EFFECTS OF A LARGE SCALE GEOTHERMAL HEAT PUMP INSTALLATION ON AQUIFER MICROBIOTA

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1 EFFECTS OF A LARGE SCALE GEOTHERMAL HEAT PUMP INSTALLATION ON AQUIFER MICROBIOTA Karen P. York, Z.M.G. Sarwar Jahangir, Tatiana Solomon, And Linda Stafford The Richard Stockton College Of New Jersey Natural And Mathematical Sciences P.O. Box 195, Pomona, NJ USA (609) FAX (609) ABSTRACT In 1993, the Richard Stockton College of New Jersey installed a large closed-loop, groundcoupled (geothermal) heat pump system to heat and cool its academic buildings. Heat is exchanged with the ground to a depth of approximately 130 m, affecting three aquifers, the Upper Cohansey, the Lower Cohansey, and the Rio Grande. The installation at Stockton College is designed with monitoring wells, which allow access to the subsurface environment, and provide a unique opportunity to assess the impact of thermal release into the environment. Specifically, we have initiated a study on the effects of thermal fluctuation on the microorganisms in the aquifers of the geothermal well field. We have determined the microbial biomass by direct bacterial enumeration, and compared samples taken from within the well field to those taken at a control site outside the well field. These samples contained a diversity of bacterial types based on our observations of cell morphology, colony morphology, and Gram staining of cultured bacteria. In the Lower Cohansey aquifer samples, there were increases in total microbial number, which correlated with the increase in temperature in the geothermal well field. Moreover, counts of cultured bacteria suggested that even when no significant differences in total bacterial number were observed, there may have been changes in the types of microorganisms present in the aquifers of the geothermal well field. 1. INTRODUCTION In 1993, The Richard Stockton College of New Jersey installed a large geothermal (closed-loop ground-coupled) heat pump system (GHPS) to heat and cool the majority of its academic

2 buildings (Taylor, Stiles, and Hemphill, 1998). The GHPS is a heat exchange system that takes advantage of the temperature differential between the surface and the subsurface environments. Thermal energy is exchanged through a system of 400 U-shaped high density polyethylene pipes placed in boreholes, which extend to a depth of 130 m. Each vertical loop is arranged in a well field, containing 10 rows of 40 wells each occupying a total area of approximately 3.5 acres (14,164 m 2 ) located beneath one of the college s parking lots. Groundwater in the system is neither discharged nor recharged, only thermal energy is exchanged between the surface and the underground environment. As an alternative to conventional heating, ventilation, and air conditioning systems (HVAC), geothermal heat pump technology can provide an energy efficient, cost effective HVAC system, which contributes to a reduced dependence on fossil fuels, and a reduction in emissions of CO 2, and other greenhouse gases. The estimated savings in natural gas and electrical usage for the first year of operation of the GHPS at Stockton College indicate that the reduction of carbon dioxide emissions is roughly equivalent to that obtained by taking 450 cars off the road permanently (Sweikart, 1995, Sanner and Stiles, 1997). While reductions in carbon dioxide emissions are desirable, the environmental effects of thermal fluctuations due to thermal energy released in the subsurface environment from the GHPS have not been well studied. The closed loop system of the Stockton College geothermal well field traverses three aquifers, the Upper Cohansey, the Lower Cohansey, and the Rio Grande, at depths of approximately 15, 45, and 100 meters below the ground surface, respectively. Operation of the geothermal heat pump system at Stockton College has resulted in seasonal temperature fluctuations, and an overall increase in the temperature of the aquifers (Epstein et al., 1996). The aquifers are inhabited by a diverse community of microorganisms adapted to live in the subsurface environment. The aquifer microbiota are likely to be affected by temperature fluctuations resulting from thermal energy exchange (Hicks and Stewart, 1988). The seasonal temperature fluctuations that we have observed (12 o C to 28 o C, daily averages) are in a range, which are critical for many bacterial species. Among the broad classes of bacteria, which can grow at 12 o C, some of these are unable to grow at higher temperatures, while others grow better at higher temperatures. The monitoring wells in the Stockton College GHP installation allow access to the underground environment, and provide a unique opportunity to study the effects of thermal fluctuation on microbes in the aquifers of the geothermal well field. This work is motivated in part by concerns about the quality of the groundwater, which serves as a source of drinking water for the region. We have conducted preliminary studies on the effects of thermal fluctuations on the number and types of bacteria in the aquifers of the Stockton College GHPS.

3 2. METHODS 2.1 Sample Collection Samples were taken from a site in the well field which experiences the greatest temperature fluctuation (C site), and a control site located on College Drive, outside the well field. At each site, three high density polypropylene pipes are positioned in each of the three aquifers, and extends cm above the ground surface. Water was drawn from each aquifer through the sampling tube using a hose attached to a pump. To ensure that the sample was drawn from the aquifer, twice the volume of the sampling tube was removed prior to collecting a sample. The temperature of the run off water was measured at the time of sampling. A side valve of the pump was allowed to flush, and the samples were collected from the side valve into a sterile 50 ml conical tube. Three independent samples were collected for each aquifer, at each site. Three subsamples were fixed immediately by transferring 9 ml from the 50 ml sample into a sterile 15 ml tube containing 1 ml of fixative (10% phosphate buffered glutaraldehyde). The samples were maintained on ice until further processing in the laboratory. 2.2 Direct Count Enumeration We have estimated microbial biomass by direct enumeration of bacteria using epifluorescent microscopy (R. A. Herbert, 1990, R. L. Kepner, Jr. and J. R. Pratt, 1994). The bacteria were stained with acridine orange, a fluorescent dye, which stains nucleic acid. The bacteria in the sample were counted directly when viewed under the epifluorescent microscope at 1000X magnification. Because some of our samples contained relatively low numbers of bacteria, and contained a fine grain sediment to which the bacteria adhere, the protocol that we have implemented to prepare the samples for staining and counting includes two modifications. First, samples from the Upper Cohansey aquifer, which contained visibly more sediment and higher bacterial counts, were diluted prior to processing. Second, a bacterial dispersion step using sodium pyrophosphate and sonication was added for the preparation of all samples. Triplicate samples were filtered onto black filters, which were placed on microscope slides, and were counted within 96 hours of processing. We routinely count 100 microscopic fields or 75 bacterial cells in no less than 50 microscopic fields. The total number of bacteria per milliliter of the original sample was calculated for comparisons. 2.3 Viable Counts For a determination of viable counts, a portion of the aquifer samples were plated onto a rich Luria Bertani media (LB) in triplicate and grown at 16 o C, 20 o C, and 37 o C for 2 to 4 days. The number of bacterial colonies, each presumably arising from single cells, were recorded. The colony forming units (or cells) per milliliter of the original sample was calculated for comparisons.

4 The colony morphology of cultured bacteria was also examined. We have obtained pure cultures of several bacterial types and have characterized them further by colony morphology, Gram staining, cell morphology, and growth on MacConkey medium, which selects for Gram negative bacteria. 3. RESULTS Initially, we wanted to determine whether temperature fluctuations in the geothermal well field affected the total microbial biomass. Our strategy for addressing this question has been to take samples from a site within the well field, which experiences the greatest temperature fluctuations (C), and a control site outside of the well field (CD). We have estimated the microbial biomass in the aquifers of the geothermal well field by determining the total number of bacteria in the samples by direct bacterial counts using epifluorescent microscopy (Kepner and Pratt, 1994). In the Lower Cohansey aquifer samples, for the months of June 1996 through March 1997, we have observed that there were increases in total bacteria number which correlated with the increased temperature in the geothermal well field (Figure 1). Despite seasonal variations in bacterial number, the bacterial counts obtained for the site in the well field, which experiences the highest temperatures (C site), are significantly higher when compared to the bacterial counts obtained for the control site (CD) outside the well field. Total bacterial number x 10 4 / ml In the Lower Cohansey Aquifer Total Bacterial Counts are Higher in the Well Field Samples JUN'96 JUL'96 SEP'96 OCT'96 NOV'96 DEC'96 JAN'97 FEB'97 MAR'97 Figure 1. Direct Counts of Total Bacteria in the Lower Cohansey Aquifer. Total numbers of bacteria are compared for Lower Cohansey aquifer samples from two sites; one within the well field (gray), and a control site outside of the well field on College Drive (black). The numbers are the mean of three to six replicates for that sample. The error bars represent +/- one standard deviation of the mean. The site in the well field has a higher temperature than the control site. Samples taken from June 1996 to March 1997 are shown.

5 In contrast, when samples from the Upper Cohansey aquifer were compared, there was no significant difference in the total number of bacteria observed from the C site in the well field, which experiences the greatest increase in temperature, when compared to the control site outside the well field (Figure 2). Note that the total number of bacteria in these samples is consistently higher compared to the total bacteria obtained for the Lower Cohansey samples (Figure 1). Samples from the Upper Cohansey aquifer were also plated onto bacterial culture media, and bacteria from the aquifers cultured in the laboratory. As has been reported by others, the number of bacteria, which can be cultured from the sample represents only a small percentage (.1 to 2 %) of the total number of bacteria in the aquifer (Ward et al., 1990). However, the numbers of cultured bacteria were clearly higher for samples from the well field (C) compared to outside the well field (CD) in the Upper Cohansey samples (Figure 3). The observation that the number of cultured bacteria was increased in the samples from the well field, when there were no significant differences in total microbial numbers in these samples, suggested that there were changes in the bacterial types that were present in the aquifers of the well field. Among the cultured bacteria obtained from the aquifer samples, we have identified both Gram positive and Gram negative species with different cell and colony morphology, indicating that a diversity of microorganisms were present. Total bacterial number x 10 4 / ml In the Upper Cohansey Aquifer Total Number of Bacteria is Not Significantly Different in the Well Field Samples JUN'96 JUL'96 SEP'96 OCT'96 NOV'96 DEC'96 JAN'97 FEB'97 MAR'97 Figure 2 Direct Counts of Total Bacteria in the Upper Cohansey Aquifer. The total numbers of bacteria are compared for Upper Cohansey aquifer samples from a site within the well field (gray), and from a control site outside of the well field on College Drive (black). The numbers are the mean of three to six replicates for that sample. The error bars represent +/- one standard deviation of the mean. The site in the well field has a higher temperature than the control site. Samples taken from June 1996 to March 1997 are shown.

6 Colony forming units/ ml In the Upper Cohansey Samples Culturable Bacteria are Higher in the Well field JUN'96 JUL'96 AUG'96 SEP'96 OCT'96 NOV'96 DEC'96 JAN'97 FEB'97 MAR'97 APR'97 Figure 3. Comparison of the Viable Count of Bacteria from the Upper Cohansey Aquifer. A portion of the Upper Cohansey aquifer samples are plated on rich media and grown at 23 o C. The number of bacterial colonies that arise are compared for samples from the C site within the well field (gray) compared to a site outside the well field (black). The numbers are the mean of nine replicates for that sample. The error bars represent +/- one standard deviation of the mean. Samples taken from June 1996 to April 1997 are shown. 4. DISCUSSION Operation of the large geothermal (closed-loop ground-coupled) water loop heat pump system at the Richard Stockton College of New Jersey has resulted in seasonal variations in the temperature underground, and an overall increase in the temperature of the aquifers. We have initiated a study of the effects that thermal fluctuations have on the microorganisms in the aquifers of the geothermal well field. We have determined that in the Lower Cohansey aquifer samples, there were increases in total microbial number which correlated with the increased temperature in the geothermal well field. The highest bacterial counts were obtained for the C site in the well field, which experiences the highest temperatures. For the Upper Cohansey aquifer, our data suggested that even when there were no changes in the total number of bacteria, there may have been changes in bacterial types present in the aquifers of the geothermal well field. Our results are consistent with the possibility that there is a causal relationship between the temperature fluctuations, and the observed changes in bacterial numbers and types. However, we can not ruled out alternate possibilities that the changes we see are not caused directly by temperature fluctuation. We have cultured several bacteria from the aquifer samples. If the increase in number of these bacteria is due to the temperature increase in the aquifers of the well field, we predict that some of these cultured bacteria should grow better at temperatures of (25 o C) compared to a lower temperature (12 o C) naturally found in the aquifer, or that they may be more resilient to temperature fluctuations.

7 Our data does not address the question of whether the effects we have observed will persist or spread outside of the local environment of the geothermal well field. We anticipate that these effects will prove to be local effects, based on results from related research, which examined temperature changes, and changes in groundwater chemistry. In those studies, the effects have been shown to be somewhat confined locally, often returning to normal at the outflow edge of the geothermal well field (Sowers, et al. 1997). This work is motivated, in part, by concerns related to the wide-spread use of geothermal heating, and the effects on the water quality, which is used as a water source in this region. We are concerned about the possibility of promoting the growth of potential disease causing (pathogenic) microorganisms. We have observed in our experiments there are few bacteria in the aquifer samples which can grow at body temperature (37 o C). When monitored, there were no fecal coliform organisms typical of wastewater contamination (MacConkey +, capable of growth at 37 o C). In studies of aquifer thermal energy storage systems (ATES), no adverse affects caused by microbiological processes have been observed (Winter, 1992). We hope that a continuing study of the aquifer microbiota in the geothermal well field at Stockton College will help to confirm and extend those conclusions. 5. ACKNOWLEDGMENTS The authors are grateful for the financial support from the Environmental Protection Agency, South Jersey Transportation Authority, the Richard Stockton College of New Jersey, The Electric Power Research Institute, and the Sandia National Laboratory, which made this study possible. We acknowledge the intellectual contributions of Louise Sowers, James Pierce, Lynn Stiles, Alan Steinberg, Harold Taylor, Claude Epstein, Bradley Van Guilder, and Sipra Pal. The work would not have been possible without the assistance of many student workers including Joseph Cassara, Kelly Lewis, James Brownhill, Sony Sinha, Hadgu Hadgu, Patricia Malusa, Kim Bednar, Chris Spedaliere, Jeffrey Thomas, Joseph Kollie, Jason Winterbotom, Wendy Benenson. REFERENCES Amann, R. I., W. Ludwig, K. Schleifer (1995) Phylogenetic identification and in situ detection of individual microbial cells without cultivation. Microbiological Reviews 59: Epstein, C., W. Skinner, L. Stiles, H. Taylor, L. Sowers, and S. Pal (1996). Geothermal heating on a very large scale: the Stockton College Facility, Well Water Journal Vol. L (10): Herbert, R. A. (1990) Methods for enumerating microorganisms and determining biomass in natural environments. Methods in Microbiology Vol. 22: Hicks R. J. and D.L. Stewart. (1988) Environmental assessment of the potential effects of aquifer thermal energy storage on microorganisms in groundwater. PNL-6492, Pacific Northwest Laboratory, Richland, Washington.

8 Kepner, Raymond L., Jr. and James R. Pratt (1994) Use of fluorochromes for direct enumeration of total bacteria in environmental samples: past and present. Microbiological Reviews. 58(4): Sanner, B. and L. Stiles (1997) Status of Seasonal Cold Storage in Ground Source Heat Pumps. Proceedings of the 7th International Conference on Thermal Energy Storage MEGASTOCK: Vol. 1 : Sowers, L.S., C. Epstein, K.P. York, B. van Guilder, S. Jahangir, A. Steinberg, L. Stafford, J. Pierce, J. Brownhill and T. Solomon. (1997) Impact of a Large Scale Geothermal Project on its Surface and Subterranean Environment. Proceedings of the 7th International Conference on Thermal Energy Storage MEGASTOCK: Vol. 1 : Sweikart, M. (1995) Avoided emissions and car equivalencies for the projected energy savings of the Richard Stockton College Geothermal Project. Taylor, Harold, Lynn Stiles and William Hemphill (1998) Technical Description of the Stockton College Geothermal HVAC retrofit. Proceedings of the Second Stockton International Geothermal Conference. Ward, D.M., R. Weller and M.M. Bateson (1990) 16S rrna sequence reveals numerous uncultured microorganisms in a natural community. Nature 345: Winter, A.L. (1992) Summary of Research on Microbiological Processes. Report to the International Energy Agency, Annex VI, Subtask D: Microbiological Processes Doc. No. 42-D.

IMPACT OF GROUNDWATER FLOW ON THE STOCKTON GEOTHERMAL WELL FIELD

ABSTRACT IMPACT OF GROUNDWATER FLOW ON THE STOCKTON GEOTHERMAL WELL FIELD Dr. Claude M. Epstein Richard Stockton College of New Jersey Environmental Studies PO Box 195 Pomona, New Jersey 08240-0195 (609)