FORENSIC APPROACHES FOR DISTINGUISHING BETWEEN NATURALLY OCCURRING AND ANTHROPOGENIC SOURCES OF PERCHLORATE

This poster introduces forensic techniques for distinguishing sources of perchlorate (ClO4-) in soil and groundwater. In many instances, the origin of perchlorate and whether it is anthropogenic or naturally occurring is a key question driving investigative programs, remedial approaches, determination of clean-up levels, toxicological considerations, and cost allocations. Forensic techniques presented, along with their advantages and limitations, include isotopic analysis (37Cl/35Cl, 87Sr/86Sr), surrogate analysis (nitrates, sodium, chlorides, phosphate, nitroglycerins, metals), historical information assessment (aerial photography, propellant use and chemistry, firing range usage), geologic analysis (limestone, caliche, playa crusts, hanksite (Na22K(SO4)9 (CO3)2Cl), potash, phosphate ore, etc), and x-ray diffraction and scanning electron microscopy (SEM).

A case study is presented illustrating how various forensic techniques are employed in an actual investigation to distinguish between perchlorate potentially associated with ammunition igniters and naturally occurring sources. A forensic methodology employed to better understand perchlorate origin included modification of existing agricultural soil sampling techniques United States Department of Agriculture (USDA) Methods 60-6(26) and USDA Method 60-6(27a) along with EPA Method 314.0, x-ray diffraction (XRD), polarized light microscopy (PLM), scanning electron microscopy (SEM), surrogate analysis, geologic evaluation, and aerial photography. In order to identify naturally occurring perchlorate sources, samples from throughout Mission Valley Formation outcrops were collected and a saturated extract was then obtained. Results of this analysis indicated perchlorate originated from an evaporative horizon(s) contained within the Mission Valley Formation.

The presence of perchlorate and arid depositional history of the Mission Valley Formation is also consistent with perchlorate reported in caliche layers found in western United States locations and Chilean fertilizer.