Magnetic Resonance Imaging of Nonaqueous Phase Liquid Distribution in Unconsolidated Soils Using Discriminatory Freezing

Organic contaminants present as nonaqueous phase liquids (NAPLs) in the subsurface often pose a long-term risk to human health and the environment. Investigating the distribution of NAPLs in porous media remains a major challenge in risk assessment and management of contaminated sites. Conventional soil coring and monitoring wells have been widely used over past decades as the primary means of subsurface investigation to determine NAPL extent. Known limitations of conventional approaches have led us to explore an alternative or a complementary technique to provide high-quality information of NAPL source zone architecture. This work advances an imaging tool for a variety of organic NAPL contaminants in unconsolidated soils through magnetic resonance imaging (MRI) of frozen cores. Using trichloroethylene (TCE) and o-xylene as model species, we illustrate that discriminatory freezing of water, while keeping the NAPL in a liquid state, enables high-resolution qualitative delineation of NAPL distribution within porous media. This novel approach may help improve site conceptual models and consequentially lead to highly tailored, more efficient remedial measures.     

Cyclodextrin-Enhanced Vertical Flushing of a Trichloroethene Contaminated Aquifer

Pilot-scale testing of an innovative ground water remediation technology was conducted in a source zone of a trichloroethene-contaminated Superfund site in Tucson, Arizona. The technology is designed to enhance the removal of low-solubility organic contaminants from heterogeneous sedimentary aquifers by using a dual-screened vertical circulation well to inject and extract solutions containing a complexing sugar (hydroxypropyl-beta-cyclodextrin (HPCD]). Prior to initiating the pilot test, tracer tests were conducted to determine hydraulic characteristics of the vertical flow field and to evaluate trichloroethene-elution behavior during water flushing. The pilot test involved injecting approximately 4 m³ of a 20% HPCD solution into the upper screened interval of the well and extracting from the lower screened interval. The results of the pilot test indicate that the cyclodextrin solution increased the rate of trichloroethene removal from the aquifer. The concentrations of trichloroethene in the ground water extracted from the lower screened interval of the well increased by a factor of three (∼750 μg/L) in the presence of the cyclodextrin pulse, compared to concentrations obtained during previous water flushing (∼250 μg/L). Furthermore, the concentration of trichloroethene in water collected from the circulation well under static conditions was reduced to 6% of the levels measured prior to the test.     

Surfactant-Induced Reductions in Soil Hydraulic Conductivity

Surfactant solutions are being proposed for in situ flushing of organic contaminants from soils and aquifers. The feasibility of surfactant additives in remediation may depend in large part on how these chemicals affect the hydraulic conductivity of the porous media. While there is evidence in the literature of conductivity loss during surfactant flushing (Miller et al. 1975; Nash et al. 1987), there has been little research on quantifying the process for unconsolidated sediments. Surfactant-affected hydraulic conductivity reductions were measured in two soils (Teller loam and Daugherty sand). Testing was done with eight surfactants at a variety of concentrations (10^-5 to 10^-l mole/kg), surfactant mixtures, and added solution electrolytes. The Teller was also tested with its organic matter removed. Maximum hydraulic conductivity decreases were 47 percent for the sand and more than two orders of magnitude for the loam. Surfactant concentrations, surfactant mixtures, soil organic content, and added solution electrolytes all affected the degree of conductivity reduction. Results indicate that surfactant-affected hydraulic conductivity losses should be considered prior to in situ remediation and may preclude surfactant use in some fine grain soils.     

Evaluation of a Carbon Adsorption Method for Sampling Gasoline Vapors in the Subsurface

Monitoring of the vapor phase has emerged as a very convenient method for detecting volatile organic contaminants in the subsurface. It can provide a reliable way of placing ground water monitoring and recovery wells. The most common method uses a driveable ground probe (DGP) to extract a vapor-phase sample followed by direct injection of the vapor into a portable gas chromatograph (GC). However, many regional offices of regulatory agencies and consultants do not have ready access to such equipment. This research explores an alternative–the carbon adsorption method—in which the vapor is withdrawn by the DGP but concentrated on a small activated carbon trap (150mg). The carbon traps can be returned to a central laboratory for solvent extraction and GC analysis. This provides the advantages of increased sensitivity, reduction in field equipment and convenience of in-lab analyses (multiple GC injections are possible). A simple DGP and carbon trap system was constructed and tested at a field site. Vapor-phase concentrations of target compounds present in gasoline were mapped quite conveniently, ranging from 10,000μg/liter (vapor phase) to less than 10μg/L. These concentrations were also shown to decrease in the direction of the ground surface, as expected. Measurements of target compounds in soil showed that the vapor phase contributed a large fraction of the total contaminant burden where a non-aqueous-phase layer (NAPL) had been identified; as important, however, is the rather uniform contamination of the soil outside the NAPL region. Finally, the concentrations of target compounds in the vapor phase and ground water could be related in a manner roughly described by a simple equilibrium model, although exceptions were noted.     

Demonstration of a Microbiologically Enhanced Vertical Ground Water Circulation Well Technology at a Superfund Site

A full-scale ground water circulation well (GCW) system was installed and operated to demonstrate in situ remediation of soil and ground water impacted with a mixture of chlorinated and nonchlorinated organic compounds at a Superfund site in upstate New York. System performance and applicability under site-specific conditions were evaluated based on the system's ability to meet the New York State Department of Environmental Conservation (NYSDEC) cleanup goals for target compounds in ground water and soil. Contaminants from the unsaturated zone were mobilized (volatilized) by one-way vacuum extraction, and treated via enhanced biodegradation (bioventing). In the saturated zone, contaminants were mobilized by soil flushing (solubilized) and treated by a combination of air stripping and biodegradation. An in situ aqueous phase bioreactor, and an ex situ gas phase bioreactor, were integrated into the system to enhance treatment via bioremediation. After 15 months of operation, the mass of target contaminants in soil and ground water combined had been reduced by 75%. Removal by biological mechanisms ranged from 35% to 56% of the total observed mass reduction. The in situ and the ex situ bioreactors mineralized 79% and 76%, respectively, of their target biodegradable contaminant loads. Results indicate that some mass reduction in target contaminants may have been from aerobic and aerobic processes within the circulation cell. Nonchlorinated compounds were relatively easy to mobilize (volatilize, solubilize, and/or transport) and treat when compared to chlorinated compounds. The data collected during the 15-month study indicate that remediation could be accomplished at the Sweden-3 Chapman site using the technology tested.     

Temperature‐Activated Auto‐Decomposition Reactions: An Under‐Utilized In Situ Remediation Solution

The remediation industry has witnessed multiple innovations arising from a greater understanding of the physical, chemical, and biological processes that control the fate and transport of chemicals in the subsurface environment. In addition, increasing emphasis is being placed on remediation solutions that are greener, simpler, and more resource efficient. The positive impacts that can be derived from this emphasis include reduced energy consumption, reduced waste emissions, and lower costs. Temperature‐activated auto‐decomposition reactions represent a potentially underutilized option for the in situ remediation of certain organic contaminants, and an option that can be both highly effective and greener than other available technologies.     

Surfactant‐Enhanced Electroosmotic Flushing in a Trichlorobenzene Contaminated Clayey Soil

Remediation of the sites contaminated with organic contaminants, such as chlorobenzenes, remains a challenging issue. Electroosmotic flushing can be a promising approach which is based on mechanism of electrokinetic remediation for removal of organic contaminants from fluids in low‐permeability soil. To select an optimum surfactant that can effectively enhance electroosmotic flushing, three common surfactants, Triton X‐100 (EK2), Tween 80 (EK3), and a mixture of sodium dodecyl sulfate and Triton X‐100 (EK4) buffered with Na₂HPO₄/NaH₂PO₄ solution, were tested. The efficiency of each kind of surfactant was evaluated using a three‐dimensional box filled with a clayey soil spiked with 1,2,4‐trichlorobenzene, and compared with a test (EK1) without surfactant. The results demonstrated that the buffer solutions efficiently neutralized H⁺ and OH^? produced by electrolysis. EK3 with Tween 80 added in the flushing solution reached the highest electroosmotic permeability of 10^?4 cm²/v/s and achieved a notably high cumulative electroosmotic flow (EOF) of 5067 mL within 6 d, which was 6.3, 3.4, and 4.2 times higher than that in EK1, EK2, and EK4, respectively. There were 420 mL more cumulative EOF obtained after 50 h of electrical application in EK4 than in EK2. The introduction of nonreactive ions can increase the current, thereby benefiting the EOF. Both the higher pH caused by the buffer and the application of nonionic surfactants can make the zeta potential more negative, thereby increasing the EOF. Tween 80 can be recommended as the best flushing solution for removing organic contaminants from sites when electrokinetic remediation is applied.     

Modeling Volatile Chemical Transport, Biodecay, and Emission to Indoor Air

A model is presented for estimating vapor concentrations in buildings because of volatilization from soil contaminated by non- aqueous phase liquids (NAPL) or from dissolved contaminants in ground water. The model considers source depletion, diffusive- dispersive transport of the contaminant of concern (COC) and of oxygen and oxygen-limited COC biodecay. Diffusive-advective transport through foundations and vapor losses caused by foundation cross-flow are considered. Competitive oxygen use by various species is assumed to be proportional to the product of the average dissolved-phase species concentration and a biopreference factor. Laboratory and field data indicate the biopreference factor to be proportional to the organic carbon partition coefficient for the fuel hydrocarbons studied. Predicted indoor air concentrations were sensitive to soil type and subbase permeability. Lower concentrations were predicted for buildings with shallow foundations caused by flushing of contaminants by cross-flow. NAPL source depletion had a large impact on average exposure concentration. Barometric pumping had a minor effect on indoor air emissions for the conditions studied. Risk-based soil cleanup levels were much lower when biodecay was considered because of the existence of a threshold source concentration below which no emissions occur. Computed cleanup levels at NAPL-contaminated sites were strongly dependent on total petroleum hydrocarbon (TPH) content and COC soil concentration. The model was applied to two field sites with gasoline-contaminated ground water. Confidence limits of predicted indoor air concentrations spanned approximately two orders of magnitude considering uncertainty in model parameters. Measured contaminant concentrations in indoor air were within model-predicted confidence limits.     

Effects of In Situ Remediation Using Oxidants or Surfactants on Subsurface Organic Matter and Sorption of Trichloroethene

In situ remediation technologies have the potential to alter subsurface properties such as natural organic matter (NOM) content or character, which could affect the organic carbon‐water partitioning behavior of chlorinated organic solvents, including dense nonaqueous phase liquids (DNAPLs). Laboratory experiments were completed to determine the nature and extent of changes in the partitioning behavior of trichloroethene (TCE) caused by in situ chemical oxidation or in situ surfactant flushing. Sandy porous media were obtained from the subsurface at a site in Orlando, Florida. Experiments were run using soil slurries in zero‐headspace reactors (ZHRs) following a factorial design to study the effects of porous media properties (sand vs. loamy sand with different total organic carbon [TOC] contents), TCE concentration (DNAPL presence or absence), and remediation agent type (potassium permanganate vs. activated sodium persulfate, Dowfax 8390 vs. Tween 80). Results revealed that the fraction of organic carbon (f_oc) of porous media after treatment by oxidants or surfactants was higher or lower relative to that in the untreated media controls. Isotherm experiments were run using the treated and control media to measure the distribution coefficient (K_d) of TCE. Organic carbon‐water partitioning coefficient values (K_oc) calculated from the experimental data revealed that K_oc values for TCE in the porous media were altered via treatment using oxidants and surfactants. This alteration can affect the validity of estimates of contaminant mass remaining after remediation. Thus, potential changes in partitioning behavior should be considered to help avoid decision errors when judging the effectiveness of an in situ remediation technology.     

In Situ Remediation of Jet A in Soil and Ground Water by High Vacuum, Dual Phase Extraction

This report summarizes the initial results of subsurface remediation at Terminal 1, Kenneth International Airport, to remediate soil and ground water contaminated with Jet A fuel. The project was driven and constrained In the const ruction schedule of a major new terminal at the facility. The remediation system used a combination of ground water pumping, air injection, and soil vapor extraction. In the first five months of operation, the combined processes of dewatering, volatilization, and biodegradation removed a total of 36,689 pounds of total volatile and semivolatile organic jet fuel hydrocarbons from subsurface soil and ground water. The. results of this case study have shown that 62 percent of the removal resulted from biodegradation, 21 percent occurred as a result of liquid removal, and 11 percent resulted from the extraction of volatile organic compounds (VOC's).     

Chlorinated Solvent Source‐Zone Remediation via ZVI‐Clay Soil Mixing: 1‐Year Results

ZVI‐Clay is an emerging remediation approach that combines zero‐valent iron (ZVI)‐mediated degradation and in situ stabilization of chlorinated solvents. Through use of in situ soil mixing to deliver reagents, reagent‐contaminant contact issues associated with natural subsurface heterogeneity are overcome. This article describes implementation, treatment performance, and reaction kinetics during the first year after application of the ZVI‐Clay remediation approach at Marine Corps Base Camp Lejeune, North Carolina. Primary contaminants included trichloroethylene, 1,1,2,2‐tetrachloroethane, and related natural degradation products. For the field application, 22,900 m³ of soils were treated to an average depth of 7.6 m with 2% ZVI and 3% sodium bentonite (dry weight basis). Performance monitoring included analysis of soil and water samples. After 1 year, total concentrations of chlorinated volatile organic compounds (CVOCs) in soil samples were decreased by site‐wide average and median values of 97% and >99%, respectively. Total CVOC concentrations in groundwater were reduced by average and median values of 81% and >99%, respectively. In several of the soil and groundwater monitoring locations, reductions in total CVOC concentrations of greater than 99.9% were apparent. Further reduction in concentrations of chlorinated solvents is expected with time. Pre‐ and post‐mixing average hydraulic conductivity values were 1.7 × 10^?5 and 5.2 × 10^?8 m/s, respectively, indicating a reduction of about 2.5 orders of magnitude. By achieving simultaneous contaminant mass depletion and hydraulic conductivity reduction, contaminant flux reductions of several orders of magnitude are predicted.     

Comparison of Line-Drive and Push-Pull Flushing Schemes

The performance of cyclodextrin (CD)‐enhanced push‐pull (PP) and line‐drive (LD) approaches to remediation of a site contaminated with a multicomponent dense nonaqueous phase liquid (DNAPL) present in a surficial sandy aquifer was evaluated in this field study. The treatment techniques were compared to each other and to the projected performance of a conventional water‐flushing system. Performance was assessed based on contaminant mass removed per unit volume of extraction solution and per unit time of operation. As expected, the CD‐enhanced LD and PP approaches to remediation were more efficient than conventional flushing with water. Between the two techniques, the PP approach performed 1.5 to 2 times better than the LD approach, particularly for higher DNAPL saturation of the source zone. This result suggests that forcing the flushing solution directly into and through the DNAPL source zone minimized flow bypassing and consequently resulted in a more efficient transfer of contaminant mass between the DNAPL phase and the flushing solution. Nonuniform treatment zone contaminant concentrations and changes in contaminant composition influenced the treatment performances, but these effects were small and still permitted the comparison of successive tests. Although CD was used as the solubility‐enhancing flushing agent in this study, it is likely that the results can be transferred to other chemically enhanced flushing technologies that use, for example, surfactants or alcohols.     

Remediation of Contaminated Ground Water Using Biological Techniques

On-site biological cleanup following spills of biodegradable hazardous organic compounds in lagoon, soil, and ground water environments is a cost-effective technique when proper engineering controls are applied. Biodegradation of hazardous organic contaminants by microorganisms minimizes liability by converting toxic reactants into harmless end products.
Three case histories presented in this paper detail:
• Bench-scale evaluation of the potential for biological remediation in the spill site matrix
• Field implementation of biological treatment techniques.
Cost-effectiveness, minimal disturbance to existing operations, and on-site destruction of spilled contaminants are several of the advantages identified for implementing biodegradation as a technique for spill cleanup and environmental restoration.     

In Situ Biorestoration as a Ground Water Remediation Technique

In situ biorestoration, where applicable, is indicated as a potentially very cost-effective and environmentally acceptable remediation technology. Many contaminants in solution in ground water as well as vapors in the unsaturated zone can be completely degraded or transformed into new compounds by naturally occurring indigenous microbial populations. Undoubtedly, thousands of contamination events are remediated naturally before the contamination reaches a point of detection. The need is for methodology to determine when natural biorestoration is occurring, the stage the restoration process is in, whether enhancement of the process is possible or desirable, and what will happen if natural processes are allowed to run their course.
In addition to the nature of the contaminant, several environmental factors are known to influence the capacity of indigenous microbial populations to degrade contaminants. These factors include dissolved oxygen, pH, temperature, oxidation-reduction potential, availability of mineral nutrients, salinity, soil moisture, the concentration of specific pollutants, and the nutritional quality of dissolved organic carbon in the ground water.
Most enhanced in situ bioreclamation techniques available today are variations of hydrocarbon degradation procedures pioneered and patented by Raymond and coworkers at Suntech during the period 1974 to 1978. Nutrients and oxygen are introduced through injection wells and circulated through the contaminated zone by pumping one or more producing wells.
The limiting factor in remediation technology is getting the contaminated subsurface material to the treatment unit or units, or in the case of in situ processes, getting the treatment process to the contaminated material. The key to successful remediation is a thorough understanding of the hydrogeologic and geochemical characteristics of the contaminated area.     

Monitored Natural Attenuation of Contaminants in the Subsurface: Processes

Among the alternatives considered for the remediation of soil and ground water at hazardous wastes sites are the use of natural processes to reduce or remove the contaminants of concern, Under favorable conditions, the use of natural attenuation can result in significant cost savings and compensate for uncertainties encountered in complex subsurface settings. In order to demonstrate that natural processes are effective in reaching established goals it is necessary to determine that transformation processes are taking place at a rate which is protective of human health and the environment, and that these processes will continue for an acceptable period of time.
While chemical transformation, dispersion, dilution, sorption, and volatilization are discussed, aerobic and anaerobic degradation comprise the major processes for the reduction of contaminant mass in the subsurface. In discussing the mechanisms of natural attenuation, chlorinated aliphatics and petroleum hydrocarbons are used as examples because of their significant impact on subsurface contamination and the effect of their physiochemical properties on attenuation processes.     

Ground Water Remediation Using an Extraction, Treatment, and Recharge System

Ground water remediation of volatile organic compound (VOC) contamination at a site in Michigan was initiated as a result of a consent agreement between the Michigan Department of Natural Resources (MDNR) and the responsible party. Under the direction of the MDNR, the responsible party conducted a remedial investigation/feasibility study using federal guidelines to define the extent of contamination at the site and to select a response action for site remediation. The selected alternative included a combination of ground water extraction, treatment, and recharge, and soil flushing. The extraction system withdraws ground water from various depths in heavily contaminated areas. The ground water is treated using an air stripper. A spray distribution system spreads effluent from the stripper over a recharge basin constructed over the most contaminated areas. Additional contaminant removal is achieved by volatilization from the spray and percolation through the gravel bed. Recharge water moves downward through the contaminated soils, thus flushing residual soil contaminants. The initial operating data demonstrated that the system can effectively remove trichloroethylene (TCE) from ground water (approximately 95 percent overall removal efficiency). The annualized capital and operation and maintenance (O & M) costs of the remedial action were estimated for several operating periods (15, 20, and 30 years).     

The Application of Petroleum Hydrocarbon Fingerprint Characterization in Site Investigation and Remediation

Tremendous resources have been and continue to be spent investigating and remediating petroleum hydrocarbon compounds (PHCs) in soil and ground water. Investigating and planning a remedial strategy for sites affected by PHCs is often a challenging task because of the complex chemical nature of the PHCs. the complex regulatory environment related to PHC cleanup, and the use of analytical methods that provide quantitation but not identification of PHCs. From a technical standpoint, the PHC impacting soil and/or ground water is frequently inadequately characterised, both in identification as well as in is general properties (solubility, toxicity). From a regulatory standpoint, promulgated or recommended total petroleum hydrocarbon (TPH) cleanup levels generally relate to assumed properties of specific unweathered products and are inconsistent among different agencies and regions. This produces a prime situation for unwillingly spending more resources on investigation or remediation than may be necessary, especially when the PHC in the subsurface has different properties from unweathered products such as gasoline or diesel.
Accurately identifying the PHC and its nature, a process known as fingerprint characterization, is critical to the determination of appropriate regulatory goals and design of cost-effective remedial approaches. This paper presents several case studies in which fingerprint characterization made a significant difference in the project outcome. In each instance the nature of the organic material was better understood, the regulatory cleanup levels were negotiated based on the nature of the material, and a remedial approach was implemented that differed significantly from and was generally less costly than what would have been required without fingerprint characterization data.     

A Comparison of Field Techniques for Confirming Dense Nonaqueous Phase Liquids

Dense nonaqueous phase liquids (DNAPLs) are immiscible fluids with a specific gravity greater than, water. When present, DNAPLs present a serious and long-term source of continued ground water and soil contamination (Pankow and Cherry 1996). Accurate characterization and delineation of DNAPL in the subsurface is critical for evaluating restoration potential and for remedy design at a site. However, obtaining accurate and definitive direct evidence of DNAPL is difficult. A field study was recently performed comparing several approaches to DNAPL characterization at a site where anecdotal and limited direct evidence of DNAPL exists. The techniques evaluated included a three-dimensional high-resolution seismic survey, field screening of soil cores with a flame ionization detector (FID)/organic vapor analyzer (OVA), hydrophobic (Sudan IV) dye-impregnated reactive FLUTe® (Flexible Liner Underground Technologies) liner material in combination with Rotasonic drill cores, centrifuged soil with Sudan IV dye, ultraviolet light (UV) fluorescence, a Geoprobe® Membrane Interface Probe (MIP®), and phase equilibrium partitioning evaluations based on laboratory analysis of soil samples. Sonic drilling provided reliable continuous cores from which minor soil structures could be evaluated and screened with an OVA, The screening provided reliable preliminary data for identifying likely DNAPL zones and for selecting samples for further analyses. The FLUTe liner material provided the primary direct evidence of the presence of DNAPL and reliable information on the thickness and nature of its occurrence (i.e., pooled or ganglia). The MIP system provided good information regarding the subsurface lithology and rapid identification and delineation of probable DNAPL areas. The three-dimensional seismic survey was of minimal benefit to this study, and the centrifuging of samples with Sudan IV dye and the use of UV fluorescence provided no benefit. Results of phase equilibrium partitioning concentration calculations for soil samples (to infer the presence of DNAPL) were in good agreement with the site screening data. Additionally, screening data compared well with previous ground water data and supported using 1% of the pure phase solubility limit of Freon 113 (2 mg/L) as an initial means to define the DNAPL study area. Based on the results of this study, the preferred approach for identifying and delineating DNAPL in the subsurface is to initially evaluate ground water data and define an area where dissolved concentrations of the target analyte(s) approach 1% of the pure phase solubility limit. Within this study area, the MIP device is used to more specifically identify areas and lithologic zones where DNAPL may have accumulated. Core samples (either Rotasonic or Geoprobe) are then collected from zones where MIP readings are indicative of the presence of DNAPL. Soil samples from the free-product portions of the core(s) are then submitted to a laboratory for positive analyte identification. Soil analyses are then combined with site-specific geotechnical information (i.e., fraction organic carbon, soil bulk density, and porosity) and equilibrium partitioning algorithms used to estimate concentrations of organic contaminants in soil samples that would be indicative of free product. Used in combination, the soil analysis and the MIP records appear to provide accurate DNAPL identification and delineation.     

Chlorinated Decreasing Solvents: Physical-Chemical Properties Affecting Aquifer Contamination and Remediation

Chlorinated degreasing solvents are multicomponent liquids containing not only the chlorinated hydrocarbons with which their name is associated (e.g., trichloroethylene or |TCE]. perchloroethylene or [PCE], 1,1,1-trichlorocihane [TCA]) but also a number of organic additives included as corrosion inhibitors and antioxidants. The additives, such as 1,4-dioxane, are likely to be of significant public-health importance as ground water contaminants due to their toxicity, solubility, and mobility. Following their use in vapor degreasing systems by industry, chlorinated degreasing solvents will also contain about 25% solubilized oil and grease.
A number of physical-chemical properties become especially important in the light of the multicomponent nature of these solvents. First, the higher aqueous solubility and lower sorption of the additives makes it is reasonable to expect that faster moving plumes of these solvent additives will precede plumes of the chlorinated hydrocarbons. Second, due to high losses of chlorinated hydrocarbons by volatilization from vapor degreasers during years in the middle of the century, it is probable that background concentrations of these hydrocarbons are present in ground water flow systems due to their downwind washout. Finally, the solubilized oil and grease may cause profound changes to the wettability of aquifer materials contacted by the solvents during their subsurface migration. It is argued, therefore, that the wettability of aquifer materials contaminated by chlorinated degreasing solvents needs to be experimentally determined before remediation of DNAPL at each site, rather than being simply assumed as water wet.