Evaluation of organic compound source and natural attenuation, Liepaja Latvia

Abstract

Liepaja harbor is a former Soviet military site. Remediation of the harbor basin, including dredging of the sediments heavily contaminated with petroleum hydrocarbons and heavy metals is necessary to convert the harbor for civilian use. Abandoned pollution sources on land still continue to leach contaminants into the harbor basin. Our long-term research objective therefore is to identify transport pathways into the harbor sediments and to assess the in-situ degradation of pollutants in the system. The Liepaja harbor is treated as a complex system, where processes in the water column interact with the sediments and the nepheloid sediment boundary layer. For this research PAHs are used as the model organic contaminant. In this project the seasonal variation in biodegradation of PAHs is measured. This analysis is coupled with total bacterial production to establish the maximum degradation rate. With complex mixing of organic contaminants and need for understanding the ground water circulation it is difficult to determine the contaminant species. For this study a thorough assessment of PAH speciation has been used to determine the variation of sources. Variation in the PAH speciation is coupled with stable carbon isotope analysis to provide additional information on the range of sources in the harbor. Radio carbon isotope analysis of CO2 in the vadose zone from a site at the Naval Station Norfolk is introduced as an approach to survey natural attenuation in this region. The Liepaja harbor is the first contaminated harbor site to be remediated in Latvia. Knowledge gained within the project will help to develop the management of harbors and polluted sites in the country. At the same time, the Liepaja harbor can be regarded as a “typical” abandoned former Soviet army site. Experiences from the Liepaja harbor will be useful in future common efforts between the former Soviet Union and the US Navy.