Aquifer Recharge, Storage, and Recovery - Southwest Hydrology ...

Hydrogeology and ASR DesignGreg Bushner – Vidler Water CompanyToday there are many choicesfor the design and operation ofan aquifer storage and recovery(ASR) facility, since such facilitiescan serve a variety of needs. An ASRfacility has the capability to recharge,store, and recover all or a portion of thesource water recharged regardless ofthe recharge method. It might consistof shallow or deep infiltration basins,vadose zone wells, direct injection wells,wells that can both inject and recoverwater, or a combination thereof.Evaluating Land and WaterThe selection of a facility initially isdriven by the available source water,available or needed land, and theplanned end use of the water. What isthe source water? It may be wastewatereffluent, seasonal surface water, vested orcertificated water rights, or another watersource. Once identified, its chemistrymust be evaluated to determine if itwill need pretreatment or if the qualityis adequate for the project method.Next, how much land is needed and ofwhat type? A vadose zone, injection,or dual-use (recharge/recovery) wellin an urban setting has a significantlysmaller footprint than an infiltrationbasin; however, the unit land costmay be much higher. How will thefacility design be incorporated into theavailable land or vice versa? Is the landundeveloped or has it been disturbed?Finally, what is the end use of thestored water—what type of recharge/recovery cycle will be needed?How long will the water be storedbefore it is recovered, and howwill it be accounted for untilit is recovered? Answeringthese questions will guidethe project design andbudget through thenext phases of projectplanning. A life-cycle cost analysis isalso useful to determine the appropriaterecharge method and its application toa specific project and water source.Now the HydrogeologyNo matter what type of recharge methodis decided upon, all ASR projects requirecharacterization of the hydrogeologicconditions in the vicinity of the projectsite. This begins with identifying theland use and land owners, and anyexisting wells and their use, proximityto the project site, water source,conveyance options, and water quality.Baseline hydrologic data are critical topredict future impacts from the project.These data should include a water-levelelevationcontour map showing directionof groundwater flow and hydraulicgradient, and determination of storagecapacity or transit capacity of the vadosezone. Are water levels at surrounding wellsincreasing, decreasing, or both? Areasof subsidence should be mapped relativeto the project location. Baselinegroundwater chemistry data should becollected if they are not already available,and constructing one or more projectmonitoring wells may be warranted.Data NeedsDepending on the type of recharge methodto be used, additional hydrogeologicdata may be needed. Infiltration basinfacilities require a detailed investigationof the surficial soils and vadose zone.Soil samples should be analyzed forlithologic characteristics such as grainsize, distribution, intrinsic permeability,residual moisture content, and pore-waterchemistry. A similar investigation shouldbe conducted in the vadose zone throughuse of soil borings strategically locatedto represent site conditions for the projectarea. The goal of this investigation is toidentify positive attributes of the soils andvadose zone, such as high porosity andpermeability that would be conducive fora particular recharge method, as well asnegative attributes such as the presenceof subsurface impermeable layers orAerial view of the Vidler Recharge Facility, aprivately-owned project in western Arizona thatcontains over 460 acres of surface infiltration basins.Photo: Kenney Aerial18 • May/June 2008 • Southwest Hydrology