5 Ground-Water Sample Pretreatment: Filtration and Preservation Gillian L. Nielsen and David M. Nielsen CONTENTS Sample Pretreatment Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Sample Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 What Fiter Pore Size to Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Functions of Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 Which Parameters to Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 Sources of Error and Bias in Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Filtration Methods and Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Filter Preconditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 Sample Preservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 Objectives of Sample Preservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 Physical Preservation Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Chemical Preservation Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Sample Pretreatment Options Another group of parameter-specific field protocols that must be evaluated and included in the SAP are methods for sample pretreatment, including sample filtration and physical and chemical preservation. Sample pretreatment must be performed at the wellhead at the time of sample collection to ensure that physical and chemical changes do not occur in the samples during the time that the sample is collected and after the sample container has been filled and capped. ASTM International has published Standard Guides that address both types of sample pretreatment. ASTM Standard D 6564 (ASTM, 2006a) provides a detailed guide for field filtration of ground-water samples, and ASTM Standard D 6517 (ASTM, 2006b) discusses physical and chemical preservation methods for ground-water samples. Each type of sample pretreatment is discussed subsequently. Sample Filtration Ground-water sample filtration is a sample pretreatment process implemented in the field for some constituents, when it is necessary to determine whether a constituent is truly ‘‘dissolved’’ in ground water. Filtration involves passing a raw or bulk ground- water sample directly through a filter medium of a prescribed filter pore size either under 131 © 2007 by Taylor & Francis Group, LLC negative pressure (vacuum) or under positive pressure. Particulates finer than the filter pore size pass through the filter along with the water to form the filtrate, which is submitted to the laboratory for analysis. Particulate matter larger than the filter pore size is retained by the filter medium. In the case of most ground-water monitoring programs, this material is rarely analyzed, although it may be possible to analyze the retained fraction for trace metals or for some strongly hydrophobic analytes such as PCBs or PAHs. Figure 5.1 illustrates a common vacuum filtration setup, and Figure 5.2 illustrates one form of positive pressure filtration. What Filter Pore Size to Use The most common method for distinguishing between the dissolved and particulate fractions of a sample has historically been filtration with a 0.45 mm filter (see, e.g., U.S. EPA, 1991). The water that passes through a filter of this pore size has, by default, become the operational definition of the dissolved fraction, even though this pore size does not accurately separate dissolved from colloidal matter (Kennedy et al., 1974; Wagemann and Brunskill, 1975; Gibb et al., 1981; Laxen and Chandler, 1982). Some colloidal matter is small enough to pass through this pore size, but this matter cannot be considered dissolved. For this reason, Puls and Barcelona (1989) reported that the use of a 0.45 mm filter was not useful, appropriate, or reproducible in providing information on metals solubility in ground-water systems and that this filter size was not appropriate for determining truly dissolved constituents in ground water. The boundary between the dissolved phase and the colloidal state is transitional. There is no expressed lower bound for particulate matter and no clear cutoff point to allow selection of the optimum filter pore size to meet the objective of excluding colloidal FIGURE 5.1 A vacuum filtration system used for ground-water samples. This practice is not encouraged. 132 The Essential Handbook of Ground-Water Sampling © 2007 by Taylor & Francis Group, LLC particles from the sample. The best available evidence indicates that the dissolved phase includes matter that is less than 0.01 mm in diameter (Smith and Hem, 1972; Hem, 1985), suggesting that a filter pore size of 0.01 mm is most appropriate. However, filters with such small pore sizes are subject to rapid plugging, especially if used in highly turbid water, and are not practical to use in the field. Kennedy et al. (1974) and Puls et al. (1991) provide a strong case for the use of a filter pore size of 0.1 mm for field filtration to allow better estimates of dissolved metal concentrations in samples. Puls et al. (1992) and Puls and Barcelona (1996) also recommend the use of 0.1 mm (or smaller) filters for determination of dissolved inorganic constituents in ground water. Such filters are considerably more effective than filters with larger pore sizes (e.g., 0.45 or 1.0 mm) in terms of removing fine particulate matter. These filters are widely available and practical for use in the field for most situations, although in some highly turbid water, filter plugging may make the filtration process difficult and protracted. All factors considered, 0.1 mm field filtration, although it is a compromise, appears to offer the best opportunity for collecting samples that best represent the dissolved fraction. Yao et al. (1971) indicate that colloids larger than several microns in diameter are probably not mobile in aquifers under natural ground-water flow conditions due to gravitational settling. Puls et al. (1991) also suggest that colloidal materials up to 2 mmare mobile in ground water systems. With the upper bound for colloidal matter described by many investigators as being between 1.0 and 10 mm, it seems reasonable to suggest that a filter pore size of 10 mm would include all potentially mobile colloidal material and exclude the larger, clearly nonmobile artifactual fraction. However, it should be noted that using this filter pore size, artifactual colloidal material that is finer than 10 mm in diameter will be included in the sample. Although this filter pore size is a compromise, it will lead to conservative estimates of total mobile contaminant load while excluding at least a portion of the particulate matter that is artifactual in nature. The collection and analysis of both filtered and unfiltered samples is sometimes suggested as a means of discriminating between natural and artifactual colloidal material or between dissolved and colloidal contaminant concentrations. FIGURE 5.2 A positive-pressure filtration system is a better option to use for ground-water samples. Note the removal of sediment achieved by the cartridge filter. Ground-Water Sample Pretreatment: Filtration and Preservation 133 © 2007 by Taylor & Francis Group, LLC Functions of Filtration Historically, filtration of ground-water samples has served several important functions in ground-water sampling programs. Filtration helps minimize the problem of data bounce, which commonly results from variable levels of suspended particulate matter in samples between sampling events and individual samples, making trend analysis and statistical evaluation of data more reliable. In addition, by reducing suspended particle levels, filtration makes it easier for laboratories to accurately quantify metals concentrations in samples. Perhaps most importantly, filtration of samples makes it possible to determine actual concentrations of dissolved metals in ground water that have not been artificially elevated as a result of sample preservation (acidification), which can leach metals from the surfaces of artifactual or colloidal particles (Nielsen, 1996). The assumption that the separation of suspended particulates from water samples to be analyzed eliminates only matrix-associated (artifactual) constituents may often be incorrect (EPRI, 1985a; Feld et al., 1987), as at least some potentially mobile natural colloidal material will be retained on most commonly used filter pore sizes. Filtration is often performed as a post-sampling ‘‘fix’’ to exclude from samples any particulate matter that may be an artifact of poor well design or construction, inappropriate sampling methods (use of bailers, inertial-lift pumps, or high-speed, high-flow-rate pumps), or poor sampling techniques (agitating the water column in the well). Filtration may be considered particularly important where turbid conditions caused by high particulate loading might lead to significant positive bias through inclusion of large quantities of matrix metals in the samples (Pohlmann et al., 1994). Alternatively, as discussed earlier, the presence of artifactual particulate matter in samples may also negatively bias analytical results through removal of metal ions from solution during sample shipment and storage as a result of interactions with particle surfaces. However, filtration is not always a valid means of alleviating problems associated with artifactual turbidity, as it often cannot be accomplished without affecting the integrity of the sample in one way or another. Which Parameters to Filter During the planning phase of a ground-water sampling program, each parameter to be analyzed in ground-water samples should be evaluated to determine its suitability for field filtration and the most suitable filtration medium. As a general rule of thumb, parameters that are sensitive to the following effects of filtration should not be filtered in the field: . Pressure changes that would result in degassing or loss of volatile constituents . Temperature changes . Aeration and agitation that may occur during filtration processes Table 5.1 presents a summary of parameters for which filtration may be used and of parameters for which filtration should not be used in the field. Samples to be analyzed for alkalinity must be field filtered if significant particulate calcium carbonate is suspected in samples, as this material is likely to impact alkalinity titration results (Puls and Barcelona, 1996). Care should be taken in this instance, however, as filtration may alter the CO 2 content of the sample and, therefore, affect the results. Filtration is not always appropriate for ground-water sampling programs. If the intent of filtration is to determine truly dissolved constituent concentrations (e.g., for 134 The Essential Handbook of Ground-Water Sampling © 2007 by Taylor & Francis Group, LLC geochemical modeling purposes), the inclusion of colloidal matter less than 0.45 mmin the filtrate will result in overestimated values (Wagemann and Brunskill, 1975; Bergseth, 1983; Kim et al., 1984). This result is often obtained with Fe and Al, where ‘‘dissolved’’ values are obtained which are thermodynamically impossible at the sample pH (Puls et al., 1991). Conversely, if the purpose of sampling is to estimate total mobile contaminant load, including both dissolved and naturally occurring colloid-associated constituents, significant underestimates may result from filtered samples, due to the removal of colloidal matter that is larger than 0.45 mm (Puls et al., 1991). A number of researchers have demonstrated that some metal analytes are associated with colloids that are greater than 0.45 mm in size (Gschwend and Reynolds, 1987; Enfield and Bengtsson, 1988; Ryan and Gschwend, 1990) and that these constituents would be removed by 0.45 mm filtration. Kim et al. (1984) found the majority of the concentrations of rare earth elements to be associated with colloidal species that passed through a 0.45 mm filter. Wagemann and Brunskill (1975) found more than twofold differences in total Fe and Al values between 0.05 and 0.45 mm filters of the same type. Some Al compounds, observed by Hem and Roberson (1967) to pass through a 0.45 mm filter, were retained on a 0.10 mm filter. Kennedy et al. (1974) found errors of an order of magnitude or more in the determination of dissolved concentrations of Al, Fe, Mn, and Ti using 0.45 mm filtration as an operational definition for ‘‘dissolved.’’ Sources of error were attributed to passage of fine-grained clay particles through the filter. Evidence from several field studies (Puls et al., 1992; Puls and Powell, 1992; Backhus et al., 1993; McCarthy and Shevenell, 1998) indicates that field filtration does not effectively remedy the problems associated with artifactual turbidity in samples. These and other studies indicate that filtration may cause concentrations of some analytes to decrease significantly, due to removal of colloidal particles that may be mobile under natural flow conditions. Puls and Powell (1992) noted that 0.45 mm filtered samples collected with a bailer had consistently lower As concentrations than samples obtained using low-flow-rate pumping. They suggested that the difference may have been due to filter clogging from excessive fines reducing the effective pore size of the filters or adsorption onto freshly exposed surfaces of materials brought into suspension by bailing. Puls et al. (1992) found that high-flow-rate pumping resulted in large differences in metals concentrations between filtered and unfiltered samples, with neither value being representative of values obtained using low-flow-rate sampling. Ambiguous sampling results found by McCarthy and Shevenell (1998) were attributed to analytical values for metals obtained using low- flow sampling that fell between filtered and unfiltered values from samples collected using TABLE 5.1 Analytical Parameter Filtration Recommendations Examples of parameters that may be field filtered Alkalinity Trace metals Major cations and anions Examples of parameters that should not be filtered VOCs TOC TOX Dissolved gases (e.g., DO and CO2) ‘‘Total’’ analyses (e.g., total arsenic) Low molecular weight, highly soluble, and nonreactive constituents Parameters for which ‘‘bulk matrix’’ determinations are required Source: U.S. EPA, 1991. Ground-Water Sample Pretreatment: Filtration and Preservation 135 © 2007 by Taylor & Francis Group, LLC bailing or high-flow-rate pumping. Discrepancies in analytical values for some metals (Al and Fe) exceeded an order of magnitude in this study. They determined that filtration of turbid samples may have occluded pores in filters, leading to removal of colloidal particles that may be representative of the load of mobile contaminants in ground water. Puls and Barcelona (1989) also point to the removal of potentially mobile species as an effect of filtration, indicating that filtration of ground-water samples for metals analysis will not provide accurate information concerning the mobility of metal contaminants. If the objective of a ground-water sampling program is to determine the exposure risk of individuals who consume ground-water from private water supply wells, filtration of those samples would not produce meaningful results. To make this type of exposure risk determination, it is important to submit samples for analysis that are representative of water as it is consumed, and, because most people do not have 0.45 mm filters at their taps, unfiltered samples should be collected. In addition, it is important to remember that MCL and MCLG values set for drinking-water standards are based on unfiltered samples. Sources of Error and Bias in Filtration The very act of filtration can introduce significant sources of error and bias into the results obtained from analysis of sample filtrate (Braids et al., 1987). Some of these changes in sample chemistry result from pressure changes in the sample, as well as sample contact with filtration equipment and filter media. It is critical to evaluate the suitability of filtration on a parameter-specific basis and to carefully select filtration methods, equipment, and filtration media when developing site-specific filtration protocols to minimize sample bias caused by filtration. The following sources of negative and positive sample bias need to be considered: . Potential for negative bias to occur due to adsorption of constituents from the sample (U.S. EPA, 1991; Horowitz et al., 1996). For example, Puls and Powell (1992) found that in-line polycarbonate filters adsorbed Cr onto the surface of the filter medium, resulting in an underestimation of Cr concentrations in the ground-water samples being filtered. . Potential for positive bias to occur due to desorption or leaching of constituents into the sample (Jay, 1985; Puls and Barcelona, 1989; Puls and Powell, 1992; Horowitz et al., 1996). In the Puls and Powell (1992) study, K was observed to leach from nylon filters that were not adequately preconditioned prior to use. . Removal of particulates smaller than the original filter pore size due to filter loading or clogging as filtered particles accumulate on the filter surface (Danielsson, 1982; Laxen and Chandler, 1982) or variable particle size retention characteristics (Sheldon, 1965; Sheldon and Sutcliffe, 1969). . Removal of particulate matter with freshly exposed reactive surfaces, through particle detachment or disaggregation, that may have sorbed hydrophobic, weakly soluble, or strongly reactive contaminants from the dissolved phase (Puls and Powell, 1992). This material itself may have been immobile prior to initiation of sampling and mobilized by inappropriate sampling procedures. . Removal of solids (metal oxides and hydroxides) that may have precipitated during sample collection (particularly where purging or sampling methods that may have agitated or aerated the water column are used) and any adsorbed species that may associate with the precipitates. Such precipitation reactions can occur within seconds or minutes (Reynolds, 1985; Grundl and Delwiche, 1992; Puls et al., 1992), and the resultant solid phase possesses extremely high reactivity 136 The Essential Handbook of Ground-Water Sampling © 2007 by Taylor & Francis Group, LLC (high capacity and rapid kinetics) for many metal species (Puls and Powell, 1992). Most metal adsorption rates are extremely rapid (Sawhney, 1966; Posselt et al., 1968; Ferguson and Anderson, 1973; Anderson et al., 1975; Forbes et al., 1976; Sparks et al., 1980; Benjamin and Leckie, 1981; Puls, 1986; Barrow et al., 1989). Additionally, increased reaction rates are generally observed with increased sample agitation. . Exposure of anoxic or suboxic ground water (in which elevated levels of Fe 2' are typically present) to atmospheric conditions during filtration can also lead to oxidation of samples, resulting in formation of colloidal precipitates and causing removal of previously dissolved species (NCASI, 1982; EPRI, 1987; Puls and Eychaner, 1990; Puls and Powell, 1992; Puls and Barcelona, 1996). The precipita- tion of ferric hydroxide can result in the loss of dissolved metals due to rapid adsorption or co-precipitation potentially affecting As, Cd, Cu, Pb, Ni, and Zn (Kinniburgh et al., 1976; Gillham et al., 1983; Stoltzenburg and Nichols, 1985; Kent and Payne, 1988). . During sample filtration, care should be taken to minimize sample handling to the extent possible to minimize the potential for aeration. If sample transfer vessels are used, they should be filled slowly and filtration should be done carefully to minimize sample turbulence and agitation. Stoltzenburg and Nichols (1986) demonstrated that the use of sample transfer vessels during filtration imparted significant positive bias for DO and significant negative bias for dissolved metal concentrations. For this reason, the use of transfer vessels is discouraged. In-line filtration is preferred because of the very low potential it poses for sample chemical alteration. Filtration Methods and Equipment After a decision is made to field filter ground-water samples to meet DQOs for an investigation, decisions must be made regarding selection of the most appropriate field filtration method. The ground-water sample filtration process consists of several phases: (1) selection of a filtration method; (2) selection of filter media (materials of construction, surface area, and pore size); (3) filter preconditioning; and (4) implementation of field filtration procedures. Information on each part of the process must be presented in detail in the SAP to provide step-by-step guidance for sampling teams to implement in the field. A wide variety of methods are available for field filtration of ground-water samples. In general, filtration equipment can be divided into positive-pressure filtration and vacuum (negative pressure) filtration methods, each with several different filtration medium configurations. As discussed previously, ground-water samples undergo pressure changes as they are brought from the saturated zone (where ground water is under pressure greater than atmospheric pressure) to the surface (where it is under atmospheric pressure), potentially resulting in changes in sample chemistry. The pressure change that occurs when the sample is brought to the surface may cause changes in sample chemistry, which include loss of dissolved gases and precipitation of dissolved constituents such as metals. When handling samples during filtration operations, additional turbulence and mixing of the sample with atmospheric air can cause aeration and oxidation of Fe 2' to Fe 3' .Fe 3' rapidly precipitates as amorphous iron hydroxide and can adsorb other dissolved trace metals (Stolzenburg and Nichols, 1986). Vacuum filtration methods further exacerbate pressure changes and changes due to sample oxidation. For this reason, positive-pressure filtration methods are preferred (Puls and Barcelona, 1989, 1996; U.S. EPA, 1991). Ground-Water Sample Pretreatment: Filtration and Preservation 137 © 2007 by Taylor & Francis Group, LLC Table 5.2 presents equipment options available for positive pressure and vacuum filtration of ground-water samples. When selecting a filtration method, the following criteria should be evaluated on a site- by-site basis: . Possible effect on sample integrity, considering the potential for the following to occur: a. Sample aeration, which may result in sample chemical alteration b. Sample agitation, which may result in sample chemical alteration c. Change in partial pressure of sample constituents resulting from application of negative pressure to the sample during filtration d. Sorptive losses of components from the sample onto the filter medium or components of the filtration equipment (e.g., flasks, filter holders, etc.) e. Leaching of components from the filter medium or components of the filtration equipment into the sample . Volume of sample to be filtered . Chemical compatibility of the filter medium with ground-water sample chemistry . Anticipated amount of suspended solids and the attendant effects of particulate loading (reduction in effective filter pore size) . Time required to filter samples. Short filtration times are recommended to minimize the time available for chemical changes to occur in the sample . Ease of use . Availability of an appropriate medium in the desired filter pore size . Filter surface area . Use of disposable versus nondisposable equipment . Ease of cleaning equipment if not disposable . Potential for sample bias associated with ambient air contact during sample filtration . Cost, evaluating the costs associated with equipment purchase price, expendable supplies and their disposal, time required for filtration, time required for decontamination of nondisposable equipment, and QC measures TABLE 5.2 Examples of Equipment Options for Positive-Pressure and Vacuum Field Filtration of Ground-Water Samples Positive-pressure filtration equipment In-line capsules Á /Attached directly to a pumping device discharge hose Á /Attached to a pressurized transfer vessel Á /Attached to a pressurized bailer Free-standing disk filter holders Syringe filters Zero headspace extraction vessels Vacuum filtration equipment Glass funnel support assembly 138 The Essential Handbook of Ground-Water Sampling © 2007 by Taylor & Francis Group, LLC The filtration method used for any given sampling program should be documented in the site-specific SAP and should be consistent throughout the life of the sampling program to permit comparison of data generated. If an improved method of filtration is determined to be appropriate for a sampling program, the SAP should be revised in lieu of continuing use of the existing filtration method. In this event, the effect on comparability of data needs to be examined and quantified to allow proper data analysis and interpretation. Statistical methods may need to be used to determine the significance of any changes in data resulting from a change in filtration method. Filtration equipment and filter media are available in a wide variety of materials of construction. Materials of construction should be evaluated in conjunction with parameters of interest being filtered with particular regard to minimizing sources of sample bias, such as adsorption of metals from samples (negative bias) or desorption or leaching of constituents into samples (positive bias). Materials of construction of both the filter holder or support and the filter medium itself need to be carefully selected based on compatibility with the analytes of interest (Puls and Barcelona, 1989). Filter holders that are made of steel are subject to corrosion and may introduce artifactual metals into samples. Glass surfaces may adsorb metals from samples. Table 5.3 presents a summary of the most commonly used filtration media available for field filtration of water samples. The potential for sample bias for these filter media materials is variable, therefore, filter manufacturers should be consulted to determine recommended applications for specific filtration media and for guidelines on the most effective preconditioning procedures. Large-diameter filter media (!47 mm) are recommended for ground-water sample filtration (Puls and Barcelona, 1989). Because of the larger surface area of the filter, problems of filter clogging and filter pore size reduction are minimized. High-capacity in- line filters have relatively large filter media surface areas, which may exceed 750 cm 2 . This can improve the efficiency of field sample filtration. Filter Preconditioning Filter media require proper preconditioning prior to sample filtration (Jay, 1985; U.S. EPA, 1995; Puls and Barcelona, 1996; ASTM, 2006a). The purposes of filter preconditioning are: (1) to minimize positive sample bias associated with residues that may exist on the filter surface or constituents that may leach from the filter, and (2) to create a uniform wetting front across the entire surface of the filter to prevent channel flow through the filter and increase the efficiency of the filter surface area. Preconditioning the filter medium may not completely prevent sorptive losses from the sample as it passes through the filter medium. In most cases, filter preconditioning should be done at the wellhead immediately prior to use (Puls and Barcelona, 1989). In some cases, filter preconditioning must be done in a laboratory prior to use (e.g., GFuF filters must be baked prior to use). Some manufacturers ‘‘preclean’’ filters prior to sale. These filters are typically marked ‘‘precleaned’’ on filter packaging and provide directions for any additional field preconditioning required prior to filter use. The procedure used to precondition the filter medium is determined by the following: (1) the design of the filter (i.e., filter capsules or disks); (2) the material of construction of the filter medium; (3) the configuration of the filtration equipment; and (4) the parameters of concern for sample analysis. Filtration medium manufacturers’ instructions should be followed prior to implementing any filter preconditioning protocols in the field to ensure that proper methods are employed and to minimize potential bias of filtered samples. Ground-Water Sample Pretreatment: Filtration and Preservation 139 © 2007 by Taylor & Francis Group, LLC TABLE 5.3 Examples of Common Filter Media Used in Ground-Water Sampling Filter Medium Acrylic Copolymer Glass Fiber Mixed Cellullose Esters Nylon Polycarbonate Polyethersulfone Polypropylene Analytes XX Major ions X — — — X X X Minor ions — — — — X X X Trace metals X — — X X X X Nutrients X — X — X — — Organic compounds — X — — — X — Filter effective area (cm 2 ) 17 X X X XXX— 20 X X X XXX— 64 — X — ——X— 158 X X X — — X — 250 — — — — — X — 600 — — — X — X — 700 X — — — — — — 770 — — — X — X X Pore size (mm) 0.1 — — X — X X — 0.2 — — X — X X — 0.45 X — X X X X — 1.0 X X X X — X X 5.0 X — X X — X X Filter type Flat disk X X X X X X — Capsule X — — X X X X Syringe X X — X — X — Funnel X — X X X X — Source: ASTM, 2006a. 140 The Essential Handbook of Ground-Water Sampling © 2007 by Taylor & Francis Group, LLC [...]... M.J Barcelona, Ground- Water Sampling for Metals Analysis, EPAu540u 4-8 9u001, Superfund Ground Water Issue, U.S Environmental Protection Agency, Office of Solid Waste and Emergency Response, Washington, DC, 6 pp., 1989 Puls, R.W and M.J Barcelona, Low-Flow (Minimal-Drawdown) Ground- Water Sampling Procedures, EPAu540u 5- 9 5u504, Ground Water Issue, U.S Environmental Protection Agency, Office of Solid Waste... collection or a clean small-volume beaker) and the pH measured using either a calibrated pH probe or narrow-range litmus paper If the sample pH is not at the required endpoint, additional © 2007 by Taylor & Francis Group, LLC The Essential Handbook of Ground- Water Sampling 146 TABLE 5. 5 Examples of Commonly Used Ground- Water Sample Chemical Preservatives and Holding Times Parameter of Interest Inorganic... colloids in an anoxic ground water plume, Journal of Contaminant Hydrology, 1, pp 309 Á 327, 1987 © 2007 by Taylor & Francis Group, LLC 150 The Essential Handbook of Ground- Water Sampling Hem, J.D., Study and Interpretation of the Chemical Characteristics of Natural Water, Water Supply Paper 2 254 , U.S Geological Survey, Reston, VA, 263 pp., 19 85 Hem, J.D and C.E Roberson, Form and Stability of Aluminum Hydroxide... guidelines on ground- water sample collection and preservation Containers are specified with a number of design criteria in mind, to protect the integrity of the analytes of interest, including shape, volume, gas tightness, materials of construction, use of cap liners, and cap seal or thread design (Figure 5. 3) Table 5. 4 presents a summary of some of the more common ground- water sample containers used These... medium-specific water (e.g., distilled water, deionized water, or sample water) while holding the filter over a containment vessel (not the sample bottle or filter holder) to catch all run-off; (3) then place the saturated filter on the appropriate filter stand or holder in preparation for sample filtration; (4) complete assembly of the filtration apparatus; (5) pass the recommended volume of water. .. help reduce the incidence of container breakage during shipment and handling Use of bubble wrap around containers can also minimize container breakage Commercial carriers often recommend that absorbent pads be placed in the bottom of sample shipping containers © 2007 by Taylor & Francis Group, LLC 144 The Essential Handbook of Ground- Water Sampling and on the top of sample containers after the shipper... through the filter while holding the capsule upright, prior to sample collection In general, large-capacity capsule filters require that 1000 ml of water be passed through the filter prior to sample collection, while small-capacity filters require approximately 50 0 ml of water to be passed through the filter Sample Preservation The second form of pretreatment of ground- water samples is physical and chemical... Comparison of filtration techniques for size distribution in fresh waters, Analytical Chemistry, 54 (8), 1 350 , pp, 1982 McCarthy, J and L Shevenell, Obtaining representative ground- water samples in a fractured and karstic formation, Ground Water, 36(2), pp 251 Á 260, 1998 NCASI, A Guide to Ground Water Sampling, Technical Bulletin 362 National Council of the Paper Industry for Air and Stream Improvement, 53 ... preservative (the same as that used to prepare the container), so the required end pH can be achieved prior to shipping the sample to the laboratory This may be impossible for the laboratory to provide if they have purchased prepreserved containers from a supplier From a practical perspective, © 2007 by Taylor & Francis Group, LLC 148 The Essential Handbook of Ground- Water Sampling FIGURE 5. 6 A prepreserved... Gschwend, Sampling colloids and colloid-associated contaminants in ground water, Ground Water, 31(3), pp 466 Á 479, 1993 Barrow, N.J., J Gerth, and G.W Brunner, Reaction kinetics of the adsorption and desorption of nickel, zinc, and cadmium by geothite II: modeling the extent and rate of reaction, Journal of Soil Science, 40, pp 437 Á 450 , 1989 Benjamin, M.M and J.O Leckie, Multiple-site adsorption of Cd, . and M.J. Barcelona, Low-Flow (Minimal-Drawdown) Ground- Water Sampling Proce- dures, EPAu540u 5- 9 5u504, Ground Water Issue, U.S. Environmental Protection Agency, Office of Solid Waste and Emergency. concerning the mobility of metal contaminants. If the objective of a ground- water sampling program is to determine the exposure risk of individuals who consume ground- water from private water supply. ASTM, 2006a. 140 The Essential Handbook of Ground- Water Sampling © 2007 by Taylor & Francis Group, LLC These instructions will specify filter-specific volumes of water or medium-specific aqueous