BP projects in Azerbaijan in the past ten years have installed oil and gas export lines, interfield lines, water injection lines and produced water lines, with a total length in excess of 1000 km- all of which required hydrotesting. This paper describes BP's approach to managing and mitigating the environmental impacts of hydrotest water disposal.

The first stage was the selection of a hydrotest chemical package. Candidate chemicals were subjected (individually and in mixture at the appropriate dose levels) to toxicity tests developed specifically for the Caspian, and the least toxic package was selected. The most toxic component of the package was a biocide, which was selected in part for its low persistence and high abiotic degradation rate.

The next stage was to assess the dewatering options and to commission dispersion modelling for each option. For each scenario, an ecotoxicological risk assessment was carried out using the modelling results in combination with the toxicity data.

Risk assessment concluded that discharge to sea was acceptable offshore but not in the coastal zone. Accordingly, large onshore holding ponds were constructed receive hydrotest water which could not be discharged offshore, and to retain it until chemical analysis and toxicity tests showed that it was safe to discharge.

The holding ponds were used to receive hydrotest water in 2005 and 2007. In both cases, analysis showed that the biocide had degraded by > 90% in the pipeline, and that after one week in the holding ponds the residual chemical concentrations and toxicity had decreased to negligible levels.

The original toxicity tests had shown that phytoplankton were most sensitive to the biocide. During the 2007 de-watering process, samples taken from the holding pond showed that within one week, healthy phytoplankton populations had become naturally established, providing direct confirmation that discharge of the hydrotest water would present no risk of environmental harm.

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