United States Environmental Protection Agency Research and Development Robert S. Kerr Environmental Research Laboratory Ada OK 74820 EPA/600/S2 85/104 Feb. 1986 SER& Project Summary Practical Guide for Ground-Water Sampling Michael J. Barcelona, James P. Gibb, John A. Helfrich, and Edward E. Garske This work was initiated as the second phase of an investigation of the reliabil- ity of monitoring well construction and ground-water sampling techniques. The project also included both laboratory and field testing of sampling materials and sampling mechanisms with an emphasis on minimizing error, particu- larly for volatile organic compound sampling and analysis. The Guide is a companion volume to the Phase 1 report, "A Guide to the Selection of Materials for Monitoring Well Construc- tion and Ground-Water Sampling," (EPA/600/2-83/024). The full report explains the need to address the quality control and quality assurance considerations of a ground- water monitoring program at the outset of planning. The sampling and analytical protocols for specific monitoring instal- lations should be integrated into a well conceived design for the collection of high quality hydrologic and chemical data. Though accuracy and precision data provide measures of data quality, it is equally important to collect samples that are representative of in situ condi- tions. These goals can be achieved if the essential elements of a ground-water sampling program are addressed in the preliminary and implementation phases of monitoring program development. The essential elements of effective ground-water sampling include: • Evaluation of the hydrogeologic set- ting and program information needs, • Proper placement and construction of the well, • Evaluation of performance of the well and purging strategies, and • The design and execution of sampling and analytical protocols which entail appropriate selection of sampling mechanisms and materials as well as sample collection, handling and analysis procedures. Detailed discussions of the advan- tages and disadvantages of various approaches to selecting appropriate methods and materials for specific monitoring purposes are provided in the Guide. The emphasis is on straightfor- ward techniques which minimize both the disturbance of the subsurface envi- ronment and the potential sources of error for routine sampling applications. Further, specific recommendations are made for step-by-step sampling proto- cols which should be applied in sampling for volatile organic compounds which are among the most difficult chemical constituents to sample effectively. The recommendations are supported by extensive references, where the litera- ture permits, and it should prove useful to the planning and execution of regula- tory and research activities which demand high quality ground-water quality data. This Project Summary was developed by EPA's Robert S. Kerr Environmental Research Laboratory, Ada, OK, and the Environmental Monitoring Systems Laboratory, Las Vegas, NV, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction Ground-water monitoring is conducted for a variety of purposes, though detective and assessment compliance monitoring efforts are most common. The absence of proven recommendations for effective ------- monitoring network designs and reliable sampling protocols has resulted in the collection of ground-water quality data with questionable value. When this type of data is used as a basis for assessment or remedial action activities, the success of these actions may be very limited. Recent research has demonstrated that the details of well construction, choice of sampling mechanisms and materials and sampling protocols can introduce errors into analytical results which exceed those involved in the analytical procedures. Analytical operations have been the major focus of quality assurance and quality control (QA/AC) recommendations for monitoring programs. Sampling QA/AC is equally important to the development of high quality data which is representa- tive of the site under investigation. Re- quiring that water samples be represen- tative of the in situ condition is insufficient to ensure a high level of confidence in the monitoring results. The hydraulic per- formance of the well (i.e., sampling point) and the integrity of the sampling protocol must be established before samples are collected, if representative data are to be generated. Then the characteristics of a representative sample can be established for the specific goals of the program. The Guide provides a thorough discus- sion of the essential elements of well construction and sampling protocols for the collection of high quality ground- water quality data. Representative water samples are generally defined by being minimally disturbed samples which satis- fy charge balance considerations and permit the determination of trace organic compounds at their limits of quantitation within acceptable accuracy and precision limits. Each element of the sampling protocol for a particular investigation can be evaluated for its contribution to error in the final results. The available literature supports the approach that a representative sampling protocol for volatile or reactive chemical constituents can satisfy the most demand- ing data quality requirements applied to routine monitoring efforts. Sampling and analytical protocol development must be tailored to the actual hydrogeologic con- ditions of the site under investigation. Careful attention to the elements of the sampling protocol will permit the refine- ment of routine procedures as the moni- toring activity develops. The emphasis of the recommendations is on the simplest sampling procedures possible which provide data of known quality over the duration of the monitoring effort. Hydrogeologic Setting and Information Requirements The hydrogeologic conditions at each site (e.g., background and regulated unit) must be evaluated for the potential im- pacts the setting may have on the devel- opment of the monitoring program and the quality of the resulting data. The types and distribution of geologic materials, the occurrence and movement of ground water through those materials, the loca- tion of the site in the regional ground- water flow system, the relative perme- ability of the materials and the potential interactions between the mineral and biological constituents of the formations of interest, and the chemical constituents of interest must all be considered. Both the direction and the rate of ground- water movement are important. Piezo- metric surface data or water level infor- mation on each geologic formation at properly selected locations will provide the basis for determining horizontal and vertical ground-water flow paths at the site. There are significant differences between the hydrogeology of arid and humid climatic regions, as well as sea- sonal variations which should be taken into account. The rate of ground-water travel can be used to calculate optimum sampling frequencies, should additional detail beyond that provided in quarterly sampling become necessary. Additional site and waste information needs arise when tailoring the sampling and analytical protocols to the specific needs of the program. A minimum data set for ground-water monitoring should include general water quality parameters, hydrologic parameters and pollutant indi- cator parameters. A suggested list of basic measurements is provided below: Chemical Parameters pH, CT\ TOC, TOX Alkalinity, CL , NO3 , SO/, PO« , silicate Na*, K+, Ca++, Mg++, Fe and Mn Hydrologic Parameters Water Level, hydraulic conductivity The pollutant indicator parameters noted above [i.e., pH, Q~1, (specific con- ductance), TOC andTOX] provide minimal capability to ensure the detection of target chemical constituents in ground water. The pH and conductance parameters should be measured with care in the field. TOC and TOX determinations should be made after collection in headspace-free glass vials with Teflon®* septa to preserve the volatile organic fraction of the dis- solved organic matter The pollutant indicator parameters should also be sup- plemented with determinations of specific chemical constituents which are likely to be mobile and persistent in the subsur- face. Well Placement and Construction Procedures The placement and construction of monitoring wells are among the most difficult tasks involved in developing an effective monitoring program. The prelim- inary locations and depths of monitoring wells should be selected on the basis of the best available pre-drilling information. Then, as the installation of these wells progresses, new geologic and hydroiogic data should be incorporated into the overall monitoring plan to ensure that the wells will perform the tasks for which they are designed. It is advisableto select initially a minimum array of monitoring wells for the collection of geologic and hydrologic data. Additional wells can be positioned later at monitoring points likely to intercept contaminant flow paths. Well construction should be accom- plished with minimal disturbance of the subsurface. The selection and cleaning of both drilling equipment and well con- struction materials should be performed with the aim of minimizing the intro- duction of foreign materials into the subsurface environment. Given the rela- tively shallow depths of interest in many ground-water monitoring efforts, hollow- stem auger drilling techniques are pre- ferred because they are mobile, fast, and inexpensive. Also, disturbance of the subsurface can be effectively minimized. To properly define the movement of pollutants, in both vertical and horizontal directions, it is essential to collect depth discrete water level data. Well completion depth will depend on the location of the uppermost permeable, saturated zone (i.e., "water-table") in unconfined forma- tions or the piezometric surface of the most shallow permeable zone in confined formations. Vertically nested wells pro- vide information on the vertical direction of ground-water movement and their placement will be a function of the hydro- geologic setting, particularly the relative horizontal and vertical permeabilities of the formations beneath the site. Screen size, grouts, seals and sampling point •Mention of trade names or commercral products does not constitute endorsement or recommenda- tion for use ------- documentation are also important aspects of monitoring well construction which should be addressed in the monitoring program. Evaluation of Well Performance The effectiveness of a ground-water monitoring program may be judged on the attention which has been paid to the evaluation of the hydraulic performance of the monitoring well network. Each well should be properly developed after con- struction and periodically redeveloped to ensure that it provides useful hydraulic data. Development also reduces the time and effort necessary to collect representa- tive ground-water quality information. A variety of proven well development tech- niques are amenable to the development of shallow 2" o.d. monitoring wells. Accurate water level measurements pro- vide the primary data for the evaluation of well performance. Steel tapes(graduated to the nearest hundredth of a foot with raised lettering and divisions), electrical drop lines and sensitive pressure trans- ducers are useful tools in this regard. Field hydraulic conductivity testing of the monitoring wells will avoid the un- resolved issues which attend the inter- pretation of laboratory conductivity test results. Slug or bail tests, repeated at least threetimes, should provide accurate hydraulic conductivity determinations with a precision of ±20%. In general, multiple pump tests are too expensive to consider for evaluating the hydraulic performance of all monitoring wells with- in a site network. The results of conduc- tivity tests provide a basic measure of well hydraulic well performance which is useful for judging the significance of water level excursions and long-term well performance. The testing procedures should be repeated at least every five years and after each redevelopment effort is performed. Well performance evalua- tion also provides a basis for determining an appropriate well purging strategy prior to sampling. No single number of purge volumes to be pumped prior to sampling can be expected to suit all situations. A well conceived purging strategy that includes pumping rates and volumes calculated on the basis of well perform- ance and the transmissivity of the forma- tion of interest is essential to effective ground-water sampling efforts. Sampling Protocol The hydraulic performance of the sampling points permits the design and execution of effective water sampling and analytical protocols. These protocols should be planned for collecting verif iably high quality water chemistry results in order to distinguish natural variability in the geochemistry of the subsurface from those caused by site operations. The sampling protocol should incorporate sampling mechanismsand materialsthat are appropriate for the information needs of the program. Since contaminant migration may be detected at trace (e.g., ppb) levels of individual constituents, sampling mechanisms and materials must be very carefully chosen to avoid biases caused by contamination or sorp- tion. The materials of well construction, samplers and sample transfer tubing are as important as sample storage vessels and analytical performance in this re- spect. Recommended materials for well construction and sampling devices are shown in Tables 1 and 2. Materials' selections should be made with the long- term use of the sampling points in mind. Sampling mechanisms are devices for the collection of water samples. They are not, of themselves, sampling methods. This should be clear from inspection of Figure 1. The steps in the sampling protocol in the first column of the figure are common to all ground-water monitor- ing efforts. Though the details of indi- vidual monitoring efforts may vary, the steps in Figure 1 provide a guide for effective planning. The performance of the sampling point, materials selected and the chemical constituents of interest will dictate the choice of appropriate sampling devices. Figure 2 contains recommendations for sampling mecha- nisms according to the specific demands of the monitoring effort. Conclusions The development of reliable sampling protocols for ground-water quality moni- toring is a complex, programmatic process that must be designed to meet the specific Table 1. Recommendations for Rigid Materials in Sampling Applications (In Decreasing Order of Preference) Material Recommendations Teflon® (flush threaded) Stainless Steel 316 (flush threaded) Stainless Steel 304 (flush threaded) PVC (flush threaded) other noncemented connections, only NSF* approved materials for well casing or potable water applications Low-Carbon Steet Galvanized Steel Carbon Steel Recommended for most monitoring situations with detailed organic analytical needs, particularly for aggressive, organic leachate impacted hydrogeologic conditions. Virtually an ideal material for corrosive situations where inorganic contaminants are of interest. Recommended for most monitoring situations with detailed organic analytical needs, particularly for aggressive, organic leachate impacted hydrogeologic conditions. May be prone to slow pitting corrosion in contact with acidic high total dissolved solids aqueous solutions. Corrosion products limited mainly to Fe and possibly Cr and Ni. Recommended for limited monitoring situations where inorganic contaminants are of interest and it is known that aggressive organic leachate mixtures will not be contacted. Cemented installations have caused documented interferences. The potential for interaction and interferences from PVC well casing in contact with aggressive aqueous organic mixtures is difficult to predict. PVC is not recommended for detailed organic analytical schemes. Recommended for monitoring inorganic contaminants in corrosive, acidic inorganic situations. May release Sn or Sb compounds from the original heat stabilizers in the formulation after long exposures. May be superior to PVC for exposures to aggressive aqueous organic mixtures. These materials must be very carefully cleaned to remove oily manufacturing residues. Corrosion is likely in high dissolved solids, acidic environments, and particularly when sulfides are present. Products of corrosion are mainly Fe andMn, except for galvanized steel which may release Zn and Cd. Weathered steel surfaces present very active adsorption sites for trace organic and inorganic chemical species. ®Trademark of DuPont, Inc. * National Sanitation Foundation approved materials carry the NSF logo indicative of the product's certification of meeting industry standards for performance and formulation purity. ------- Table 2. Recommendations for Flexible Materials in Sampling Applications fin Decreasing Order of Preference) Materials Recommendations Teflon® Polypropylene Polyethylene (linear) PVC (flexible) Viton® Silicone (medical grade only) Neoprene Recommended for most monitoring work, particularly for detailed organic analytical schemes. The material least likely to introduce significant sampling bias or imprecision. The easiest material to clean in order to prevent cross-contamination. Strongly recommended for corrosive high dissolved solids solutions. Less likely to introduce significant bias into analytical results than polymer formulations (PVC) or other flexible materials with the exception of Teflon®. Not recommended for detailed organic analytical schemes. Plasticizers and stabilizers make up a sizable percentage of the material by weight as long as it remains flexible. Documented interferences are likely with several priority pollutant classes. Flexible elastomeric materials for gaskets, O-rings, bladder and tubing applications. Performance expected to be a function of exposure type and the order of chemical resistance as shown. Recommended only when a more suitable material is not available for the specific use. Actual controlled exposure trials may be useful in assessing the potential for analytical bias. ®Trademark of DuPont, Inc. goals of the monitoring effort in question. The long-term goals and information needs of the monitoring program must first be thoroughly understood. Once these considerations have been identified, the many factors that can affect the results can be addressed. In formulating the sampling protocol, the emphasis should be to collect hydro- logic and chemical data that accurately represent in situ hydrologic and chemical conditions. With good quality assurance guidelines and quality control measures, the protocol should provide the needed data for successful management of the monitoring program at a high level of confidence. Straightforward techniques that minimize the disturbance of the subsurface and the samples at each step in the sampling effort should be given priority. The planning of a monitoring program should be a staged effort designed to collect information during the exploratory or initial stages of the program. Informa- tion gained throughout the development of the program should be used for refining the preliminary program design. During all phases of protocol development, the long-term costs of collecting the required hydrologic and chemical data should be kept in mind. These long-term costs may be several orders of magnitude larger than the combined costs of planning, well construction, purchase of sampling and support equipment, and data collection start-up. It also should be remembered that high quality data cannot be obtained from a poorly conceived and implemented monitoring program, regardless of the added care and costs of sophisticated sampling and analytical procedures. Finally, the ultimate costs of defending poor quality data in court or in compliance to regulatory requirements should not be overlooked. Due to the lack of documented standard techniques for developing moni- toring programs, constructing monitoring wells, and collecting samples, quality control measures must be tailored for each individual site to be monitored. They should be designed to ensure that dis- turbances to both the hydrogeologic system and the sample are minimized. The care exercised in the well placement and construction, and sample collection and analysis can pay real dividends in the control of systematic errors. Repeated sampling and field measurements will further define the magnitude of random errors induced by field conditions and human error. The burden of assuring the success of a program relies on careful documentation and the performance of quality assurance audit procedures. ------- Step Procedure Essential Elements Well Inspection Well Purging Sample Collection Filtration* Field Determinations** Preservation Field Blanks Standards Hydrologic Measurements \ Removal or Isolation of Stagnant Water \ Determination of Well-Purging Parameters (pH, Eh. T, fT1)** Unfiltered Volatile Organics, TOX Dissolved Gases. TOO Large Volume Samples for Organic Compound Determinations Assorted Sensitive Inorganic Species NOi, NH<\ Fe (II) (as needed for good QA/QCI Field Filtered* Alkalinity/A cidity* Trace Metal Samples S°, Sensitive Inorganics Major Cation and Anions Storage Transport Water-level Measurements Representative Water Access Verification of Representa- tive Water Sample Access Sample Collection by Appropriate Mechanism Minimal Sample Handling Head-Space Free Samples Head-Space Free Samples Minimal Aeration or Depressurization Minimal Air Contact, Field Determination Adequate Rinsing Against Contamination Minimal Air Contact, Preservation Minimal Loss of Sample Integrity Prior to Analysis 'Denotes samples that should be filtered in order to determine dissolved constituents. Filtration should be accomplished preferably with in-line filters and pump pressure or by /Vz pressure methods. Samples for dissolved gases or volatile organics should not be filtered. In instances where well development procedures do not allow for turbidity-free samples and may bias analytical results, split samples should be spiked with standards before filtration. Both spiked samples and regular samples should be analyzed to determine recoveries from both types of handling. **Denotes analytical determinations which should be made in the field. Figure 1. Generalized flow diagram of ground- water sampling steps. ------- Type of Constituent Volatile Organic Compounds Organometallics Dissolved Gases Well-Purging Parameters Trace Inorganic Metal Species Reduced Species Major Cations & Anions Example of Constituent Chloroform TOX CHaHg Oa. C02 PH. rr1 Eh Fe, Cu NOi. S" Na\ 1C. Ca" Mg" cr, so** Positive Displacement Bladder Pumps Sample Sensitivit Increasing ,' Superior Performance for Most Applications Superior Performance for Most Applications Superior Performance for Most Applications Superior Performance for Most Applications Thief, in situ or Dual Check Valve Bailers May be adequate if well purging is assured May be adequate if we II purging is assured May be adequate if well purging is assured Adequate May be adequate if we/I purging is aec//r^/V Mechanical Positive Displacement Pumps Gas-Drive Devices Suction Mechanisms 'eliability of Sampling Mechanisms May be adequate if design and operation are controlled May be adequate if design and operation are controlled Adequate Adequate Not recommended Not recommended May be adequate Adequate Not recommended Not recommended May be ade- quate if materials are approp- riate Adequate Figure 2. Matrix of sensitive chemical constituents and various sampling mechanisms. . S. GOVERNMENT PRINTING OFFICE:] 986/646-116/20770 ------- Michael J. Barcelona, James P. Gibb, John A. Helfrich. and Edward E. Garskeare with the Illinois State Water Survey. Champaign, IL 61820. Marion R. Scalf is the EPA Project Officer (see below). The complete report, entitled "Practical Guide for Ground-Water Sampling," (Order No. PB 86-137 304/AS; Cost: $16.95, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Robert S. Kerr Environmental Research Laboratory U.S. Environmental Protection Agency P.O.Box 1198 Ada, OK 74820 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 All Official Business Penalty for Private Use S300 EPA/600/S2.-85/104 0000329 PS 4GENCT 230 S DEARBORN STREET CHICAGO it 60604 ------- |