The Sustainable Environmental and Economic Development (SEED) project was developed in Kuwait to undertake remediation and rehabilitation of abandoned upstream production areas within the Oil Fields of Kuwait. The aim of the rehabilitation component of the project was to leave previously contaminated areas of the oil fields, such as effluent pits, sludge pits and gatch pits, in a relative natural state in order that once remediated, they would not require ongoing management and would not pose a significant risk to sensitive environmental receptors. To this end, the rehabilitation component of the project included a native plant restoration and monitoring program with the purpose to evaluate the effectiveness of restoration methods, namely the use of irrigation and soil amendment, in facilitating the establishment of a native plant community. In addition, the remediated soil was returned to the various pits and if native plants could be established, that would provide an indication of the success of the soil remediation process. This study focuses on the remediation and rehabilitation undertaken in three pits (one sludge pit and two effluent pits). The contaminated soil was subjected to either bioremediation or thermal treatment, then reapplied to the pits. A reference area was planted in a location that represented a relatively undisturbed site in the oil field to establish an experimental control. If plant establishment was similar or better in rehabilitated features to the undisturbed reference areas, then rehabilitation could be considered on a similar trajectory as a natural ecosystem. Components of the rehabilitation program included eight native plant species, high-level and low-level irrigation and soil amendment (biogenic fertilizer). Plants were installed in the features using a block design whereby equal numbers of plants received the irrigation and soil amendment treatments, as applicable. The planting blocks were subdivided with half established with amended soil and half in unamended soil, these were then further divided into areas of high and low irrigation. In the reference area blocks, half of all plants received high-level irrigation and the other half received low-level irrigation. Plant survival and growth were measured over the monitoring period. Results of the monitoring showed that several factors can play a role in affecting establishment of native plant species. Overall, plant survival varied quite markedly depending on the site. It was hypothesized that plant survival would be best in the reference areas where soil disturbance was minimal. This hypothesis is consistent with the findings of this study. It was also hypothesized that high-level irrigation may result in better plant survival and growth by providing more available water at the root zones of plants. However, results showed that although irrigation events generally improved soil moisture levels, the difference in soil moisture between high and low irrigation rates was overall, not significant. This indicates that plants receiving high-level irrigation had similar moisture near their roots as plants receiving low-level irrigation. This could be the reason why in general, high irrigation resulted in only small improvements to plant survival and plant growth in some pits. In the sludge and effluent pits, the addition of an amendment to remediated soil was tested because of the potential to provide useful nutrients to plants and to improve soil texture and water holding capacity, thereby potentially improving plant survival and growth. There were significant differences in plant survival among the features; however, the addition of the soil amendment did not provide a clear or consistent improvement in plant survival, nor did it result in much greater plant growth (small improvements were realized). Rather, plant survival appeared to be more influenced by the size of plants at the time of installation. Because established criteria for planting the rehabilitated features was used, there was some control over certain variables that could affect plant establishment, such as species selection, site preparation, spacing of plants, and frequency and amount of irrigation. However, other variables not controlled could have also affected plant establishment and played a role in the results of this research. Differences in site conditions (i.e. location, aspect, wind, natural rainfall), soil texture and micronutrients, and the propagation and handling of plant material (in the plant nursery and during planting) could be confounding factors, together with irrigation rate and soil amendments. Several lessons learned were identified from this study and may be worth consideration in future restoration and rehabilitation of decommissioned facilities and/or disturbed landscapes across Kuwait oil fields. Adaptive management (i.e. the ability to direct change based on feedback from monitoring as one gains experience with local conditions) is very important, and it allows for the effective incorporation of lessons learned into the decision making process as the project evolves, and to positively affect the delivery of new projects as they are developed. The findings of this study lead to amendments to statutory remediation standard for future remediation projects within the oil fields of Kuwait.
