MiProbe Environmental Sensing Technology for the Continuous Real-Time Management of Redox, Microbial Degradation Rates, and Metabolic Gases
CEC has collaborated with Burge Environmental of Tempe, Arizona, in the development and deployment of a sensor system called MiProbe that was supported by a series of grants from the U.S. Department of Energy.
The sensor is part of a full package of environmental sensors and data management tools that incorporates telemetry, the Cloud, and computer-generated graphics to bring the dynamics of contaminated site management to life. The system is unique in many ways, but one feature that makes it truly special is its use of biofilm as the sensor itself. The sensor also has a metabolic gas capture capability that gives it a second level of application in line with the current interest in Natural Source Zone Depletion (NSZD). Taken separately, the system’s features include:
Microbial Sensing Capabilities
The microbes and the associated electrode-support structure comprise a revolutionary redox sensor that is both instantaneous in reporting to the Cloud and robust to the point where, for all practical purposes, it has an operational life of several years.
A brief explanation of how it works: a biofilm/electrode combination with associated circuitry generates a steady-state voltage that is held by the electrode, noting that every redox state has an associated voltage. For example, the voltage is highest in an anaerobic environment, but it drops upon the encroachment of aerobic conditions because electrons are drawn away; this change is then recorded and transmitted. The system can work in reverse with voltages rising as anaerobic conditions develop. The sensor data may allow for better management and cost control associated with use of reagent applications (e.g. for providing oxidizing or reducing conditions in the subsurface).
It is also possible to understand the metabolic turnover rate in the environment. Based on the voltage output for the sensor (turning it on and off via remote control and allowing the voltage to drain and recover), a rate of substrate consumption can be calculated. This then factors into natural attenuation petitions or the progress of remedial intervention with oxidative or reductive processes as noted.
Metabolic Gas Capture Capabilities
The application targets a growing interest in documenting NSZD as a means of more enlightened management of complex sites with non-aqueous phase liquids (NAPLs). At present, the focus is on Light NAPLs (LNAPLs) like petroleum hydrocarbons. Depending on the subsurface conditions, LNAPLs will naturally attenuate through aerobic and anaerobic pathways while generating carbon dioxide and methane as metabolic gas end products. Capturing representative samples of these metabolic gases can be useful in calculating the Time of Remediation (TOR) of palpable contaminant masses in the subsurface. Of course, overlaying intervention activities such as oxidants or temperature inputs on this process can accelerate the TOR, and this will be recorded.
Other Applications and Features
Because MiProbe is sensitive to microbial activity, it can detect an uptick in electron flow as a function of a change in substrate availability. This would manifest when, for example, a dissolved-phase hydrocarbon plume impacts the sensor, which has major applications in managing UST sites or accidental releases. Conversely, a lack of electron flow could indicate a lack of bioavailability of contaminants.
The bioavailability application is important in sediments work in support of Monitored Natural Recovery (MNR) strategies. In effect, if a contaminant is unavailable, a case can be made for limited environmental impacts. Additional sediment and landfill management applications include the use of the redox sensor components to allow for characterization and modeling of the water exchanges between capped sediments or landfills and surrounding sources of water. Applications for ecological monitoring are also of interest and are ripe for further exploration by interested parties.
All of these analytical results have been obtained with extremely high reproducibility. The MiProbe system can be deployed several ways, including direct insertion into the subsurface or into monitoring wells, or as part of a floating deployment configuration. Also, the system is solar powered with real-time data transmitted using either cellular or satellite communications. In locations where communications are difficult, a data logging option is available.
This information on the MiProbe System is also available as a downloadable brochure on the Environmental Site Investigation and Remediation page of CEC’s website: http://www.cecinc.com/enviro_site_redevelopment.html.
New regulations are coming for underground storage tank (UST) owners and operators in Ohio. The Bureau of Underground Storage Tank Regulations (BUSTR), a division of the State of Ohio’s Fire Marshal’s office, has issued a second draft of its revised rules in the Ohio Administrative Code (OAC) at 1301:7-9-01 et. seq. The draft rules are currently being prepared for filing with the Joint Committee on Agency Rule Review (JCARR) in March/April 2017 with an anticipated effective date of July 2017, according to BUSTR.
The proposed rule revisions are intended to align with new federal UST regulations issued by the U.S. Environmental Protection Agency, which became effective October 2015, and also to comply with the bureau’s own five-year rule review requirement. The proposed amendments and rule changes include the following:
Compliance with New Federal Rules
- Certain types of UST systems that were previously exempt or deferred from state and federal regulations are now required to comply with certain BUSTR rules. These include airport hydrant fuel distribution systems, UST systems with field constructed tanks, and UST systems that solely store fuel for emergency generators.
- Six new terms were added; five to align with federal changes and one (“sole source aquifer”) to accommodate the rescission of OAC 1301:7-9-09 (“Rule 9,” see below). Eleven existing terms were amended, either for clarification or to align with federal changes.
- Rules were amended to implement new federal requirements for: 1) periodic checks of UST system and release detection components, 2) compatibility of release detection components and UST systems with tank contents, 3) methods of UST release detection, 4) retrofitting of older single-wall UST systems, 5) qualifications of persons performing work on UST systems, 6) records retention for UST system components and release detection records, and 7) requirements for release detection on airport hydrant and field-constructed systems. Numerous standards were updated relating to the construction and operation of UST systems to match corresponding federal standards.
- Rule 9, regarding USTs located above sensitive areas, was rescinded because these areas generally correspond to federally designated sole source aquifers, and more accurate geographical information now exists for owners and operators to use in determining whether an UST site is located above a sole source aquifer.
- The definition of “free product” and “suspected release” were revised in OAC 1301:7-9-13 (“Rule 13”) to match the federal version, and references were changed from “sensitive area” to “sole source aquifer” to accommodate rescission of Rule 9.
Permitting, Registration, and Closure
- The annual registration application deadline is being changed from July 1 to June 30. Registration requirements were added for compartments of a manifolded UST and for previously (but no longer) exempt UST systems. BUSTR also added a requirement to modify a registration within 30 days when there is a change of product.
- Clarified that partially exempt UST systems do not require a permit, a certified UST installer, or a certified UST inspector for tank-related activities.
- Clarified changes to the installer license renewal process.
- Clarified timeframes in OAC 1301:7-9-12 (“Rule 12”) for initiating closure assessments, added closure sampling requirements for piping runs, and revised the closure action levels table to reflect current science.
- Added Class A operators to the Class B retraining requirements, but makes retraining discretionary on the part of the State Fire Marshal instead of mandatory.
- Extended the validity of inspector certifications from two to three years, and simplified and streamlined the license renewal process.
Corrective Action, Chemicals of Concern (COCs), and Petroleum Contaminated Soils (PCS)
- The applicability section of Rule 13 was revised to allow ongoing corrective actions to continue under a previous rule version.
- Added “Biodiesel blended fuels” to the list of middle distillation products; added three new chemicals of concern (1,2,4-trimethylbenzene, 1,2-dibromoethane, and 1,2-dichloroethane); and revised action levels throughout Rule 13 to reflect current science.
- Updated public notice requirements for certain advanced corrective actions; owner/operators are now required to submit proof of notification within 90 days.
- Revised the list of re-use chemicals of concern and the action levels for petroleum contaminated soils (PCS) to incorporate most recent science, and clarified that if PCS above action levels are returned to the excavation, the cavity must be lined.
If you would like to learn more about how the new regulations may impact your operations or would like further information regarding the new BUSTR rules, contact Ron Wells (firstname.lastname@example.org), Tom Maher (email@example.com), or Andy McCorkle (firstname.lastname@example.org), or call (800) 365-2324.