ISSN:
1745-6584
Quelle:
Blackwell Publishing Journal Backfiles 1879-2005
Thema:
Energietechnik
,
Geologie und Paläontologie
Notizen:
High concentrations of dissolved nitrate in the ground water in the Redlands, California, vicinity threaten public water supplies. Dissolved nitrate-nitrogen concentrations in water from wells, which frequently exceed 10 mg/1 (milligrams per litre), are attributed to the previous applications of large quantities of commercial nitrogen fertilizer on citrus crops. In a city of Redlands public water-supply well field, wells 1 and 2 normally produce water with dissolved nitrate-nitrogen concentrations of about 18 and 30 mg/1, respectively. Well 1 is a large-capacity well capable of yielding 3,700 gal/min (gallons per minute) [233 1/s (litres per second)] and is the major source of water in the well field.The very permeable unconfined alluvial aquifer is composed of sand, gravel, boulders, and discontinuous clayey deposits. Well 1 is 742 feet (226 metres) deep and is perforated throughout most of the zone of saturation. A major clayey interval from 425 to 480 feet (130 to 146 metres) effectively separates the aquifer into an upper and lower zone. Well 2 is 426 feet (130 metres) deep and is perforated throughout most of the upper zone of saturation. At the well field the static water level (February 1976) was 180 feet (55 metres) below land surface.Independent tests were made on wells 1 and 2 to evaluate aquifer characteristics and to determine the sources of the high-nitrate water. Chemical analyses of water collected from well 1 during the first 48-hour test showed an increase in dissolved nitrate-nitrogen from 4.1 mg/1 to a maximum of almost 20 mg/1. Dissolved nitrate-nitrogen concentrations during the 48-hour test of well 2 stayed constant at 30 mg/1. Interpretation of the chemical data and the results of previous studies indicate that the upper zone of saturation is the higher in concentration of dissolved nitrate.To reduce the concentration of dissolved nitrate in water from well 1, an inflatable packer was placed in the casing at 480 feet (146 metres) to coincide with the bottom of the clayey interval. The packer sealed off the upper part of the well and, as determined from a final test of well 1, reduced dissolved nitrate-nitrogen concentrations from 20 to 4 mg/1 while only reducing well yield from 3,700 to 2,600 gal/min (233 to 164 1/s).
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1111/j.1745-6584.1976.tb03138.x
