BBC: Research Objectives
 
Overall Objectives

Expected Benefits of BBC Research
Proposed Research
Research Approach and Schedule
  Overall Objectives:

The overall objectives of the BBC are to conduct research in order to:

  1. More efficiently and economically characterize the direction of groundwater flow and fracture patterns (size, direction, secondary mineralization) in the contaminated bedrock aquifers.

    Without an understanding of the fracture patterns, flow paths and contaminant distributions (sorbed and dissolved phases), it is very difficult to develop strategies for implementing bioremediation in situ.
     
     
  2. Improve and develop new field technologies to control hydraulic and flow conditions in the contaminant zone.

    Without controlling these parameters, the ability to affect biodegradation is limited.
     
     
  3. Develop laboratory and field methods to estimate and accelerate in situ rates of bioremediation of organic contaminants in bedrock aquifers.

    Knowing these rates is crucial because they must be used in fate and transport models to predict whether bioremediation will reduce the organic concentrations to acceptable levels before the contaminants reach the nearest receptors (e.g., drinking water wells).
     
     
  4. Develop and apply innovative microbiological and molecular biology techniques to:
     
    • Identify and characterize the specific components of the microbial communities in the fractures of competent (deep) bedrock responsible for contaminant biodegradation
       
    • Enhance in situ bioremediation and assess the efficacy of bioremedial strategies.
       
Expected Benefits of BBC Research:

Until recently, there was little evidence that microorganisms existed in bedrock. Now studies like those by Petersen et al. (1996) and others (e.g., Fry et al., 1997) have shown that bacteria exist in uncontaminated bedrock, living along the fractures that permeate the rock and in the water that flows through them. Indeed, research teams at two major bedrock contamination sites – the TCE-contaminated basalt at the INEEL TAN site and TCE-contaminated dolomite in upstate New York – have shown that in situ bacteria are capable of degrading TCE by a variety of metabolic processes. Using these naturally-occurring, metabolically active microorganisms to degrade the contaminants in the groundwater and sorbed to the fracture surfaces may offer the best alternative for cost effective and efficient remediation. Other remedial alternatives used in unconsolidated sediments (e.g., pump and treat) may not work in bedrock because of the complex and variable hydraulics of the fractures.
 

Proposed Research:

The BBC proposes to conduct research on bioremediation in contaminated bedrock including developing:

  • Improved methods of site characterization
     
  • Innovative microbiological and molecular methods to enhance bioremediation and assess the efficiency to remedial strategies
     
  • New laboratory procedures to estimate the rate of biodegradation, and new engineering technologies to improve the success of in situ bioremediation.

The BBC will focus on applied research and technology transfer in order to improve the ability of regulatory agencies and the private sector to characterize, remediate and monitor organically-contaminated bedrock aquifers.
 

Research Approach and Schedule:

There are several innovative aspects to the bedrock bioremediation research that the BBC is proposing to conduct in Year I. We will be conducting an evaluation of several methods of assessing the sources and extent of bacterial contamination in bedrock cores. Understanding whether significant microbial contamination of the cores occurs from the overburden and/or drilling fluid is important because much of the initial information gained about the in situ microbial community and its metabolic capabilities is derived from these samples.

While various types of tracers have been used during drilling to determine the extent and sources of contamination, this will be the first time that several methods (i.e., bacterial tracers, inorganic tracer, community-level physiological and phylogenetic profiling, total and culturable cell enumeration) are tested simultaneously in a single borehole. The information derived from this experiment will enable us to compare the various tracer techniques and recommend appropriate applications of them.

   By assessing whether the bacteria possess the genes that encode for various oxidative and reductive dehalogenating enzymes, we can decide what engineered approach(es) to bioremediation might be appropriate.
 
     
       

Currently, the major mechanism for identifying whether biodegradation of organic contaminants is occurring in situ is to monitor for the decrease in the parent compounds and the increase in their breakdown products. However, the metabolic process(es) responsible are oftentimes difficult to ascertain from such chemical data alone, particularly during biodegradation of chlorinated ethenes. In addition, it is impossible to know from this kind of an approach whether the in situ microorganisms have the genetic potential to use other more efficient metabolic process(es), if the appropriate electron donors or acceptors could be provided. There are several methods that have been developed to assess the capabilities of bacteria to degrade chlorinated ethenes, but they have never been used as a suite of tests to address the issue of what the current and potential in situ metabolic processes are (could be). We will use several new and traditional methods (multiplex and reverse transcriptase PCR with primers specific for genes encoding for TCE degrading enzymes, DGGE, and enrichment cultures) to evaluate the microorganisms obtained from our test boreholes (cores and groundwater). In addition, we propose to use hydrogen analyses of the groundwater to corroborate what anaerobic metabolic process(es) are operative in situ. By assessing whether the bacteria possess the genes that encode for various oxidative and reductive dehalogenating enzymes, we can decide what engineered approach(es) to bioremediation might be appropriate. For example, if the microbial community at a site does not possess genes that encode for methane monoxygenese, addition of methane and air would probably not be a successful bioremediation alternative.

Protists are known to impact the rate of bacterial degradation of organic contaminants in unconsolidated aquifer sediments (Kinner et al., 1997, 1998). There is no data available concerning whether protists exist in bedrock aquifers. This research will provide a first indication of whether they are present in situ. If they are, we will try to elucidate their role in the biodegradation process during Year II. Laboratory microcosms can be very useful in estimating the rates of reductive dechlorination occurring in the field as shown by Wilson et al. (1996). However, most microcosm methods have been developed for use with unconsolidated aquifer sediments. Yaeger et al. (1997) used groundwater alone and with sterile pulverized dolomite from a bedrock aquifer to conduct their microcosm studies. Other microcosm models for bedrock aquifers need to be developed and tested that also include the microbial communities associated with the fracture faces. This is especially important because it is often very difficult to compare contaminant and by-product concentrations along the groundwater flow path in bedrock aquifers because of the limited number of wells and the uncertainty regarding their connectivity. During Year I, we will develop four microcosm models that use rock faces or chips. During Year II, we will evaluate the models using fresh fracture material from Site 32 along with the groundwater microcosm used by Yaeger et al. (1997). This will allow us to recommend laboratory methods that will generate useable estimates of in situ biodegradation rates and microcosms that can be easily replicated to study the effects of in situ conditions (e.g., secondary mineralization of the rock) on biodegradation rates.

Fracture skins, the thin weathered layer on the surface of the bedrock in contact with the groundwater, can play an important role in solute transport and reactions (e.g., Robinson et al., 1998). For example, fracture skins can affect contaminant movement. Because the chemistry (mineralogy) of the rock can be important in understanding microbial reactions (e.g., Chapelle, 1993; Erlich, 1988), it is important to examine the rock composition, especially along the fractures. During Year I, we will begin petrographic analysis of the rock to determine what the mineralogy is in uncontaminated and differently-contaminated (e.g., TCE, DCE and VC) fractures. This examination will continue in Year II using XPS and SIMS. The data will help determine whether core samples can be used to infer the history of contamination and chemical/biochemical reactions at a specific location within the plume and how the presence of the contaminant(s) affects the secondary mineralization of the rock and the fate of potential electron donors or acceptors.

For subsequent years of the BBC's research, it is imperative that a series of hydraulically-connected wells be available within different biogeochemical regions of the plume (TCE, DCE, VC and uncontaminated zones). This will enable us to test new approaches to site characterization and bioremediation. As a result of the Year I drilling and geophysical and packer testing, we will have established such a network of wells for future in situ experiments at Site 32. The discrete fractures within these boreholes will be isolated to prevent cross-contamination between water masses from discrete fractures.

 

 
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