After years of work, Aspect recently finished a pilot test that will help the City of White Salmon (City) implement one of only a handful of Aquifer Storage and Recovery (ASR) systems in the state. ASR—essentially taking advantage of natural geology, man-made wells, and climate patterns to create an underground reservoir—is an attractive water supply concept. It’s relatively low-cost (compared to building an above ground reservoir), has a small environmental footprint, and in arid climates reduces losses from evaporation. However, permitting of an ASR system involves overcoming technical operational hurdles that hinge on two key questions:
- How much water are you getting back? (recoverability)
- Will injection or withdrawal affect water quality? (Washington State Department of Ecology’s (Ecology) antidegradation policy)
During Aspect’s monthly technical exchange series, Aspect’s Tim Flynn, Joe Morrice, and Jared Bean gave a presentation and explained Aspect’s experience with ASR in the state and what it means for future water supply.
Creating an Underground Reservoir
Essentially, this concept uses nature’s pre-built reservoirs (aquifers) to create an underground reservoir or tank to store water when it’s plentiful and withdraw it when it’s scarce. In water resources terminology, ASR typically uses seasonally available surface water to help recharge—or move water from the surface into the ground—an aquifer. It does this by capturing excess water during the winter and spring months, when surface water flows are generally high and water system demands low, and injecting that water via a well (or engineered infiltration basin) into the underground aquifer. During the dry summer season, water is withdrawn for use when surface water flows are low and water system demand is at its peak.
Figure 1. ASR System Cycle
Source: www.groundwatergeek.com
The basic components of an ASR system include:
- The right kind of Aquifer. Bedrock or unconsolidated aquifers may both be suitable for ASR, but ideally the target aquifer would be bounded by geologic faults or other barriers that limit the flow and loss of stored water in storage before it is recovered from the aquifer.
- Source water of suitable quality. This is typically surface water from rivers or streams, but with the appropriate water quality treatment and permitting process can include stormwater runoff, remediated groundwater, reclaimed water, and industrial process water. These sources should be chemically compatible with ambient groundwater and do not contain constituents that would violate the State groundwater quality standards, including the antidegradation standard, or can be treated to meet these standards.
- A way to put water in and to take it out. This means infrastructure for ASR source water diversion, treatment (as needed), conveyance, and injection to the subsurface through one or more wells, with subsequent pumping to recover stored water.
ASR in Washington State
Although ASR has been in practice for many years in other parts of the nation, it’s a fairly new concept to northwestern states that have typically relied on mountain snowpack as a form of water storage to provide supply during summer months. Because of Washington’s recent drought and the scarcity of water in many surface water basins, especially during summer low flows, ASR’s popularity is growing. In Washington state, there are approximately 9 projects in development. The existing policy framework for ASR in Washington state came about in the early 2000s with two developments:
- In 2000, the state’s expansion of the definition of “reservoir” to include “…underground geologic formation(s)… as part of an (ASR) project” (RCW 90.03.370); and
- In 2003, Ecology’s adoption of the ASR rule (WAC 173-157) which established standards for ASR projects, including standards related to water rights, water quality, water treatment, and geotechnical impacts.
Aspect is currently working on three ASR projects in Washington, Arizona, and California. Our ASR projects locations in the PNW currently span western, central, and southern Washington and include both basalt (bedrock) and unconsolidated, glacial outwash host-aquifers.
Figure 2. Groundwater Recharge Projects in Washington State
(ASR = Aquifer Storage and Recovery; SAR = Shallow Aquifer Recharge)
Source: http://www.ecy.wa.gov/programs/wr/asr/asr-home.html
City of White Salmon ASR
The City has historically relied on surface water from Buck Creek for the City’s water supply. In 2002, the City switched to groundwater wells as their primary supply but with decreasing well yields and limited water rights along with the WA Department of Health issuing a moratorium on new connections the City is seeking new alternatives to boost their water supply. One of these alternatives is to explore the possibility of ASR. Aspect has helped the City pursue this option by coordinating with Ecology throughout the process. After receiving an Ecology grant, and approval of the feasibility study, an AKART analysis was completed which secured Ecology approval for pilot testing.
The most recent pilot test involved the injection of 32 acre-feet of water over the span of 53 days (135 gallons per minute, or about 200,000 gallons per day). With the current well and conveyance configuration the City can expect to inject, store and recover about 100 acre-feet per year, which provides approximately 25% of peak (summer) demand. These numbers are with current operational constraints of a gravity fed non-continuous injection. If the City upgrades to pressurized injection (continuous) then they can expect more than 300 acre-feet per year, or about 74 percent of peak summer demands.
Figure 3. Conceptual Hydrogeologic Model of White Salmon Project Area
Source: Aspect Consulting
One major concern is to make sure the quality of the water isn’t degraded while in ‘storage’. The pilot test showed the formation of disinfection byproducts (DBPs) from treating the injected water with chlorine prior to injection. Ecology’s antidegradation policy says injected water cannot impact native groundwater or source water quality. Groundwater quality monitoring throughout the pilot test showed that DBPs did form in the injection water, but quickly dissipated in the aquifer.
The other hurdle is the recoverable quantity of water or the amount of water recouped from what was originally injected, i.e., “recoverability”. Ecology requires that the same water that is stored be recovered, and any stored water that migrates past the capture zone of the recovery well is no longer available for use. Aspect has estimated, based on water quality monitoring and aquifer hydraulic response to injection and recovery, that the White Salmon ASR system has 85% recoverability of injected water.
Aspect is engaged in ongoing discussions and interactions with Ecology’s water quality and water rights permitting programs regarding these issues and how to efficiently complete the required permitting while protecting groundwater quality and water rights, including instream flows for the City of White Salmon and other ASR projects.
The interpretation and understanding of water quality and water right permitting requirements for ASR projects is evolving as project proponents advance their plans through Ecology. Aspect will continue to work with clients across the state to use ASR as a viable option in providing water where and when it’s needed most.