Over 380 hectares of evaporation pits were used to manage produced water required remediation in response to environmental master planning at the Wafra oil field. To facilitate closure of these impoundments, a risk-based cleanup was selected wherein the former pit areas were backfilled using the reclaimed contents which were temporarily stored as stockpiles after stabilization and sampling. A risk assessment conducted for the site identified 3.2% total petroleum hydrocarbon (TPH) as a cutoff protective of human health, however, to adhere to the precautionary principal, material containing 1 to 3.2% TPH (type B) was consigned to deeper areas of the former pits, capped with 1 m of <1% TPH material (type A), and overlain by a minimum 30 cm of clean sand to facilitate revegetation. This paper describes a novel, multi-year approach to streamlining the remediation of >2 million m3 of impacted sand in a complex environmental setting, while meeting stringent international risk guidelines.

Initially, laboratory analytical data from a stockpile boring program were correlated with field test-kit and color analyzer measurements to develop a simple field TPH measurement tool. Then statistical analysis coupled with computation of pit volumes and three-dimensional modeling of the site was used to describe the spatial distribution of types A and B in the stockpiles and a redistribution strategy developed to meet remedial goals.

Quantification of spatial TPH distribution in the five stockpiles allowed optimization of hauling distances to the pit locations, while use of real-time global positioning system (GPS) survey data of the stockpile reduction in conjunction with geographic information system (GIS) applications allowed for accurate calculation of volumes excavated and placed as backfill, facilitating contractor invoicing. The use of sophisticated computer technology as part of the overall project design streamlined engineering design, while the GIS methodology also tracked real-time progress and provided final documentation for the project.

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