF TOTAL HYDROCARBON
   .  CONCENTRATIONS (INCLUDING METHANE) OF NON-
     CONTAMINATED SITES-
It may be useful  to report total  hydrocarbons as
two reasons:
               'Including  methane"  for
       -•  Methane  can   also  occur  by  the  natural  decomposition  of
          petroleum fuel In  soil, and
       •  Some UST  leak detection methods  are  based on detection equip-
          ment that  1s  sensitive to any  hydrocarbon compound.  Therefore,
       .  these detection  devices will  detect the presence of methane in
          soil gas in addition to other hydrocarbon  compounds.

The   empirical   distribution   of   average   total    hydrocarbon   vapor
concentrations  (including  methane)  is compared  to   the  distribution of
average  total   hydrocarbon  vapor  concentrations   (less  methane)  in
micrograms per  liter in Table 11-4, and  in parts  per million by volume in
Table 11-5.

The distribution  of total  hydrocarbons  including methane are similar to
total  hydrocarbons  less methane in two  class ranges:  5,001 - 10,000  ug/1
and 50,001  - 100,000 ug/1.   However,  differences  exist In the other class
ranges.    These  differences can  best  be  shown   by   summarizing  the
distributions into two  classes as follows:
      CONCENTRATION RANGES
     (Mlcroarams  Per  Liter)
               i
          ฃ 100,000
          > 100,000
   RELATIVE FREQUENCY PERCENT
Less Methane      Including Methane
     93.2
      6.8
    100.0
 73.8
 26.2
100.0
                                      68

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                                TABLE 11-4 •"

            MCTurF TOTAL HYDROCARBONS INCLUDING
            METHANE AND LESS METHANE AT NON-CONTAMINATED SITES

                          (Micrograms Per Liter)   .;



 CONCENTRATION  RANGES        RELA™E  ^QUENCY DISTRIBUTION  (PERCENT)
 (Mlcroqrqms Per  HtPr          Less Methane          Includina
      < 5,000^*                   59 2                      AO o
   5,001 -  10,000                  43                      4?'f
  10,001 -  50,000                 20.*0                      n'n
  50,001 -  100,000                 96                      'H
 100,001 -  400,000                 64                      •>? o
 400,000 -  1,000,000               -                        Z\'*
   1,100,000                       05
   1,250,000                       .                         "
                  •  .   .           100.0
* Includes non-detected values.
                                   69

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                                TABLE 11-5

                COMPARISON OF TOTAL HYDROCARBONS  INCLUDING
               METHANE AND LESS METHANE AND LESS  METHANE AT
                          NON-CONTAMINATED SITES

                       (Parts Per Mi 11 i on by Vol ume)>
CONCENTRATION RANGES
(Mlcroorams Per Liter
                 RELATIVE FREQUENCY DISTRIBUTION (PERCENT)

                     Less Methane          Including Methane
       < 500 .*.
    •501 - 1,350
  1,351 - 2,700
  2r701
 13,501
 27,001
 72,901
250,001 -
   > 600,000
13,500
27,000
72,900
250,000
600,000
54.6
 5.0
 3.9
20.4
 9.6
 6.1
 0.4
                                  100.0
45
 2.1
 2.5
 8.9
 5.0
11.1
15.0
 6.4
                                                  100.0
  Include non-detected values.
                                   70

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 The  effect  of Including methane  In  the total hydrocarbon concentration is
 to lower  the percentage of  samples  with concentrations equal to  or less
 than  lOO.OOOug/1  Kor  30,000  ppmv)  by  21  percenj.    This  effect  was
 -expected  since  the ;soil gas data  showed high concentrations of methane at
 many of the  sites.   This was probably due to naturally-occurring  methane
 as well  as .methane which occurs  from the decomposition  of  hydrocarbon
 compounds.

 11.3 COMPARISON OF TOTAL HYDROCARBON CONCENTRATIONS FOR NON-
      CONTAMINATED SITE AND CONTAMINATED SITE DATA SETS
 The data  distribution  in  Section 11.1  has shown  that  a wide  range of
 background  hydrocarbon  vapor  concentrations exist in  the  soil  gas in
 backfill at  non-contaminated UST  sites.  These  concentrations ranged  from
 the  lower detection limits of  0.02  micrograms  per liter (ug/1)  to
 1,100,000  ug/1  for  total  hydrocarbons  (less methane).   Although  much
 variability  exists  in  these data, a  comparison of  these data to  data
 from  known  contaminated  sites 1s  required  to  determine if background
 vapor concentrations differ  from  vapor concentrations  at sites with  known
 contamination.    If statistically  significant differences exist  between
 these data distributions,  then the results  of  this comparison could be
 useful  to  UST  regulators,  service station  owners  and  others who  must
 interpret  soil  gas  data to  determine if contamination  exists at a UST
 site.

 An   evaluation   of   these   differences   could   also   determine   the
 appropriateness  of   establishing  a  threshold  concentration  for  total
 hydrocarbons  (less  methane).  Statistical testing was  performed  (Section
 11.4) to determine  If observed  differences  concluded from the descriptive
 statistics are significant  differences.
               i
 In order for the data sets to be  comparable,  the data in each set  must be
 collected  In  a  similar  fashion.   Since the  contaminated site data  set was
 obtained from historical  records,  data for  this  set  were  selectively
 chosen to  be  iconslstent  with the samples taken at non-contaminated sites
during the field Investigation.
                                      71

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 The  sampling "Strategy  for  non-contaminated  sites,  as outlined  In the
 Field Methods  (Section  5.0)  was to collect samples  from the backfill of
 the  tanks  and -at depths  of  2,  6  and  10  feet. ; Although  samples at
 contaminated.sites-were .usually not  in backfill, data  were  chosen that
>wefe within approximately  50 feet of the USTs,  and  at 2,  6,  and 10-foot
 depths.   The method  of sampling was  similar for  both data  sets  since  soil
 gas  samples were collected  by Tracer  Research  Corporation  (TRC)  using-
 slmllar procedures.   . r-r .

 In this comparison,  total  hydrocarbons  are reported "less  methane" and in
 micrograms  per  liter for  both data  sets. - The  total  hydrocarbon  (less
 methane) concentrations in the non-contaminated data set were calculated
 from average  response  factors for  benzene,  toluene,  ethyl benzene  and
 xylenes  (BTEX).   However,  in the contaminated  data  set, total hydrocarbon
 concentrations  (less  methane)  were calculated  from the response factor
 for benzene.  Therefore,  contaminated site  data could  be as much as 50 to
 100 percent higher  If it were reported on  the basis  of an  average BTEX
 response factor.  A  comparison of calculation  methods and their effects
 on total hydrocarbon concentrations was  presented in Section 7.0.

 The sample size  for  the non-contaminated data set was 279  samples from 25
 sites.   The sample  size for the contaminated data set was  60  samples  from
 9  sites.

 The  descriptive   statistics  used  to compare  the  non-contaminated  and
 contaminated data sets  were:    mean,  median,  upper  quartile and  the
 relative frequency distribution percentages.   These statistics  are  useful
 because   they  show   the   distribution   of  each  data set   and  these
 distributions  cSn be  compared  even though the  sample  sizes  in each data
 set are different.   The descriptive statistics for  the non-contaminated
 sites were shown  in Table 11-1  and  those for  the contaminant  sites are
 shown In Table  11-6.  A  comparison  of these descriptive  statistics are
 shown in Table 11-7  in micrograms  per liter  for total hydrocarbons (less
 methane).   The  relative frequency distribution for the hon-contaminated
                                      72

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                   TABLE 11-6

DISTRIBUTION OF CONTAMINATED SITE DATA FOR TOTAL
           HYDROCARBONS LESS METHANE
CONCENTRATION RANGES-
(MICROGRAMS PFR I JTFR)

  Not Detected       ..
 50,000- -• 100,000
100,000 - 270,000
270,000 - 1,100,000

    >1'000'000
                              NUMBER OF
                              '
                1
                6
                13
                         FREQUENCY
                         DlimSrinil

                               33%

                                                100.0%
                                             CUMULATIVE
                                             RELATIVE
                                                     w
                                                 100.0
Mean
Median
Upper Quart He
160,000
  9,000
 22,000
                   73

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                               TABLTir-7 -

             COMPARISON OF NON-CONTAMINATED AND CONTAMINATED
                       SITE DATA DISTRIBUTIONS FOR
                        HYDROCARBONS LESS METHANE
 ---  '   -•-:                 RELATIVE                  RELATIVE
                 .      - -      FREQUENCY                 FREQUENCY
CONCENTRATION RANGES          PERCENT                   PERCENT
fHICROGRAMS JER LITER).        CONTAMINATED              NON-CONTAMINATED
  Not Detected                   -3.3                      23.2
        < 1500                    31:7                      30.0
   1501 - 5000                    10.0                       6.0
   5001 - 10,000                  10.0                       4.3
 10,001 - 50,000                  10.0                      20.0
 50,001 -  100,000                  1.7                       9.6
100,001 - 270,000                 10.0                   .    6.4
270,001 - 1,100,000  *  .           21.6                       0.4
    2,200,000                      1.7                       0.0
                                 100.0                      100.0
Mean                            160,000                     23,300
Median                            9,000                        800
Upper Quartlle                  220,000                     33,000
                                   74

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 site data  was shown  in Figure 11-1  and  that for  the  contaminated site
 data 1s shown in Figure 11-2.
                                                    /
 The relative  frequency distributions show much variability  in both data
 sets.   Nine concentration ranges were selected to show this variability.

 An evaluation of the  means and medians gives  additional information about
 these  data sets.   The mean is an arithmetic  average  that  is computed by
 summing the  concentration values  and dividing  by the  total number  of
 samples.    The median  is  defined  as the  middle  value after  the  samples
 have been  arranged  in  order of magnitude (Hoel 1967).

 In both data  sets, ,the  medians  are much lower than  the  means.   These
 differences show that both data  distributions are skewed  to the  right
 with a majority of samples 1n the  lower  concentration ranges. The high
 mean values show the  effect  of a  few high concentration  values that exist
 in both data distributions.

 Although similarities  exist in the distribution of these data sets, some
 differences can also  be  seen.  An  order  of magnitude difference  exists
 between the mean of each  data set,  and between the medians of each data
 set.   This suggests that although similarities exist in how  these data
 sets are skewed,  that an  order of magnitude difference exists for  much  of
 the data.

The  order  of magnitude can best be  seen 1n the concentration  ranges above
 10,000  ug/1.    The  relative  frequency percentages  from Table 11-7 are
 summarized  below for  concentrations  above 10,000  ug/1, or  about 3000
 parts per nillion by volume.
               i         '
      CONCENTRATION RANGES            RELATIVE  FREQUENCY PERCENT
     (Hicroarams Per Liter)        Non-Contaminated    Contaminated
      10,000 -   100,000                29.6               13  4
     100,000 - 2,200,000                 6.9               33[3
                                        36.5               46.7
             ;    ~   '       '           75

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            RELATIVE FREQUENCY DISTRIBUTION (%)
                  01
                  O
                            01
                            O
                                  at
                                  O
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01
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o
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 vl
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                                                             00
                                                             -H

                                                             O

-------
CONTAMINATED  SiTE  DATA DISTRIBUTION
           TOTAL HYDROCARBONS LESS METHANE
iuu -
90 -
& 80 -
Z
o
g 70 -
m
1 60 "I
Q
RELATIVE FREQUENCY
\
:> S. 8 ป•- ฃ g
U- 	 1 - I 	 1. _.l 	 L_

' " • '• -- ' . ' ' ••• '- ' i '" '

. • ..



///
% ^
-r-^n Y//A fySA ^/// ^//A V// V//
777\ \/// \//A \/// '/// (/// y///
•••••ill i
0 1500 5000 10000 50000 100000 270000 1100000 220onnn
            MAXIMUM CONCENTRATION (ug/!)



                  FIGURE 11-2

-------
Most of the non-contaminated  samples  occur in the 10,000 to 100,000 ug/1
range, while most of the contaminated samples occur above 100,000 ug/1.
                    y M                             ;
                                                   i
The order of .-magnitude  difference  between  the data sets can also be seen
by comparing'-the upper quartiles  of each  data  set.    The  definition  of
upper quartile is that  75% of the  samples  occur below the upper quartile
(Hoel 1967).

The  upper  quartile for the non-contaminated and  contaminated  data sets
are 33,000 ug/1 and 220,000 ug/1, respectively.

The observed  conclusions from these descriptive,  statistics  is  that both
data sets contain much  variability and  both are skewed to the right.  An
order  of   magnitude   difference  exists   between  the  data  sets  for
concentrations above  10,000  ug/1.   Statistical testing  is  Section 11.4
confirms the significance of these differences between the data sets.

11.4 NON-PARAMETRIC STATISTICAL TESTING
The  purpose of statistical methods is to  describe data quantitatively,
and  to  draw  inferences  for decision-making  (Kilpatrick  1987).    The
descriptive statistics  have been examined  in the previous sections, and
these  described   the   means,  medians,  upper  quartiles  and  relative
frequency distributions for the data sets.

In  this section,   statistical  methods  are  employed  to  determine what
Inferences  can be made  about  the  non-contaminated site and contaminated
site data sets.

The statistical testing in this data analysis served two purposes:
               i
       •  The  testing   determined  the  significance  of  the  observed
          statistical differences  between  the data sets  (non-contaminated
          and  contaminated) noted  in the descriptive statistics, and
      •••  The  testing   delineated  data  patterns  that  existed among such
          parameters as location of.site,  depth  of sample, tank material,
          tank age  and  backfill material.
                                      78

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 The types  of statistical tests chosen were  dictated by the characteris-
 tics of  the data  set  distributions.   These  distributions,  as described
 previously,  did  not  appear  to  correspond  to  apy   known  statistical
 distribution :such  *s ,a  Normal  distribution.   Non-parametric statistical
 metiiods were usfld since these methods did  not require that  the sample
 data correspond to a kiipwri statistical distribution (Harval).

 These statistical" methods also  introduce  the element  of  probability as
 related  to  the  drawing of  conclusions.     Probability  was  considered
 Important 1n developing  conclusions about  these data  sets  because these
 data sets do not  contain complete Information about the entire data set
 of underground storage tanks  that exist.   Therefore,  a probability must
 be attached to any conclusions made about  the data sets.  A discussion of
 the risks associated with  statistical  testing, and how these  risks were
 controlled  is given in  Section 11.4.1.

 11.4.1  The Risks  Associated with Hypothesis  Testing
 There  1s always  the possibility of  making  an  Incorrect  decision  when
 testing  a  hypothesis.    This  is  because  inferences about  a  particular
 distribution are based  upon  random samples  from  that  distribution.  A
 statistical  hypothesis  1s simply  an assumption or statement, which may or
 may not be  true, concerning one or more populations.

 There are  two types of error  or risk associated with the testing  of any
 hypothesis.   Type  1  error Is  the probability of  rejecting  a true  null
 hypothesis,  while  Type 2 error  1s  the probability  of rejecting a  true
 alternative  hypothesis.   A null hypothesis  Indicates that no differences
 exist  between  distributions.    An  alternate hypothesis  indicates  that
 differences do exist between distributions.
               t
 Type 1 error Is usually  controlled  by  setting the significance level of
 the test to a small value.  This significance level, designated as  "p",
 numerically  describes the  probability that  a particular  hypothesis is
true.  Typically this value Is set at 0.05.   This corresponds to a
                                      79

-------
 confidence level  (probability) of  95 percent.   The significance  level
 becomes a specification of the Type  1 error rate of probability.    :
                     -'  '                            i
                                                    >  •   --.
'Type-2  error  Is usually-con trolled by  taking  a properly-si zed  sample.
 Th~is'study did not  consider the control  of Type 2  error  as a criteria for
 determining sample size*.   However,  when  large discrepancies exist between
 the  Information  contained in  the .samples and  the  specification of  the
 null hypothesis with respect  to the sample's, then  the Type 2  error will
 generally be small.     :;         "     .    .

 When testing  more than one hypothesis,  the  Type .1  error rate must  be
 controlled.  A simple  example -will  demonstrate  what happens to the Type 1
 error rate when testing several hypotheses.

 Suppose that  each of  10  independent  hypotheses are to be  tested at  a
 significance level  of  0.05.   If  the null hypothesis is true  in all  10
 cases,  the probability of detecting this  is only  0.60.   Therefore,  the
 Type 1  error  rate Is  0.40,  which is  totally unacceptable.   One way  to
 control the Type 1 error  rate  when  testing several  hypotheses  is to test
 each hypothesis  at  a  reduced  significance level.    A good conservative
 procedure for  determining the  significance  level  in a  multiple  testing
 situation  1s  the  Bonferroni  procedure.    This procedure 1s  described
 below.

 If  an   overall   Type   1   error rate  of  0.05  is   to be  attained,  the
 significance level  for each  hypothesis  tested  is  computed by dividing
 0.05 by the number of hypotheses to  be tested.

 In the  example -above,  the  significance  level  of each  hypothesis  should
 be:            '

                             0.05 / 10 - 0.005

 Thus,  1f each hypothesis  1s  tested  at  a  Type 1  error rate of 0.005, then
 an overall Type 1 error rate of 0.05 will be maintained.
                                      80

-------
 There were  16 statistical  tests performed  In  this  study.   Therefore, in
 -order to  maintain an overall  Type  1 error rate of  0.05  for this study,
-each hypothesis was be tested at;a Type 1 error rate of 0.003.

 11.4.2  Comparison of Non-Contaminated,Site and
         Contaminated Site Data Distributions
 The  descriptive  statistics  showed  some similarities  in  how the  non-
 contaminated  and  contaminated isite  data   were  distributed.     The
 distribution of both data  sets were skewed to the right with a majority
 of samples  in  the lower  concentration ranges.   However,  an order  of
 magnitude difference  existed   in  the  data above   10,000  ug/1.    This
 difference was  seen by  a  comparison of  the  means,  medians and  upper
 quartiles of  each  data  set.   In  this section of the  report,  a  non-
 parametric test  is used to compare  these  data sets.   This test  will
 determine if  the  distributions of these  data sets  are  significantly
 different.

 The  non-parametric test  used  for  this  comparison  1s  the  Two-Sample
 Wilcoxon  Rank Sum Procedure  (Siege!  1956).   This test  Is designed  to
 determine  if  two  independent samples  are  from different distributions.
 Since the sample  values  within each data set  contain much variability,
 the question is whether  the differences observed between  the data  sets
 signify  genuine differences  in distributions  or whether they represent
differences  that can be expected between two  random  samples from the  same
distribution.

The Wilcoxon technique  tests the  null hypothesis that  two  independent
samples  come  from Identical   distributions.  This  is  called  a   null
hypothesis  because  It  assumes  that  there  is  no  difference  between
distributions.ป  If the outcome  of  the test rejects  the null hypothesis
(that  Is,  p  < 0.003),  then  1t  can  be concluded that the samples came  from
two different distributions.

This  test  was  computed  using a  computer   software  package  called
Statgraph.   Results of  the  test are Included in  Appendix M.   In  most
                                      81

-------
 cases,  the  data -used  In  this test  represent the mean  of three  GC-FID
 Injections for  each  sample.   The concentrations at non-detection  levels
-were approximated  by-dividing the detection limit iri half.

 The outcome of "this test is show below.
 DISTRIBUTION- •
 Non Contaminated
 Contaminated- -'-
-SAMPLE SIZE
     279
      60
AVERAGE RANK
     160
     215
  LEVEL OF  .
SIGNIFICANCE

   0.00008
 This test result shows  that there is a significant difference (p < 0.003)
 between the distributions  of the non-contaminated and  contaminated  site
 data.    This  test 'result  confirms  that  the  distributions   of  non-
 contaminated  and  contaminated  data,  as  shown in  Table 11-7,  actually
 represent two different distributions.

 11.4.3  Non-Parametric Testing for Data Patterns Within
         the Non-Contaminated Data
 Non-parametric techniques  can be 'used to  Identify patterns in  the  non-
 contaminated  data  set  if  they  exist.   The  results of  non-parametric
 testing can be used to draw Inferences about the data.

 The  purpose  of this  testing was to  examine the effects that  different
 parameters had on the  data.   These  parameters  Included  site  location
 sample depth,  tank material, tank age and  backfill material.  The  testing
 was  designed  so that  Independent effects  from each parameter  could be
 seen.    However,   Insufficient  data  were  available to  delineate  the
 Individual effect of tank material, tank age and backfill material.
                i
 The  determination  of Insufficient data was  made  from observations about
 the  data  at  a time when further data could not  be  collected  (I.e., the
 field Investigation had been completed).  Two observations were made:
                                       82

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        -•All   the  fiberglass   tanks   used  pea  gravel   backfill   and
            corresponded to newer tank ages (1978 to 1984),  and
        -•All  the "steel  tanks  used sand backfill/  and corresponded  to
          .older  tank ages (1940 to 1984).           '

 The  data co.uld  not  be separated  to  distinguish between tank materials,
 tank age and backfill  material.   In this analysis, these  three parameters
.are  combined  and  referred  to  *s  either a   steel  tank  system  or *a
 fiberglass  tank  system.   The presentation  of  test results are organized
 according  to  €he parameters  of  location, sample, .depth  and  steel  or
 fiberglass  tank  systems.   Test  results  that  involve  fiberglass tank
 systems  are  only shown  for  the  locations  of Austin,  Texas,  Suffolk
 County,  New York and  San Diego,  California  since  no  fiberglass tank
 systems were sampled'in Providence, Rhode  Island or Storrs, Connecticut.

 11.4.3.1  Location
 The  first parameter  examined was site location.   The Kruskal-Wallis One-
 Way  Analysis  of  Variance  by Ranks (Siege! 1956) was  chosen  to  test the
 null hypothesis  that samples from different locations come from the same
 distribution.

 This testing was  again accomplished by  the use  of the Statgraph computer
 software package.  In order to  test only for the effect of location, the
 data set was broken  down into subsets  corresponding  to sample depth and
 the  combined  group  of  tank material,  tank age and  backfill  material.
 The above breakdown yields six subsets as follows:

        •  fiberglass tank  systems  at sample depths  of 2, 6  and  10 feet
           and
        •  steel, tank systems  at sample depths of 2, 6 and 10 feet.

 The  mean  concentrations  for  each  sample  were  used  as  data.    The
 concentrations  below detection limits were set to  positive  values at the
 detection limits  to represent the worst  case for concentrations  at these
 sample  points.

                                      83

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The results  of these tests  are shown In  Table  11-8 for  the  steel  tank
systems  and  Table  11-9 for  the fiberglass  tank  systems, and  are  also
Included In Appendix M.                .            j

The subsets  consisting  of steel tank systems  at 2, -6 and 10 foot sample
depths  show significance  at  p <  0.003.    The  interpretation  of these
results  1s  that  the null  hypothesis,  which states  that these  subset
samples  are  from  the  same distribution  set, must be  rejected.   I.t is
concluded  that   significant  differences   do  exist  among   the  total
hydrocarbon  (less  methane)  vapor concentrations from the five locations
studied  for  steel  tank systems; The differences were significant at all
three sample depths  (2, 6 and  10 feet).

The  average  rank  1s  an  Indication of how  these  concentrations  were
ranked.   The total  hydrocarbon concentrations in Austin,  Texas and San
Diego,  California  were  greater than in Providence, Rhode  Island, Suffolk
County,  New  York and Storrs,  Connecticut.

The subsets  consisting of fiberglass tank systems  at  each  of the 2, 6  and
10  foot sample depths  do -not  show  significance  ( p > 0.003) at any of
the "sample depths.  The  Interpretation  1s that the null  hypothesis,  which
states  that  these  subset  samples  are  from  the  same distribution, is
accepted.    It Is  concluded that no  significant  differences exist among
the total  hydrocarbons (less  methane) vapor concentrations from the three
locations  studied for  fiberglass tank  systems.  This conclusion can  also
be  seen by  examining  the average  ranks.   The value of these ranks  are
similar within each sample  depth subset.
 11.4.3.2  Sample Depth
 The  second  parameter examined  was  sample  depth.    The  analysis  was
 designed  to  determine  if  differences existed  among  samples taken  at
 different depths.  This analysis Is  based  on  the assumption that samples
 taken from  different depths  within a hole  are  related,  and  the  tests
 determine if  data at different  sample depths  have  been drawn  from the
 same distribution.
                                      84

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                                        TABLE 11-8

                       RESULTS OF  KRUSKAL-WALLIS TESTS FOR  LOCATIONS
                   WITH  STEEL TANK SYSTEMS USING .NON-CONTAMINATED DATA
 STEEL TANK SYSTFMS   ;

 Sample Depth - 2 Foot
Sample Depth - 6 Toot
Sample Depth - 10 Foot
                        SAMPLE   ' AVERA'&E
 LOCATION               SIZE       RANK

 Austin,  TX             14          51
 San Diego.CA           29          49
 Providence,  RI    -     14          30
 Suffolk  County,  NY      8          20
:Stores,.  CT             10          15

 San Diego, CA           28          48
 Austin,  TX             13          43
 Suffolk  County,  NY      6          28
 Providence,  RI          15          22
.Storrs,  CT             9          17

S*n  Diego, CA           17         33
Austin,  TX              n         27
Suffolk  County,  NY      5          18
Providence,  RI          n         14
Storrs,  CT              37
SIGNIFICANCE
LEVEL

0.000003
                                                                         0.00002
                                                                         0.0006
                                            85

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                                       TABLE  11-9  :

                      RESULTS OF KRUSKAL-WALLIS TESTS FOR LOCATIONS
                WITH  FIBERGLASS TANK SYSTEMS  USING  NON-CONTAMINATED DATA
FIBERGLASS'TANK SYSTEMS

Sample Depth - 2 Foot



Sample Depth - 6 .Foot



Sample Depth - 10 Foot
                       SAMPLE     AVERAGE
LOCATION               SIZE       RANK

Suffolk County, NY       10         21
Austin, TX      - '        9         20
San Diego, CA           -14         12

Suffolk County,~ NY       11         18
Austin, TX                8 .        14
San Diego, CA            11         14

San Diego, CA             8         13
Suffolk County, NY        9         12
Austin, TX                5          9
SIGNIFICANCE
LEVEL

0.06
0.4
0.5
                                            86

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 Two  non-parametric tests  were chosen.   These were the  Page L Test  for
 Ordered  Alternatives  based  on  Friedman Rank  Sums,  and  the Wilcoxon
 Matched-Pairs Signed-Ranks Test  (Siege! 1956).      .
•   ••.    '.-..-                           .   •    '  •      '
 The'Page  L~'Test-was  chosen  to  test the null  hypothesis  that  data  at
 different sample depths  have been drawn  from  the  same distribution.   If
 differences do exist,  this  test  also reveals  how these data  are ordered.
 Specifically, this  test will  determine  if one  of the  following  trends
 exist for total  hydrocarbon  (less  methane)  vapor concentrations taken
 from non-contaminated sites:

                               2' < 6' .- 10'"
                               2' - 6' < 10'
                               2' < 6' < 10'
                               2' - 10' < 6'

If test results  show  a level of significance ( p < 0.003)  then the null
hypothesis is rejected and  one of these conditions  exist.

In cases  where these  test  results showed a  level  of  significance for a
particular data  subset, the Wilcoxon Matched-Pairs  Signed-Ranks Test was
employed  to further test the following hypotheses  for total  hydrocarbon
(less methane) vapor concentrations at non-contaminated sites:

                                  2' < 6'
                                 6' < 10'
               i                 2' < 10'
            •  -.1    -     ,.
A  separate calculation was  required  to  test  for each  of  these conditions.

The  benefits  in  using  the  Wilcoxon Test  as  a supplement to the  Page  L
test are not  only to determine exactly  how the data at different  depths
are ordered,  but  also to utilize  more data from the non-contaminated data

                                      87

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set.   There  were  service stations  In San  Diego  and Austin  in which

shallow  perched  water .zones  were  encountered  that  precluded  taking

samples ปat  10 fe.et.-^  Therefore,  soil  gas  samples were only collected at 2

and 6 foot  depths.   By using the Wilcoxon Test, these data could  also be

utilized.  'The computations  for.both  techniques  (Page L  and Wilcoxbn)

were d~one. by hand, under  the direction of  a qualified statistician and

are shown 1n Appendix M.
The  results of  the Page  L Tests  and the  Wilcoxon Tests  are  shown  in

Tables  ll-10'and 11-11, respectively.  Calculations .for these tests are
Included  In Appendix M.  These  test  results show variations in signifi-
cance  levels at  individual  locations  in  both the  steel  and fiberglass

tank systems.  A summary of the  significant  test results is  given  below.


     1)   Two  significant  test  results were shown  from the Page L Test
          for  the overall  data.  The significant differences were  among
          total  hydrocarbon  (less  methane)  vapor  concentrations  at the
          different  sample depths (2, 6 and 10 feet) for both steel and
          fiberglass  tank  systems.   The overall  test represents data that
          are  combined  from the  different  locations.

     2)   Significant  test results were also  shown from the Page L Test
          for  Individual  locations.   There  were significant differences
          among  total  hydrocarbon (less methane) vapor concentrations  at
          the  different sample  depths  (2, 6 and 10  feet) for steel tank
          systems in San Diego,  CA and for  fiberglass tank  systems in  San
          Diego, CA and Suffolk  County, NY.

     3)   One  significant test  result was  shown  from the  Wilcoxon Test
          for  San Diego, CA.  The  significant difference was shown in  the
          test of  2'<6'.   Therefore, total  hydrocarbon  (less  methane)
          concentrations  are  greater at  6  feet than at  2 feet  for  the
          steel  tank system In San  Diego,  California.
The  variations 4n significance  at the different locations could be due to
two  factors:  il)   The differences  in the  locations,  such  as  geology,
hydrology,  backfill  material,  etc.,  and  2)  insufficient data to detect
significant differences using the statistical methods.

-------
                                    TABLE 11-ia

                      RESULTS OF PAGE L TEST FOR DIFFERENCES
                         IN DATA ACCORDING TO SAMPLE DEPTH
STEEL TANK- SYSTEMS
FIBERGLASS TANK SYSTEMS
LOCATION

Austtn, TX
Suffolk Co, NY
San Diego, CA
Providence, RI

Overal1
                               Austin, TX
                               Suffolk Co, NY
                               San Diego, CA

                               Overall
'SAMPLE
SIZE

  II
  3
  15
  5

  34
                          6
                          7
                          8

                          21
SIGNIFICANCE
   LEVEL

 < 0.05
 > 0.05
 < 0.001
 > 0.05

 < 0.0002
                 <  0.05
                 <  0.001
                 <  0.001

                 <  0.0002
                                     89

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;          .                         TABLE 11-11

                     RESULTS OF-WILCOXON TESTS FOR DIFFERENCES
                         IN DATA ACCORDING TO SAMPLE DEPTH


                                                      SAMPLE       SIGNIFICANCE
STEEL TANK SYSTEMS      LOCATION            TEST      SIZE           LEVEL

                         San Diego, CA  -   2'<6'        24          <0.001
                         San Diego, CA      6'<10'        16           0.004
                         San Diego, CA      2'<10'        11           0.0012-
                                       90

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 Unfortunately, the paired-sample Wilcoxon  test is not as sensitive as the
 Page 1 test  for detecting significant  differences.   This is due  to the
 nature of the hull  distribution of  the paired-sample Wilcoxon  test for
 small samples.   Thus,  even  though  the Page  L test  may'have  detected
 significant  differences in total  hydrocarbon concentrations  between the
 three sample  depths, "the paired-sample ^Wilcoxon  may  not  uncover  the
 nature of these differences.   Also,.the W11coxon could only be applied in
 cases where the sample:size was greater  than nine samples.

 Each  of  the  paired-sample-Wilcoxon tests were  tested  at individual
 significance  levels of  0.0015.  This  was  derived  by dividing  0.003  by
 two,  since two independent test cases (2'<6' and 6'<10')  were  performed.

 11.4.3.3  Conclusions  from Non-Parametric Tests
          Within the Non-Contaminated Data
 The  data patterns  associated with site location and  sample  depth  were
 delineated  by  the  use of   Kruskal-Wallis, Page  L  and Wilcoxon  non-
 parametric  statistical  methods.   The  Kruskal-WalUs  method,   used  to
 delineate  patterns  according  to  location,  revealed that   significant
 differences  in  total   hydrocarbon  (less  methane)  vapor concentrations
 among the  five locations studied for steel  tank systems.  The differences
 were  significant  at all three  sample depths (2, 6  and  10 feet).  There
 were  no  significant   differences  between  the  total  hydrocar-bon  (less
 methane)  vapor concentrations  at  the  three  locations  studied   for
 fiberglass tank systems.

 The  Page  L  method,   used  to  delineate  patterns  according  to   sample
 depths,  revealed  that ^significant  differences  exist between the  total
 hydrocarbon  (less  methane)   vapor  concentrations  among the different
 sample depths  .{2,  6  and  10  feet)  for  both  steel  and  fiberglass tank
 systems.                                 ......'

The results of  these tests Indicate that data from steel  tank systems at
different locations and sample depths represent significantly different
                                      91

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 data distributions.   Also, data  from fiberglass  tank  systems from  all
 locations,   but  ,at  different  .sample  depths   represent   significantly
.-different distributions.                            ;
                                                    >
'The means,  medians,  lower rand upper  quartiles  are shown in Table  11-12
 for the  steel  tank systems  .and  Table  11-13  for the  fiberglass tank
 systems  for  total  hydrocarbon  (less  methane)   vapor  concentrations  in
 mlcrograms  per liter.

 The difference  in  total  hydrocarbon (less methane) vapor concentrations
 at different sample  depths  can  be seen In these tables.  The  steel tank
 systems  in  Austin,  TX,  San  Diego,  CA  and  Suffolk  County,  NY show
 Increasing  concentrations  with  depths in the means,  medians, and  lower
 and upper quartlles.  The differences In concentrations  at  the different
 locations can also be seen.

 11.5 RESULTS AND CONCLUSIONS OF  DATA ANALYSIS
 The distribution of  total  hydrocarbon (less methane)  vapor concentrations
 was  skewed  to  the  right  with  a  majority of  samples  In  the  lower
 concentration  ranges.   The relative  frequency  distribution showed  53.2
 percent of the samples below 1,500  ug/1  and 93.1 percent  below  100,000
 ug/1.    The  median  was  800  ug/1  and the  mean  was  23,300  ug/1.    The
 difference  between  the mean  and  the  median 1s  because of  a few  high
 concentration values.

 The  distribution   of  total   hydrocarbon   (Including  methane)   vapor
 concentrations showed that  21 percent more  samples existed  above  100,000
 ug/1   as   compared  to   total   hydrocarbons   (less   methane).      High
 concentrations  of  methane were   seen  at  many  of  the sites.    These
 concentrations i are  probably due  to decomposition  of the  background
 hydrocarbons as well as naturally occurring methane.

 Although much  variability  existed  in  both  the non-contaminated  and
 contaminated data, significant differences  could be seen between  the two
 distributions.  Both distributions were skewed to the right with a
                                       92

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                                    TABLE 11-12 :.

                   DESCRIPTIVE STATISTICS FOR TOTAL HYDROCARBON
                     LESS METHANE CONCENTRATIONS IN STEEL TANK
                 .SYSTEMS AT DIFFERENT LOCATIONS AND SAMPLE DEPTHS

                              (Micrograms Per Liter)  -•'
 Austin,  TX
   -Mean  .
    Median
    Lower Quartile
    Upper Quartile

 Providence,  RI
    Mean
    Median
    Lower Quartile
    Upper Quartile

 San Diego, CA
    Mean
   Median
    Lower Quartile
   Upper Quartile

Storrs,  CT
   Mean
   Median
   Lower Quartile
   Upper Quartile

Suffolk County, NY
   Mean
   Median
   Lower Quartile
   Upper Quartile
     2 Foot -  -

      41000
      15000'-
       570
      36000
       1700
          1
Detection Limit
        0.1
     30000
     27000
      5100
     37000
        270
Detection Limit
Detection Limit
        1.0
      5300
        1.6
Detection Limit
      2100
        SAMPLE DEPTH

     6 Foot

      24000
      16500
     .   380
      35000
     10  Foot

     120000
      12000
        160
      36000
       1200
        0,3
Detection Limit
       450
     44000
     41000
      2400
     70000
      5300
       0.3
Detection Limit
      11.0
     16000
      1100
Detection Limit
     39000
       1300
        0.1
Detection Limit
       350
     72000
     71000
     39000
     104000
        1.0
       0,06
Detection Limit
        3.0
     27000
       110
Detection Limit
     36000
                                      93

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                               TABLE 11-13  :

               DESCRIPTIVE STATISTICS FOR TOTAL HYDROCARBON
              LESS METHANE CONCENTRATIONS IN FIBERGLASS TANK
                       SYSTEMS AT DIFFERENT DEPTHS

                          (Mlcrograms Per Liter)    1
Mean
Median
•Lower Quartile
Upper Quartile
2 FOOT

16142.9
28
.1
21000
SAMPLE DEPTH

    6 FOOT

    21689.1
    780
    2
    38500
10 FOOT

49132.7
5850
27
58000
                                    94

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majority  of  samples  1n  the lower  concentration  ranges.    However,  an
order of magnitude  difference existed between the mean of each data  set,
and between  the -median of each  data  set.   The order of magnitude  was  best
seen  1n  concentrations  above   10,000  ug/1.    Of; the  non-contaminated
sampler, 29,6 percent  occurred  In the  range of 10,000 to  100,000 ug/1
while 33.3  percent of the  contaminated samples occurred  1n  the range
above 100,000 ug/1.
                                    95

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12.0  CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER STUDY

12.1  CONCLUSIONS

The following conclusions are derived from the results of this study:
                                                  ~)               •  •

       '•  Underground  storage  tank sites  evaluated in  this  study where
          total  hydrocarbon  (less methane) concentrations  In soil vapor
          exceeded  100,000  ug/1  (27,000 ppmv) were generally considered
          contaminated,  whereas  sites  that  exhibited vapor  values less
          than  100,000 ug/1 typically  had not  had  a release  and were
          considered non-contaminated.   This  apparent threshold value of
          100,000 ug/1  (27,000 ppmv)  of total hydrocarbon (less methane)
          vapors  may   be  used  to  help  differentiate  between  non-
        .  contaminated and contaminated sites.

      -*  Calculation of  total hydrocarbon values  "as BTEX" based on the
          average   of   the  response   factors  for   benzene,   toluene,
          ethyl benzene   and   ortho-xylene  provides   a   more   accurate
          representation than when calculated "as benzene".

       •  Because of the regional  variability of  the data collected in
          this study, any soil vapor  concentration  limits that are to be
          utilized   to  differentiate  between  contaminated  and  non-
          contaminated  sites may  best  be established on  a  regional  or
          local basis.

       •  Soil  gas  techniques can effectively  be  used  to evaluate the
          backfill   areas  of  underground  gasoline  storage  tanks  to
          determine  if  significant leaks exist,  especially if appropriate
          regional or local threshold levels are established.

       •  Limited analysis of  butane  vapor concentrations indicates, that
          butane  analysis may  be  useful  in  detecting  recent  leaks  or
          spills.


12.2  RECOMMENDATIONS FOR FURTHER STUDY

Analysis of  the data collected 1n  this  study revealed several areas where

additional   study  would  be  useful   in  developing  a  more  complete

understanding of the occurrence  and characteristics  of  soil  gas at both

clean   and  cqntamlnated  underground   gasoline   storage  tank   sites.

Recommendations for further study are:


       •  Develop   a   standardized  method   for   reporting  soil  gas
          concentrations  In the  backfill areas of  underground  storage
          tanks.   This can  be done by a more thorough  analysis of soil
          gas  in each  of the three geographical areas used in this study.
          The objectives would be to measure the concentrations,  develop

                                      96

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    simplified   calculations   to   be  used   1n   reporting   the
    concentration  values and determine the  appropriate  assumptions
   .and  approximations.

*•  /Determine the minimum  amount  of data required  to decide If  a
   .site 1sr contaminated  by a  leak.   The  objectives would be to
    determine the required number and  locations  of sampling points,
  : the  number of samples above a  specified  threshold limit that
   •would  be acceptable,  and  whether butane concentrations can be
   -used to distinguish  between  a  leak and a spill.

••   Determine the effects  of  geology, backfill material,  tank  age
    and  tank material  on  soil  gas  concentrations.   A  sufficient
    amount of data was  not collected in this  study  to determine  the
    effects of these .parameters.

 •   Examine the  dispersion and decomposition  of contamination  by
    additional  sampling  at  Austin  16,  taking  advantage of  the
    recent documented spill.
              r         •

 •   Determine the effects  of  a leaking pipeline on  an  underground
    storage  tank  system  as  compared to  the  effects  of only  a
    leaking tank.
                                97

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 13.0  REFERENCES CITED

 American  Petroleum   Institute,   Publication  No.   4395,   Auqust  1985
      Laboratory Study on  Solubilities  of Petroleum, Hydrocarbons  in  Ground
    •ซwater,  August" 1985                            '

 Harvel,  Chuck,  Statistician Consultant,  Personal  Communication

 Himnielblau,  David  M.,  Basic  Principles  and  Calculations  1n  Chemical
      Engineering, Third  Edition,  Prentice-Hall,  IncV,  New Jersey,  1974?

 "^'in?"! New  YEorek,eni96r7  Stat1st1cs' Second Edition, John Wiley  &  Sons,
                                                UtUS 1-2'3' John
Radian Corporation, Personal Communication

                                            for the  Behaviorai
Tracer Research Corporation, Personal Communication
U*S> Molht^cT 1tacl fr0tlcl1on. ^9^nc^ป  Underground Tank  Leak Detection
     Methods:  A State-of-the-Art Review, 1986
                      Pฐllut1onป STS Ori91n  and  Control>  "^Per and Row,
                                                            UST\FINAL.RPT

                                     98

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.1

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                    NOTICE
This  report is  an  external draft  for review
purposes  only  and does not constitute agency
policy.   Mention of trade names or commercial
products  does  not  constitute endorsement  or
recommendation for use.

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