Final data report for factors controlling DDE dechlorination rates on the Palos Verdes Shelf: A field and laboratory investigation

This data report provides a compilation of information developed over the last 6+ years by a
multi-disciplinary, multi-institutional research team. The overall goal of this work has been to
identify the biological, chemical, and physical factors that control rates of reductive
dechlorination of DDE and DDMU in sediments of the Palos Verdes Shelf (PVS). More specific
questions and objectives are delineated in the Scope of Work (section 12.1., Appendix 1).
The study was composed of two parts: 1) field characterization studies, and 2) laboratory
microcosm experiments. The goal of the field characterization studies was to define the
conditions under which reductive dechlorination of DDE (and DDMU) is occurring in PVS
sediments. This involved two separate cruises (2009, 2010) during which sediment cores,
bottom water and other real-time field measurements (e.g., conductivity, temperature, depth of
the water column) were acquired. The sediment cores were distributed among research team
members for detailed chemical (R. Eganhouse, B. Orem, M. Reinhard), microbiological (A.
Spormann), and physical (B. Edwards) analysis as well as for laboratory microcosm experiments
(M. Reinhard). A team of collaborating USGS scientists generously contributed valuable
information pertaining to geochronology (P. Swarzenski), the character of sedimentary
geosorbent phases (P. Hackley), mineralogy (D. Webster), and grain-size characteristics (C.
Sherwood) of PVS sediment samples.
Together, this information will serve as framework for a conceptual model of natural degradation
processes in the DDT-contaminated sediments on the PVS. These findings will enable the
USEPA to gain a better understanding of the controls on reductive dechlorination and how
dechlorination rates vary spatially and temporally. This, in turn, should facilitate decision
making concerning the progress of natural attenuation and when monitoring at the site can be
terminated. Toward that end, a brief Synthesis Report, summarizing and interpreting the
acquired data, is being prepared and will be released in the coming year.