Conventional methods of well development at the Savannah River Site generate significant volumes of investigative derived waste (IDW) which must be treated and disposed of at a regulated Treatment, Storage, or Disposal (TSD) facility. Pulse Wave technology is a commercial method of well development utilizing bursts of high pressure gas to create strong pressure waves through the well screen zone, extending out into the formation surrounding the well. The patented process is intended to reduce well development time and the amount of IDW generated as well as to micro-fracture the formation to improve well capacity.

The Pulse Wave development process was demonstrated in three M-Area recovery wells and in three soil vapor extraction (SVE) wells at the C-Area Burning/Rubble Pit (CBRP) facility. The results at the groundwater wells in the M-Area were poor with significant reductions to flow rates from all of the wells. The flow rates have improved recently, indicating that the reductions may be temporary. Two of the SVE wells tested in the C-Area showed significant improvement after the process was demonstrated. Unfortunately, these improvements disappeared after a few weeks. A subsequent down hole camera inspection of the third SVE well revealed that part of the screen was missing. It is not known for sure whether this condition existed before the Pulse Wave tests. The shallow, 2" CBRP wells were pushed into place with a cone penetrometer truck and the PVC screen may have been damaged during installation.

Although the brief improvement in air flow rates at two of the SVE wells was significant, the short duration of the improvement and the possible damage incurred at well #10C are major problems with the Pulse Wave technology. The loss of production at the M-Area recovery wells is also a disturbing occurrence. It is unlikely that this technology will be used further at SRS unless the approach and/or installation are significantly modified.

The Savannah River Site (SRS) is a Department of Energy facility occupying approximately 310 square miles of land adjacent to the Savannah River in South Carolina. Across the broad expanse of this site there are numerous manufacturing facilities and waste sites. Past releases of chlorinated solvents to the environment have contributed to soil and groundwater contamination at many of these locations. Since the discovery of this contamination, the Savannah River Site has pursued an aggressive remediation program involving extensive subsurface characterization, groundwater monitoring, and the application of conventional as well as emerging remediation technologies. This report describes the application of a recently commercialized well development tool (Pulse Wave Technology) which was deployed in the M-Area and the C-Area of the Savannah River Site.

Figure 1: Savannah River Site Regional Map

The use of industrial solvents in the M-Area, a manufacturing complex located in the northwestern portion of the Savannah River Site, has resulted in vadose zone and saturated zone contamination, principally from Trichloroethylene (TCE) and Tetrachloroethylene (PCE). With the post Cold War reduction in the need for defense related nuclear materials, manufacturing activities in the M-Area have ceased and this area has been designated as the M-Area Hazardous Waste Management Facility. The geology of this area is typical of the Atlantic Coastal Plain, consisting of interbedded sands, silts, and clays. Clay rich confining intervals are interspersed with more transmissive, sandier intervals. The ground surface is approximately 365 feet msl with the water table at approximately 135 feet deep (230 feet msl). Previous contaminant characterization has provided significant insight into the nature and location of subsurface solvents. Data indicate a substantial amount of solvent is trapped in the clays and silts in the vadose zone above the water table. The data also suggest that solvents below the water table exist in thin (<1 m) as opposed to thick, solvent saturated layers. Both above and below the water table solvents are accumulating and migrating in highly discrete and vertical intervals. Vadose zone wells have been installed to remove source contamination through soil vapor extraction units. The plume of contaminated groundwater is being addressed with a series of recovery wells that pump the water to an air stripper. The recovery wells are typically screened across the full depth of the water table aquifer, either with continuous screens or with multiple screens.

Figure 2: Savannah River Site Map

The C-Area Burning/Rubble Pit (CBRP) was constructed in 1951 for use as a burning pit. It is located in the central part of SRS, west of the C-Area Reactor. It served as a repository for organic materials (i.e., waste oils, paper, plastics and rubber). Periodically the collected materials were burned to reduce the overall waste volume. In 1973 disposal of combustible wastes in the pit were discontinued and the pit was covered with a thin layer of soil. The pit received inert rubble thereafter until it was filled. It was then backfilled with soil to grade level. The pit sits above a 20 foot thick sandy aquifer bounded at the bottom by an interval of interbedded silts and clays. The water table surface is approximately 60 feet below grade. Groundwater samples indicate significant solvent contamination in the top of the aquifer, primarily from TCE, although PCE is present in lesser amounts. In 1998 an Interim Action Proposed Plan (IAPP) identified two interim remedial action objectives for the CBRP facility. The first involved the installation of a two layered soil cover system to prevent direct contact with contaminated soils, to reduce infiltration, and to minimize further contaminant migration. The second objective involves the operation of an air sparging (AS) system in conjunction with a soil vapor extraction (SVE) system. There are 39 Soil Vapor Extraction (SVE) wells installed at the CBRP facility, each with a design flowrate of 10-18 cfm. The soil vapor extraction system was placed in service in mid-October, 1999 and has had ongoing problems with fine silt passing into the SVE wells, restricting flow. The silt is periodically removed, however the air flow from the wells has only averaged 5 – 10 cfm. The inability of the wells to sustain design flow rates has limited the effectiveness of the remediation program.

Figure 3: CBRP Air Sparge/SVE System

Periodically, the production rates of wells decline to the point that the redevelopment of the wells is necessary. Although there may be a number of reasons for the reduced flow, the redevelopment techniques used are generally the same. The most common redevelopment technique at the Savannah River Site involves a combination of airlift surging and pump and swab methods. An airlift pump is used to remove the bulk of solid material from the well. The surging action caused by the turbulent, dual phase (air/water) flow helps loosen fine materials in the gravel pack and in the adjacent formation so that they can flow into the well casing and be removed. The pump and swab technique relies upon hydraulic pressure pulses created by a close fitting swab as it is moved up and down repeatedly through the well screen. The pressure pulses jostle the gravel pack and loosen additional fines which are then drawn into the well and pumped to the surface. These methods can generate substantial volumes of Investigative Derived Waste (IDW). The IDW consisting primarily of contaminated water must be collected and transported to a regulated Treatment, Storage or Disposal (TSD) facility.

Pulse Wave technology is a newly commercialized method of well development. Originally implemented in Russia, it has been used extensively in the oil and gas industry in the United States. Modified to allow operation at lower pressures, it is being tested in groundwater and vadose zone wells. The technology utilizes the release of high pressure nitrogen in the screen zone to create "pressure bursts" which micro-fracture the formation, removing obstructions to flow. It is easily implemented and results in less wastewater than conventional methods.

The underlying goal in using Pulse Wave treatment is to improve contaminant mass removal. This was to be accomplished in the water wells through the selective development of the screen intervals with the highest contaminant concentration. In the vadose zone wells the intent was simply to increase air flow (specific capacity).

Three M-Area recovery wells (RWM-1, RWM-6, and RWM-10) were selected for redevelopment, based primarily on proximity to monitoring well clusters which indicated a well defined vertical contaminant gradient.

Table 1 depicts the screen zones of each well with corresponding TCE and PCE concentrations. The recovery wells are 8" diameter wells. RWM-1 has a continuous 60 foot long wire wrapped screen (15 slot). RWM-6 and RWM-10 each have four 30 slot wire wrapped screens installed at 10 foot intervals. Well construction details are shown in Figures 4, 5 and 6 respectively in the Appendix.

The wells installed in the CBRP Area are vadose zone wells and are connected to soil vapor extraction (SVE) units. They were installed using Cone Penetrometer Technology (CPT) which saved both installation cost and Investigative Derived Waste (IDW) costs. This method of installation had not been previously used at SRS for production wells so few design, installation and redevelopment standards existed. The SVE wells are 2" PVC wells with one 10 ft. long slotted PVC screen.

The wells selected to undergo Pulse Wave technology at CBRP were well #’s SVE-10A, SVE-18C, and SVE-20C. Well construction details are shown in Figures 7, 8 and 9 respectively in the Appendix. Well # 10 straddles the water table. It serves as both a monitoring well and as an extraction well for recovering sparged VOCs as soon as they enter the vadose zone above the water table. The cause of clogging is thought to be a consequence of well design. There is no filter pack to screen fines and prevent them from entering and clogging the well.

Wells 18C and 20C are not in the water table. They were installed beneath the pit where liquids were disposed of for many years. Rainwater also collected in this area and there is evidence of perched water remaining even today.

Pulse Wave technology was originally developed and tested in Russia and has been further tested in the oil and gas industry in the United States. Pulse Wave technology utilizes the release of high pressure nitrogen to generate high amplitude, low frequency "pressure pulses" in wells. Pulse Wave technology has several novel features that make it potentially valuable for enhancing environmental cleanup and contributed to its selection for redevelopment efforts at SRS. Implementation of the technology is straightforward and cost competitive with most other well development methods and can be tailored to fit the specific conditions of each well. It uses nitrogen gas that is non-toxic, widely available, and inexpensive. The bulk of the well development (performance improvement) results from in-well generated pulse waves that generate no investigative derived waste (IDW). Electric lines or hydraulic control lines are not required, as the system is self-contained and self-regulating.

Various implementations and objectives for Pulse Wave development are possible, depending on whether the well is completed above or below the water table. The work performed in the M-Area focused on "pump and treat" water wells used in the remediation of solvents dissolved in groundwater plumes. The work at the C-Area Burning Rubble Pit focused on vadose zone wells used for soil vapor extraction.

Pulse Wave technology provides a method and apparatus for stimulating the production zones of wells. A rapid series of high pressure shock waves is generated by a downhole pulse wave generator which is actuated by the high pressure gas supply resulting in a series of gas pulses. The technique is designed to stimulate production by microfracturing the formation and by breaking up and removing obstructions to flow. In water wells the released gases also create a bubble which expands and collapses. The expansion and collapse of the bubble produces a surging action that displaces fine sediment, mineral scale, and biomass within the formation. Once the near wellbore zone has been microfractured and obstructions to flow have been circulated out of the well, the permeability of the producing formation in the region should increase significantly.

The mechanics of operation of the pulse generator are quite simple. As high pressure gas is supplied to the inlet of the device, a sealed chamber formed by an outer housing and a main piston valve begins to pressurize. As the increasing pressure in the chamber approaches 80% of the supply line pressure, a small trigger piston or pilot valve in the top end of the main piston valve becomes "un-balanced" and disengages itself from the main piston valve. The large surface area of the head of the main piston valve is now suddenly exposed to the high pressure in the formerly sealed piston chamber, causing the main piston valve to accelerate downward and "fire". This rapidly vents the chamber pressure to the wellbore. The explosive release of energy in the form of compressed gas creates a pulse wave. The pressure at which the pulse generator fires, is a function of the line pressure leading downward to the pulse wave generator. The rate of firing, typically one discharge every three seconds, is determined by the size of the orifice supplying the high pressure gas to the gas storage chamber of the pulse wave generator.

Any compressed gas may be used for Pulse Wave deployment. Nitrogen usually is the gas of choice because it does not support combustion, is relatively inert, is inexpensive, and is easily transported. Although nitrogen may be pumped at high pressures in its liquid state by means of "nitrogen pumper" trucks, standard nitrogen gas cylinders were utilized in the demonstration at SRS. Figure 10 depicts the method of nitrogen delivery utilized during the Pulse Wave demonstration in A/M Area and at the C-Area Burning Rubble Pit.

Figure 10: Pulse Wave Nitrogen Delivery System

The Pulse Wave technology utilized for the demonstration was provided by Pulse Wave Technology Incorporated. All activities were conducted in accordance with SRS procedures and South Carolina State regulations. Westinghouse Savannah River Corporation (WSRC) provided all permits and safety guidance as required. Drillers assisting in the demonstration were provided by the Environmental Monitoring and Testing Company (EMTC).

The method of nitrogen delivery was identical in all of the wells receiving Pulse Wave treatment. Figure 10 is a schematic diagram depicting the mode of delivery. WSRC provided the nitrogen cylinders. Cylinders were received with the following specifications: nitrogen @ 99.9993% purity, containing 305 standard cubic feet (nominal) @ 2640 PSIG (nominal). All hoses and fittings that were under pressure met or exceeded SAE J517 or CGA 580 standards. All hoses, fittings, and equipment were documented to have a rated operating pressure of 4,000 psi or greater and a rated burst pressure of 16,000 psi or greater.

The same procedure was used in pulsing the RWM wells. RWM # 1 has only one 60 foot screen. The Pulse Wave tool (generator) was lowered into the target zone. Pulsing was generated at a rate of one pulse every three seconds. The tool was slowly raised and lowered throughout the targeted screen zone in one foot intervals. RWM #1 was selectively pulsed from 176 to 186 feet (elev.). Five nitrogen cylinders were utilized in a 37 minute period. RWM # 6 was pulsed in the 157 to 167 foot range (elev.) using four nitrogen cylinders in 28 minutes. RWM-10 received Pulse Wave treatment in the 184 to 194 foot range (elev.) utilizing four bottles of nitrogen in 39 minutes.

At the CBRP facility, ten foot screens are installed at the bottom of the shallow wells. Each of the wells, SVE-10A, SVE-18C, and SVE-20C, was cleaned to remove accumulated fines prior to the demonstration to assure access of the Pulse Wave tool. Three nitrogen cylinders were used in the pulsing of each well.

Dixon, K. and Nichols, R., 2000, Summary of results from the zone of influence testing at the C-Area Burning/Rubble Pit (U), WSRC-TR-2000-00426, Westinghouse Savannah River Company, Savannah River Site, Aiken, SC.

Driscoll, Fletcher G., 1986, Groundwater and Wells, Second Edition, Johnson Filtration Systems, Inc., St. Paul, MN.

Morgenstern, M. 1997, Interim Action Proposed Plan for the C-Burning Rubble Pit (U), WSRC-RP-97-437, Rev. 1, Westinghouse Savannah River Company, Savannah River Site, Aiken, SC.

Morgenstern, M. 2000, Test plan for clogged wells and interim report, C-Area Burning/Rubble Pit Remediation System (U) WSRC-RP-99-4196, Westinghouse Savannah River Company, Savannah River Site, Aiken, SC..

U.S. Patent No. 5,836,393, Nov. 17, 1998, Pulse Generator for Oil Well and Method of Stimulating the Flow of Liquid.