Feasibility of greenhouse gas emissions offsets for natural source zone depletion of petroleum hydrocarbons

Abstract

Hydrocarbon biodegradation is an important process for remediating petroleum hydrocarbons and managing large sites. However, this biodegradation results in what are essentially unavoidable CO 2 emissions to the atmosphere. A feasibility assessment was conducted to quantitatively consider reuse options for petroleum brownfields that would offset contaminant respiration emissions rates in the 2 to 10 micromoles CO 2 per meters squared per second ( mol CO 2 m −2 s −1 ) typically observed. Under a wide range of solar resource scenarios, placement of solar panels over only a fraction (no more than 35%) of the site footprint is estimated as necessary to achieve an emissions offset. Similarly, placement of one 30-meter tall wind turbine of moderate rating (approximately 30 to 50 kW) is sufficient to provide an offset for a nominal 1,000 square meters site. For spreading of spent calcium-rich construction materials, under even a high emissions scenario, the required footprint for the offset is less than the site footprint. While these approaches appear feasible, revegetation as forestland is estimated as sufficient only at contaminant respiration rates up to 2 mol CO 2 m −2 s −1 . Revegetation as rangeland and cropland, which sequesters CO 2 mainly in soil organic carbon, is estimated as requiring more than the site footprint under many contaminant respiration rates. Revegetation as a wetland fares slightly better from a carbon storage perspective, but it also has the potential for N 2 O and CH 4 emissions that may largely undo the benefit from sequestration in soil organic matter. Overall, the results indicate several methods that are viable for achieving emissions offsets and a quantitation method that can be honed with site-specific input parameters as appropriate.