Aquifer nitrate

Hutchins and co-workers. Nitrate for Biorestoration of an Aquifer Contaminated with Jet Fuel, ReportforJune 1988—Sept. 1990, U.S. Environmental Protection Agency in cooperation with Solar Universal Technologies, Inc., NSI Technology Services Corp., Traverse Group, Inc., and 9th Coast Guard District, 1991. 

Even when horticultural crops leave substantial amounts of nitrate in the soil at harvest, they are not usually a very important factor in the nitrate problem because horticulture occupies only about 6% of the cultivable land. However, there could be a problem if, because of the type of soil, a number of market gardens were concentrated above an aquifer that was an important source of potable water. 

Sandy Soils. The particles in sandy soils are relatively large, with correspondingly large spaces between them. Because these soils are also fairly homogeneous, water moves freely through much of the soil matrix. Any nitrate that is in the soil, whether from fertilizer or from microbial activity, is likely to be carried through the soil slowly but surely with little impediment. A sandy soil above an aquifer is usually seen as a threat to the quality of the water in the aquifer. 

Hutchins SR (1991) Biodegradation of monoaromatic hydrocarbons by aquifer microorganisms using oxygen, nitrate or nitrous oxide as the terminal electron acceptors. Appl Environ Microbiol 57 2403-2407. 

Istok JD, JM Senko, LR Krumholz, D Watson, MA Bogle, A Peacock, Y-J Chang, DC White (2004) In situ bioremediation of technetium and uranium in a nitrate-contaminated aquifer. Environ Sci Technol 38 468-475. 

Hutchins SR, DE Miller, A Thomas (1998) Combined laboratory/field study on the use of nitrate for in situ bioremediation of a fuel-contaminated aquifer. Environ Sci Technol 32 1832-1840. 

In view of experience with the groundwater nitrate problem and the possibility of a large unsaturated time-lag in British aquifer systems (especially in the Chalk), it is necessary to address the following questions in the above investigation ... 

Are any pesticides being leached in significant quantities from permeable agricultural soils into the unsaturated zone of British aquifers in a similar manner to that observed for nitrate ... 

Postma, D., C. Boesen, H. Kristiansen, and F. Larsen (1991), "Nitrate Reduction in an Unconfined Sandy Aquifer Water Chemistry, Reduction Processes, and Geochemical Modeling", Water Resources Research 27/8, 2027-2045. 

GeoSiphon has several potential limitations and will not be applicable at all sites. Groundwater at a site must demonstrate a difference in hydraulic head in order for the system to operate. In addition, fluctuations in the water table may inhibit the system s performance. The technology may not be applicable at sites with deep contamination and nonsurficial aquifers. When iron is used as the reactive media, performance may also be limited by factors such as pH and high nitrate levels in groundwater. 

When aquifers were amended with nitrate in order to stimulate biodegradation, the results were generally consistent with those obtained in laboratory investigations. In a field injection experiment at Seal Beach, California, Ball et al. (1994) demonstrated complete removal of w-xylene and the m-,/-xylene fraction decreased significantly in parallel bioreactor experiments. A Canadian study showed a decrease in m- and /-xylene of 14% and 15%, respectively, over aim flowpath in the Borden aquifer (Barbara et al., 1992). Very little degradation was observed beyond that point, presumably due to the availability of preferred electron donors in the landfill leachate impacted aquifer. 

With modem methods of intensive farming in which nitrate-based fertilisers are employed, there has been a noticeable increase in nitrate levels from aquifers lying beneath agricultural land. The recommended limit for nitrate has been given as 50 mg/1 by the World Health Organization (WHO). The principal health risk of nitrates involves a condition seen in infants known as methaemoglobinaemia. 

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