Hilmar Supplemental Environmental Project
This study constitutes a Supplemental Environmental Project
(SEP) authorized as part of a settlement agreement between Hilmar Cheese
(Hilmar) and the Central Valley Water Quality Control Board, (Regional Board). It is
intended to enhance the understanding of the role the food processing industry
has on salinity discharge to ground and surface waters of the
The study is organized into three volumes. Volume I
introduces the problem, discusses the current framework for regulation of
salts, and lays out the framework for study and comparison of alternatives.
Volume II presents a study of the physical aspects of salinity discharge, including
detailed analyses of the food industry waste water discharge by chemistry,
geography and industrial affiliation, and analyses of flow and transport
processes in the unsaturated and saturated zones in the Central Valley. In
addition, it provides an inventory of environmentally sensitive sites in the
Framework for Analysis
Food processing is an important economic activity in the
There are a large number of food processing facilities in
the region, owing to the fact that
The study analyzes and compares four basic approaches to management of saline wastewater discharges from the food processing industry. There are
The framework for comparison of alternatives can be understood with the aid of the following figure which shows the flow of wastewater from food processing plants, through environmental media, and which ultimately affect the benefits obtained from groundwater consumption.
Land application of food processing wastewater, for example, flows through groundwater and may affect groundwater users regionally. Diverting these wastes to a local POTW may also affect regional groundwater, but in a different way and at a different location. Out of basin alternatives include a brine line and deep well injection.
The numerical analysis of salt management alternatives is
conducted for a representative area centered on the city of
Using data for the representative area on groundwater use, groundwater movement, soil and other environmental conditions, configuration of food processors, and the cost of various treatment alternatives, the impacts of alternatives are compared. The timeframe for the comparison is 30 years.
Physical Modeling of Land Application
Volume II presents the models developed by the SEP study team for tracing the movement of salts from food processing facilities through the vadose and unsaturated zones. Land application is by far the most common method of wastewater disposal, either at the facility or via a local POTW. The Volume concentrates on a detailed analysis how land application affects the salinity of regional groundwater resources.
The term “salinity” encompasses multiple individual ion
species and is commonly represented as either electrical conductivity (EC) or
fixed dissolved solids (
Waste Discharge Requirements (WDRs) issued by the Central Valley Regional Water Quality Control Board to the food processing facilities and periodical monitoring reports for California Central Valley food processors were obtained from the Regional Water Quality Control Board offices in Fresno and Sacramento. The files were copied and subsequently scanned for use on the project. These reports were condensed to create templates recording all chemical constituents reported by the food processors; the templates were populated with water quality and volume data for 2003, 2004 and 2005.
Volume II contains a detailed physical and chemical analysis of land application and the movement of salts through the unsaturated zone. This investigation indicates that the unsaturated zone has a limited capacity to attenuate salts. Thus, salts will break through to the saturated zone in the vicinity of land application sites. As a result, it is expected that the salinity at the water table at these areas will be equal to the salinity of the effluent, and possibly higher, over the long term. Site conditions can mitigate or even eliminate the effects of nitrogen compounds on groundwater quality, whereas in the case of salinity, site conditions have only a limited and temporary ability to reduce salinity.
While even carefully managed land application can noticeably
affect the salinity of groundwater, an important finding of this study is that
the degradation to groundwater quality due to land discharge is likely to occur
only in the close vicinity of the discharge sites. This general finding is
illustrated by the following figure that displays changes in groundwater
salinity around the various land application sites in the representative area
Whereas solutes can migrate downstream of the land discharge sites over distances of thousands of meters, depending on local hydogeological conditions, increases in FDS concentrations larger than 500 mg/L compared to background concentrations are limited to the groundwater underneath the discharge sites and over distances of the order of magnitude of hundreds of meters downstream of the land discharge sites. The probability for observing increases in concentrations of such magnitude over larger distances were found to be close to zero.
What explains the limited spatial extent of the spreading of solutes underneath the discharge sites? The answer is a combination of effects, including the reduction in concentrations due to dispersion, and in a few locations the buffering effects of the vadose zone. Groundwater pumping in the representative area also creates a strong vertical downward pointing pressure gradient in the shallow aquifers which leads to vertical migration of solutes, deeper into the earth. This fact limits the spatial extent salt migration, but at the same time it also leads to development of areas of high salt concentration just underneath and downstream of the land discharge sites. Such hotspots will be sustainable as long as vertical gradients of sufficient magnitude persist.
In the event that pumping in the deeper formation ceases or due to pumping from deeper formations or due to reversal of the vertical gradient due to change in hydrologic conditions the containment effect of groundwater extraction in the representative area can diminish. In this case, salts can migrate over a much larger area than modeled here. However, this migration will be noticeable primarily in the upper aquifer where there is relatively little groundwater pumping and hence only minor impacts on water users. With time, vertical migration of solutes, albeit at a slow rate, may cause salts to move deeper.
Economic Impacts of Land Application and Analysis of Alternatives
Volume III of the study contains an analysis of the economic
losses resulting from land application in the representative area. Such
estimates are essential to gauge the significance of the problem that exists
under status quo practices, and provide a benchmark for comparison with other
salt management alternatives. Economic impacts from changes in groundwater
salinity were calculated using current and forecasted water demands in the
representative area. Current water use patterns were assembled from a variety
of sources, including municipalities and irrigation districts in the study
region. Future water uses were derived using a land use forecasting model
developed as part of this study. The land use change model predicts the
probable location of future development in the
There are two basic conclusions resulting from the economic analysis of land application in the representative area. First, the current and future annual losses resulting from land application are small, around $400,000 annually. These losses include effects experienced by urban water users and farmers using groundwater for crop irrigation. Second, the effects of land application occur largely within the confines of the land application sites themselves. They are thus internalized by the food processors owning or renting these sites, and do not represent an external effect that contributes to a collective problem.
The limited impact of land application reflects the groundwater modeling described earlier. The downward gradient in the representative area groundwater limits the real extent of salt migration. For similar reasons, the environmental impacts of salts in food processing wastewater are also expected to be minimal. Section II.5 of the report shows the location of environmentally sensitive sites in the representative area in relation to various food processing facilities. While there are areas of critical habitat, wildlife refuges and other environmental amenities located within several miles of food processing facilities, there is little evidence that salts will migrate to these sites over the time frame of the analysis, assuming that current patterns of groundwater use continue.
While land application does not appear to pose a general or significant threat to groundwater users in the representative area, it is still of interest to examine the configuration, effectiveness and relative cost of measures to manage salts from the food processing industry. The first such set of measures is aimed at reducing salt discharges through the use of technologies and management practices at food processing plants. These include supply water treatment, end-of-pipe treatment and process changes.
Another class of salt management alternatives collects food processing industry wastewater and treats it at a central location. Two such alternatives considered in this study are collection and treatment at a POTW, and at a dedicated facility owned and operated by the food processing industry. While the treatment technologies applied at such facilities are well accepted, access to existing POTWs may be problematic.
The study also examines disposal of wastewater to a brine
line. This option is more expensive than either of the two in-region central
treatment alternatives. The average cost of salt disposal via a brine line
varies with the configuration and length of the line. As the line is extended,
more food processors can be added which reduces average cost, but requires
extra investment in capacity and construction costs. The minimum-average cost
configuration is a line running 220 miles through the representative area to
Deep well injection is examined as an alternative out-of-region salt management approach. Brine is effectively removed from the region by disposing it where it cannot reach groundwater that is or can be reasonably expected to serve a beneficial use. The technology has been used since the 1950’s and provides a low cost means of disposal. It is, however, a highly regulated activity and requires very specific geologic conditions that may not be readily available to some food processors.
The costs of these in-plant and regional treatment measures are generally well above the negative impacts of land application. For example, consider the POTW alternative that has relatively lower costs of salt removal than the other regional alternatives. For this alternative, the capital and operating costs of the POTW option range from $13 to $34 million annually for the entire representative area. The negative impacts of land application are around $400 thousand annually, again for the entire representative area. Although this suggests that the costs of substantial restrictions on existing food processing wastewater discharge is unwarranted in the representative area by the limited benefits that would arise, it is possible that this will not be the case throughout the Regional Board’s jurisdiction.
Salinity Management Strategy
Based on these results and a review of salinity management
strategies implemented in
The Regional Boards are required to consider economic factors when assessing the reasonableness of alternative water quality objectives. The tools exist to base this analysis on actual and reasonably foreseeable water uses rather than on blanket statements about protection of beneficial uses and anti-degradation objectives. Advances in GIS technology, groundwater modeling and economic analysis make it possible to determine changes in groundwater quality and use at a highly disaggregated level.
As part of the effort to measure the benefits of water
quality improvements, the study developed and implemented a detailed model of
land use change for the entire
The physical modeling undertaken for this study shows
convincingly that there is not a single inventory of salt in the