The Benefits of Pilot Studies for Remedial Injections
Published On: July 14, 2023
When completing remediation projects for contaminated sites, there are many factors that come into play. The type of contaminants and the corresponding concentrations, site characteristics, implementation feasibility, timeframe, overall goal of remediation, and cost all contribute to design of a remedy. Site-specific characteristics that are also taken into consideration include lithology, groundwater elevation, facility status (active, abandoned, etc.), accessibility, and health and safety.
One way to better design effective and efficient remediation processes is to perform pilot studies. Pilot studies can be conducted for different technologies such as remedial injections, soil vapor extraction (SVE), or thermal remediation. For technologies such as these, pilot studies can be utilized to gather data including radius of influence (ROI), effectiveness, implementability, and overall implementation process, which in turn help with designing full-scale remedies.
One example is pilot studies for SVE systems, which involve installing only a few ports to evaluate ROI. Samples are collected over time to determine flow and general effectiveness of the systems. Thermal remediation can also be pilot tested using a similar process of installing a few probes and collecting samples over time.
One very common treatment method that utilizes pilot studies is remedial injections. The variability of injection reagents, methods, and other site-specific factors can make it difficult to design accurate, efficient remedial injections. Common technologies implemented via injections are in-situ chemical reduction (ISCR) and in-situ chemical oxidation (ISCO). When designing pilot studies for ISCR/ISCO, general information regarding reagent dosing and site lithology is used and assumptions are made for the ROI as a starting point. Detailed notes and observations should be recorded throughout the pilot test with respect to flow rates, process, pressures, and how well the subsurface accepts the reagent.
Once the injections are complete, there are different methods for determining the effectiveness. Confirmation soil borings can be advanced directly following pilot test injections to determine the ROI. Depending on the injection reagent, collecting soil borings and looking for visual confirmation of the reagent may be sufficient to determine ROI. Grab groundwater samples may also be collected from the borings and analyzed in the field for parameters such as dissolved oxygen (DO), oxidation reduction potential (ORP), and pH. There should be pre-injection data to compare these parameters to in order to understand the potential impacts of the injection reagent. Once the ROI is determined for the specific site, then the full-scale injections can be spaced appropriately for maximum coverage of the desired area(s).
Effectiveness can be determined by collecting soil and/or groundwater samples for laboratory analysis. This may include samples collected from existing monitoring wells or newly advanced soil borings in the vicinity of the pilot test. Although some technologies may take months to make complete remediation progress, initial data often show trends that are sufficient to draw a conclusion on whether or not the pilot dosing was effective. This dosing can then be adjusted as necessary during the full-scale design.
Another factor that may be evaluated during pilot studies is the implementability of the technologies. For example, in the case of remedial injections, observations would be made regarding how well the subsurface accepted the injection material. This is observed via pressures, flow rates, and potential surfacing of the reagent. Implementability would also include accessibility of the treatment area. Questions such as “can equipment be easily staged near the treatment area?” and “is this an active facility?” should be considered when determining implementability.
Pilot studies also allow for a trial run of the overall implementation process. If a need arises for different or new equipment, this can be reconciled between the pilot study and full-scale implementation, eliminating potential setbacks in the timeline. Modifications or additions of items such as hoses, pumps, or injection tooling can be identified as well.
Pilot studies are a good time to ensure any necessary energy source and/or water source will be sufficient to support the full-scale remedy. Any step-by-step instructions that were prepared for the pilot study can also be revised with more detail or for added clarity to help make the full-scale implementation run more smoothly.
Although pilot studies could be considered an additional expense for treatment of contaminated sites, they provide valuable information that can actually save time and money when performing full-scale remedies. Understanding site-specific details is critical when designing treatment options. Although assumptions can be made, hard data collected during pilot studies can help ensure full-scale plans are efficient and effective, on-time and within the budget.