WPC 2 BP Courier 10cpi3|i" Os i P7 PCG Times (Scalable)HPLASIII.PRSx  @HgMX@2<-L ZD3|i!CG Times (Scalable)CG Times Bold (Scalable)CG Times Italic (Scalable)"Sh5^4:QXX:::X::::XXXXXXXXXX::N~nxnh~:D{n~d~u^n~~~q:::XX:NXNXN:XX11X1XXXXAD1XX~XXNNXNX:XXXXX:XXXXXXXXX1~N~N~N~N~NuxNnNnNnNnN:1:1:1:1X~X~X~X~XXXXX~X~NX~X~X~XXdX~X~X~XxXxXxXXnXnXnXnX~X~X~X~X~XXXX1XXXX:XaXX{XnXnXn1n1hXX~X~X~uXuX^D^X^XnXnXnXXXXXX~~XqN:XX:::WxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxN~~~XXX:NGGXXXXXX>XXXX>::[[X--XXkkXX~Xhaa:[X>"~~X~[~~X圜X::~k~~~~~~~~~~x:X~XaX~uX:X~NXd~q~~~~~~~~~~Q~~~~~~uk~Jh~~~~~~~X~~~~~~~N~~~~N~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~:~~~:~~~:~~~:~~~~~~~~~~~~~~knakauNnDqNX~N:1{NuaaNuX~N~kdXkXXnN~Nuk~akkk~n:X~~~kNkkkk::XXXX~XXX~~~k:dXN:xHP LaserJet IIISiHPLASIII.PRS h PE37HgM P2!vpFka8DocumentgDocument Style StyleXX` `  ` a4DocumentgDocument Style Style . a6DocumentgDocument Style Style GX  2M kSvc t a5DocumentgDocument Style Style }X(# a2DocumentgDocument Style Style<o   ?  A.  a7DocumentgDocument Style StyleyXX` ` (#` BibliogrphyBibliography:X (# 2    c a1Right ParRight-Aligned Paragraph Numbers:`S@ I.  X(# a2Right ParRight-Aligned Paragraph Numbers C @` A. ` ` (#` a3DocumentgDocument Style Style B b  ?  1.  a3Right ParRight-Aligned Paragraph Numbers L! ` ` @P 1. ` `  (# 2M A  }a4Right ParRight-Aligned Paragraph Numbers Uj` `  @ a. ` (# a5Right ParRight-Aligned Paragraph Numbers _o` `  @h(1)  hh#(#h a6Right ParRight-Aligned Paragraph Numbersh` `  hh#@$(a) hh#((# a7Right ParRight-Aligned Paragraph NumberspfJ` `  hh#(@*i) (h-(# 2XX(a8Right ParRight-Aligned Paragraph NumbersyW"3!` `  hh#(-@p/a) -pp2(#p Tech InitInitialize Technical Style. k I. A. 1. a.(1)(a) i) a) 1 .1 .1 .1 .1 .1 .1 .1 Technicala1DocumentgDocument Style Style\s0  zN8F I. ׃  a5TechnicalTechnical Document Style)WD (1) . 2cha6TechnicalTechnical Document Style)D (a) . a2TechnicalTechnical Document Style<6  ?  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A. a.(1)(a) i) a)Documentg2:e1PleadingHeader for Numbered Pleading PaperE!n    X X` hp x (#%'0*,.8135@8:18heading)8<13*.26+np2(,X`%-X%.X&/h&4,jl3-hj2.fhProposal CovrCover/* ! a~> pfQ WPROPOSAL QLANDFILL OPERATIONAL UIMPROVEMENTS [ :PCONCORD, MASSACHUSETTS MVAUGUST 1989 PS E A CONSULTANTS INC. _QEngineers/Architects ^OCambridge, Massachusetts OGlastonbury, Connecticut NLondonderry, New Hampshire#$$$hhԌ$$$hh 2*0X(1X )2Xb)3X)50ln71pr102(,93tv2-4XD*5]*6+7,84rtLtrstyleS E A Letterhead Style5J  ЊX` hp x (#%'0*,.8135@8:S#2pQ~#2.8G-9X-:X.;Xv.HugeForm"255" or "254"8'Z#2pQ~#119*.12:,017;6:23<X/=X/>T91?T216-key<48Resume1Resume Header=NN^  X` hp x (#%'0*,.8135@8:~R^X` hp x (#%'0*,.8135@8:`J aK~TnPage-7a255 Page 7 formHH3O W9> (P@fQ[  hh  (, y! x# 00hdd'3y Figure 1 ! Figure 1 Ax#0dd/' W9> (P@fQ[  7. Brief resume of key persons, specialists, and individual consultants anticipated for this project. ax#0dd/' a. Name & Title: ğx#0Hdd/' b. Project Assignment: ĥx#0 0 dd/' c. Name of Firm with which associated: ĵx#0dd/' d. Years experience: With This Firm _______________ With Other Firms _______________ x#0dd/' e. Education: Degree(s)/Year/Specialization Ļx#08pdd/' f. Active Registration: Year First Registered/Discipline  Figure 1  Figure 1 !x#0 dd '3 g. Other Experience and Qualifications relevant to the proposed project:  W9> (P@fQ[  hhhh  Figure 1 ! Figure 1 Page-7b255 Page 7 formatI g/ W9> (P@fQ[    (,(, ` p` pPage-8a255 Page 8 formmJ gQ ه '3,--pDDate: 03/LE^,^eEz^'3Standard0 m`HP Lt " '3,--pDDate: 03/LE^,^eEz^'3Standard0 m`HP Lt "   W9> (P@gQ8Z  hhhh  hhhh y! 0/x#00dd3'y Figure 1 ! Figure 1 A0/00hdd3 8. Work by firm or joint venture members which best illustrates current qualifications relevant to this project 0a0/80Hgdd38 E9> (P@gQ8x  e. Estimated Cost (thousands)  B   `  d. Completed Work for which date (actual or Entire firm is a. Project name and location b. Nature of firm's responsibility c. Owner's name and address estimated) project responsible 0y4 dddyy4dddyy4h%dddyy4X)dddyyT-ddddy '3,--pDDate: 03/LE^,^eEz^'3Standard0 m`HP Lt " 3'3'Standard255 Page 8 formm(  W9> (P@fQ[  hhXX  hh  Figure 1 a Figure 1 Page-8b255 Page 8 formatK& 3'3'Standard255 Page 8 formm'3'3Standard0 m`HP Lt "   W9> (P@gQ8Z  XXXX     2yL]pMIavNxO^yPage-10255 Page 10 formrmLMA  W9> (P@fQ[  hh  '! x# 00dd-'3 W9> (P@fQ[   ,   10. , Use this space to provide any additional information or description of resources , supporting your firm's qualifications for the proposed project ' Figure 1 ! Figure 1 Ax#\0|.-dd'  h 11.  The foregoing is a statement of facts./h(Typed Name and Title<K Date Signature:h( yH.dddy W9> (P@fQ[  hhhh  Figure 1 A Figure 1 Page-8c255 Page 8 2nd page formatM '3^81(%p&h(T*,t.81'3Standard'3^81(%p&h(T*,t.81'3Standard  W9> (P@gQ8Z  XXXX     X81҇HeadingChapter HeadingNJ d  ) I. ׃  Right ParRight-Aligned Paragraph NumbersO>a݅@  I.   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P7;Pl*Z2,,3Z P7P@6,6 P7Pm)\2,,Y\_ p^7&/f:4,-. f&_ x$&7 X&L=#,-c;=&_ x$&7;X3n=6,z&n P7&P8xC;,oXx P7XP"Sh5^6=U\\===\====\\\\\\\\\\==Qs~sm=Gsizbsw===\\=Q\Q\Q=\\33\3\\\\DG3\\\\QQ\Q\=\\\\\=\\\\\\\\\3QQQQQz~QsQsQsQsQ=3=3=3=3\\\\\\\\\\Q\\\\\i\\\\~\~\~\\s\s\s\s\\\\\\\\\3\\\\=\f\\\s\s\s3s3m\\\\z\z\bGb\b\s\s\s\\\\\\\wQ=\\===WxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxN\\\=QKK\\\\\\@\\\\@==__\00\\pp\\\mff=_\@"\_\壣\==px=\\f\z\=\Q\iwUzpNmń\QQ====ńpsfpfzQsGwQ\Q=3QzffQz\Qpi\p\\sQQzpfppps=\pQpppp==\\\\\\\p=i\Q=x"Sh5^;C]ddCCCdCCCCddddddddddCCȲY~~vCN~sk~CCCddCYdYdYCdd88d8ddddJN8ddddYYdYdCdddddCddddddddd8YYYYYY~Y~Y~Y~YC8C8C8C8ddddddddddYdddddsdddddddd~d~d~d~ddddddddd8ddddCdoddd~d~d~8~8vddddddkNkdkd~d~d~dddddddYCddCCCWxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxNdddCYQQddddddFddddFCChhd44ddzzdddvooChdF"Ȑdhd岲dCCȐzȲxCddodȐȅdCdYdsȐ]ȐȐȧzȐUvŐdȐYYCCCCŐz~ozoY~NYdYC8YooYdYzsdzdd~YYzozzz~CdzYzzzzCCdddddddzCsdYCx2X01Í ÍX01Í Í  ~R$| INSITU AIR SPARGING WITHOUT INORGANIC NUTRIENT AMENDMENT:  V AN EFFECTIVE BIOREMEDIATION STRATEGY FOR TREATING   PETROLEUMCONTAMINATED GROUNDWATER SYSTEMS c   ~R 0p  I. Richard Schaffner, Jr. and Armand A. Juneau, Jr.  ~R 0T GZA GeoEnvironmental, Inc., Manchester, New Hampshire c   ~R $ABSTRACT  !Insitu air sparging (IAS) without inorganic nutrient amendment is an innovative strategy for enhancing the  !s intrinsic (natural) biodegradation of petroleum hydrocarbons (PHCs) in groundwater systems. Published data  !7show that IAS can significantly increase dissolved oxygen (DO) concentrations in PHCcontaminated  ! groundwater systems, and that increased DO levels often stimulate an increase in the population densities of  !L indigenous PHCdegrading microbes. Reported increases in microbial population densities stimulated by IAS  !|are on the order of those stimulated by conventional insitu bioremediation (ISB) strategies employing both  ~Rl !L molecular oxygen (O2) and inorganic nutrient amendment, suggesting that intrinsic biodegradation is often not inorganic nutrient limited.  !Rationale for inorganic nutrient amendment during conventional ISB studies has typically been based on an  !assumption that groundwater is oligotrophic, and that inorganic nutrients limit intrinsic biodegradation within  !petroleum contaminant plumes. Previous benchscale biotreatability studies have reported that inorganic  !nutrient amendment has stimulated an increase in microbial population densities; however, few studies have  !evaluated the effects of nutrient amendment on biodegradation kinetics. Moreover, many conventional ISB studies were performed without regard to the subsurface distribution of indigenous microbes at subject sites.  ! Microbial enumeration studies from the literature report that large population densities of PHCdegraders exist  ! in petroleum contaminant plumes. These studies have shown an inverse relationship between DO and PHC  !concentration, and a positive correlation between population density and PHC concentration during intrinsic  !biodegradation. Pertinent conclusions which can be inferred from these studies with respect to intrinsic  ! biodegradation are: (1) PHCs often stimulate microbial activity by providing an organic carbon/energy source  !Hto indigenous microbes; (2) DO depletion typically limits further biodegradation; and (3) ambient inorganic nutrient concentrations are usually not limiting.  !2 Conventional ISB strategies were often limited by technical, logistical, and/or cost factors. The development  ! of IAS in the mid to late 1980s potentially overcame many of the drawbacks associated with conventional ISB  !L approaches. Since that time, IAS has been implemented to treat many petroleumcontaminated groundwater  !systems. IAS without inorganic nutrient amendment is an effective ISB strategy because petroleum  !Dcontaminant plumes are typically oxygen and not inorganic nutrient limited. IAS can potentially supply  ~R0&l !significant amounts of O2 at relatively low cost. Additionally, inorganic nutrient amendment is typically not  !L necessary and can be deleterious unless carefully controlled. The results of three case studies are presented  !to illustrate the success of IAS without inorganic nutrient amendment for stimulating aerobic biodegradation of petroleum constituents. "(0*0*0*P("  ~R- INTRODUCTION   For over 20 years insitu bioremediation (ISB) has been an effective strategy for remediating many petroleum  contaminated overburden and some bedrock groundwater systems. ISB has typically involved injection of  ~R@K  molecular oxygen (O2) and inorganic nutrients into contaminant plumes to enhance the aerobic biodegradation   of petroleum constituents by indigenous microbes. Petroleum products targeted for ISB have included gasolines, turbine fuels, fuel oils and certain organic solvents.   The first reported use of ISB was by Suntech, Inc. in 1972 to remediate a gasoline release which contaminated   a fractured bedrock aquifer in Ambler, Pennsylvania (United States Environmental Protection Agency   i[USEPA], 1985). A benchscale biotreatability study was performed to assess whether microbes capable of   hmetabolizing petroleum hydrocarbons (PHCs) were present in the contaminant plume. Based on biotreatability  ~R K  ?study findings, Suntech, Inc. concluded that lack of O2 and inorganic nutrients were limiting PHC   biodegradation insitu. An oxygen/nutrientamendment strategy were developed. Ambient air was sparged   continuously into the water column within wells to increase dissolved oxygen (DO) levels in the contaminant  ~R0 -  plume.EH0  lK  #Y PE373P#э Note that this older strategy in which ambient air was sparged into water columns within wells (inwell sparging) differs from the current strategy in which air is injected under pressure into formation matrices (insitu sparging). E Inorganic nutrients were also supplied on a batchfeed schedule. Groundwater injection/extraction   wells were operated to establish a treatment zone through which oxygen/nutrients were circulated. Results   ;of this study indicated that gasoline constituents were not detected within onsite groundwater 10 months after oxygen and nutrient amendment ceased (USEPA, 1985).   zAn oxygenamendment alternative to inwell sparging was utilized at a LaGrange, Oregon site in 1982   (USEPA, 1985). Groundwater was extracted and ambient air added using inline static mixers to increase DO   -levels in groundwater recharged to the aquifer (hereafter, "inline mixing"). Both inwell sparging and inline  ~RK  Kmixing had limited oxygen loading rates due, in part, to the relatively low aqueous solubility limit of O2 (i.e.,   [approximately 10 milligrams per liter [mg/l] at standard temperature and pressure). Consequently, these   strategies were ineffective for significantly increasing DO levels. In fact, DO concentrations of 10 mg/l can   xonly enhance biodegradation of 5 mg/l PHCs based on the stoichiometry of common petroleum constituents.   iBased on the limited ability of these strategies to significantly increase DO levels in groundwater, alternative  ~RK  oxygenamendment strategies involving O2, O2ĩenriched ambient air, ozone, and hydrogen peroxide (H2O2)  ~R`K  xwere studied under field and laboratory conditions (USEPA, 1987). Based on several years of studies, H2O2   amendment became the strategy most frequently used to enhance PHC biodegradation (Baker and Herson,  ~RK  1994). Due to its complete miscibility with water, the injection of H2O2 into groundwater systems can  ~RK  [significantly increase DO concentrations (Norris, 1994). For example, the dissociation of 100 mg/l H2O2 yields 50 mg/l DO (RiserRoberts, 1992).  ~R@K  According to USEPA (1985), one of the first reported uses of H2O2 amendment for ISB was in 1984 in  ~RK  xGranger, Indiana. H2O2 was injected into a gasolinecontaminated aquifer at concentrations ranging from 100  ~RK  to 500 mg/l. Inorganic nutrients were also injected with H2O2. Yaniga and Smith (1984) provided early  ~RK  evidence that H2O2 amendment enhanced biodegradation. They demonstrated that injection of 100 mg/l H2O2   increased DO concentrations from 4 to 10 mg/l resulting in a concomitant decrease in dissolved PHC  ~RP!K  concentrations from about 4 to 2.5 mg/l. Yaniga and Smith also reported that H2O2/nutrient amendment resulted in a substantial increase in microbial population densities.  ~R#K  Although H2O2 amendment can supply significantly more O2 than the other oxygenamendment strategies discussed above, the following drawbacks have restricted its widespread usage: "0&0*0*0**"  ~R-  0*XSpecial precautions must be taken so as to not inhibit microbial activity during subsurface injection  ~RKdue to H2O2 cytotoxicity at high concentrations (Norris, 1994);(#  ~RK 0*XPremature decomposition of H2O2 at concentrations exceeding 100 mg/l can cause oxygen to exsolve  ~Rp-and form gas bubbles thereby reducing permeability (Baker and Herson, 1994);(#  ~R@K 0*XH2O2 amendment can cause metal oxides/hydroxides and magnesium/calcium phosphates to precipitate which can also reduce permeability (RiserRoberts, 1992; Levin and Gealt, 1993); (#  ~RKXH2O2 is relatively expensive; and(#  ~RKXTransportation, storage, and handling issues make H2O2 unsuitable for smaller sites.(#  -Irrespective of the oxygenamendment strategy selected, inorganic nutrient amendment has been a fundamental  -Yelement of ISB since its inception. Inorganic nutrients principally consist of nitrogen and phosphorus, but may  -include potassium, magnesium, calcium, sodium, and sulfur, as well as the trace elements copper, zinc, cobalt, iron, manganese, and molybdenum.  -jThe injection of inorganic nutrients into contaminant plumes was generally based on the assumption that  -groundwater systems are oligotrophic and contain small population densities of indigenous petroleum -ydegrading microbes (RiserRoberts, 1992). Levin and Gealt (1993) indicated that "as recently as the mid -1970s one could find in the literature statements about the extremely low numbers of microorganisms in  -lgroundwaters." Moreover, though microbial enumerations were sometimes performed on soil and  -xgroundwater samples collected from contaminant plumes, few studies included enumeration of samples from  -\uncontaminated (background) locations such that population density distributions could be assessed.  ~RK -Furthermore, benchscale biotreatability studies demonstrated that injection of O2/inorganic nutrients increased  -population densities substantially (USEPA, 1987; Canter and Knox, 1986). However, few studies compared  -ithe relative effect which oxygen and nutrient amendment induced on biodegradation kinetics, with that effect  -,induced solely by oxygen amendment (Baker and Herson, 1994). Consequently, nutrient amendment has often  -been performed without regard to the population density and spatial distribution of indigenous microbes and the relationship between inorganic nutrient amendment and biodegradation rates.  ~R- InSitu Air Sparging  -Insitu air sparging (IAS) was first implemented in Germany in 1985 as a saturated zone remedial strategy  -(Brown, 1994), and was introduced to the United States in 1989 as a hybrid of soil vapor extraction (SVE).  -Ardito and Billings (1990) referred to this hybrid as the Subsurface Volatilization and Ventilation System.  -,Because SVE treats the unsaturated zone whereas IAS treats the saturated zone, a discussion of SVE is beyond the scope of this paper. However, IAS is often performed with SVE as a source control measure.  -IAS involves the injection of pressurized air into the saturated zone. The physics of air movement through  -the saturated zone in response to air sparging is not well understood. According to Brown (1994) and others,  -IAS induces a transient, airfilled porosity in which air temporarily displaces water as air bubbles migrate  -laterally from the sparge point and also vertically towards the water table. This theory is hereafter referred  -to as the "transient flow" model in this paper. Alternatively, Hinchee (1994) and Johnson (1994) suggest that  -IAS induces a separate phase flux in which air travels in continuous, discrete air channels of relatively small  -diameter from the sparge point to the water table. Furthermore, Dahmani et al. (1994) suggest that air  -movement through the saturated zone typically does not occur as migrating air bubbles, with the exception  -Kof within homogeneous, highly permeable formations (e.g., unconsolidated course sand and gravel deposits).  -Hereafter, this theory is referred to as the "channel flow" model. To date, there is uncertainty with respect  -,to the validity of each model and the conditions under which each may or may not apply. Many practitioners, however, have assumed the transient flow model to be the operative mechanism. "'0*0*0*+"  -yIAS enhances physical and/or biological attenuation processes within the sparge point radius of influence  ~R- -(Brown, 1994; Johnson, 1994).dH lK0 -#Y PE373P#э Due to the current uncertainty with respect to the physics of air movement within the saturated zone, radius of influence  lKis a qualitative parameter empirically delineated using such parameters as DO, groundwater mounding, tracer gases, etc. d IAS enhances physical attenuation by volatilizing PHCs adsorbed to the  -jformation matrix and stripping those dissolved in groundwater. IAS stimulates aerobic biodegradation of  -adsorbed and dissolvedphase PHCs amenable to metabolism. Physical processes are a more significant  -attenuation mechanism for volatile PHCs (VPHCs) of low aqueous solubility, whereas biological processes  -yare a more significant attenuation mechanism for PHCs of low volatility and varying aqueous solubilities. Detailed discussion of enhanced physical attenuation due to IAS is beyond the scope of this paper.  -Based on a literature review of 37 references in which enhanced biodegradation was a remedial objective of  ~RP- -IAS,>HP lK  -#Y PE373P#э The references were obtained by performing a key word search of the National Ground Water Information Center's Ground Water Network. "Sparging" was selected as the key word and the search constrained from 1989 to the present.> only one (i.e., Pijls et al., 1994) indicated that inorganic nutrient amendment was performed to enhance  -biodegradation. It is unclear why nutrient amendment has not been performed in these studies, considering nearly all preIAS approaches to ISB involved nutrient amendment.  ~R - PURPOSE AND OBJECTIVES  -KThe purpose of this paper is to illustrate the effectiveness of IAS without inorganic nutrient amendment for  -jaerobically enhancing petroleum biodegradation, especially in comparison to other aerobic ISB strategies. Specific objectives are to:  ~Rp- 0*]XReview the microbial ecology of petroleumcontaminated groundwater systems, and the principal  ~R@-factors which control intrinsic biodegradation@ lK#Y PE373P#э Intrinsic biodegradation refers to the natural process of microbial degradation without engineered controls. insitu;(#  ~R-XDiscuss the effects of IAS on enhancing PHC biodegradation; and(#  ~R- 0*\XSummarize three case studies which illustrate the effectiveness of IAS for aerobically enhancing PHC biodegradation without inorganic nutrient amendment.(#  ~RP- MICROBIAL ECOLOGY OF PETROLEUM CONTAMINANT PLUMES  -xThe aerobic biodegradation of petroleum constituents in groundwater systems is effected by microorganisms  ~R- -which metabolize PHCs for organic carbon and energy..Hg lK -[#Y PE373P#э Biodegradation refers to mineralization (conversion of organic carbon to carbon dioxide, water, and microbial biomass) and/or biotransformation (conversion of organic carbon to simpler compounds) in this paper.. The microorganisms involved are primarily  R- -procaryotic soil bacteria such as Nocardia, Pseudomonads, Acinetobacter, Flavobacterium, Microcossus,  Rb- -Arthrobacter and Corynebacterium, though eucaryotic fungi may play a minor role (RiserRoberts, 1992;  -Chapelle, 1993). Petroleumdegrading soil bacteria consist of two different groups distinguished by unique  -respiratory capabilities. Obligate aerobic heterotrophs consist of those soil bacteria which metabolize organic  -carbon only under oxic conditions, whereas facultative anaerobic heterotrophs consist of those bacteria which  ~R- -metabolize organic carbon under either oxic or anoxic conditions.w lK%#Y PE373P#э These soil microbes are collectively referred to as heterotrophs in this paper. The bulk of viable heterotrophs are attached to the formation matrix, and a proportionately smaller fraction are suspended in groundwater.  -Intrinsic biodegradation is typically effected by a consortium of bacteria genera rather than a single genus.  -<This is because ultimate biooxidation to carbon dioxide and water involves a series of biotransformations in" 0*0*0*!"  -iwhich one genus converts one group of PHCs to intermediate compounds. The intermediate compounds are themselves metabolized by a different genus of bacteria.  -yIn uncontaminated groundwater systems, indigenous heterotrophs obtain organic carbon and energy from  - dissolved organic carbon (DOC). The DOC leaches from soil organic matter in the unsaturated zone  -(Chapelle, 1993). In petroleumcontaminated groundwater systems, certain heterotrophic bacteria having the  -genetic capability to metabolize petroleum constituents are stimulated by the supplemental organic carbon  -supplied by PHCs. This occurs even though a portion of the microbial population may be inhibited by PHC  -toxicity. Heterotrophic bacteria metabolize DOC and PHCs by breaking carboncarbon and carbonhydrogen  --covalent bonds. Examples of PHCs amenable to intrinsic biodegradation include the aliphatic hydrocarbons  ~R K -with carbon number ranges of C10 to C25 and the aromatic hydrocarbons benzene, toluene, ethyl benzene, and xylenes (BTEX).  ~R K -During biooxidation of DOC/PHCs, heterotrophs use O2 as a terminal electron acceptor$H  lK < -#Y PE373P#э Alternate terminal electron acceptors include nitrate/nitrite, sulfate/sulfite, and carbon dioxide. However, O2 is generally the most energetic electron acceptor for stimulating biodegradation.$ to collect electrons  -released during metabolism, and ambient inorganic nutrients and organic carbon to maintain cell tissue and  -increase biomass. Although oxygen is consumed in this process, nutrients are generally conserved as they are recycled during production of waste materials and lysis of cellular tissue.  ~R- LIMITING FACTORS OF INTRINSIC BIODEGRADATION  -The primary factors limiting intrinsic biodegradation of petroleum constituents in groundwater systems are biodegradability potential and microbial viability.  -Biodegradability potential is a function of PHC type, size, structure, and concentration. For example, normal  -alkanes are more easily metabolized than isoprenoids or cycloalkanes, and singlering aromatic PHCs are more  -;easily metabolized than multiring compounds. Moreover, PHC concentrations must be within specific ranges.  -[If concentrations are too low, indigenous heterotrophs may not use PHCs as a primary source of organic  -carbon in preference to DOC; however, PHCs may be inhibitory if concentrations are too high. In general,  -;insitu biodegradability potential can readily be assessed via literature searches and simple bioassays (Schaffner et al., 1994).  -Given the availability of biodegradable PHCs, microbial viability is controlled by a variety of factors including  ~RK -O2, inorganic nutrients, osmotic/hydrostatic pressure, temperature, and pH. The significance of these factors is discussed below.  -jUncontaminated groundwater systems typically contain ambient DO concentrations of about 5 to 6 mg/l  ~R@K -<(Brown, et al., 1994). DO levels are depressed below the aqueous solubility limit of O2 due to the presence  -of DOC which exerts a biochemical oxygen demand (BOD) on the groundwater. Supplemental organic carbon  -supplied by PHCs typically exerts an even larger BOD than does naturallyoccurring DOC, resulting in greater  -DO depletion. Petroleumcontaminated groundwater typically contains significantly lower DO concentrations  -than background groundwater, and is often entirely depleted of DO (Levin and Gealt, 1993; RiserRoberts,  -1992). Hence, there is an inverse relationship between DO and PHC concentrations under conditions in which  -{intrinsic biodegradation is occurring, indicating that heterotrophs deplete ambient DO during PHC  -biodegradation. Therefore, DO depletion is a significant factor limiting further biodegradation within most petroleum contaminant plumes.  -Indigenous heterotrophs use ambient inorganic nutrients and organic carbon to maintain cell tissue and increase  -biomass. Consequently, inorganic nutrient availability is reflected in microbial population densities within"0&0*0*0*)"  -contaminant plumes in which intrinsic biodegradation is occurring. Although other factors influence microbial  -viability, none are as directly related to population density as inorganic nutrient and organic carbon  -availability. Thus, population density is an indicator of ambient organic carbon and inorganic nutrient  -Mavailability. According to USEPA (1987), groundwater samples collected from background locations  -hydraulically upgradient/sidegradient of petroleum contaminant plumes typically contain total heterotroph  ~R- -population densities of about 102 to 103 colony forming units per milliliter (cfu/ml). However, densities of  ~R-up to about 106 cfu/ml have been reported in some cases (Bitton and Gerba, 1984).  -Microbial population densities within petroleum contaminant plumes typically increase in response to  ->supplemental organic carbon supplied by dissolved/adsorbedphase PHCs. Petroleumcontaminated  -groundwater typically contains significantly higher population densities than background groundwater, often  -by severalfold (RiserRoberts, 1992). Hence, there is a positive correlation between population densities and  -\PHC concentrations within contaminant plumes under conditions in which intrinsic biodegradation is  -occurring. This correlation indicates that indigenous heterotrophs are stimulated to metabolize PHCs, and that ambient inorganic nutrient levels are not limiting biodegradation insitu.  -Other potential limiting factors include osmotic/hydrostatic pressure, temperature, and pH, however, these  -factors are frequently within the range of microbial viability (Schaffner et al., 1990), and typically do not limit  -intrinsic biodegradation, with the possible exception of pH. However, microbial inhibition due to pH can readily be assessed using simple bioassay technique.  --Based on the inverse relationship between DO and PHC concentration and the positive correlation between  -,heterotroph population density and PHC concentration observed within many petroleum contaminant plumes, three generalizations are offered with respect to intrinsic biodegradation in most settings:  ~RP-XPHCs stimulate microbial activity by providing organic carbon to indigenous microbes;(#  ~R -XDO depletion limits further biodegradation; and(#  ~R-XAmbient inorganic nutrient concentrations are not limiting. (#  ~R- IASENHANCED BIODEGRADATION OF PHCs  -iIAS without inorganic nutrient amendment is an effective ISB strategy for enhancing intrinsic biodegradation  -because most petroleumcontaminated groundwater systems are oxygen limited and not inorganic nutrient  ~RK -xlimited. IAS can potentially supply more O2 than other oxygenamendment strategies at relatively low cost.  -Additionally, inorganic nutrient amendment is typically not necessary and can be deleterious unless carefully controlled. The benefits of IAS for stimulating aerobic biodegradation are discussed below.  ~R- Molecular Oxygen Supply  ~RK -<Efficient O2 supply to the contaminant plume is critical for ISB because DO depletion is the primary factor  ~R K -limiting aerobic biodegradation. Both IAS and H2O2 amendment have been demonstrated to be effective in  -significantly increasing DO concentrations in groundwater. Table 2 compares the potential effectiveness of  ~R "K -iIAS with that of H2O2 amendment for supplying O2 to groundwater systems. The table is a modification of  ~R"K -one developed by Brown (1994) comparing potential O2 loading rates calculated for both approaches as a  ~R#-function of flow rate and utilization efficiency.6H# lK &< -#Y PE373P#э Oxygen loading rates for IAS are compared with those for H2O2 amendment because H2O2 injection has been the oxygen lK&amendment strategy of choice since about the late 1980s. 6 "`%0*0*0*1)" Table 1. Molecular Oxygen Loading Rates, lbs/d. m ddx !ddx m   _@@H@P  *w*  " lKH<<\ #Y PE373P#INSITU AIR SPARGING (~20weight%) w" lKHIx HYDROGEN PEROXIDE DISSOCIATION (100 mg/l) HH lK< -#Y PE373P#э The H2O2 concentration of 100 mg/l was selected based on the empirical data which suggests instability at concentrations  lK in excess of this level (USEPA, 1987). ,_@@H@PW@ @@H@ @@P, *w*  "FLOW RATE (scfm) V"-y UTILIZATION EFFICIENCY V"FLOW   RATE !(gpm) V"UTILIZATION EFFICIENCY.W@ @@H@ @@PW@ @ H@ @ P. *WW*  " " 100% "c 50% "t10% ". "100% "50% "H 10%.W@ @ H@ @ P_  V. *YWW*  "5  Y" 128  Y"g 64  Y"x12.8  Y")10  Y"6  Y"N3  Y"J 0.6._  ?  . *Y;WW*  "d10 K;" 256 K;"d 128 K;"x25.6 K;")25 K;"Z14 K;"N7 K;"J 1.4.?  o     . *;hWW*  "d25  h" 640  h"d 320  h"64  h")50  h"Z28  h"(14  h"J 2.8!o    Kh! Notes:  lK X` hp x (#%'0*,.8135@8:months, following a six week period where SVE was performed alone. Groundwater monitoring was performed before and after startup of IAS for DO and hydrocarbondegrader population densities.  -Operated alone, the SVE system resulted in a gradual decrease in DO concentrations from 4.5 to 3.7 mg/l.  -Decreased DO levels were attributed to reduced pressure effected by SVE. Within 21/2months of IAS start -up, DO levels increased between 41 to 154 percent in three monitoring wells hydraulically downgradient of  -the IAS system. DO remained elevated in these monitoring wells between 227 to 350 percent immediately  -Yafter the system was shut down 91/2 months after startup of the IAS system. DO concentrations were about  ~RK -x7 to 11 mg/l during treatment, on the order of the aqueous solubility limit of O2. Microbial enumeration data  R- -suggested an increase in the population density of Pseudomonads of two to four orders of magnitude in  -downgradient monitoring wells in response to IAS. The IAS radius of influence was estimated at about 10 to 20 feet.  --During combined IAS/SVE, an 87 percent reduction in air flow was noted from the SVE wells. The reduced  -0air flow was attributed to biofouling of the sparge points by ironfixing bacteria. Dissolved PHC  Rd- -concentrations decreased within the IAS radius of influence from as high as 1,654 ug/l to less than 1 ug/l total  -BTEX during 91/2 months of system operation. During this time, benzene concentrations decreased from  R- -651 ug/l to less than 1 ug/l. BTEX concentrations have remained at or below analytical detection limits within  -the radius of influence of the IAS system since shutdown. Biofouling of the IAS system and the resulting  -87 percent decrease in air flow from the SVE wells resulted in a decrease in the rate of enhanced  -yvolatilization/air stripping. Nevertheless, the simultaneous increase in DO levels and petroleumdegrader  -population densities during the study suggested that biodegradation was enhanced. However, the removal rate  -of hydrocarbons due to biodegradation was not discussed. A pertinent finding of this study was that IAS was  -effective in enhancing PHC biodegradation due to the significantly increased DO levels and concomitant increase in microbial population densities.  ~RX!- CASE STUDY NO. 3  -Gasoline contaminated soils and groundwater were identified at a retail gasoline facility located in New  -NEngland in 1984. Two existing USTs were subsequently removed and replaced. Hydrogeological  -Linvestigations were performed from 1984 to 1989 which included installation of overburden and bedrock groundwater monitoring wells at and adjacent to the site property.  -Overburden site soils consist of glacial or glaciofluvial/lacustrine deposits including 4 to 20 feet of sandy silt  -to silty sand beach deposits, underlain by two discrete glacial till horizons (upper and lower till). The upper  -till consists of 8 to 19 feet of silty sand with gravel; the less permeable lower till consists of a 6 to 31feet"( 0*0*0*,"  -thick silty clay with gravel horizon. An approximately 6 to 7foot thick weathered bedrock unit underlies  -zthe lower till. Groundwater is at a depth of about 7 to 10 feet within the beach deposit horizon. The  -ioverburden contaminant plume is about 300 feet wide by 400 feet long. Concentrations of total BTEX in six  Rp- -groundwater monitoring wells ranged from about 163 to 624,000 ug/l in July 1993 prior to implementation of remedial activities at the site.  -A combined IAS/SVE program was developed to remediate soil and groundwater contamination at the site.  -ZThe objective of the program was to enhance volatilization/air stripping of VPHCs insitu to mitigate source  -Jcontamination. A pilot test was performed using two 11/4inch sparge points with 12inch screens positioned  -iwithin the upper and lower glacial till units. SVE was accomplished using a 4inch well screen placed within  -a 10foot long horizontal extraction trench within the unsaturated zone. The effects of IAS/SVE were  -monitored using four 11/2inch PVC SVE monitoring probes, four 11/2inch diameter PVC well points, and  -several existing groundwater monitoring wells. Based on the pilot study results, a fullscale IAS/SVE system  -was installed. The SVE system consisted of approximately 165 linear feet of SVE trench in which horizontal  -\4inch diameter well screens were placed beneath an asphalt pavement surface in two separate trench  -networks. The SVE wells were connected to a 1,000scfm capacity blower. The IAS system consisted of  -iseventeen 11/4inch diameter sparge points with 12inch length screens placed below the water table within  -,the upper till unit with four series of sparge points positioned between and centered on the SVE trenches. The  -<sparge points were connected to a 500scfm capacity compressor for air injection. The vacuum within each  -of the two SVE wells was maintained between 10 to 36 inches of water, with a total air discharge rate of about  -195 scfm. The IAS system was operated with air pressures of 8 to 10 psig, with a total air flow of about 114 scfm. A site plan depicting the layout of the IAS/SVE system is provided as Figure 1. Figure 1. Site Plan. "2 0*0*0*?"  -The SVE system has been operated since September 1993. The IAS system was operated from November  -1993 to March 1994, and from August 1994 to the present. The system was shut down during spring and summer 1994 due to an elevated groundwater table related to unusually high groundwater recharge.  -?Concentrations of total volatile organic compounds (VOCs) in exhaust gas were measured using a  ~RK -iphotoionization detector at 351 parts per million by volume (ppmvol) during the startup of the SVE system  ~RK -in September 1993. These concentrations decreased to about 45 to 84 ppmvol by the end of November 1993.  -Following startup of the IAS system, total VOC concentrations in the SVE exhaust gas increased to about  ~RK -y56 to 104 ppmvol indicating that IAS was enhancing volatilization/air stripping of VPHCs. By the end of  ~RPKDecember 1993, total VOC concentrations decreased further to about 24 to 26 ppmvol.  -A biodegradation screening study was performed in January 1995 to evaluate whether IAS was also enhancing  -=intrinsic biodegradation. The screening study included groundwater quality monitoring for the following  -biodegradation indicator parameters: DO, oxidationreduction potential (ORP), and pH. Groundwater  -samples were also enumerated for total heterotrophs using the serial dilution plate count method (Chapelle, 1993). The results of this study are summarized in Table 2. Table 2. Biodegradation Screening Study Results. !ddx Addxp  (o    _@@ @ PK( *YWW*  " lK#Y PE373P#Monitoring Well Y"j MW11 Y"MW8 Y"+|RW1 Y" MW7 Y"RW2 Y"E RW3 _@@ @ P_ p  *YYWW*  "DO `(mg/l) "2 IAS Off .Y"sc6.8 .Y"5.4 .Y"14.9 .Y"3.9 .Y";2.2 .Y"K 3.4_ ?  *Y;Wx*  "  "> IAS On m;"sc8.2 m;"10.7 m;"18.8 m;"7.7 m;";8.4 m;"K 7.2? ? . *;;Wx*  "  "  % Change ;"r:+21 ;"+98 ;"0+80 ;"\+97 ;"+282 ;"G +112? _ m *;YWx*  "ORP (mv) ^"2 IAS Off  Y"rW130  Y"245  Y"345  Y"35  Y";ԩ20  Y"N ԩ5_ ?  *Y;Wx*  "  "> IAS On J;"rW135 J;" 115 J;"0140 J;"y140 J;"/150 J;"M 95? ?   *;;Wx*  "  "  % Change ;"t_+4 ;"+156 ;"-+211 ;"6+300 ;"+850 ;"CL +2,000? _ J *;YWx*  "pH (standard uunits) xY"2 IAS Off Y"q>6.21 Y"6.22 Y"/6.56 Y"`6.17 Y"6.02 Y"I 5.99_ ?  *Y;W*  "  ,"> IAS On ';"q>6.43 ';"6.35 ';"/6.86 ';"`6.21 ';"6.37 ';"I 6.41? ?  *;;W*  "  ,"  % Change f;"t_+4 f;"+2 f;"2+5 f;"+1 f;"7+6 f;"L +7? _ ' *;W*  "Heterotroph Population 5Density &(cfu/ml) "2 IAS Off " lKj 1.9'105 " lKu1.1'107 " lK'4.2'10 7 " lK6.9'106 " lK3.6'106 " lKB5 8.6'105_ ? f *h,W*  "  h"> IAS On h" lKMj 7.5'105 h" lKMu7.0'106 h" lKM(+2.0'107 h" lKM1.2'107 h" lKM7.2'106 h" lKMB5 8.8'107? o   *h,W*  "  0 "  % Change s "o+300 s "ԩ40 s "1ԩ50 s "\+70 s "+100 s "A& +10,100o    Notes:  lK" 3 +X'` hp x (#%'0*,.8135@8: