This study reports on a new geoscientific method to estimate the post-burial interval (PBI) and potential post-mortem interval (PMI) date of homicide victims in clandestine graves by measuring decomposition fluid conductivities. Soil water analysis from a simulated clandestine grave (which contained a domestic pig carcass) in a semi-rural environment had significantly elevated conductivity measurements when compared to background values. A temporal rapid increase of the conductivity of burial fluids was observed until one year post burial, after this values slowly increased until two years (end of the study period). Conversion of x-axis from post-burial days to 'accumulated degree days' (ADD) resulted in an improved fit for multiple linear regression analyses. ADD correction allowed comparison with two other conductivity grave studies and demonstrated it was possible to date a discovered grave and hence the victim if past local temperatures could be obtained and burial depth measured. Contemporary soil moisture sampling was also undertaken to quantify this potential variable. Research also has implications to time illegal animal burials. Further research is required to extend the monitoring period, to use human cadavers and investigate other soil types and depositional environments. NOTICE: this is the author's version of a work that was accepted for publication in Forensic Science International. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Forensic Science International, v. 198, May 2010, doi:10.1016/j.forsciint.2010 Determining PMI of recently deceased individuals have been extensively researched using a variety of methods and revisions to said methods. However, dating PMI over a longer time period or importantly the Post-Burial Interval (PBI) emplacement within a burial site is more uncertain and lacking a simple technique.This manuscript is the first to document a new and simple technique to date PMI or estimate how long a body may have been buried for using the conductivity of the decomposition fluids. Our previous FSI paper ( Jervis et al. 2009) has suggested that these fluids are the primary reason why electrical resistivity surveys work to detect the positions of clandestine burials of homicide victims. Our new suggested PBI/PMI technique, based on a two year monitoring study, is to simply measure the conductivity of decomposing fluids as we have found this has a two-step, linear relationship. Results are reinforced by comparison to another study as well as to a simulated "discovered" burial, where a ~16% error was found between the conductivity estimated date compared to the true burial date. We have also converted post-burial days into accumulated degree days (ADD) which improved the date mis-match error (to ~12%) and will...