High-tech plumbing protects environment, cuts costs

Recent advances in groundwater sampling technologies can be compared to the development of indoor plumbing as an alternative to outhouses. Standard groundwater-sample collection methods require that large volumes of stagnant groundwater be pumped from a well before a representative sample can be obtained. For decades, this purge water was simply poured on the ground near the well. When states across the country began regulating purge water as a hazardous waste, costs for containment, treatment, and disposal became a significant expense. So DOE scientists and engineers have created a plumbing system to bring groundwater sampling technology into the 21st century.

The Purge Water Management System (PWMS, Tech ID 2920) is a closed-loop, noncontact system designed to eliminate the concerns and complications related to purge water generated by investigative and monitoring groundwater sampling. It is used in conjunction with existing wells and does not require any down-hole modifications. PWMS was developed by the Environmental Restoration Division at the Savannah River Site (SRS) and is in the Subsurface Contaminants Focus Area inventory of technologies.

The basic concept of PWMS is to temporarily store purge water that is generated during a sampling event in a bladder tank, then return it to the originating aquifer after the sample has been collected. Typically two to four well volumes of purge water, an average of 50 gallons, is isolated in the bladder during the process. Once water quality parameters stabilize in accordance with standard operating procedures, a protocol groundwater sample is obtained from the well sampling port.

This approach makes well sampling potentially safer and avoids the need to contain, treat, and dispose of this water. A careful evaluation must first be performed to determine whether the water returned into the well is likely to be resampled during the subsequent sampling event. Only those wells drawing from aquifers having a groundwater velocity sufficiently high to avoid resampling are selected for PWMS use.

Eric Schiefer, the lead project engineer, said PWMS could be applied at a number of sites around the country to help improve groundwater sampling methodology, data quality, and waste reduction. “We hope to deploy PWMS units elsewhere,” he said. “A license agreement has been signed, and the commercialization of this technology is under way.” Lawrence Livermore National Laboratory (LLNL) has already deployed two PWMS units and has plans to deploy an additional 15 units. Brookhaven National Laboratory and the U.S Army’s Ft. Gordon in Georgia are other possible deployment sites.

PWMS was invented by Joao Cardoso-Neto and Daniel Williams at SRS in 1995 and eventually received funding through OST’s Accelerated Site Technology Deployment initiative. First, a prototype was constructed from spare parts. Later, after several successful pilot studies to verify system operations and water characteristic stability, the South Carolina Department of Health and Environmental Control (SCDHEC) granted approval for SRS to deploy PWMS units to collect regulation-driven groundwater monitoring samples. Since then, PWMS has been installed on 35 wells, with plans to convert nearly 400 of the 2,060 SRS wells by FY05. These 400 wells represent the majority of monitoring wells at SRS that require containment of purged water. According to Schiefer, the potential savings from installing PWMS and other new sampling devices at SRS could be in the range of $320,000 to $640,000 annually after full deployment.

Schiefer is pleased with the data obtained from PWMS sampling. “We have a high degree of confidence that the results are accurate and can be used in making critical decisions,” Schiefer said. Our state regulator, SCDHEC, has “accepted the results, so we’re moving forward with the deployment of these units.” The SRS staff is currently in the process of having well selection criteria approved so that it is no longer necessary for state regulators to approve every PWMS well deployment.

Going Tankless

Schiefer said that enhancements to PWMS are also being demonstrated. In some cases, the wells themselves, instead of an aboveground tank, can be used to temporarily store the purge water. This approach is limited to those wells having enough available space to store the purged water. In such wells, a flow-through packer is inflated just above the screen, allowing the purge water to be isolated from the pump during the sample event. After the sample is collected, the packer is deflated allowing the water to drain back into the aquifer. These units have been called “tankless” PWMS units. Schiefer said tankless units could be used at many of the targeted PWMS wells at SRS, thus avoiding the need to dedicate a 119-gallon tank at each well. “We’re estimating that it will be about half [of the 400 target wells],” he said. “We’d like to use it as much as we can because of lower costs.”

SRS is also planning to conduct a pilot study using a no-purge sample collection system developed at LLNL called Easy Pump™. Easy Pump has limited applicability at SRS because state regulators want three well volumes purged before sampling. The pilot study will target “pump dry” wells, which are wells that cannot produce the three-well-volume purge necessary before a protocol sample is obtained. Follow-on studies may be designed to examine the applicability of this sample collection approach at ordinary wells.

The long-term savings from using PWMS and Easy Pump are expected to far outweigh the conversion expenses. Expenses for managing purge water include purchasing and maintaining tanker trucks, transportation, personnel training, storage, and treatment costs. More costs could be incurred if treatment facilities are not already in place. Schiefer said at SRS the annual purge water management cost per well is $800 to $1,600, based on two or four sampling events a year. A PWMS tank unit costs between $3,500 and $6,000 to manufacture; tankless units cost between $2,000 and $5,000. On-site testing and installation costs are minimal, averaging about $500. The potential treatment and disposal cost savings of PWMS and Easy Pump are estimated to be in excess of $15 million over the next 30 years. (TIE Quarterly, Summer 2000).

Demand for new well sampling technologies is inconsistent because regulations vary from state to state as to how purge water should be handled at low-level contaminated sites. Some states still permit low-level contaminant purge water to be discarded on the ground adjacent to the sampled well. “If technicians can discharge well purge water to the ground, there’s no need for a PWMS unit,” Schiefer said. He added that the state approval process for new groundwater sampling technologies also varies. “Some states just need to be notified,” Schiefer said. “The rules are a little more stringent here in South Carolina.”

The South Carolina regulators have been involved early in the development of the technology. SRS has obtained their buy-in at every stage, and SRS engineers are exploring additional applications for the system. According to Schiefer, PWMS use during well development activities has been proposed. The nonaqueous portion would be separated so that the aqueous portion could be returned to the well. The bladder tanks would be used as surge tanks in a phytoremediation system.

Technology has come a long way since the outdated, and often illegal, practice of dumping hazardous purge water on the ground. The innovative PWMS promises to make groundwater sampling and other related tasks easier, safer, and more economical.

For more information about PWMS, contact Eric Schiefer, (803) 952-6786, eric.schiefer@srs.gov, or Bob Hiergesell, (803) 725-5219, robert.hiergesell@srs.gov. The Easy Pump system is commercially available from Voss Technologies, Inc., San Antonio, Texas, (800) 247-6294, www.vosstech.com.