PHOTO 1
Detailed acccounting of Nitrogen removal is facilitated by moisture sampling probe.
PHOTO 2
Reclaimed water pipeline construction.
PHOTO 3
On-site weather station provides real-time estimate of crop water used.
Making Water Work
Reclaiming Water and Land to Produce Viable Agriculture in the Antelope Valley
When the Palmdale, California area was facing a complex challenge regarding its wastewater, County Sanitation District No. 20 (District) provided an original, innovative solution that was cost-effective, promoted sustainability through the use of local resources in the community, integrated protection of local water resources with reduced energy usage, and provided flexibility for future growth. Located in arid northern Los Angeles County, Palmdale is a community in transition, changing from a rural agricultural area to a suburban city. Because the area contains no river or ocean outlet for treated wastewater, land disposal is the only option. The Palmdale Water Reclamation Plant (PWRP), serving approximately 100,000 residents in the area, had traditionally practiced land disposal of its 8 million gallons per day of secondary effluent produced using oxidation ponds. However, this practice was no longer acceptable, due to nitrogen impacts on shallow groundwater reservoirs.
A solution to this complex problem had to be found quickly, to abate nitrogen impacts, while still accommodating growth and the changing nature of the community. In an era of climate change, energy consumption had to be addressed and the long-term picture of limited water resources for California also had to be considered. To this end, the District developed a plan to maximize agricultural reuse of its water in the short term, while developing the infrastructure to provide high quality tertiary recycled water in the long term to the rapidly urbanizing community. The agricultural component of the project consisted of the conversion of almost 2,000 acres of primarily abandoned farmland to production of fodder crops such as alfalfa, oats, and Sudan grass.
Driven by a need to ensure that the local groundwater was protected, a collaboration of top agricultural experts and District engineers developed an original and innovative project that combined modern farming techniques with environmental engineering technology. District engineers consulted with expert staff from the University of California Cooperative Extension, the California Polytechnic State University’s Irrigation and Research Training Center, and private agricultural consulting firms, as well as local farmers familiar with the area. A computer control system for the agricultural operation was implemented, using supervisory control and data acquisition (SCADA), remote sensing, and modeling. To optimize watering, an automated weather station linked by telemetry to the internet was used to provide real time measurement of evapotranspiration rates. This was supplemented with implementation of an irrigation scheduling model that included daily monitoring and evaluation of the irrigation system, monitoring of soil moisture and the vadose zone, optimization of the irrigation distribution to maximize distribution uniformity, and quarterly calculations of a water balance using weather and soil data. Quarterly nutrient balances were calculated using the same data along with crop leaf tissue data, and trees were planted along the perimeter of the site to minimize offsite drift from spray irrigation and provide a pleasing look to the facility. The program also involves monitoring of groundwater for an extensive suite of pollutants, including some compounds of emerging concern.
One of the primary advantages of the agricultural project is its flexibility in contributing to the social and economic advancement of the community. The District is in the process of designing and constructing a tertiary treatment facility, in conjunction with working collaboratively with local water purveyors on infrastructure for a large-scale municipal reuse distribution system for the high quality water that will be produced. Sections of the farmland can be taken out of production as needed to supply urban recycled water needs. This is particularly important as the rate of growth of the community cannot be precisely predicted. In the meantime, the production of the 12,000 tons per year of valuable crops by the farmland contribute to the success of the community by providing much-welcomed jobs.
Another key advantage of the project is that it provides a comprehensive, integrated approach that considers all environmental media. The use of recycled water for growing fodder crops improves the local water supply picture by supplanting the use of groundwater for this purpose elsewhere in the valley, preserving these precious groundwater resources for future use. Putting previously fallow farmland into production results in other environmental benefits, including the creation of wildlife habitat and improved air quality through a significant reduction in fugitive dust, a major issue for the community. The project also has significant energy benefits related to water pumping, with savings in energy of over 95% relative to pumping local groundwater and 99% over importing surface water from northern California. The energy savings represent a green house gas production decrease of approximately 20,000 tons per year of carbon dioxide over alternative water supply. Finally, the project promotes community sustainability, not just through local use of water supply but also through local production of feed to fulfill a growing market demand at local dairies.
The high quality of the farmland project is demonstrated through its proven performance and user satisfaction. The main objective for the project, protection of groundwater, has been fully realized. Additionally, over the past five years the farmland has produced crops with higher yields per acre than regional norms. The consumer of the majority of the locally-grown crops is pleased with the stable, cost-effective cattle feed source that is produced.
In this project, environmental benefits spanning air, water, and land have been achieved by applying modern technical advances to time-tested agricultural techniques, making good use of the recycled water resource.
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