1. How does SRS™ work?

As the SRS™ flows out away from the injection points, a portion sticks to the sediments until eventually all of the substrate is adsorbed.  All biological activity is in situ.  Over time, the immobilized oil forms an in situ treatment zone.  Chlorinated solvents within and migrating into this zone are degraded by bacteria using the slow release organic carbon.  Some dissolved organic carbon will also be released downgradient, enhancing biodegradation of contaminants immediately downgradient of the treatment zone.  

Once injected in the subsurface, the SRS™ substrate will be biodegraded by native microorganisms, thus producing anaerobic conditions.  After anaerobic conditions have developed, the continued fermentation of the SRS™ substrate will stimulate the reductive dehalogenation of  PCE, TCE,  cDCE, and VC.  Since the SRS™ substrate is sparingly soluble, its slow dissolution will allow the continued biodegradation of HVOCs for approximately three to five years.  The final end products in the biodegradation of the HVOCs present at the facility will be ethene and ethane if a microbial population capable of complete dechlorination is present at the site.  The SRS^TM will be degraded to volatile fatty acids (VFAs), methane, and carbon dioxide. 

The edible oil is augmented with a fast release substrate to enhance establishment of anaerobic conditions. 

Our approach eliminates the need for groundwater recirculation systems or above ground treatment and their associated high capital and operating costs.  The SRS^TM technology is especially useful in low permeability formations where it is difficult and expensive to circulate treatment fluids.  The SRS™ process is superior to soluble substrate systems, in which the substrate can be rapidly biodegraded and must be frequently replenished.  Our low solubility oil technology overcomes this problem by placing the slowly biodegradable oil with a droplet size of 1 micron or less in close contact with the contaminant through conventional wells or using direct push technology.

The key to successful implementation of an in situ bioremediation project is cost-effective distribution of electron donors.

2. What is SRS™ made of?   - back to top -

SRS™ is a combination of soybean oil, emulsifiers, and a proprietary nutrient package.  Our standard substrate package contains 60% oil, 4% sodium lactate, emulsifiers and nutrients, and carbon filtered water.  All components are Generally Recognized As Safe (GRAS) by the U.S.D.A.  Since Terra Systems manufactures SRS™ in its own facility, the nutrient package can be altered if site conditions warrant. 

The average droplet size is below 1 micron for our standard package.  However, we have the ability to produce a larger droplet size if the site conditions warrant.  For example, we typically recommend a 5 micron droplet for fractured rock formations.

3. How much SRS™ is required?   - back to top -

The volume of SRS™ required for a site will depend on the site geochemistry, mass of contaminant, and groundwater flow velocity.  Terra Systems’ can assist you in determining the SRS™ requirement.

4. What is the viscosity of SRS™?   - back to top -

The SRS™ concentrate is approximately 60 centipoises (similar to a thick cream).  The dilute fluid that is injected into the formation is approximately 6 centipoises (similar to milk). 

5. Will the SRS™ float on top of the water table?   - back to top -

No.  The SRS™ droplets sorb onto the aquifer soil.  Depending upon the chase water injection volumes, there may be some SRS remaining in the injection wells. 

6. How long does the SRS™ work?   - back to top -

The time that SRS™ continues to work depends on the amount injected and site conditions.  Based on extensive laboratory and field studies, the typical time frame is 3 to 5 years.  Unlike soluble substrates like sodium lactate and molasses that degrade in one to two months, SRS™ is designed to last for three to five years.

7. Will the SRS™ continue to move in the aquifer after the injection process is complete?   - back to top -

No.  Typically the emulsion will break and absorb into the soil. It then slowly degrades over time.

8. Do I need special equipment for SRS™ injection?   - back to top -

No. The SRS™ is delivered as a concentrate. The concentrate can be diluted in a tank or with a Dosatron^R dilution unit.

9. Is SRS™ hazardous?   - back to top -

No.  All of the components of SRS™ are food grade materials that are Generally Recognized as Safe (GRAS) by the U.S. Food and Drug Administration.  However, we do not recommend that humans ingest the substrate.

10. What are the advantages of using SRS™?   - back to top -

We believe the SRS^TM approach has several very significant advantages over other approaches.  First, SRS^TM can be distributed and immobilized over substantial distances in a range of aquifer materials.  At a recent project in Long Island, NY, edible oils were distributed 35 ft away from the injection point.  However at most sites, we find that it is more economical to use closer injection point intervals to reduce the time required for injection.  Second, the edible oil substrate (SRS^TM) can be designed to be very long lasting, tremendously reducing long-term operation and maintenance costs.

11. How is the SRS™ injected?   - back to top -

The SRS™ substrate can be injected using either a direct push (Geoprobe® or similar) drilling equipment or through installed wells.  If the direct push method is selected, the drive rods are pushed to the bottom of the contaminated zone and the substrate is injected as the rods are withdrawn. 

If injection wells are used, there are two methods for injecting the SRS™ emulsion.  The first method utilizes a recirculation loop system that allows the fluid to recirculate in a hose loop with branches into each well.  The equipment for this type of injection system can consist of a water tank, 1-inch water hoses, appropriate transfer pumps, flow meters, pressure gauges, and valves for each well being injected.  Terra Systems, Inc. has rental equipment available for substrate injection. 

The second injection well substrate delivery method utilizes a manifold that blends water and SRS™ and distributes the emulsion simultaneously to a number of injection wells. 

We recommend that the substrate injection be followed by a water chase.  The chase water can be either untreated site groundwater or carbon filtered tap water.  The alternative is to dilute the SRS™ further than the standard 4 parts water to 1 part SRS™ concentrate.

12. Is bioaugmentation necessary?   - back to top -

This is a qualified maybe.  It has been established that the only known species of bacteria capable of complete reductive dechlorination is the Dehalococcoides ethenogenes bacteria.  There are several laboratories in North America that are capable of using Quantitative Real Time PCR test methodology to evaluate the microbial community for the presence of Dehalococcoides spp.  If the bacteria are not present, we recommend bioaugmentation.

There is considerable debate about the cost effectiveness of bioaugmenting a site even if the dehalorespirers are already present.  In these situations, our experience is that the bioaugmentation decision should be based on the site conditions and project objectives.