Nationâ€™s largest project to provide recycled water for irrigation of vegetable crops begins operation
Robert S. Jaques, P.E.
Director of Engineering Planning and Technology
Monterey Regional Water Pollution Control Agency
There are an estimated 2.68 million hectares (6.7 million acres) of land in the United States where fresh vegetable crops are grown (National Research Council, 1996). This large new market for recycled water has been previously almost untapped. The operation of this large-scale reclamation plant demonstrates, in a highly visible manner, that reclaimed water is safe to use. This will have widespread benefit to agencies needing to â€œcreateâ€ potable water without having to develop new services.
As described below, reclamation projects require a great deal of confidence-building among all parties involved. Confidence in the local growers and local health officials, as well as state and regional officials, had to first be developed by conducting an eleven-year-long study, which included five years of full-scale farming operations using reclaimed water. The study demonstrated that reclaimed water could be safely and economically used to irrigate fresh vegetable crops.
The Salinas Valley of northern Monterey County is a rich agricultural region. Artichokes are a major crop, but a variety of annual crops are also grown in this area, including broccoli, cauliflower, celery, and lettuce. Heavy agricultural and municipal groundwater demands have led to development of a severe groundwater overdraft condition in the underlying aquifers. Groundwater data showed this condition had begun to develop in the early 1940s. The aquifers in the Salinas Valley, the principal water supply for the region, were experiencing an ever-increasing seawater intrusion problem with seawater from adjacent Monterey Bay entering these aquifers to make up for the overdrafting causing concern over threatened water supply.
A separate reclamation plant was constructed adjacent to a regional secondary treatment plant to provide tertiary treatment for flows that would be destined for irrigation purposes. A distribution system to serve 4,800 hectares (12,000 acres) of irrigated farmland was constructed to deliver the recycled water. The reclamation plant and the distribution system are collectively called the Monterey County Water Recycling Projects (MCWRP). To guide both the planning and the conduct of this significant study, a Task Force was formed comprised of representatives of federal, state, regional, and local governments; the academic community; farm advisors; and local growers.
MWRSA was an eleven-year-long study commencing in 1976. It was a combination pilot project and demonstration project to assess the safety and feasibility of agricultural irrigation using reclaimed water to irrigate vegetable crops which may be eaten raw. A portion of the secondary plantâ€™s effluent was diverted to each of two parallel treatment process trains:
Well water produced from local wells was the control for the study. Local farming practices were followed throughout the study. The design allowed comparison of irrigation with different water types and the effect of varying fertilization rates. Separate irrigation systems were constructed to supply the three water types to the plots, selected to provide soil uniformity.
The results of the study are significant:
Virus Survival: Throughout the entire study, no insitu viruses were recovered from the chlorinated effluent of either process, and no viruses were recovered from any of the crop samples, or the soil irrigated with the reclaimed water.
Bacteria and Parasites: All three types of water, including the well water control, periodically showed the presence of coliform. However, no salmonellae, shigellae, Ascaris lumbricoides, Entamoeba histolytica, or other parasites were ever detected in any of the irrigation waters. The levels of total and fecal coliform in soils and plant tissues irrigated with all three types of water were generally comparable. No parasites were ever detected in soil samples.
Groundwater: No discernible relationship existed between the quality of the shallow groundwater underlying the sites and the type of irrigation water applied.
Aerosols: Numerous aerosol tests conducted during both daytime and nighttime irrigation events concluded that microorganisms carried by aerosols from FE sprinklers were not significantly different from those generated by well water sprinklers.
Health of Field Workers: The health status of each person assigned a field task was monitored regularly through frequent questionnaires and through initial and exit medical examinations administered by qualified medical professionals. One hundred questionnaires were completed by personnel over the five-year duration of the MWRSA field activities, and no complaints were found to be related to contact with reclaimed water.
Irrigation Water Quality: The reclaimed waters had higher levels of most chemicals and metal constituents than the well water. The nutrient value of both reclaimed waters was substantial. Levels of electrical conductivity, total dissolved solids (TDS), boron, chloride, and sodium in the two reclaimed waters were comparable to each other, and were higher than those in the well water. However, concentrations of TDS in all three water types were below the severe problem range for irrigation water.
Heavy Metals and Soils: There was no significant difference in the levels of any of the nine heavy metals studied among plots irrigated with the different water types.
Heavy Metals and Plant Tissues: The nine metals investigated in samples of the edible plant tissues revealed no consistent significant differences in heavy metal concentrations between plants irrigated with any of the waters.
Crop Yields: For most vegetables, yield was somewhat higher when irrigated with either of the reclaimed waters than with well water.
Crop Quality: Neither field quality assessments nor shelf life measurements revealed any difference between produce irrigated with reclaimed water and produce irrigated with well water. Visual inspection similarly revealed no differences. No problems with increased spoilage of produce irrigated with effluent with reclaimed water were encountered.
Marketability: A study to define the key issues of marketability of crops grown with reclaimed water was performed by a marketing research firm. Interviews were conducted with individuals involved with produce distribution, such as wholesale-retail buyers, brokers, and store managers. The responses to the interviews indicated that produce would be accepted, and that labeling would not be necessary. The major requirement of buyers was that the produce have a healthy appearance and be aesthetically attractive.
Because of the favorable results obtained from the study, funding for design and construction of the MCWRP was provided by the U.S. Bureau of Reclamation Small Projects Loan Act, the State of Californiaâ€™s State Revolving Fund Loan Program, and local share contributions. Local public agencies were responsible for design and construction of the reclamation project and treatments. Growers were extensively involved in the pipeline and alignment design of the CSIP to produce a successful project from the growersâ€™ standpoint.
The treatment process:
As mentioned earlier, a marketability study was conducted in conjunction with the study. However, in the 14 years that ensued after this marketability study was performed and the MCWRP was preparing to start up, several important things happened: A number of other reclamation projects around the country were designed, constructed, and placed into operation. Most of these were reclamation projects for landscape, golf course, or other non-food crop irrigation purposes. Some projects, however, were intended to irrigate certain types of food crops, such as citrus crops and other orchard crops, but not for vegetable crops which come into direct contact with the irrigation water. In some ways this was beneficial, because reclamation became more of a publicly accepted practice as a result of publicity about these other projects. However, consumers also became more aware of reclamation and became more interested in the health effects and other issues associated with reusing water.
Also, in the mid-1990s, there were several incidences of foodborne disease which received widespread publicity and had devastating economic impacts on the growers and marketers of the affected crops. There were several incidents involving bacterial contamination and illnesses initially linked by the media to California-grown strawberries, but subsequently determined to be caused by imported raspberries. There were illnesses and even one death reportedly linked to consumption of an unpasteurized fruit juice product. Bacterially-contaminated lettuce was also reported in Florida. An increasing number of articles and reports in the media turned the publicâ€™s attention to the question of whether or not the food they were consuming, particularly fresh fruits and vegetables, was as safe as they had previously assumed it was.
In order to pave the way for startup of the project, a public education program was developed and implemented. Each of the phases is briefly described below:
Robert S. Jaques can be reached at (831) 645-4607 or at email@example.com. Bill Reichmuth, P.E., Public Works Director for the City of Monterey and member of APWAâ€™s Water Resources Management Committee, assisted in the editing of this article.
Overall Study Conclusions