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| Publication Type:
| Proceedings |
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| Author(s): | Sheikh, Bahman |
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| Author Affiliation: | Director, Office of Water Reclamation, City of Los Angeles, Los Angeles, California |
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| Title: | The city of Los Angeles gray water pilot project: Gray water is as safe as low-voltage electricity |
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| Section: | 2D
Other records with the "2D" Section
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| Meeting Info.: | Las Vegas, NV: December 12-16, 1993 |
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| Source: | Proceedings of CONSERV 93: The New Water Agenda. 1993, p. 773-788. |
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| Publishing Information: | Denver, CO: American Water Works Association |
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| # of Pages: | 16 |
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| Keywords: | TIC Keywords: Greywater; Drip irrigation; Bacteria; Comparisons; Water conservation; Irrigation water; Minerals
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| Abstract/Contents: | "The Gray Water Pilot Project consisted of eight gray water test systems installed at residences in the City of Los Angeles, sampled monthly and monitored over a year-long period for safety and water savings. Drip irrigation was the primary method of application of water in all but two of the sites. Samples of soils and water were tested at a certified laboratory for indicator bacteria and pathogens to compare areas receiving gray water with those irrigated with tap water. Twelve monthly sample sets were taken from the each of the eight pilot sites. Each sample set was tested for a dozen parameters. The resulting data formed the basis for statistical analyses to determine the significance of differences between the control areas and the gray-water-irrigated areas. Total and Fecal Coliform bacteria and the enterococcus group in control and gray-water irrigated soils fluctuate widely and inconsistently. There appears to be no smooth trend with time or with irrigation treatment. Results of pre-irrigation (baseline) sampling also show great variability among sites, with indicator bacteria counts in the same range as the post-irrigation samples. Therefore, it is not possible to correlate occurence of indicator bacteria in the top soil with use of gray water at the pilot sites. It may be that background variation of these bacteria in the soil environment--from domestic and wild animals--overwhelms any contributions from human sources through the gray water distribution system. The statistical analysis of the data from the soil samples indicates a significant difference in the total coliform levels between gray-water-irrigated areas and control areas. This can be attributed to the possibility that gray water contains organic matter which can support growth of soil microorganisms, including coliform bacteria deposited by animals as well as those coming from the gray water sources. However, the statistical tests did not show any significant differences for fecal coliform or for Enterococci on the irrigated soils. Three of the Disease-causing organisms monitored in the sampled soils--Salmonella, Shigella, and Entamoeba histolytica--were negative at all sites in all sampling rounds, in gray water and in soil--both control and gray-water-irrigated. Apparently, neither the gray water nor the soil carried any of these particular organisms. The fact that throughout the year, none of the samples yielded a positive for any pathogens tested is encouraging for the possibility of safe use of gray water--even where total adherence to hygienic handling of the water in not assured. pH, sodium, chloride, calcium, magnesium and total salts were measured in gray water and in the soil extract to determine if any of the agronomic characteristics of the soil might be affected by gray water irrigation. For the same purpose, sodium adsorption ratio was computed for each sample, using the basic data. As expected, sodium and sodium adsorption ratio were both significantly higher in gray-water-irrigated soils than in control soils. Boron concentrations in the storage tanks and in the soil were measured once, during round 9 sampling. Since boron was not detected in any of the gray water samples, gray water is not expected to affect boron concentrations in the soil. From the results preasented, including baseline data, it is clear that backyard soils are highly contaminated, whether they are in the control areas or in the gray-water-irrigated areas. If these findings can be generalized, the implication is that gray water irrigation does not by itself elevate the health risks from handling the garden soil, as long as sanitary practices are followed." |
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| Language: | English |
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| References: | 8 |
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| Note: | Tables
Graphs |
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| ASA/CSSA/SSSA Citation (Crop Science-Like - may be incomplete):
Sheikh, B. 1993. The city of Los Angeles gray water pilot project: Gray water is as safe as low-voltage electricity. p. 773-788. In Proceedings of CONSERV 93: The New Water Agenda. Las Vegas, NV: December 12-16, 1993. Denver, CO: American Water Works Association. |
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