TABLE 4.

Summary of assumed biodegradation rate constants in vapor intrusion models

Reaction kinetics	Models	Rate constants
Monod equation $$\frac{\mathit{\text{dS}}}{\mathit{\text{dt}}}=\frac{V_{\mathit{\text{max}}}S}{S+K_m}$$	Ostendorf and Kampbell (60)	Hydrocarbons: Vmax = (5.56~11.3) × 10−9kg/m3/s Km = (5.56~8.67) × 10−4kg/m3
Zero order reaction $$\frac{\mathit{\text{dS}}}{\mathit{\text{dt}}}=-k_0$$	VADBIO (82)	BTX and fuel hydrocarbons k0 = (1.56~3.78) × 10−7kg/m3/s
	Parker (80)	k0 = 1~10 mg/kg/day (maximum decay rate)
First order reaction $$\frac{\mathit{\text{dS}}}{\mathit{\text{dt}}}=-k_{1}S$$	R-UNSAT (65)	k1 (MTBE) = 1 × 10−8s−1 k1 (BTEX) = (1~100) × 10−7s−1
	IMPACT (83–85)	k1 (VOC) = 4.46 × 10−8~5.01 × 10−7s−1
	VADBIO (82)	BTX and fuel hydrocarbons k1 = (1.39~3.33) × 10−4s−1
	T & R model (76)	k1 (Benzene) = 1.93 × 10−8s−1 in soil k1 (Benzene) = 5.99 × 10−7s−1 in air
	The ASU model (87–88)	k1 (BTEX) = (0.018~2) × h−1 in water
	Devaull (79)	Aromatic hydrocarbons k1 = 9.14 × 10−6s−1 in water Straight chain and branched aliphatic hydrocarbons k1 = 8.22 × 10−4s−1 in water
	Verginelli and Baciocchi (81)	BTEX and other hydrocarbons k1 = 0.79 − 71h−1 for aerobic biodegradation k1 = 1.9 × 10−4 − 1.55 × 10−2h−1 for anaerobic biodegradation
Second order reaction $$\frac{\mathit{\text{dS}}}{\mathit{\text{dt}}}=-k_{2}S[\mathit{0}]$$ Where [O] is the oxygen concentration	The Brown model (86)	k2 (Benzene) = (1.79~179) × 10−5m3/kg/s in water

Note: (MTBE: Methyl tert-butyl ether; BTEX: benzene, toluene, ethylbenzene and xylene; BTX: benzene, toluene and xylene)