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.