Field Deployment of a Novel Approach for the Acquisition of Deep Groundwater Samples at Nevada Test Site

Groundwater sampling is routinely conducted at hundreds of wells at multiple DOE facilities to monitor changes in groundwater quality as a function of time. Some of these wells are very deep (greater than 600 m) which presents unique problems that must be overcome in order to obtain a representative, undisturbed sample. Current technology consists of the use of submersible pumps, bailed samples, and samples collected using a variety of manufactured systems. Each system or method has its advantages and will be limited to specific applications. The only types of pumps that can handle deeper wells are those specially designed for the oil industry. They are expensive and were originally designed for continuous operation with highlubricity liquids. Therefore, these pumps are prone to failure or require extremely frequent maintenance to reduce the risk of failure when functioning as samplers. The pumps have a high power requirement and, for wells not on the power grid, require the setting up of a large amount of support equipment and its associated labor for each sampling event. A sample of approximately 1 liter is typically required. However, the majority of wells on the DOE complex are stagnant or near-stagnant. It is necessary to purge these wells prior to sampling in order to remove stagnant water. Standard practice requires the purging of three well volumes (typically several thousand gallons). The value of the sampling system will be increased if it can improve on the purge rate of the Bennett pump, which is approximately 1 liter/min in deeper wells. Pneumatically-driven pumps specifically designed for sampling wells of intermediate depth (200’–1500’), are frequently used but have limited depth capability and become increasingly unreliable as they approach their maximum operating depth. The down-hole location of the pump means that the entire bundle must be retrieved in the event of failure. This is time-consuming and precludes its use for permanent installations. Repeated deployment and retrieval causes progressive damage to the tubing bundle. AEA Technology has developed a fully-automated pneumatic sampler that employs compressed air to force a polyurethane pig up and down a borehole to retrieve samples. The sampler employs two moving parts and has demonstrated purge rates between 3 to 4 liters per minute. The limited number of moving parts deployed down-hole, improve the system’s reliability and costeffectiveness. In addition, a single sampling trailer can service several wells with significantly reduced labor requirements, further improving the cost benefits. WM’05 Conference, February 27 – March 3, 2005, Tucson, AZ INTRODUCTION Deep well sampling of groundwater is routinely conducted at hundreds of wells at the following DOE facilities: Los Alamos National Laboratory, Sandia National Laboratory, Nevada Test Site, Idaho National Environmental Engineering Laboratory and Pantex Processing Facility to monitor potential hazards to the local environment. Sampling water from depths of several thousand feet presents unique problems that must be overcome in order to obtain a representative, undisturbed sample. Conventional mechanical pumps have been routinely deployed to collect the sample. Mechanical pumps deployed under such conditions are subject to extreme pressures (up to 200 atmospheres) and repeated failure due to their intermittent operation. During FY 02, AEA Technology developed and demonstrated a concept design of a deep well sampler at Sandia National Laboratory. The system was based on a simple tube design, compressed air and a pipe pig. The trials were conducted in conjunction with the Desert Research Institute and Sandia National Laboratory. The work evaluated the performance of the novel design of Deep Well Sampler developed by AEA Technology and compared the technology to the baseline system. The design of the system tested at Sandia had sufficient promise to further develop the system and deploy it in a deep well at the Nevada Test Site (NTS). Based on the success of the NTS deployment during 2003, the decision was made to further refine the engineering and to deploy a semi-permanent installation in Nye County, adjacent to NTS during 2004. PRINCIPLES OF AEA TECHNOLOGY SAMPLER AEA Technology has developed a novel technique for sampling deep boreholes that does away with the need for expensive, unreliable and labor-intensive equipment and operates at low pressures (less than 10 atmospheres) regardless of the depth to the aquifer. Compressed air is used to push a foam ‘pig’ along the sample tubing. This pig pushes a small volume of water in front of it, requiring much lower pressure than conventional systems where the entire sample line is full of water. The sampler is initially deployed into the well. This consists of a sampling head attached to a small diameter tubing bundle. At the base of the sampling head is a positive pressure relief valve. A commercially available foam pipe pig is driven by compressed air from the surface to the sampling head. Water is then allowed to flow into the tubing immediately above the foam pig. Compressed air is applied behind the foam pig driving the pig and the column of water back to the surface as shown in Figure 1. The water is collected in a sample container and the pig is driven back down to the base of the well. WM’05 Conference, February 27 – March 3, 2005, Tucson, AZ