Using Low Ethene Concentrations to Discern Chlorinated Ethene Natural Attenuation Patrick W. McLoughlin, Robert J. Pirkle - Microseeps Inc. and John Catches - Jones Edmunds & Associates, Inc. Gainesville, FL A former municipal landfill in Georgia was contaminated with concentrations of tetrachloroethene (PCE), cis-1,2-dichloroethene (cDCE), 1,1-dichloroethene (11DCE) and some other trace solvents. The chlorinated ethene concentrations were low, but exceeded the Georgia Environmental Protection Division’s maximum contamination level (MCL). The contamination exists in a surficial aquifer. Specifically, this site is underlain by at least 50 feet of very fine to coarse-grained clayey sands, sandy clays and clay. The site hydraulic conductivity is 10-5ft/min, leading to an estimated ground water seepage velocity of 14 ft/yr. Public supply wells extend far below the contaminated aquifer and only four private potable water wells are within a 0.5-mile radius of the site, all of which are located either up?]gradient or side-gradient of the site and are not threatened by the contaminant plume. Because of this monitoring only was conducted for several years. There appeared to be a decline in concentrations, but noise made the data such that there was no obvious trend. Throughout four semiannual samplings, a full suite of geochemical parameters was measured to see if a case could be made for monitored natural attenuation (MNA). That sampling revealed low (<0.1 ug/l) ethene concentrations. Despite the magnitude of those concentrations, they were clearly above background and indicated active complete reductive dechlorination. The ethene observation meant that, despite several misleading preliminary indications that MNA was not significant, a thorough assessment of the contribution of MNA was warranted. A procedure for such an assessment was conceived of and executed. cDCE was the most substantial problem. A Mann-Kendall analysis showed the cDCE concentrations to be declining. Hits of ferrous iron and nitrite indicated that there were reducing conditions at the site but dissolved oxygen (DO) ranged between 1-9 mg/l, suggesting that the site was only mildly anaerobic. DO was seen to be directly correlated with DCE concentrations. This correlation was seen as an inhibition of the reductive dechlorination and the fact that DO temporarily reversed the declining trends meant that those trends were dominantly the result of biodegradation. Point decay rates were then calculated for two wells, one currently containing cDCE below the MCL and another containing cDCE above the MCL. The first validated the model, and the second predicted the cDCE concentration to be below the MDL by 2007.
Implications From An Overview of Volatile Fatty Acid and Ethene Observations Patrick W. McLoughlin, Robert J. Pirkle (Microseeps, Inc. Pittsburgh, PA) Volatile fatty acids (VFA 's) have long been recognized for their ability to stimulate reducing conditions in ground water. However, the ability to measure a spectrum of ground water VFA concentrations in a sensitive and reliable manner has only recently become available. While biochemists recognize the many roles of VFA's, concentrations have been interpreted for little more than their potential to stimulate reducing conditions. Ethene is the product of complete reductive dechlorination. While many laboratories only provide minimum reporting levels of 1 ug/l or even higher, it is becoming recognized that for sites exhibiting only slow but significant dechlorination, the ethene concentrations may be below these levels. Using sensitive analyses for both VFA’s and ethene, data was recorded from 1055 samples. That dataset, comprised of results from samples from a wide variety of sites and remediation techniques, was analyzed for correlations that would help environmental professionals use volatile fatty acid concentration data to make informed decisions about site management. Three such correlations were found. An index of the VFA profile was chosen and with that three more correlations were found. These correlations are significant because they link VFA concentrations and the ratio’s of those concentrations to complete reductive dechlorination, demonstrating the utility of using sensitive analyses for both VFA’s and ethene.
Microseeps offers solid phase analyses to assess the quantity of iron that can participate in bioremediation Microseeps has refined and is performing a suite of analytical methods for clients who seek more definitive evaluations of their sites.Over the last decade, Microseeps has developed the means to determine that intrinsic biodegradation is an active process at sites by studying their aqueous geochemistry. There is growing evidence that these efforts may be helped by consideration of the minerals which participate in bioremediation as well as those which accumulate as a result of the in-situ redox processes associated with each plume, particularly the reduced iron and sulfur minerals. Bioavailable ferric iron (BAFeIII) analysis is used to assess the quantity of iron that can participate in bioremediation. Aqueous and Mineral Intrinsic Bioremediation Analyses (AMIBA) are used to assess the quantity of reduced iron and sulfide bioremediation products. These analyses can be used to evaluate site suitability for natural attenuation and for monitoring effectiveness and efficiency of ongoing natural attenuation. Microseeps offers these analyses in three different combinations: BAFeIII alone; the AMIBA suite; and AMIBA with BAFeIII.
AMIBA analyses are useful to:
Microseeps adds the Air Knife to its Field Service Capabilities The air knife is the best alternative to conventional hand clearing, such as the hand auger, post hole digger or spud bar and hammer. Any of these methods can result in damage to unknown utilities. The air knife will expose any utility lines without causing damage to the lines. Air knives are so safe that they are also used by arborists to expose delicate root systems for treatment. In addition, the air knife can be used to install shallow vapor points for vapor intrusion studies. Using the air knife for this purpose reduces the cost of the actual vapor point used, resulting in a greatly reduced project cost. Call or email Microseeps the next time you have a project that requires utility clearance, vapor implants, or any other reason that intrusion into the vadose zone is a requirement. Click here to learn more about Microseeps’ field services capabilities
Last month, Microseeps provided technical data on the value of lower Ethene detection limits in demonstrating the occurrence of natural degradation. The real question is how to get these detection levels for your analyses. Click here to learn about obtaining the lowest detection limits
Reporting limits for ethene are critical to identifying and demonstrating complete natural biodegradation of chlorinated ethenes. In fact, reporting limits for ethene that are 200 times lower can be crucial. Microseeps Reveals Progress at Battelle Pat McLoughlin, Director of Research at Microseeps displayed the results of a year's research at the Battelle In-situ and On-site Bioremediation Symposium on June 5th-9th, 2005. Click here for more information about the 2005 Battelle Conference
Microseeps received secondary NELAC accreditation from the state of Louisiana on June 14, 2004. This certification includes an extensive list of volatiles by SW846-8260, 8021 and 8015, and metals by SW846-6010 in both soil and water matrices. Also certified are a variety of wet chemistry methods including Anions by Ion Chromatography and Total Organic Carbon. Additionally, Microseeps is certified to run an in-house equilibrium headspace method for certain fuel oxygenates. This certification is based upon reciprocity from the state of Florida, which is Microseeps primary NELAC accrediting authority. Microseeps also holds secondary NELAC accreditation in the states of New York and New Jersey. Other states where Microseeps holds certifications include West Virginia, Connecticut, South Carolina, Kentucky, and Pennsylvania. Contact our Customer Service Office for specific parameter lists for your state of interest. Microseeps plans on expanding its list of approved analytes for NELAC accreditation when Pennsylvania broadens its NELAC accrediting authority status. Those methods will include BNAs, PCBs, Pesticides, and an extensive list of wet chemistry parameters. Microseeps is currently awaiting an audit from the state of Louisiana in order to certify a variety of performance-based analyses including our Biodegradation Indicator Gases, Low Level Volatile Fatty Acids, Fuel Oxygenates, and Volatile Organic Compounds in Soil Gas methods. Microseeps hopes this will set a precedence for other states to begin recognizing the value of these performance-based analytical methods for any site where monitored natural attenuation is a viable alternative to more traditional site clean-up techniques.
Microseeps Receives Research Grant Microseeps
scientists Dr. Bob Pirkle and Dr. Pat McLoughlin worked with Dr.
Microseeps launches new website: Be sure to watch for changes over the coming months as Microseeps.com becomes more interactive and continues to grow. Click to watch a video message from Microseeps' founder and president Bob Pirkle.
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