Fingerprinting Approach for Relating Nonaqueous Phase Liquid, Soil, and Groundwater Data

Abstract

An advanced chemical fingerprinting approach, called nonaqueous phase liquid (NAPL)-groundwater (GW) finger printing, is presented for relating NAPL, soil, and groundwater data. This approach is accomplished by utilizing the "effective solubility" relationship and a hypothetical n-component NAPL to convert NAPL, soil (containing residual NAPL), and groundwater data to common frames of reference with respect to both phase and dilution. The resulting NAPL-GW fingerprints make it possible to perform detailed forensic analysis incorporating all three data types (assuming minimal confounding effects of attenuation processes and non-ideal solution behavior). Three case histories using the NAPL-GW fingerprinting approach are presented, illustrating its utility in forensic analysis when appropriately applied.

Assessing Temporal and Spatial Variations of Gasoline-Impacted Groundwater Using Relative Mole Fractions and PIANO Fingerprinting

“…The use of: 1) effective solubility theory to calculate relative mole fractions in a hypothetical NAPL, or "NAPL-GW fingerprints" (Burris et al, 2006), and 2) solubility-based fingerprinting (Sauer and Costa, 2003), made possible by the use of detailed paraffin, isoparaffin, aromatic, naphthene, and olefin (PIANO) fingerprinting techniques (Uhler et al, 2003), have proven successful in this regard. Determining the age of gasoline-derived contamination in groundwater is difficult.…”

“…In performing this conversion of measured absolute concentrations into relative mole fractions in a corresponding theoretical 4-component NAPL, hereafter referred to as NAPL-GW fingerprints, the fingerprints of groundwater samples can be readily compared to each other and, for this study, to the relative mole fractions for a population of 88 freshly dispensed gasolines whose concentrations of BTEX had been measured over the past 14 years by the authors. The calculation of the gasolines' NAPL-GW Table 1. fingerprints required converting the measured concentrations in gasoline (mg/kg) into moles (moles/kg) and then into relative mole fractions in a theoretical 4-component "gasoline" (Burris et al, 2006). These data are summarized in Table 2.…”

“…The historic, temporal (BTEX/MTBE) data and newly collected PIANO fingerprinting data were used to evaluate the source(s) and timing of impacts to groundwater in on-site and off-site locations. Downloaded by [Kungliga Tekniska Hogskola] Burris et al, 2006). Aqueous solubility data from TPH Working Group (1998 …”

“…However, if the groundwater samples are to be compared with NAPLs or soils, the effects of partitioning remain and prohibit such comparisons between matrices. As described by Burris et al (2006) aqueous concentrations can be converted to their relative mole fractions in a corresponding theoretical four-component (i.e., BTEX) "NAPL", or NAPL-GW fingerprint that facilitates the comparison among groundwater, NAPLs, and soils. (Note: If data from an additional component such as MTBE is available, a corresponding five-component NAPL-GW fingerprint can be used.…”

“…This was not done as part of this study because the use of MTBE-laden gasoline in the study area was not mandatory per the Clean Air Act.). For groundwaters this conversion is simply achieved by (1) dividing the measured aqueous concentrations by each compound's pure (single) compound aqueous solubility, which attains the mole fraction of each compound in the corresponding true NAPL if no dilution had taken place, and (2) account for any dilution by normalizing each compound's mole fraction to the total BTEX mole fraction (i.e., divide each by the sum of the BTEX mole fractions; Burris et al, 2006). An example of this conversion is given in Table 1.…”