EPA/600/A-93/005 Comparison of Ground-Water Sampling Devices Based On National GrOUndwdtcr Equilibration of Water Quality Indicator Parameters Sampling Symposium Comparison of Ground-Water Sampling Devices Based On Equilibration of Water Quality Indicator Parameters by Cynthia J. Paul and Robert W. Puls ManTech Environmental Technology, Inc. R.S. U-S' Environmental Protection Agency, R.S. Ken- Environmental Research Laboratory Kerr Environmental Research Laboratory P.O. Box 1198 P.O. Box 1198 Ada, OK 74872 Ada, OK 74820 Cynthia J. Paul and Robert W. Puls Page 21 ------- National Groundwatcr Comparison of Ground-Water Sampling Devices Based On Equilibration of Water Quality Indicator Parameters . Sampling Symposium Abstract: The sampling device selected when obtaining ground- watersamples can have a significant impact on the representativeness and reproducibility of the sample. This study evaluated several different sampling devices (low speed submersible pump, peristaltic pump, and bladder pump) in two monitoring wells to obtain ground-water samples based on the equilibration of water quality indicator parameters. The indicator parameters were continuously monitored during purging and sampling with all devices and include: turbidity, specific conductance, pH, oxidation- reduction potential, dissolved oxygen, and temperature. Contaminant (chromium, trichlorethylene (TCE)) concentration levels were also measured for all devices. The bladder pump produced the highest equilibrium turbidity levels, although this effect may be compensated for by careful control of the charge discharge cycles of the pump controller. The peristaltic pump produced the highest levels of dissolved oxygen, specific conductance and pH, whereas the low speed submersible pump generated the highest temperatures. There were no significant differences in Cr concentrations among the various sampling devices. TCE concentration values were generally in the order: low speed submersible > bladder > peristaltic. The submersible pump generates excess heat which might be expected to impact concentrations of volatile organic compounds. The peristaltic pump resulted in sample degassing adversely impacting the sample quality. As this is a suction lift device, its use is limited to shallow wells. Results of this study indicate the low speed submersible pump produced the least negative impacts in trying to obtain representative and reproducible ground-water samples in these wells at this site. Introduction: Proper sampling methods for obtaining accurate, representative, and reproducible ground-water samples has been atopic of considerable debate during the past several years. Amyriad of reports, articles, guidance documents and handbooks have been written addressing this problem (U.S. EPA, 1982; NCASI, 1982; Claasen, 1982; Gillham et al. 1983; Barcelona et al. 1985; EPRI, 1985; U.S. EPA, 1986; Barcelona et al. 1987; Nielsen, 1991; U.S. EPA, 199la; U.S. EPA, 1991b). Factors such as complex chemical, geological, physical, and biological processes make quality sample collection extremely difficult (Puls and Powell, 1992). Puls and Powell (1992) also note that the best sampling approach is one which creates as little disturbance as possible at the sampling point, with minimum change in the chemical properties of the sample. The method of sample collection can significantly impact the quality of the data obtained. Many examples exist of questionable analytical data generated by haphazard sampling methods (Barcelona, 1983). Nielsen and Yeates (1985) point out that ground-water samples should be representative of water within the aquifer, and Powell and Puls (1992) state the necessity for ground-water samples to "...truly define the aqueous geochemistry of the subsurface system at the point of collection". Potential sources of sample alteration include: the method and extent of well development and purging; the choice of sampling device; and filtration, preservation and sample handling (Barcelona, 1983; Barcelona et al. 1984; Nielsen and Yeates, 1985; Kent and Payne, 1988; Barcelona et al. 1988; Puls and Barcelona, 1989; Puls and Powell, 1992). While all of these factors can significantly impact ground-water sample integrity, perhaps the most crucial element of ground-water sample collection is the sampling mechanism itself (Barcelona, 1983). Also of particular importance is how wells are purged prior to sample collection. Puls and Powell (1992) recommend the use of low flow rates during both purging and sampling, with placement of the sampling device intake at the desired sampling point and minimal disturbance of the stagnant water column above the screened interval. Excessive sample turbidity may indicate disturbance of the sampling zone. Puls and Barcelona (1989) and Puls et al (1991) advocate monitoring of water quality indicator parameters (turbidity, temperature, specific conductance, pH, oxidation- reduction potential, and dissolved oxygen) while purging to establish baseline conditions to initiate sampling, thus providing a consistent basis for sample comparison. Puls and Powell (1992) have shown specific conductance, pH, and temperature to be the least sensitive of these indicator parameters while contaminant concentration, dissolved oxygen, redox and turbidity are most sensitive. Comparably low flow rates were used in this study in an attempt to diminish any effects caused by this variable. The purpose of this study was to evaluate three distinctly different sampling devices based on the equilibration of ground-water quality indicator parameters. Materials and Methods: Ground-water samples were obtained from two monitoring wells located on the U.S. Coast Guard Air Support Center near Elizabeth City, NC. A chrome plating shop on the base has discharged a mixture of chrome- plating wastes into the soils and aquifer below the shop, which is located 197 ft. (60 m) south of the Pasquotank River. The site geology consists of Atlantic coastal plain sediments composed of variable sequences of surficial sands, silts and clays. Ground-water flow near the plating shop is complicated by wind tides but is generally to the north. Hydraulic conductivity is estimated to average about Page 22 Cynthia J. Paul and Robert W. Puls ------- Comparison of Ground-Water Sampling Devices Based On National Groundwater Sampling Symposium xiuilibration of Water Quality Indicator Parameters ;0 ft/d (IS m/d) but may be somewhat lower in the region of he waste plume. Ground water is about seven feet (2.J m) >elow ground surface. Both wells are completed 15 feet 4.57 m) below ground surface with PVC casing and 5 foot >creens (0.010-inch (0.025 cm) slot size). Three different rypes of ground-water sampling devices were evaluated: a low speed submersible pump, a bladder pump, and a peristaltic pump (Table 1). An open-end Teflon® bailer was used to collect samples for comparison of contaminant concentrations only. Ground-water quality indicator parameters were continuously monitored during purging and sampling with all devices. A multi-parameter instrument with a flow- through cell was used to monitor temperature, pH, specific conductance, dissolved oxygen, and oxidation-reduction potential. Turbidity values, measured in nephelometric turbidity units (NTUs), were also measured using a flow- through cell. A diagram of the sampling set-up is shown in Figure 1. Alkalinity values were determined in the field using a portable colorimetric titration kit (Hach Co.). Flow rates were kept comparably low (< 500 ml/min) during purging and sampling to minimize turbidity and allow for more rapid equilibration of other parameters as recommended by Puls and Powell (1992). It should be noted that the flow rate for the bladder pump was measured by ml/ pump cycle and converted to ml/min. That is, flow was measured over time at the surface which is different (lower) than the actual flow rate during an intake cycle within the well screen. Also, the flow rate of the submersible pump while in MW17 was increased from 250 ml/min to 940 ml/min after 99 min to observe effects on the ground-water indicator parameters. The volume of water removed from the wells, as well as purge time required to achieve stabilized indicator values, varied with each device used (Table 2). Samples were collected unfiltered after all indicator parameters had stabilized. Atmospheric exposure was kept to a minimum during sample collection through the use of thick walled tubing and in-line monitoring. Samples were collected for volatile organic compound (VOC) analysis in 40 ml glass vials, filled to overflowing and capped with zero headspace using Teflon® septum caps. These samples were immediately placed on ice for transportation to the laboratory. Samples for metals analysis were collected in polyethylene bottles and acidified to pH <2 with concentrated ultra-pure HNOr Metals analyses (e.g. Cr, Fe, A], Ca, etc.) were performed in the laboratory using inductively coupled plasma (ICP). A Technicon® Autoanalyzer was used for major inorganic anions (e.g. Cl~, SO4", NO3~). TCE was analyzed by headspace-gas chromalography (GC) with a flame ionization detector (FID). Results and Discussion: Ground-Water Quality Indicator Parameters Data shown in Table 3 represents the final equilibrated values for specific conductance, turbidity, dissolved oxygen, pH, redox, and temperature. Sampling device appeared to have no significant impact on redox values. While temperature is considered a fairly insensitive parameter, it does have some significance in this study. Figures 2 and 3 show temperature values to be highest with the submersible pump. This increased temperature appears to be due to the operational design of the pump. The sharp peak in MW17 was generated when the flow rate of the submersible pump was intentionally increased from 250 ml/min to 940 ml/min to monitor the effect on the indicator parameters. Although the temperature increased sharply initially, it quickly re- equilibrated to lower values and within the range of the peristaltic pump. This pump appears to generate more heat when operating at the lower flow rates. The effect of this increased temperature on contaminant concentration will be discussed later. Variation in dissolved oxygen levels are indicative of the degree of aeration and degassing produced by the various sampling devices. Figures 4 and 5 reveal the peristaltic pump produced the highest levels of dissolved oxygen (DO) in both wells. Peristaltic pumps subject the water sample to strong negative pressure which causes degassing (Nielsen and Yeates, 1985; Kent and Payne, 1988). The low speed submersible pump produced fairly low DO values in MW16; however, the bladder pump generated the lowest values in both wells. Bladder pumps minimize aeration and gas stripping of the sample by allowing water flow to only contact the bladder (Nielsen and Yeates, 1985), resulting in lower dissolved oxygen values. Equilibrated turbidity values are compared with levels of Fe and Al in Table 4. There is a direct association between high turbidity (solid particles) and increased levels of Fe and Al. X-ray diffraction analysis and scanning electron microscopy have identified the mobilized particles as iron oxide and iron-coated kaolinite and feldspars. Figures 6 and 7 show turbidity equilibrating rapidly to low levels using the low speed submersible and peristaltic pumps. Turbidity values with the bladder pump decreased slowly and never reached acceptably low levels (< 10 NTUs) as determined for this particular site. The equilibrated turbidity values for MW16 and MW17 using the bladder pump were 42 and 15 NTUs, respectively. More careful adjustment of the charge and discharge cycles of the bladder pump can result in lower flow rates which in turn would probably result in lower turbidity. Flow rate at the surface was averaged over several cycles for the bladder pump. This is somewhat misleading for evaluating turbidity since the intake velocity of the pump within the screen is much faster, with water drawn in during Cynthia J. Paul and Robert W. Pub Page 23 ------- National Groundwatgr Comparison ol Ground-Water Sampling Devices Based On Equilibration of Water Quality Indicator Parameters . Sampling Symposium one portion of the complete cycle. As a result, actual flow rate into the bladder pump is much faster than the time-averaged flow at the surface and elevated turbidity compared to the other devices can be explained. Specific conductance and pH were higher in both wells with the peristaltic pump (Table 5). As previously mentioned, peristaltic pumps exert a vacuum that can cause degassing whereby CO2 evolution causes consumption of hydrogen ions, resulting in increased pH values (Loux et al, 1990). Figures 8 through 11 show a definite correlation between specific conductance and pH values. Contaminant Concentrations Table 6 shows contaminant concentrations for both wells. As previously discussed, the sample temperature was significantly higher with the low speed submersible pump. There has been some concern that the increased temperature generated by this pump could volatilize certain organic contaminants, resulting in artificially low sample values. Clearly, this was not demonstrated in this study, where the VOC of interest was TCE (Henry's law constant 0.0099 atm3 • m/mol at 20°C (Roberts and Dandliker, 1983)). The bailer recovered the lowest TCE values while the peristaltic and bladder pumps were slightly higher. The low speed submersible pump obtained the highest TCE values in both wells; however, this may not be true for more volatile compounds which have a higher Henry's law constant. Further evaluation of this phenomenon with more volatile compounds is suggested. There was very little difference in chromium concentrations among the various sampling devices. Even in the more turbid samples, (bladder, bailer) no significant differences were observed. Cr (VI) adsorbs very weakly to mineral surfaces and at this particular site has been shown to be only slightly retarded in dynamic column tests (Rr= 1.6 — 1.8, Puls et al, 1992) using the actual aquifer material. With such low adsorption to solid surfaces, variations in turbidity would not be expected to significantly impact aqueous Cr concentration differences. If strongly adsorbing contaminants were present in the samples, the influence of turbidity differences could be important. Conclusions: Monitoring of ground-water quality indicator parameters during well purging has been shown to be an effective guide for obtaining representative and reproducible ground-water samples. The sampling device selected can affect these parameter values and time required for their equilibration, and must therefore be chosen carefully. As demonstrated in this study, disadvantages of the peristaltic pump are excessive degassing of the water and its limitation to shallow wells. A disadvantage of the bladder pump is excessive turbidity. The only disadvantage of the low speed submersible pump determined by this study appears to be the increased heat generated, which might affect certain volatile organic compounds. Even with this possibility, however, it gave the highest recoveries for TCE of any of the tested devices. Disclaimer Although the research described in this article has been funded wholly or in part by the United States Environmental Protection Agency, it has not been subjected to the Agency's peer and administrative review and therefore may not necessarily reflect the views of the Agency and no official endorsement may be inferred. Page 24 Cynthia J. Paul and Robert W. Puls ------- Comparison of Ground-Water Sampling Devices Based On National Groundwater Sampling Symposium Equilibration of Water Quality Indicator Parameters Acknowledgements:. The authors would like to thank Robert M, Powell (ManTech Environmental Technology, Inc.) for his helpful advice and editing assistance. We wish to acknowledge the analytical support of Don A, Clark (U.S. EPA RSKERL) and Steve A. Vandegrift (ManTech Environmental Technology, Inc.). Biographical Sketches: Cynthia J. Paul is currently employed with ManTech Environmental Technology, Inc. at the R.S. Kerr Environmental Research Laboratory (RSKERL) in Ada, Oklahoma. She received her bachelor's degree from East Central University and is currently pursuing her master's degree in Environmental Science at the University of Oklahoma- She was employed by RSKERL, U.S. EPA for three years before joining ManTech two years ago. Her research interests include ground water sampling methods and metal sorption-desorption reactions as related to subsurface contaaminant fate and transport. Robert W, Puls is currently employed at the R.S. Kerr Environmental Research Laboratory, U.S. EPA, in the Processes and Systems Research Division. He received a bachelor's degree in soil science from the University of Wisconsin-Madison and a master's degree in forest resources from the University of Washington. He received his pH.D. in soil and water science (minor in analytical chemistry) from the University of Arizona, Following completion of his doctorate he worked on the High Level Nuclear Waste Repository Research Program (DOE) investigating the fate and transport of radionuclides in ground water. He has been employed at RSKERL since 1987. His recent publications have covered a range of topics including ground water sampling for inorganics, colloidal transport ir ground water, organic-metal-mineral interactions, aquifer remediation, and metal and metalloid sorption-desorption reactions governing subsurface contaminant transport. References: Barcelona, M.J. 1983. Chemical Problems in Ground- Water Monitoring Programs. Proceedings of the Third National Symposium on Aquifer Restoration and Ground- Water Monitoring. National Water Well Association, Worthington, OH, pp 263-271. Barcelona, M.J., J.A. Helfrich, E.E. Garske, and J.P. Gibb, 1984. A Laboratory Evaluation of Ground Water Sampling Mechanisms. Ground Water Monitoring Review. V.4, no.2, pp 32-41. Barcelona, M.J., J.P. Gibb, J.A. Helfrich, and E.E. Garske. 1985. Practical Guide for Ground Water Sampling. EPA/ 600/2-/85/104, 169pp. Barcelona, M.J., J.F. Keeley, W. A. Pettyjohn, and A. Wehrmann. 3987. Handbook: Ground Water. EPA/626/6- 87/016,212 pp. Barcelona, M.J., J.A. Helfrich, and E.E. Garske. 1988. Verification of Sampling Methods and Selection of Materials for Ground-Water Contamination Studies. Ground-Water Contamination: Field Methods. ASTM STP 963. A. G. Collins and A.I. Johnson, Eds., American Society for Testing and Materials, Philadelphia, pp 221- 231. Classen, J.C. 1982. Guidelines and Techniques for Obtaining Water Samples that Accurately Represent the Water Chemistry of an Aquifer. U.S. Geological Survey Open File Report 982-1024, 49 pp. EPRI. 1985. Field Measurement Methods for Hydrogeologic Investigations: A Critical Review of the Literature. Electric Power Research Institute. EA 4301, 241 pp. Gillham, R.W., M.J.L. Robin, J.F. Barker, and J.A. Cherry. 1983. American Petroleum Institute. API Publication 4367, 206 pp. Kent, R.T., and K.E. Payne. 1988. Sampling Groundwater Monitoring Wells — Special Quality Assurance and Quality Control Considerations. Principles of Environmental Sampling. L.H. Keith, Ed., American Chemical Society, Washington, D.C., pp 231-246. Loux, NT., A.W. Garrison, and C.R. Chafm. 1990. Acquisition and Analysis of Groundwater/Aquifer Samples: Current Technology and the Trade Off Between Quality Assurance and Practical Considerations. Intern. J. Environ. Anal Chem.. Vol 38, pp 231-253. Cynthia J, Paul and Robert W. Puls Page 25 ------- National Groundwatcr Comparison of Ground-Water Sampling Devices Based On Sampling Symposium Equilibration of Water Qualirylndicator Parameters Nielsen, D.M., and G.L. Yeates. 1985. A Comparison of Sampling Mechanisms Available for Small-Diameter Ground Water Monitoring Wells. Ground Water Monitoring Review, v.5, no.2, pp 83-99. Nielsen, D.M. (ed) 1991. Practical Handbook of Ground Water Monitoring, Lewis Publishers, Chesea, Michigan, 717pp. NCASI. 1982. A Guide to Ground Water Sampling. National Council of the Paper Industry for Air and Stream Improvements. Tech. Bull. No. 362, 53 pp. Panko, A.W., and P. Earth. 1988. Chemical Stability Prior to Ground-Water Sampling: A Review of Current Well Purging Methods. Ground-Water Contamination: Field Methods. ASTM STP 963. A. G. Collins and A. I. Johnson, Eds., American Society for Testing and Materials, Philadelphia, pp 232-239. Powell R.M., and R. W. Puls. 1992. Passive Sampling of Ground Water Monitoring Wells Without Purging: Multilevel Well Chemistry and Tracer Disappearance. Journal of Contaminant Hydrology (in press). Puls, R.W., and M.J. Barcelona. 1989. Ground Water Sampling for Metals Analyses. EPA/540/4-89-001,6 pp. Puls, R.W., R.M. Powell, D.A. Clark, and C.J. Paul. 1991. Facilitated Transport of Inorganic Contaminants in Ground Water: Part II. Colloidal Transport. EPA/600/M-91-040, 12 pp. Puls, R.W., D. A. Clark, B. Bledsoe, R.M. Powell and C.J. Paul. 1992. Metals in Ground Water: Sampling Artifacts and Reproducibility. Hazardous Waste & Hazardous Materials, v.9, no. 2, pp 149-162. Puls, R.W., and R.M. Powell. 1992. Acquisition of Representative Ground Water Quality Samples for Metals. Ground Water Monitoring Review. Summer-92, pp 167- 176. Roberts, P.V., and P.O. Dandliker. 1983. Mass Transfer of Volatile Organic Contaminants from Aqueous Solution to the Atmosphere During Surface Aeration. Environ. Sci. Techno!., v.17, no. 8, pp 484-489. U.S. EPA. 1982. Handbook for Sampling and Sample Preservation of Water and Wastewater. EPA/600/4-82-029, 402 pp. U.S. EPA. 1986. RCRA Ground-Water Monitoring Technical Enforcement Guidance Document. OSWER 9950.1,207pp. U.S. EPA. 1991a. Compendium of ERT Ground Water Sampling Procedures. EPA/540/P-91-007, 63 pp. U.S. EPA. 1991b. Handbook: Ground Water Volume II: Methodology. EPA/625/6-90/016b, 141 pp. Page 26 Cynthia J. Paul and Robert W. Puls ------- Comparison of Ground-Water Sampling Devices Based On National Groundwater Sampling Symposium Equilibration ol Water Quality Indicator Parameters TABLES TABLE 1. Ground-Water Sampling Devices Evaluated Mechanism Type Commercial Brand Positive Displacement Bladder inflation Geoiech® (Small (bladder, Diameter Well Pump) gas displacement) Positive Displacement Submersible, (mechanical) centrifugal Suction-lift Peristaltic Grundfos® (Redi-Fto2) Millipore® (Variable Speed) TABLE 2. Purge Volume and Time To Reach Equilibration (three successive readings ±10 %). * One casing volume was 5.85 L Device MW16 Peristaltic Bladder Low Speed Submersible MW17 Peristaltic Bladder Low Speed Submersible Casing Volumes* 3.02 14.31 2.95 1.06 8.41 2.14 Time (min) 82 140 80 31 105 37 TABLE 3. Equilibrated Ground-water Indicator Values Cond MW16 Peristaltic Bladder Submersible MW17 Peristaltic Bladder Submersible .760 .705 .706 ,622 .547 .504 Turb 7.6 42 4.3 1.29 15 1.13 DO 0.13 0.02 0.03 1.90 0.02 0.30 pH 5.90 5.81 5.87 6.57 6.33 6.27 Redox .320 .362 .331 .312 274 zn Temp 26.28 25.68 32.14 25.73 25.25 2B.64' Temperature for submersible in MW 17 is before pump rate was turned up from 250 ml/min to 940 ml/mm. Final temperature was 25.94' C. TABLE 4. Comparison of Turbidity Values With Element Concentrations Turbidity (NTUs) Fe (mg/L) MW16 Peristaltic 4.3 Bladder 42 Submersible 7.6 MW17 Peristaltic 1 .3 Bladder 15 Submersible 1.1 0.32 3,45 1.43 <0.10 1.48 0.27 Al (mg/L) 0.2? 2.23 0.55 <0.10 0.93 <0.10 Cynthia J Paul and Robert W. Puls Page 27 ------- National Groundwater Comparison of Ground-Water Sampling Devices Based On L Sampling Symposium Equilibration of Water Quality indicator Parameters TABLE 5. Comparison of Specific Conductance, pH, Alkalinity and Calcium, Cond pH Alk Ca (mS/cm) (mg/L) (mg/L) MW16 Peristaltic Bladder Submersible MW17 Peristanic Bladder Submersible ,760 5,90 62 28.3 .705 5.81 51 25.0 .706 5,87 61 26.5 .622 6.57 137 27.5 .547 6.33 110 17.5 .504 6.27 106 16.6 TABLE 6. Ground-Water Contaminant Concentrations (ppb). Device Peristaltic Bladder Submersible Bailer MW16Cr 220 200 240 220 MW16TCE 8945 9030 9445 8195 MW17Cr 1790 1780 1530 1550 MW17 TCE 212 224 378 190 Page 28 Cynthia J. Paul and Robert W. Puls ------- Comparison ol Ground-Water Sampling Devices Based On National Groundwater Equilibration of Water Quality Indicator Parameters Sampling Symposium FIGURES Figure 1 Sampling Device Turbidimeter Multiparameter Monitoring Device Sample Bottle Figure 1: Sampling set-up for monitoring ground-water quality indicator parameters. Cynthia J. Paul and Robert W. Puls Page 29 ------- National Groundwatcr Comparison of Ground-Water Sampling Devices Based On Equilibration of Water Quality Indicator Parameters Sampling Symposium Figure 2 34 33 32 31 ^ 30 (A % 29 & 28 27 26 25 24 15 30 , Peristaltic 45 60 Time (min) Bladder 75 . Submersible 90 105 Figure 2: Equilibration of temperature values during purging and sampling for MW16. Page 30 Cynthia J. Paul and Robert W. Puls ------- Comparison of Ground-Water Sampling Devices Based On National Groundwater Sampling Symposium Equilibration of Water Quality Indicator Parameters Figure 3 33 32 31 30 29 8. 28 Eb Q 27 26 25 24 23 0 15 30 45 60 75 Time (min) , Peristaltic t Bladder A Submersible Note: Submersible pump rate was increased to 940 ml/min after 99 min. Figure 3: Equilibration of temperature values during purging and sampling for MW17, 90 105 120 Cynthia J. Paul and Robert W Puls Page 31 ------- National Groundwater Comparison of Ground-Water Sampling Devices Based On Sampling Symposium Figure 4 Equilibration of water Quality Indicator Parameters 0.35 0.3 0.25 0.2 0.15 0.1 0.05 15 30 , Peristaltic 45 60 Time (min) Bladder _ 75 Submersible 90 105 Figure 4: Equilibration of dissolved oxygen values during purging and sampling for MW16. Page 32 Cynthia J. Paul and Robert W, Pub ------- Comparison of Ground-Water Sampling Devices Based On National Groundwatcr Equilibration of Water Quality Indicator Parameters Sampling Symposium Figure 5 0.6 0.5 0.4 0.3 0.2 0.1 0 15 30 45 60 75 90 105 Time (min) , Peristaltic t Bladder A Submersible Note: Submersible pump rate was increased to 940 ml/min after 99 min. 120 Figure 5: Equilibration of dissolved oxygen values during purging and sampling for MW17. Cynthia J. Paul and Robert W. Puls Page 33 ------- National Groundwater Comparison of Ground-Water Sampling Devices Based On Equilibration of Water Quality Indicator Parameters Sampling Symposium Figure 6 1500 - 1000 500 15 30 Peristaltic 45 60 75 Time (min) _+_ Bladder (2Y) 105 . Submersible 120 Figure 6: Equilibration of turbidity levels during purging and sampling for MW16. Page 34 Cynthia J. Paul and Robert W. Puls ------- Comparison of Ground-Water Sampling Devices Based On National Grounduater Equilibration of Water Quality Indicator Parameters Sampling Symposium Figure 7 90 80 70 60 50 40 30 20 10 0 15 30 45 60 75 90 Time (min) m Peristaltic » Bladder (2Y) _A,_ Submersible Note: Submersible pump rate was increased to 940 ml/min after 99 min. 300 250 200 150 100 50 105 120 135 150 Figure 7: Equilibration of turbidity levels during purging and sampling for MW17. Cynthia J. Paul and Robert W. Puls Page 35 ------- National Groundwater Comparison of Ground-Water Sampling Devices Based On Sampling Symposium Figure 8 Equilibration of Water Quality Indicator Parameters 0.82 0.8 0.78 0.76 I 0.74 B 0.72 0.7 0.68 0.66 15 30 - Peristaltic 45 60 Time (min) . Bladder _ 75 Submersible 90 105 Figure 8: Equilibration of specific conductance during purging and sampling for MW16, Page 36 Cynthia J. Paul and Robert W. Pub ------- Comparison of Ground-Water Sampling Devices Based On National Groundwater Equilibration of Water Quality Indicator Parameters Sampling Symposium Figure 9 t/3 0.7 0.65 0.6 0.55 0.5 0.45 0 15 30 45 60 75 90 105 120 Time (min) , PerisLaitic + Bladder A Submersible Note: Submersible pump rate was increased to 9-SO ml/mm after 103 min. Figure 9: Equilibration of specific conductance during purging and sampling for MW17. Cynthia J, Paul and Robert W Pub Page 37 ------- National Groundwater Comparison o( Ground-Water Sampling Devices Based On Sampling Symposium Equilibration of Water Quality Indicator Parameters Figure 10 6.1 6.05 5.95 5.9 5.85 5.8 5.75 15 30 Peristaltic 45 60 Time (min) _ Bladder 75 Submersible 90 105 Figure 10: Equilibration of pH during purging and sampling for MW16. Page 38 Cynthia J. Paul and Robert W. Puts ------- Comparison ol Ground-Water Sampling Devices Based On National Groundwater Sampling Symposium i Equilibration of Water Quality Indicator Parameters Figure 11 7 6.9 6.8 6.7 3 6.6 c 3 % 6.5 6.4 6.3 6.2 6.1 0 15 30 45 60 75 Time (min) 90 105 120 _f_ Peristaltic » Bladder _A_ Submersible Note: Submersible pump rale was increased to 940 ml/min after 99 min. Figure 11: Equilibration of pH during purging and sampling for MWI7. Cynthia J. Paul and Robert W Puls Page 39 ------- TECHNICAL REPORT DATA {Please reatl Instructions on the reverte btfort complet' EPA/600/A-93/005 4. TITLE AND SUBTITLE Comparison of Ground-Water Sampling Devices Based on Equilibration of Water Quality Indicator Parameters S. REPORT OATS. November 1992 6, PERFORMING ORGANIZATION CODE 7. AUTHORIS1 *Cynthia J. Paul - ManTech Environmental Technology, Inc. **Robert W. Puls - RSKERL - U.S. Environmental Protection , 8. PERFORMING ORGANIZATION REPORT NO. ency SJ*ERFORM1NG ORGANIZATION NAME AND ADDRESS *ManTecn Environmental Tech., Inc. R.S, Kerr Environmental Res. P.O. Box 1198 Ada, OK 74820 Lab **R.S. Kerr Env. Res U.S.E.P.A. • P.O. Box 1198 Ada, OK 74820, to. PROGRAM ELEMENT NO, Lab 11. CONTRACT/GRANT NO. 12. SPONSORING AGENCY NAME AND ADDRESS Robert S. Kerr Environmental Research Laboratory U.S. Environmental Protection Agency P.O. Box 1198 Ada, OK 74820 13. TYPE OF REPORT AND PERIOD COVERED Proceedings - Presentation 14. SPONSORING AGiNCY CODE EPA/600/15 IS. SUPPLEMENTARY NOTES In Proceedings: National Ground Water Sampling Symposium, Washington, DC, November 30, 1992. 16. ABSTRACT The sampling device selected when obtaining ground-water samples can have a significant impact on the representativeness and reproducibility of the sample. This study evaluated several different sampling devices (low speed submersible pump, peristaltic pump, and bladder pump) in two monitoring wells to obtain ground-water samples based on the equilibration of water quality indicator parameters. The indicator parameters were continuously monitored during purging and sampling with all devices and include: turbidity, specific conductance, pp, oxidation-reduction potential, dissolved oxygen, and temperature. Contaminant (chromium, trichloroethylene (TCE) concentration levels were also measured for all devices. 17. KEY WORDS AND DOCUMENT ANALYSIS DESCRIPTORS b.lOENTIFlERS/OPEN ENDED TERMS . COSATi Field, Group Ground Water Sampling Devices Indicator Parameter Water Quality 18. DISTRIBUTION STATEMENT EP* Form 2220-1 (R«». 4-77} previous eo 19. SECURITY CLASS {ThisRtportl 21, NO. OP "AGES 18 20. SECURITY CLASS iT/iis ptigi" 22. ------- |