SB 4 and SB 83 Oil and Gas Production Reform Oil and Gas regulation in California has undergone extensive reform across multiple agencies to strengthen protections for fresh groundwater aquifers and public health and safety. The Natural Resources Agency has been given a statutory role in implementation of Senate Bill 4 Pavley for well stimulation and Senate Bill 83 Committee on Budget and Fiscal Review for underground injection programs.
Zerovalent iron Zerovalent Iron was the first material to be used in PRBs for groundwater remediation. It continues to be the main material used in the construction of these barriers.
Biological barriers[ edit ] Sometimes material will be put into the ground to stimulate the growth of microbes that facilitate the groundwater remediation.
Many environmental pollutants are highly reducedthus, the oxidation of these pollutants to harmless compounds is thermodynamically viable. Other pollutants, such as chlorinated solvents, are highly oxidized and as such are easily reduced. Microorganisms commonly facilitate such redox reactions, exploiting contaminant degradation as a means to obtain energy and materials for cell synthesis.
This transfer of electrons releases energy to drive microbial life functions. Under aerobic conditions, molecular oxygen is used for this purpose. When oxygen is not present, a variety of other molecules can serve as electron acceptors.
Oxygen is preferentially utilized over the anaerobic electron acceptors because using oxygen gives more energy and, as an added benefit, results in faster contaminants oxidation rates. Unfortunately, the available oxygen is often not sufficient for the contaminants in highly contaminated areas, and as a result the anaerobic electron acceptors must be utilized.
Reactive barriers containing oxygen-releasing compounds have been used successfully to stimulate aerobic biodegradation of monoaromatic hydrocarbons. They do this by creating a net negative charge by substituting lower-valent cations e.
However, clay's low permeability means it cannot be used in flow-through PRBs,  but have been proposed for use in slurry wallslandfill liners, and containment barriers.
Groundwater modeling[ edit ] Modeling groundwater flow is important for optimizing the design of a PRB. Most importantly, by modeling the flow, the hydraulic capture zone width HCZW and the residence time can be determined.
The HCZW is the width of the zone of groundwater that will pass through the reactive cell or gate for funnel-and-gate configurations. The residence time is the time that the contaminated groundwater will spend in the treatment zone for decontamination.
Contamination outside the capture zone or that does not have a long enough residence time will not be properly decontaminated. Groundwater modeling can also be used for the following: Determining the location of the PRB Determining a suitable configuration Determining the width of the reactive cell and funnel for funnel-and gate Evaluating potential for underflow, overflow, or flow across aquifers Providing knowledge of groundwater flow fluctuations velocity and direction for use in the design Determining reactive media selection based on hydraulic conductivity to match the conductivity of the aquifer Evaluating possibilities for flow bypass due to reduced porosity Helping determine monitoring well locations and monitoring frequencies  Iron barriers[ edit ] click to enlarge The accompanying figure shows two approaches to application of iron particles for groundwater remediation: A, a conventional PRB made with mm-sized granular iron and Fig.
B, a "reactive treatment zone" formed by sequential injection of nano-sized iron to form overlapping zones of particles absorbed by the grains of native aquifer material.
In A, groundwater flows through the barrier and is remediated. In B, nanoparticles of iron are represented by black dots; the nanoparticles have little mobility in the porous medium.
Note that reaction will only occur when contaminants, either dissolved in the groundwater or as DNAPLcome into contact with the iron surfaces. The funnels are non-permeable, and the simplest design consists of a single gate with walls extending from both sides. The main advantage of the funnel and gate system is that a smaller reactive region can be used for treating the plume, resulting in a lower cost.
In addition, if the reactive media needs to be replaced, it is much easier to do so because of the small gate. The trench is then filled with the reactive materials typically iron, carbon, or limestone. Sand can be mixed with the reactive material to aid in allowing the water to flow through the materials.
Sometimes, there will be a wall that directs the groundwater to the reactive parts of the barrier. After the trench has been filled with reactive material, soil will typically be used to cover the PRB, thus eliminating visibility from the surface.
This method involves containing the area of excavation using sheet piles before excavating using a trackhoe. This method may be slow and therefore expensive and is only viable for plumes less than 35 feet deep.
Continuous trenching can be fast and thus, inexpensive, but can only be used for trenches less than 50 feet deep. In addition, the machinery used for this technique cannot be used effectively for soil with large cobbles.
The beam is covered as it is driven in, and the cover is removed once the beam has been placed. Next, the hollow is filled with iron filings.
The Mendrel is then vibrated as it is removed, allowing the iron to flow to the bottom, forming the PRB. The Mendrel is then moved one width over, the process is repeated, and a continuous PRB is made.
Jets of water scour out a zone that is then filled with guar gum and iron. The guar gum holds the iron in place before degrading, leaving a permeable zone of iron the PRB.5 Key Barriers to Educational Technology Adoption in the Developing World. Clayton R. Wright. Educational technology will continue to be implemented incrementally in .
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