Targeted Adaptive Remediation Services

Targeted Adaptive Remediation Services (TARS) is an approach to site remediation developed by GeoCore and Greenfield Contractors that makes the most of your most powerful remediation tool - your well-constructed Conceptual Site Model (CSM) - to aggressively target source mass and transport zones. Our TARS approach has the following characteristics:

Designed for low power demands, targeting mass and transport zones identified during High-Resolution Site Characterization (HRSC). This makes it suitable for use with the intermittent, low-wattage energy available from solar panels (although shore power can be used where available).

Takes advantage of the inherent mobility of a solar powered system. Our approach "Cuts the cord", eliminating both the need for electrical service and subsurface trenching. Systems can be easily moved around and between sites as needed to optimize performance and minimize costs.

Collects key operating and performance data, which are uploaded continuously for real-time evaluation of progress. Data collection capabilities minimize labor costs associated with implementation.

Maximize treatment effectiveness. Using low pressure injection, the TARS approach essentially trades time (remote operation at low labor costs) for the higher injection rates that create potential distribution problems that lead to rebounds in contaminant concentrations. While we can operate the system at modest injection pressures, our overall goal is to create conditions where the amendment follows the same transport zones as the contaminants, accelerated by the push-pull of recirculation instead of elevated injection pressures.

The TARS approach has been designed around injection-based remedies where recirculation can be effectively implemented. However, some of the key benefits of the TARS approach can also be used for pilot testing other in-situ remediation techniques. GeoCore has successfully tested the TARS approach for SVE, biosparging, and bioventing. In each of these cases, the TARS approach has the potential to be part of a full-scale remedy under the appropriate conditions. Additional remedial techniques are continually being evaluated.

Lessons we have learned that make the most of the TARS approach:

Take maximum advantage of HRSC tools to identify both residual mass and transport zones prior to implementing TARS. Then take advantage of the robust data collection of the TARS systems to both build on the existing CSM and optimize treatment effectiveness.

TARS is an inherently empirical, iterative tool ideally suited to an adaptive site management approach, optimizing performance, reducing costs, and maximizing flexibility. This is true of both individual treatment events (where robust data collection allows for real time decisions on dosing, pumping rates, and duration) and full-scale implementation (spacing of injection locations and frequency of events).

Rapid implementation. Targeting source area reduction, containing an expanding plume, or collecting pilot test data for full scale implementation all contribute to reducing life-cycle outcomes. The approach is also ideally suited for an aggressive interim remedy approach at sites where the regulatory conditions allow.

Amendment Delivery using Recirculation

GeoCore's most mature TARS approach was constructed to conduct amendment delivery using solar powered pumps to treat and recirculate groundwater, eliminating the need for most site infrastructure. Robust data collection was designed into the system to monitor progress and allow for remote operation. Initially designed for use at a low to moderate permeability site to economically address a large, diffuse plume, the system has since been used at a variety of sites. For example:

At the least permeable site, only 500 gallons was circulated over a 3-week ERD pilot test. While modest distribution and subsequent treatment was observed, the 10-6 to 10-5 cm/sec permeabilities at this location were likely to low for recirulation as conducted with the TARS system to be effective.

A second site achieved recirculation of 5,000 gallons over a 3-week ERD pilot test. Dye distribution observed during the testing and the subsequent treatment response over the target area confirmed amendment distribution and treatment success. The results indicated that

At a final site, a 3-week pilot test was conducted to evaluate neutralization of a caustic release and conduct a dye tracer test to evaluate both distribution and aquifer characteristics such as mobile porosity and back diffusion rates. In the much more permeable sediments (10-3 cm/sec), shore power was used to operate the system 24/7 for just short of three weeks at a daily recirculation rate of approximately 7,000 gallons per day (approximately 1/2 of the maximum capacity of the unit).

Operation at these varied sites indicate the system can be effective at distributing amendment over a wide range of conditions.

The ability to incorporate dye tracers into pilot testing or full scale implementation at reasonable costs provides enormous benefits and is one of the key data collection components of the TARS recirculation system. Configured to continuously monitor dye response in monitoring wells and/or extraction well effluent, the data can provide real time and concrete data on the rate and extent of amendment distribution. In addition, the dye response can generate insights into aquifer characteristics such as mobile porosity, transport rates (natural and under recirculating conditions), and where the test is carefully designed and evaluated, may even provide indications of back diffusion rates.

Since we often deal with complex site hydrogeology, no matter how robust the automatic data collection, field observations are always useful and we make final decisions based on "converging lines of evidence" as indicated by the testing. While dye probes are incorporated to indicate the rate and magnitude of dye response in observation wells, visual evidence is also useful. Note distribution of dye in the bailer indicating transport rates vary with depth - something we would miss with probe data only.

The TARS recirculation system is configured based on groundwater production rates. Where rates are low, below 1 to 2 gpm, the system is configured to fill a batch tank following GAC treatment. To ensure accuracy, dosing (amendment and dye) is conducted by pumping at a constant rate using a transfer pump. The amended groundwater is transferred to the mix tank where it gravity drains (or pumped under low pressures) to the injeciton well(s), At higher flow rates, the batch tank and transfer pump are bypassed.

Changes in flow rates over time (in both extraction and injection wells) are key data points indicating both aquifer characteristics, and especially in the case of ERD injection wells, loss of production over time. Continuing the multiple lines of evidence theme, at low K sites where extraction and injection flow rates are low, changing levels in the surge tank and/or mix tank allow for accurate estimates of flow rates (and changes over time), even in very low permeability sites where low and/or intermittent flows fall below outside of the flowmeters range of operation.

Combined with flow rates, levels in amendment and/or dye tanks provide accurate measures of dosing rates over time and provide immediate indications if mechanical problems arise.

Sensor data is presented in tables and charts in real time, allowing for immediate indications of performance, equipment malfunctions, or a change in site conditions. While in depth evaluation of the

Safety first - The system was designed to minimize risks, from electrical shock, chemical handling, and tripping hazards, while also considering equipment security and emergency response (note shower on outside of trailer installed due to acid handling requirements for this project).

The TARS system is designed to remove VOCs from extracted groundwater prior to reinjection. We incorporate GAC vessels suitable for the site. Note below on the right, pressure rated, 400-lb GAC vessels were used when operating continuously, and on the left, more economical, 200-lb GAC vessels were utilized where lower flow rates resulted in lower VOC loading. The system incorporates pressure sensors to monitor GAC condition.

SVE Trailer - Solar

While the TARS approach for amendment distribution was developed to economically treat large diffuse plumes, the same general approach can be used for more targeted uses with techniques such as SVE.

GeoCore and Greenfield Contractors have built and tested a solar powered SVE system that has many of the same characteristics as the recirculation system, including optimization for low power, mobility, and robust data collection to allow system/test optimization. Designed to be easily implemented for targeted treatment in a cost effective manner.