One of the most important design considerations is the dispersal of the substrate ian the subsurface.
Our approach to substrate dosing is based on site conditions. JRW Bioremediation L.L.C. provides substrates and nutrients for anaerobic bioremediation. The substrates provided include highly soluble materials such as WILCLEAR® sodium and potassium lactate, SoluLac® ethyl lactate, and Wilke Whey® whey powder and slowly soluble substrates including LactOil® soy micro-emulsion, and ChitoRem® chitin complex.
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One of the most important design considerations is the dispersal of the substrate in the subsurface. If you cannot obtain and maintain control of the system (aquifer), you cannot consistently manage the microbial processes responsible for reductive de-chlorination. This is directly related to the selection of a substrate delivery method. In most cases, there are three methods of delivering a substrate: injection through existing wells or injection galleries, injection through direct push equipment, and direct mixing with soil. The physical properties of the substrate can also directly affect the delivery method
One popular substrate delivery method is injection through permanent wells. Permanent wells have the advantage of being readily available for additional applications. The disadvantages of permanent wells is their capital cost, limited coverage, their susceptibility to damage, and their limited use with solid or very viscous substrates. Since most plumes require multiple injections, permanent wells have become popular. This limits the number of times that a drilling crew must be mobilized and provides some level of flexibility with regards to re-injection timing. Permanent wells are best suited to long-term systems such as re-circulation systems or barriers and are less suited to very large plumes where control of the aquifer is impractical.
Highly viscous substrates can significantly complicate injection through permanent wells and the injection of solid substrates may not be possible. Also, the capital costs of permanent wells may not be financially justifiable on sites that do not have groundwater recirculation or control systems and require only one or two injection events.
Direct push injection of substrates allows the practitioner to optimize injection point placement but the direct push process is limited to the depth capability of the available equipment. Generally speaking, light to moderate weight direct push equipment is limited to less than about 75’ below ground surface in most situations. Deeper injections have been accomplished but these are not the norm. The advantages of direct push injection are the short site time and cost. Generally, direct push points can be completed in an hour or so each, thereby increasing the amount of plume that can be covered in a given time period. Direct push injection can also be very valuable at sites requiring fracturing of the soils. With solid substrates like ChitoRem® this can be done by suspending the substrate in a slurry of guar and water. The resulting mixture can be injected with standard direct push tools or with specialized hydraulic fracturing equipment for deep applications.
Substrates can also be mixed with the soils at the bottom of an excavation or at the surface. This is usually done with solid substrates but can also be done with liquid substrates. The technique is limited in that it can only impact the soil and groundwater in the immediate vicinity of the substrate, and any water flowing through the substrate but this is the most inexpensive application method. Generally, the substrate is spread across the surface and then “raked’ into the top few inches of exposed soil. The ”raking” can be done with the teeth of a bucket on an excavator or even by hand. In theory, any water that flows through the treated area picks up carbon and moves that carbon into the same groundwater zones responsible for contaminant travel. This technique can be an excellent addition to injections. JRW provides information regarding our products as a service to our clients. JRW is not a consultant and does not provide professional services. Every site is unique and care must be exercised by the practitioner to fully understand their own circumstances
Enhanced reductive dechlorination is based on attaining and maintaining control of an aquifer for a period of time sufficient to degrade all constituents of concern and their daughter products. Attaining and maintaining control of an aquifer is highly dependent on the hydrogeology and geochemistry of the site along with the microbial populations present. Since the hydrogeology and geochemistry is different for every site, a blanket cost can not be given for any specific site. In general, enhanced reductive dechlorination will cost less than $10 per cubic yard of media treated on most non-DNAPL sites. This compares with about $60 per cubic yard for excavation (without disposal) and about $90 per cubic yard for chemical oxidation.
Because freight is costed from a warehouse to a delivery point, freight costs are quoted separately. Unless otherwise stated, due to the volatility of the fuels market, freight costs are generally valid for 30 days. Consideration should be given to the receiving facility’s capacity to off load a truck. In situations where the product is delivered to a facility without the capacity to off-load a delivery vehicle, arrangements can be made (for an additional charge) for delivery on a vehicle with a lift gate and pallet jack.
Reinjection schedules should be based on the geochemistry of an aquifer and not on a calendar schedule. In many cases, multiple injections can be spaced further apart over time.
Since the main goal of adding a substrate to an aquifer is to attain and maintain anaerobic conditions for an extended period of time, because of the limited flows clay sites should be ideal for enhanced reductive dechlorination. In practice, clay sites with adequately spaced injection points usually show very rapid response to substrate addition.
Injection spacing should be sufficient to promote robust reductive dechlorination throughout the treatment zone for a time sufficient to attain complete reductive dechlorination. Injection spacing is dependent upon the dissolution rate of the substrate, the dosage, aquifer velocity, and competing electron acceptor and contaminant flux.
