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164 4&rA 1C CONTAMINANTS IN SUBSUFWACE ENVIRONMENTS SEA 7 16 Co 7.2 EVALUATION OF CRITERIA FOR REMEDIATION N x 0 o 7.2.1 Introductlim O x En X o i Liquid contaminant is present in 7 w 0 " qui pr locus because of a leak which � � UNSATURATED occurred in the subsurface or upon the land surface. The infiltrating ZONE is �O A liquid contantinant loses mass by volatilization into soil air and by dtsso- 1 x lotion Into soil water. Liquid contaminant is also lost to retention in the f - voids of the vadose zone by captilanty, If the leak has released a quantity '""TER Cn of liquid contaminant larger than losses to volatilization, dissolution, TABLE rR x and capillary retention, the liquid contaminant accumulates upon the x Lo water table. For a continuous leak in a homogeneous, Isotropic, and a'i ZONE TED x " r^ uneorifimed porous medium,a mound of liquid contaminant may form, x -- : which deflects the water table under its weight (see Figure 7-3). 1 The remainder of this section describes in some detail the factors affecting the mobilization. fixation, and transformation of liquid con- " x _ taminants in locus 7 This is followed by an assessment of the liquid X ; contaminant storage capacity of locus 7, guidance for the assessment, NOTE NOT ALL PHASE ediIN0AR1Es ARE SK"and sample calculations. 7.2.2 NablllztttlonlRemobilixtstlon i FCFNn cowr NmNT voce S n WATER W SATMATEo ZONE i 7. 21 Parffloning roto Mobile Phase r-� AIR^AIN W "AREAS N x SMA(MID 610TA INCLUDED) � - Locus 7 consists of free (mobile) liquid contaminants floating upon UNSAr1iRATFD aoNsl O Soil PARTICLE the water table. Contaminants in the free phase of this locus are resent D IN UN TURVE WATERWATER IWOU PM P p N UNSAIURATI:D TONE) r COltOtOAL PARTICLE because of their relative Immiscibility with water and high mobility in A&" WAWA FILM /n# uouio comy"mAws the subsurface Historically, remedial efforts (e g., free-product pump- _ ing)exploited these properties of the contaminants, alternative coffee- Figura 7-1 Schematic cross-sectional dlagmrri of locus no 7-I1quld contaminant) live action may Involve removal of contaminants via other loci. Figure noaling on the groundwater lable 7-2 presents these loci which may be affected by the liquid contaminants in locus 7 and the pathways or partitioning processes whereby inter-loci transfer occurs A discussion of the factors affecting the movement and Dissolution Dissolution is the primary direct mechanism by whict transfer of liquid contaminants in locus 7 follows partitioning of liquid contaminant from locus 7 to loci 3, 8, and 12 occurs The extent to which contaminant transfer occurs by the dissolu Volatilization. Volatilization is the primary direct mechanism by tion of liquid contaminant is limited.In part, by the aqueous solubility which partitioning of liquid contaminant from locus 7 to locus I occurs of the liquid contaminant. Once contaminants have moved Into the soil vapor phase of locus 1.the Solubility of additive-free gasoline ranges between about 130 and 250 volatilized liquid contaminants move through the vadose zone by diffu- tng/L in water at 20°C Solubility values for the chemical constituents cion and advection (see Section 1.2 2) where they may be treated or of a hypothetical. 23-component gasoline are reported in Table 7-1; the w removed from the subsurface by various corrective actions such as vac- mole-fraction-weighted average solubility of the synthetic gasoline is uum extraction about 130 mg/L. i i