ES&T LETTERS Sewage and groundwater quality Dear Sir: I have read with interest R. W. Crites's article entitled "Land use of wastewater and sludge" (ES&T, May 1984, p. 140A) and would like to draw the attention of your readers to the results of similar research carried out recently in the U.K. (/). Research to assess the effects on groundwater quality of recharging sewage and sewage effluents to the major aquifers of the U.K. has been undertaken by the Water Research Centre (WRC) at eight working sites over the seven years from 1975 to 1982. The work, which was partly funded by the Department of the En vironment and the Commission of the European Communities, was under taken in response to a rising concern about the vulnerability to pollution of
aquifers that are being used both for effluent recharge and for drinking water abstraction. The objectives of the research were: • to determine the effectiveness of the saturated and unsaturated zones in improving the quality of recharged effluent, • to determine the effects of efflu ent recharge on the aquifers, • to determine travel times within the U.K. aquifers, and • to establish aquifer management guidelines. The investigations at all sites began with a detailed study of the effects of the inorganic components of the efflu ent on the quality of the receiving groundwater. At some sites, however, more detailed studies were made of the fate of the organic and microbial constituents of the sewage effluent.
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The results of the WRC research show that effluent recharge is an ef fective method of improving the qual ity of the effluent. The majority of the contaminants are markedly reduced in concentration during infiltration through the unsaturated zone, and on reaching the groundwater their con centrations are further reduced by di lution. The levels of most contamin ants are at background within a few hundred meters of the site. Inorganic, organic, and microbiological contam inants are all attenuated in this way, and these results agree with the work of other researchers both in the U.K. and abroad. The travel time of the effluent de pends on the type of aquifer studied, but tracer tests on chalk show rapid transit times (5 m/d) through the un saturated zone. In certain places in the saturated zone very rapid lateral flow has been observed (18-350 m/d). These rapid transit times, how ever, do not appear to affect the treat ment capacity of the sites and may represent short-circuit fissures. The main conclusions of the WRC research are that effluent recharge is a satisfactory method of sewage treat ment and, under controlled condi tions, does not present a pollution threat to groundwater. The hydraulic and chemical loading of the site, how ever, must be governed and the qual ity of the receiving groundwater must be monitored. The recharge method requires large areas of land, about 7 m 2 /capita, and therefore may not be feasible for large communities. Effluent recharge and related re search have emphasized the role of the unsaturated zone in the control of groundwater quality. Research is continuing at WRC into the chemical and microbiological processes in the unsaturated zones of our major aquifers.
international light INC Specialists in Light Measurement Since 1965 DEXTER INDUSTRIAL GREEN, NEWBURYPORT, MA 01950 U.S.A. • TEL. 617-465-5923 • TELEX 94-7135 Write for name of sales représentât ve in your area (over 40 countries worldwide)
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Environ. Sci. Technol., Vol. 18, No. 10, 1984
Κ. Μ. Baxter Water Research Center Medmenham Laboratory, U.K.
Reference (1) Baxter, K. M.; Clark, L. "Effluent Re charge: The Effects of Effluent Recharge on Groundwater Quality," Technical Report TR 199; Water Research Centre, 1984.
