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Copy and Paste This Permanent Link:http://www.waterefficiency.net/may-june-2009/climate-change-greenhouse.aspx

Additional Article Content

• Figure 1 2005 electricity use in Santa Rosas water and wastewater systems
• Figure 2 2005 GHG emissions from Santa Rosas water and wastewater systems
• Figure 3 2005 energy costs for Santa Rosas water and wastewater systems
• Figure 4 2005 unit GHG emissions from Santa Rosas water and wastewater systems
• Figure 5 2005 water-related GHG emissions from Santa Rosas urban water cycle
• Figure 6 2005 water-related unit GHG emissions from Santa Rosas urban water cycle
• Figure 7 2005 water-related energy costs for Santa Rosas urban water cycle
• Figure 8 2008 electricity use and potential reductions for Santa Rosas main reclaimed wastewater pumps
• Figure 9 2008 installed cost and potential savings for Santa Rosas main reclaimed wastewater pumps
• Figure 10 GHG reductions from high-performance end-use efficiency and residential solar
• Creating a Greenhouse Gas Inventory
• Acknowledgements

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Water Availability
Water supply in California is becoming constrained by climate change, both directly and indirectly through the need to protect endangered species. Although the current water shortages in California are still referred to as droughts or often seen only as regulatory cutbacks to protect endangered fish species, they are undoubtedly part of a climate-driven trend. The State Water Project (SWP) depends on snowpack in the Sierra, which is projected to decrease drastically over the next few decades from changes in climate, and supply from the Colorado River to southern California has already been severely curtailed because of human-induced changes in hydrological cycles across the western US.

A July 2008 Federal Court ruling to protect endangered fish in the Sacramento–San Joaquin Delta mandated a significant reduction of pumping to the SWP which supplies most of central and southern California. After compilation of snowpack and reservoir data for winter 2008/2009, the California Department of Water Resources (DWR) estimates that the reduction in deliveries to the SWP will be 85%. In anticipation of the Federal Court ruling, the Governor of California directed state agencies in February 2008 to prepare and implement a water conservation program to achieve a 20% reduction in statewide average per capita water use by the year 2020 (the 20x2020 Program).

GHG Emissions From Water-Related Energy Use
Greenhouse Gas (GHG) emissions from electricity generation and combustion of natural gas and other fuels to operate water and wastewater systems—and to use water—is surprisingly large. A 2005 report by the California Energy Commission (CEC) estimated that 19% of California’s annual electrical energy and 32% of natural gas use is related to water (including water supply, customer end-uses, and wastewater treatment). The CEC report reveals that the largest energy demands in the urban water cycle lie not within water/wastewater utility operations, but on the customer’s side of the meter. For example, electricity for residential, commercial, and industrial customer end-uses of water is approximately four times larger than electricity required for urban water supply and wastewater treatment combined (and 92 times larger for natural gas). As a strategy for reducing GHG emissions from the urban water cycle, water planning now needs to include more effective and direct intervention to reduce water demand and its end-use energy.

Combining end-use water and energy efficiency can reduce GHG emissions much closer to targets for climate protection than focusing only on energy efficiency or purchasing renewable “green” power for water and wastewater systems—and can be cost-effective for both customers and water/wastewater utilities. It is very likely that the savings from avoiding future expansion of water/wastewater infrastructure will more than offset the cost of efficiency measures. After implementing end-use efficiency, a smaller investment will then be required for renewable energy and water recycling systems to meet even the most stringent targets for GHG reductions.

GHG Emissions From the City of Santa Rosa’s Water Cycle
In 2005, the Santa Rosa City Council endorsed a GHG emissions reduction target of 25% below 1990 levels by the year 2015. All other cities in Sonoma County, the Sonoma County Water Agency (SCWA), and the County Board of Supervisors, passed similar resolutions and supported the preparation of a Countywide Community Climate Action Plan (CCAP) that was published in 2008. The CCAP and shows that reductions of 50% will be needed to meet the 2015 target, and that by 2005, a 46% reduction was already required.

Initial evaluations for the urban water cycle were performed in 2003, and then a detailed GHG Inventory Report was prepared for the SCWA’s wholesale water supply in 2006 (SCWA Inventory Report). A detailed GHG Inventory report for the City of Santa Rosa’s Utilities department was prepared in 2007 to complete the water cycle using the same 2004–2005 data as the SCWA Inventory Report (SR Inventory Report).

The GHG inventory for the City of Santa Rosa’s urban water cycle is based on the following:

• SCWA is the wholesale water supplier, mostly sourced from the Russian and Eel Rivers with some summer supply from wells in the Santa Rosa Plain.
• Santa Rosa has an extensive wastewater reclamation system, with a relatively small fraction of direct discharge. Most reclaimed wastewater is pumped to the Geysers where it is injected to produce ~7% of the Geysers’ geothermal electrical output. A smaller fraction of reclaimed wastewater is used for agricultural irrigation.
• The federal Western Area Power Authority (WAPA) provides hydroelectricity to meet approximately half of SCWA’s demand through a purchasing pool. Pacific Gas & Electric Co. (PG&E) supplies electricity and natural gas to all elements of the urban water cycle.

Santa Rosa Utilities Operating Data
Data Sources. Monthly electricity and natural gas billings were obtained from PG&E for all water/wastewater facilities operated by Santa Rosa Utilities. For the cogeneration system at the wastewater treatment plant, daily data on biogas use, natural gas use, and electrical output was aggregated into the same monthly periods as PG&E’s billings. Monthly water supply volumes were obtained from SCWA and validated against Santa Rosa’s Water department records. Daily water balances contained in monthly Self-Monitoring Reports to the North Coast Regional Water Quality Control Board provided volumes of wastewater plant influent, effluent, discharge, and reclaimed wastewater usage and storage. Cross-referencing multiple sources of data was critical for validation and correctly estimating GHG emissions—and for identification of potential reductions.

Flow. As is common across California, monthly variability in Santa Rosa’s water demands is driven by outdoor irrigation that reaches its highest levels from June to September. On average, 38% of annual water use is outdoors, and 62% is indoors. In general, this implies that reclaimed wastewater could displace all potable water demands for urban landscape irrigation, but detailed examination reveals that although significant expansion is feasible, there are practical limitations to full displacement.

Monthly variability of influent to the wastewater treatment plant is driven by Inflow & Infiltration (I&I) into the sewers during wet weather. On an annual basis, I&I is 23% of the influent volume, but during storms, it can reach up to 47% of the monthly volume. The wet weather peaks from I&I give rise to large electricity demands (and GHG emissions) for treatment, and determine the storage capacity required for the reclamation system.

Energy Use. Monthly energy use for each water cycle element in the Santa Rosa Utilities system (and California in general) can be traced back to weather and water demand patterns. Disaggregation is vital in understanding energy patterns and performance—and for evaluating potential improvements. The wastewater plant has already implemented energy efficiency improvements for secondary treatment aeration and for reclaimed wastewater pumping based on such evaluations. Cogenerated electricity is included in Figure 1, since it is used exclusively by the wastewater treatment plant, and would otherwise be purchased from PG&E. The large amount of electricity used by SCWA is part of SCWA’s GHG inventory, and not included in Santa Rosa’s.

GHG Emissions. Converting energy use into GHG emissions was relatively easy for Santa Rosa since PG&E was the only supplier. PG&E reported that its annual GHG emissions intensity for electricity in 2005 was 0.489 pounds carbon dioxide (CO2) per kilowatt-hour; this is one of the lowest factors for any utility in the US, because of the large fraction of hydropower in PG&E’s supply. Natural gas GHG emissions (from end-use water heating and cogeneration at the wastewater plant) were calculated by applying 11.67 pounds CO2 per Therm.

Calculating GHG emissions for a cogeneration system requires a detailed analysis of site-specific conditions. Cogeneration provides 40% of the annual electricity used by Santa Rosa’s wastewater plant, and biogas provides 40% of the fuel used by the cogeneration engines. Biogas has a much higher CO2 emissions factor than natural gas, but since biogas is a renewable fuel, its emissions are not counted in the GHG inventory according to GHG Protocol.

Although the emissions from biogas are very large, they are not included in the GHG inventory because biogas is a renewable fuel. However, it is worthwhile paying attention to biogas since its combustion—even if flared only for safety—converts methane to CO2 with 23 times less Global Warming Potential. In addition, increasing utilization of biogas and exhaust heat from cogeneration can displace natural gas combustion—which is counted in a GHG inventory—in various heating applications. Overall, displacement of natural gas is the foremost GHG benefit of biogas production and utilization.

SCWA’s GHG emissions are very low relative to the electricity shown in Figure 1, because approximately half of the electricity is from WAPA hydropower. However, the hydropower is mostly available from spring through early summer, and by mid-July through September when water demand is highest, a large fraction of SCWA electricity is from PG&E’s market mix of generation sources including “dirty” gas-fired peaker plants. Thus, outdoor water efficiency measures in Santa Rosa could still significantly reduce SCWA’s already-low GHG emissions. Besides efficiency, expanding urban irrigation with reclaimed wastewater in Santa Rosa can further reduce SCWA’s GHG emissions. Although this would increase Santa Rosa’s GHG emissions from new reclamation pumps, a detailed evaluation would likely reveal an overall GHG reduction across several entities and jurisdictions (e.g. SCWA, the City of Santa Rosa, PG&E, and the state as a whole).

Energy Costs
The SCWA energy cost is part of wholesale cost of Santa Rosa’s water supply, and is 28% of the $4.2-million annual energy cost for the entire water/wastewater system. Santa Rosa’s wells have very high-unit GHG emissions, because deep groundwater wells have high unit electricity requirements. Until 2007, these wells were for emergencies only, which is why the total values in Figures 4, 5, and 6 are so small. In 2006, severe restrictions were imposed on SCWA’s extractions from the Russian and Eel Rivers to protect endangered fish species, so the City of Santa Rosa produced 8–11% of its summer potable water supply from the wells. With the onset of the third consecutive year of dry conditions, more well pumping is planned for 2009. Figure 4 reveals that, although it would be wise to evaluate energy efficiency improvements for the wells, water efficiency improvements to eliminate the need to operate the wells might be a more feasible path, since it is unlikely that unit GHG emissions could ever be reduced close to SCWA’s. This is reinforced by unit energy costs: $440 per MG for the wells and $160 per MG for SCWA—almost three times less.

Figure 4 also shows that the unit GHG emissions from the combustion of biogas are large (and the absolute value shown in Figure 2), and even though not included in the GHG inventory, they could be reduced as part of an overall strategy to increase cogeneration efficiency. The SR Inventory Report prioritizes potential cogeneration efficiency improvements for site-specific conditions in Santa Rosa. Since biogas has zero energy cost, increasing its production to reduce natural gas purchases from PG&E will reduce unit energy costs of cogeneration. The SR GHG Inventory Report contains a detailed discussion of possibilities to increase biogas production for site-specific conditions in Santa Rosa.

Comparison of Water and Wastewater Systems With Customer End-Uses
Water includes Santa Rosa’s wells and booster pumps (800 tons CO2 per year), and SCWA’s wholesale supply (2,000 tons CO2 per year). Wastewater includes all elements from sewage lift stations through treatment and reclamation, and biogas for cogeneration. End-users are Santa Rosa’s customers and their water-related energy demands (mainly for water heating).

Figure 5 shows that water-related GHG emissions from end-users are approximately 10 times larger than the combined GHG inventory for water and wastewater systems. This implies that end-use efficiency improvements could have a much larger impact on GHG emissions from the urban water cycle than improvements in water/wastewater operations. Figure 6 reinforces this point by showing unit GHG emissions. On average, for each gallon of reduced water demand, there will be approximately nine times more reductions in GHG emissions from end-users than from water and wastewater systems combined.

Energy Costs
The energy cost for water includes SCWA’s wholesale supply ($1.2 million per year), and Santa Rosa’s wells and booster pumps ($320,000 per year). Costs for the wells will increase dramatically in the future unless water efficiency measures are implemented (as described for Figure 4). The energy cost for wastewater includes all electricity and natural gas purchased from PG&E, but not biogas since it has no energy cost. The energy cost for end-users is for electricity and natural gas purchased from PG&E for water-related energy.

Water-related energy costs for end-users are approximately six times larger than the energy costs for Santa Rosa’s water and wastewater systems, which implies that end-use efficiency improvements would generate much larger savings than improvements in water/wastewater operations. Examination of unit energy costs reveals that on average, for each gallon of reduced water demand, there will be approximately six times more savings for end-users than for the water and wastewater systems combined. This, in turn, suggests that if the obstacles limiting widespread customer participation in existing water efficiency programs were removed, the resulting end-use energy savings could be used to offset implementation costs.

Efficiency Projects in the Wastewater System
The Santa Rosa Utilities department has implemented numerous energy efficiency improvements in its water and wastewater systems. Figure 8 shows the energy reductions for upgrades at the two main reclaimed wastewater pump stations—and the reductions in GHG emissions (based on PG&E’s 0.489-pound CO2-per kilowatt-hour intensity factor in 2005).

Figure 9 shows that even with only a modest financial incentive from State energy efficiency programs, and without any increases in electricity rates, there will be a 7.4–year simple payback period from the project. A life cycle evaluation, including CEC loan conditions and electricity rate escalation, demonstrated that cash flow for the project will be always be positive (i.e. during the 10-year loan period, electricity savings will always be larger than loan repayment).

From a GHG reductions perspective, the life-cycle analysis showed that $476 will be saved for every ton CO2 reduced. Similarly, a 2003 upgrade of aeration blowers at the wastewater plant resulted in savings of $253 per ton-CO2 reduced. This kind of result—short payback periods and saving money while reducing GHG emissions—is common for many energy efficiency projects.

Although the energy efficiency projects at water/wastewater facilities can be very cost-effective, they do not reduce GHG emissions nearly enough to meet GHG reduction targets—neither for the facilities themselves, nor for the urban water cycle as a whole. For example, the 200-ton-CO2-per year reduction from the reclaimed wastewater pump upgrades is only 2% of the GHG inventory for the wastewater plant—and only 0.2% of total GHG emissions for Santa Rosa’s urban water cycle.

The Sonoma County Community Climate Action Plan (CCAP) reveals that a 46% reduction was already required by 2005 to meet Santa Rosa’s GHG reduction target. This implies the need to immediately find projects to reduce GHG inventory by 4,400-ton CO2 per year in the wastewater system—22 times more than the reclaimed wastewater pump upgrades. Based on the GHG emissions shown in Figure 5, 52,000-ton CO2 per year of GHG reductions were already needed in 2005 across the entire urban water cycle. Several times more than that will be needed to reach the AB-32 target for 2050 (80% below 1990).

End-Use Efficiency Improvements
Although the water-related end-use GHG emissions are large, they also represent the largest opportunity for feasibly meeting reduction targets. As shown in the previous wastewater system examples, water and energy efficiency improvements have short payback periods, and their financing can be structured for positive cash flow while reducing GHG emissions. However, restricting investments in efficiency only to measures with short paybacks severely limits the effectiveness of most existing efficiency programs. Requiring short paybacks from efficiency projects is arbitrary in comparison to supply-side projects that are financed through rate increases without any expectation of savings. A more balanced approach would be to provide incentives for efficiency measures when they (a) have lower marginal costs (dollars per MG or dollars per ton-CO2) than the supply side projects they avoid, and (b) ensure more reliable water service than severely constrained supply sources.

After efficiency improvements, investments in renewable energy needed to provide the remaining reductions to meet GHG targets will be smaller and more cost-effective, than first attempting to meet GHG reduction targets with renewables alone. A balanced strategy would be to start immediately with efficiency while developing plans for optimally sized (and located) combinations of renewable energy projects.

An evaluation of high-performance indoor water efficiency products and measures in cities in the USA and abroad shows that reductions of 30–40% in water demands through efficiency are feasible—but only with an implementation program that enables high levels of customer participation. For Santa Rosa and other cities supplied by SCWA, such large reductions would offset the 32% increase in water demand due to anticipated population growth by 2020—and could significantly reduce large water and wastewater infrastructure expansion costs. Although detailed evaluation of infrastructure cost reductions and implementation costs for efficiency measures is still needed to confirm cost-effectiveness, it already appears that water efficiency could stabilize urban water cycle GHG emissions—even with anticipated population growth.

High-performance water efficiency improvements may be achieved with relatively little direct budget impact on water and wastewater agencies based on an implementation system that (a) removes the market barriers experienced today, (b) recognizes energy cost savings for customers, and (c) can utilize municipal bond financing to capitalize efficiency investments. A key objective in a high-performance program is large participation—more than 50%—from existing customers to obtain immediate climate protection results. All these elements were combined in a specific evaluation of how to develop a high-performance indoor water/energy efficiency program for the City of Santa Rosa.

Adding widely available outdoor efficiency measures to the measures evaluated in the indoor high-performance program, and assuming high participation rates achievable when market barriers are removed, indoor water use (and wastewater) could be reduced by 26% and outdoor use by 19%—for an overall reduction of 24%. This would reduce daily water use per person (gallons per day, per person) from 133 gallons per day (gpd) per person to 102 gpd per person.

To provide perspective, 133 gpd per person is lower than the baseline for Santa Rosa’s region (Region 1) in the 20x2020 Program and far lower than the statewide baseline of 192 gpd per person; it is even lower than the target of 135 gpd per person required for 2020. From a global perspective, 102 gpd per person would be in line with the current average of 99 gpd per person in Melbourne, Australia, which is however, facing a water supply shortage of 4–15% by 2020, and 10–40% by 2050.

Figure 10 superimposes the results of the high-performance indoor efficiency program on the GHG emissions shown in Figure 5. This reduces a total of 25,000 ton CO2 per year across the urban water cycle. The 23,000-ton-CO2-per year reduction by end-users alone is larger than the total GHG emissions from the water and wastewater systems combined. In other words, the efficiency program essentially wipes out the carbon footprint of the water and wastewater facilities.

The average cost of the indoor residential efficiency package is $1,800 per home, but instead of hoping that a small incentive and the 4-year payback will encourage participation, the high-performance program offers free installation. Payment is added to the homeowners’ utilities billings in a way that ensures $200 per year net savings from the first year. Similar packages could be developed for site-specific measures at commercial, institutional, and industrial facilities. Besides repayment from customers, the water and wastewater utilities save on their own energy costs. An even larger economic benefit will likely result from avoiding infrastructure expansion costs—and rapidly approaching fees for carbon emissions.

After implementing the efficiency measures, Figure 10 shows that solar installations could further reduce the remaining water-related end-use GHG emissions (these installations would be much smaller than required without first implementing efficiency). For example, solar thermal systems could easily displace 27,300 tons CO2 per year from natural gas, and solar photovoltaic could displace 1,950 tons CO2 per year from electricity. Efficiency improvements followed by solar energy installations could reduce water-related GHG emissions by 47% across the entire urban water cycle.

Only 4% more would be needed to meet California’s mandated GHG target of returning to 1990 emissions by 2020, and this could easily be achieved with improvements in the wastewater system—especially for the biogas/cogeneration system. To approach AB-32’s 2050 target of 80% reduction below 1990 GHG emissions, it will be necessary to pay close attention to site-specific details in order to capture large opportunities for efficiency improvements—especially in commercial/industrial settings. It will also be necessary to develop high-performance implementation programs for solar and other low/no carbon energy generation. It is conceivable that meeting the 2050 target will be just as cost-effective as meeting the 2020 target when upstream and downstream infrastructure investments are included in the analysis.