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> > > > > > > > >

Departments

6 On the Ground• Middle Rio Grande Basin Study• Mosquito Abatement in Tucson• Cloud Seeding in Santa Barbara

9 PeopleAwards, promotions, and newpositions.

10 GovernmentNews from the legislature, agencies,and the courts.

12 State of the NationsUpdates and news ofreservations and tribes

14 R & DWhat’s happening in research,education, and technology.

31 The Company LineWhat’s new in the consulting world: project announcements,company news.

32 Business Directoryand Job Opportunities

33 The Society PageActivities and announcements fromassociations, NGOs, and non-profitorganizations.

35 In Print“Water Follies” reviewed by GaryWoodard, Ph.D..

37 Product Announcements andSoftware ReviewSWAT reviewed.

38 The Calendar Meetings, conferences, training, andshort courses.

A bimonthly trade magazine for hydrologists, water managers, and other professionals working with water issues.

In this issue, we look at the use of isotopes to determine groundwater ages and flowpaths. The original title for this issue was “Tracking Ancient Waters,” but as we startedgathering the feature articles, we realized that much of the water being tracked wasactually relatively young. The nuclear bomb testing of the 1950s and 1960s wasdestructive in so many ways, however it did produce many isotopes useful in hydrologytoday. Alternatively, ancient waters are also being identified by isotopes in severalSouthwest basins.

As these articles demonstrate, the information we can gain from isotopes is impressive,as is the magnitude of what we’re working with. One tritium unit is equal to one atomof tritium in every 1018 atoms of “regular” hydrogen, a difficult concept to grasp. Thedistance from Earth to the moon is on the order of 1010 inches, to the sun is 1012 inches,and our orbit around the sun is some 1013 inches. As little as 0.6 tritium unit, thecurrent detection limit, can tell us something about the last time groundwater was incontact with the atmosphere, or when it was recharged.

We are grateful to our features authors for their hard work on these articles.

As the expression goes, all good things must come to an end. Beginning with theMay/June 2003 issue, subscriptions to Southwest Hydrology will cost $35 per year (6issues). Individual and extra copies will cost $10 each. We are pleased by the steadygrowth of our advertising support. We have shown that this is a valuable endeavor, andnow we need to develop it into a viable product. Don’t wait until the last minute andrisk missing an issue – send us your check using the envelope inserted in this issue.

Our thanks to all the contributor listed on opposite page, and as always, we welcomeyour comments and ideas.

Betsy Woodhouse

Editor

Inside This Issue

Cover: Mushroom cloud from Ivy Mike, the first truehydrogen bomb tested. The Nov. 1, 1952 explosion obliteratedthe island of Elugelab in the South Pacific and producedhuge atmospheric releases of radioactive isotopes, many ofwhich are used extensively as environmental tracers. Imageoriginally from Los Alamos National Laboratory, obtainedthrough the High Energy Weapons Archive atnuketesting.enviroweb.org/hew/Usa/Tests/Ivy.html.

16 Dating Groundwater with IsotopesBrenda Ekwurzel, Ph.D.

An introduction to the isotopes that areused to determine residence time,sources for age-dating isotopes, andguides for assessing which isotopes areappropriate with regard to their age-range, sample volume size, andanalytical measurement.

19 Isotopic Tracers in Groundwater HydrologyRichard W. Hurst, Ph.D.

What isotopes are commonly used forwhich applications? How and where arethey analyzed? What are typical costs?Isotopes are powerful tools, but theymust be carefully applied.

22 Locating Recharge Zones with Isotopes C.J.Eastoe, Ph.D

Does recharge to the regional aquiferoccur uniformly along the washes? Therelative rates of water movementbetween flood-plain sediment and theregional aquifer have been determinedsemi-quantitatively using radioactiveisotopes with appropriate half-lives.

24 Use of Isotopes to EstimateGroundwater Age and Flow PathRoy L. Herndon, R.G., Greg D.Woodside, R.G., M. Lee Davisson, andG. Bryant Hudson, Ph.D.

The distinct oxygen isotopic character ofColorado River water allowed it to beused as a tracer to determinegroundwater flowpaths. Tritium/heliumisotopes provided groundwater ages andrecharge rates.

26 Isotope Investigations in the Middle Rio Grande Basin Compiled from U.S. Geological Surveyreferences

Isotope analyses allowed significantregional patterns of groundwater age andcharacter to be mapped throughout theMiddle Rio Grande Basin. These patternsappear to reflect recharge from the basinmargins and from the Rio Grande.

29 Isotope Hydrology Web and Print ResourcesJames F. Hogan

An annotated listing of helpful Web sitesand textbooks to learn more aboutisotopes and their applications inhydrology.

> > > > > > > > >

Tracking Groundwater with IsotopesIsotopes can be powerful tools in the field of hydrology, able to provide definitiveanswers to questions of recharge and flowpaths that many thousands of dollars’ worthof aquifer tests, new boreholes, and models may not. But what are isotopes, really,and how does one begin to figure out which ones could be applied in a particularsetting? Several experts in the field discuss interpretation, analyses, and costs, andpresent case studies to illustrate how they have been applied successfully inSouthwest basins. And, if you want to learn more, we provide the references to takeyou further.

Southwest HydrologyPublisher and Editor

Betsy Woodhouse, Ph.D.

Publications and Business ManagerHoward Grahn

Features EditorAlison Bolen

Assistant EditorsLeslie Ferre

Alex Etheridge

Graphic DesignDebra Bowles/Sun People Studios

ContributorsBrad Baum

Robert S. Bowman, Ph.D.Martha Conklin, Ph.D.

M. Lee DavissonC. J. Eastoe, Ph.D.

Brenda Ekwurzel, Ph.D.Bryan Grigsby

Deborah HathawayRoy L. Herndon, R.G.

James F. HoganG. Bryant Hudson, Ph.D.Richard W. Hurst, Ph.D.

Paula Jo LemondsFidel Lorenzo

John E. McCray, Ph.D.Talon NewtonPage PegramBruce Prior

Elizabeth RobbinsKris Schafer

Rolf Schmidt-PetersenNabil Shafike, Ph.D.

Laura WilcoxChristopher Wolf

Gary Woodard, Ph.D.Greg D. Woodside, R.G.

Printed in the USA by Arizona Lithographers

Published by Woodhouse Press, L.L.C., copyright © 2003

Southwest Hydrology is printed six times per year byWoodhouse Press, L.L.C. All rights reserved. Limited

copies may be made for internal use only. Credit must begiven to the publisher. Otherwise, no part of this

publication may be reproduced without prior writtenpermission of the publisher.

SubscriptionsSubscriptions to Southwest Hydrology are available free of

charge through March 2003. As of May 2003,subscriptions are $35 per year for six issues.Send

subscription requests, checks, and inquiries to SouthwestHydrology, PO Box 65690, Tucson, AZ 85728; or send

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Southwest Hydrology, PO Box 65690, Tucson, AZ 85728,phone (520) 615-2144 or toll-free (866) 615-2144, or

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Editorial ContributionSouthwest Hydrology welcomes contributions of news,

project summaries, product announcements and items forThe Calendar. Send submissions to Southwest Hydrology,

PO Box 65690, Tucson, AZ 85728; or email tomail@swhydro.com. Visit www.swhydro.com for additional

guidelines for submissions.

Web Sitewww.swhydro.com

Sharla Schuller, manager

Upcoming Features Riparian RestorationDesalinationGroundwater/Surface Water RegulationColorado River Delta

Groundwater/Surface WaterMonitoring in the Middle RioGrande BasinRolf Schmidt-Petersen, Nabil Shafike andPage Pegram – New Mexico Interstate StreamCommission

Deborah Hathaway and Bryan Grigsby – S. S.Papadopulos and Associates, Inc.

Robert S. Bowman, Laura Wilcox, and TalonNewton – New Mexico Institute of Mining andTechnology

Kris Schafer – United States Army Corps ofEngineers

A groundwater-surface water monitoringprogram has been initiated as part of anextensive regional hydrologic assessmentbeing undertaken by the New MexicoInterstate Stream Commission (NMISC).The NMISC program is focused oncharacterization of groundwater/surfacewater interactions, and includesgroundwater and surface watermonitoring; characterization of seepageconditions; drilling, sampling and aquifertesting; and hydrologic modeling. Data

and analyses developed through thisprogram will augment the understandingof hydrologic conditions important formanaging water use and maintainingcompliance with the Rio Grande Compact,the Endangered Species Act and meetingdiverse water needs in this region. TheNMISC initiated this program in thesummer of 2000, and has continued workover the past two and a half years, usingstate and federal funding to support aunique team including the expertise ofstate, private and university entities. TheU.S. Army Corps of Engineers (USACE)joined the effort as a 50/50 funding

partner under their Water ResourceDevelopment Act (WRDA-Section 729)authority. The study area extends along theRio Grande from San Acacia DiversionDam north of Socorro to the ElephantButte Reservoir; it includes the Low FlowConveyance Channel (LFCC), whichparallels the Rio Grande in this reach ofthe valley.

In the first year of this program, fieldinvestigation focused on seepage runs ofthe river, canals and drains; a preliminarygroundwater model that dynamically linkssurface water and groundwater using

O N T H E G R O U N D

Site map with locations of well transects to be completed in spring 2003.

See Middle Rio Grande, page 13

Mosquito Abatement at theSweetwater WetlandsBruce Prior — Tucson Water

In the six years since construction of theSweetwater Wetlands began, the City ofTucson has significantly reduced themosquito population at the site. The siteincludes 17.5 acres of constructedwetlands, 14 acres of recharge basins, anda recurring mosquito problem. TheSweetwater Wetlands was initiallyconstructed to treat filter backwash waterfrom the City’s Reclaim Water TreatmentPlant but also has the advantages ofproviding a wildlife habitat and publiceducation opportunities.

The treatment plant, built in 1984,produces reclaimed water by filteringsecondary effluent through granularsilica/carbon filters. The filters plug upperiodically and plant operators mustbackwash the filters to clean them. TheSweetwater Wetlands is designed toreceive and treat the backwash waterproduced during this filter cleaningprocess. The backwash water, high insuspended solids, drains by gravitythrough settling basins and wetland ponds,and into adjacent recharge basins.

The wetland ponds contain areas of deep,open water alternating with zones of

shallow water planted with bulrush andcattail. The shallow vegetated zones have,over the years, been prone to producemosquitoes. The species of mosquito thatproliferate in a wetland environment arepotential carriers of encephalitis virus.Since the wetland brings together people,birds, and mosquitoes, creating a potentialpublic health risk, the city has undertakena rigorous mitigation program to controlthe mosquito population.

Water Department staff monitor mosquitopopulations weekly at the SweetwaterWetlands by setting carbon dioxide traps.University of Arizona EntomologyDepartment staff analyze the trappopulations and provide speciesidentifications and total numbers. Since

July 1998, the city has contracted to havegranular mosquito larvicide appliedweekly to the water at the SweetwaterWetlands using a remote controlledhelicopter built by Yamaha. The larvicideis specific to mosquito larvae (it isdesigned to dissolve at the pH of themosquitoes mid-gut) and is therefore non-toxic to the many beneficial aquaticinsects present at the wetlands.Additionally, during periods of higher trapcounts, the city contracts to have thewetlands treated using a truck-mountedaerial fogger that produces an Ultra LowVolume (ULV) mist. The product appliedis a synthetic pyrethroid (Anvil 2+2) witha very low toxicity that has been approvedby the U.S. Environmental ProtectionAgency for use in aquatic environments.

Remote-controlled helicopter used to distribute mosquito larvicide at Sweetwater Wetlands.

See Mosquito Abatement, page 13

Sweetwater Wetlands

Cloud Seeding in SantaBarbara CountyThe Santa Barbara County Public WorksDepartment prepared to begin a cloudseeding program in November in order toaugment their water supply. Cloudseeding is not new to this agency; theyfirst began weather modificationactivities in 1948. Precipitation fromcloud seeding has provided the countywith infiltration of significant amounts ofwater into groundwater basins, increasedrunoff into reservoirs, and irrigatedgrasslands and crops.

How It WorksPrecipitation forms when supercooledwater vapor in a cloud contacts a particleor nuclei. The vapor freezes to the particle

and forms an ice crystal. The crystalgrows larger as more vapor contacts it,and if it becomes large enough, it falls outof the cloud as precipitation. The existenceof supercooled water vapor constitutes themost opportune conditions to seed cloudsfor rainfall augmentation purposes. It ispossible to seed clouds withoutsupercooled water vapor under certainmeteorological conditions, though.

Typically, storms in Santa Barbara Countyhave much more moisture available thanthere are condensation nuclei. Therefore,the county’s weather modificationprogram focuses on adding morecondensation nuclei to clouds to increaserainfall. While a number of substanceshave been shown to work for cloudseeding, silver iodide (AgI) is used mostcommonly. Both aerial and land-basedmethods are used to inject silver iodideinto clouds. In aerial seeding, silver iodidegenerators are mounted on the wing tips ofan airplane that flies directly into the mostproductive part of the cloud. Land-basedgenerators are placed at the top ofmountains where updrafts carry the silveriodide into passing clouds. The generatorsburn a solution of silver iodide andacetone that releases the seeding agent in asmoke form.

In Santa Barbara County, the cloudseeding program is operated between

See Cloud Seeding, page 30

Mountaintop cloud seed generator near Twitchell Reservoir, northwest of the town of Santa Maria, California

Robert McMillon NamedPresident of WaterEnvironment FederationRobert McMillon, of Fort Worth, Texas, hasbeen elected President of the WaterEnvironment Federation (WEF), aninternational technical, scientific, andeducational water quality organization. Hewas elected to the post during WEFTEC2002, the Federation's annual technicalconference and exposition. McMillon iscurrently the Assistant Water Director,Pollution Control Division, for the City ofFort Worth. He joined the WEF in 1962 andhas held positions on various committeesand the Board of Directors since 1995. Inaddition, he has won several WEF awardsand was the principal contributing author oftwo WEF manuals of practice. McMillon isa certified water utilities instructor and holdsthe highest operator's certification offered bythe State of Texas. The Water EnvironmentFederation is a not-for-profit technical andeducational organization with members fromvaried disciplines who work toward thepreservation and enhancement of the globalwater environment. Visit www.wef.org/

Greg Wallace JoinsMontgomery & AssociatesGreg Wallace, who previously held positionsas Chief Hydrologist and Assistant Directorof Arizona Department of Water Resources(ADWR), has recently joined the staff ofErrol L. Montgomery & Associates, Inc. intheir Phoenix-area office. Mr. Wallacereceived a Bachelor of Science degree ingeology from the University of South Dakotaand served as the Director of the OklahomaState Water Resources Division beforejoining ADWR in 1986. His knowledge andexperience managing a broad range ofADWR programs and investigations will bevaluable in addressing water resource needsof clients throughout Arizona.

Montgomery & Associates is a consultingfirm with more than 20 years of experienceaddressing groundwater problems in Arizonaand other states and countries. The principal

office of Montgomery & Associates islocated in Tucson; branch offices aremaintained in Scottsdale and Flagstaff,Arizona and Santiago de Chile. Visit www.elmontgomery.com or call (480) 948-7747for more information.

John Ward Opens NewConsulting PracticeJohn Ward, R.G., formerly an AssociateHydrologist at Hydro Geo Chem, Inc., hasrecently opened a private groundwaterconsulting practice in Tucson. Mr. Ward hasmore than 25 years of professionalhydrogeologic experience in the West, theSoutheast, and the South Pacific, and hasspecialized in site cleanups, groundwaterresource assessments, geochemistry, andwater rights adjudications. In his newpractice, he will focus on litigation support,water rights, peer review, and groundwatermodeling. He can be reached at (520) 490-2435 or Ward_Groundwater@cox.net.

Jan Oster Transfers toMissouri DESI FacilityJan Oster recently moved to St. Louis,Missouri to manage the Drilling EquipmentSupply, Inc. (DESI) facility in that area. Shehas been very active and supportive of

several trade associations and events in theSouthwest including the ArizonaHydrological Society, Mountain StatesGround Water Expo, National Ground WaterAssociation, and the Arizona Water WellAssociation. Oster will attend eventswhenever possible, but in the meantime, shecan be reached at (800) 735-3374 or atjanoster@sprintmail.com.

Paul Johnson of ASU NewEditor for NGWA PublicationPaul C. Johnson has been named the neweditor for the National Ground WaterAssociation (NGWA) journal, Ground WaterMonitoring and Remediation. A tenuredassociate professor and assistant chair of theDepartment of Civil Engineering at ArizonaState University, Johnson will serve as editorbeginning Jan. 1, until Dec. 31, 2005. Johnsonhas been active in groundwater monitoring andremediation for the past 15 years, includingindustry, private consulting, and academicpositions. His principal areas of research andteaching include chemical migration and fatein the environment, environmental riskassessment, aquifer restoration andmanagement, and groundwater hydrology. Hewon NGWA’s Outstanding Ground WaterRemediation Project Award in 2001.Visit www.ngwa.org

P E O P L E

USGS Introduces Web-Searchable Database ofEnvironmental MethodsOn the 30th Anniversary of the CleanWater Act, the U.S. Geological Surveyannounced a new standardized, web-searchable database of environmentalmethods called the NationalEnvironmental Methods Index (NEMI).The database will allow professionals whomonitor water quality to compare datacollection methods at a glance and find themethod that best meets their needs. Thetool also allows monitoring data to beshared among different agencies andorganizations that use different methods atdifferent times. The database wasdeveloped in conjunction with the U.S.Environmental Protection Agency andother partners in the federal, state, andprivate sectors. The NEMI databasecontains method summaries of lab andfield protocols for regulatory and non-regulatory water quality analyses. To date,

NEMI contains more than 600 chemical,physical, and microbiological methods.For each method, NEMI provides asummary of the procedures andperformance data needed to assessimplementation requirements.

For more information or to use the database, visit www.nemi.gov.

Info on USGS RemediationProjects Available Online A new series of Web pages is availablecontaining information on U.S.Geological Survey (USGS) projects andactivities related to the remediation ofcontaminated sites. The projects arecategorized both by type, includingtesting of remediation technologies,natural attenuation evaluation,performance monitoring, and sitecharacterization; and by contaminant.This is the first time that this USGSinformation has been available in one place.

The series of web pages and links issponsored by the USGS's ToxicSubstances Hydrology Program.

Visit toxics.usgs.gov/topics/remediation.html.

Arizona Department of WaterResources Revamps DrillingPermits, Licensing ProceduresIn December, the Arizona Department ofWater Resources (ADWR) planned tounveil its new online applicationprocedure for permits for drillingmonitoring and domestic wells, whichaccount for approximately 70 percent ofthe 8,000 new wells drilled per year in thestate. When the application is up andrunning, licensed well drillers will be ableto log on to a secure site, fill out theappropriate well design and locationinformation, affirm that the well meetslocal zoning requirements, provide a creditcard number, and print out anauthorization to drill. The original paper

G O V E R N M E N T

version of the Notice of Intent to Drill isstill available, but the wait forauthorization is, and will continue to belong, due to extensive budget cuts and lossof personnel.

After the well is drilled, drillers are stillrequired to submit the driller’s log andwell completion report to ADWR. Untilthat paperwork is processed, the well willnot be legally permitted or assigned aregistration number. ADWR personnelwill review the completion reports andenter the information into the Web-accessible database.

ADWR licenses between 280 and 320drillers in the state each year. Thelicensing procedure consists of a writtentest for the initial license and a yearly feethereafter. Fall 2002 budget cutseliminated the ADWR licensingdepartment, but that does not meanlicensing will no longer occur. ADWR iscurrently exploring options for out-sourcing the testing and renewal procedureand has until June 30, when licensesexpire each year, to come up with asolution. The agency is also looking intoalternative ways to test new drillers priorto June 30.

For more information, visit www.adwr.state.az.us

Metropolitan Water Districtand Palo Verde Farmers Reach Agreement on Water Transfer ProgramOn Oct. 22, California's MetropolitanWater District (MWD) announced that itsboard of directors finalized a long-termprogram with farmers in the Palo VerdeValley. The agreement states that thefarmers agree to set aside a portion oftheir land, rotate their crops, and transfersaved water to urban Southern Californiaon an annual basis.

Metropolitan's board authorized thedistrict to pursue agreements withindividual farmers in the Palo VerdeIrrigation District that will secure 8 to 36billion gallons of additional water eachyear for 17 million Southern Californians.Under the approved program, Palo Verde

Valley farmers will stop irrigating from 7to 29 percent of their land in any year atthe request of Metropolitan, making25,000 to 111,000 acre-feet of wateravailable for urban consumers.

The land taken out of production will bemaintained and rotated once every one tofive years. The maximum amount offarmland taken out of production in anyyear will be 26,500 acres. For each acreset aside as part of the program, farmerswill receive a one-time payment of $3,170for signing up and $550 annually.

Ronald R. Gastelum, Metropolitan's chiefexecutive officer, said "This crystallizesMetropolitan's resolve to assure that theCalifornia plan continues to make progresstoward allocating water from the ColoradoRiver between the cities and agriculturalareas and preventing future lawsuits overColorado River water entitlements."

Visit www.mwd.dst.ca.us/mwdh2o/

California Governor Signs Billto Prohibit Nuclear Dump Site On Sept. 12, California Governor GrayDavis signed bill AB 2214, which limitsthe Department of Health Services (DHS)from issuing or renewing a license for thedisposal of low-level radioactive wasteunless the siting, design, construction,operation and closure of the facility meetsspecified federal and state requirements.According to this bill, DHS will make that determination.

AB 2214 also prohibits a facility fromdisposing low-level radioactive waste

using shallow land burial. Furthermore, itprohibits the proposed Ward Valleyradioactive waste disposal site fromserving as the State's facility for theSouthwestern Low-Level RadioactiveWaste Commission. The Commission,which consists of Arizona, California,North Dakota, and South Dakota, wascreated by Public Law 100-712 in 1988. Itskey duties include controlling theimportation and exportation of low-levelwaste into and out of the region. TheCommission has no authority over disposalfacility siting, which is the responsibilityof the host state of California.

For more information, visit www.leginfo.ca.gov/. The Commission’s Web site is www.swllrwcc.org

Texas Outlines Legal Positionon U.S.-Mexico Water TreatyOn Oct. 30, the Texas Commission onEnvironmental Quality (TCEQ) releasedTexas' position on the legal status of the1944 Utilization of Waters Treaty betweenthe United States and Mexico.

In exchange for 1.5 million acre-feet,which the United States is obligated todeliver each year from the Colorado Riverto Mexico, the United States is entitled toan annual average minimum of 350,000acre-feet from treaty tributaries beforeMexico's entitlement to any water. Underthe 1944 treaty, the United States iscredited one-third of the water that reachesthe main channel of the Rio Grande fromthe Conchos, San Diego, San Rodrigo,Escondido and the Salado rivers, and fromthe Las Vacas Arroyo. Mexico receivestwo-thirds of that water.

Continued on page 30

Wetland Evaluation andRestoration Along RinconadaCreek, Pueblo of Acoma, New MexicoChristopher Wolf – Daniel B. Stephens &Associates, Inc., Fidel Lorenzo – Haakú WaterOffice, Pueblo of Acoma, and Brad Baum –Daniel B. Stephens & Associates, Inc.

The Haakú Water Office at the Pueblo ofAcoma is working in conjunction with theU.S. Environmental Protection Agency(EPA) under a wetlands grant to enhance theriparian corridor along Rinconada Creek inwest-central New Mexico. Riparianinvestigations and improvements undertakenby the Haakú Water Office and Daniel B.Stephens & Associates include:• Developing a restoration plan.• Restoring riparian, stream channel, and

wetland areas.• Enhancing wildlife habitat.• Establishing day-use facilities for

education and recreation.

The Pueblo of Acoma is located withinCibola County, about 60 miles west ofAlbuquerque. Acoma established the HaakúWater Office to assist the tribal councilwith water rights, quality, and resourceissues at the Pueblo. They have beenproactive in creating water qualitystandards and establishing active CleanWater Act and Wetlands programs inconjunction with EPA.

Rinconada Creek, a tributary of the Rio SanJose, lies on the north side of the puebloalong the southwestern flank of Mt. Taylor.The creek is an ephemeral stream rechargedby precipitation, snowmelt and springs as itflows through lava flows from Mt. Taylor,Cretaceous sandstones, and colluvium.Elevations vary from about 6,650 to 7,100feet above mean sea level.

The Rinconada Creek corridor is a healthyand unique riparian system as evidenced bythe health and composition of the riparianvegetation, the condition of the stream banks,and diversity of wildlife. The quality of theecosystem at Rinconada Creek will serve as areference for additional stream assessmentand restoration activities at Acoma. Initial

assessments of the site noted the invasion bynon-native species such as Siberian Elm andTamarisk, but native species are abundant andhealthy. The riparian corridor lacks largestands of typical riparian vegetation such ascottonwood and willow but does include anabundance of Thinleaf alder. The aldersprovide bank stabilization, shade along thestream, and habitat in the canopy as well aswoody debris. Water and stream quality isgenerally very good and reflects a healthywatershed. Suspended and dissolvedconstituents are low and meet the AcomaWater Quality Standards. The creek is animportant wildlife corridor as noted by thevariety of wildlife signs from elk, deer, blackbear, mountain lions, and numerous birds.

Site assessment activities have included:• Surveying property boundaries, channel

length and cross sections. • Observing flora and fauna. • Monitoring water quality.• Performing a Stream Visual Assessment.

During the stream assessment, scientistsnoted that the creek lacks high quality

habitat for native species, so restorationactivities emphasized habitat enhancementand improvement. Following the removalof invasive species, the riparian corridor isbeing enhanced with native species ofgrasses, wildflowers, and trees to create amulti-tiered canopy. Pools and riffles arebeing created using boulders and woodydebris in conjunction with plantings toprovide habitat and shade for aquaticspecies along the stream's course.Ultimately, the area will become an outdoorclassroom for educating children and adultsabout hydrology, geology, wetlands andwildlife conservation.Contact Christopher Wolf at cwolf@dbstephens.comand Fidel Lorenzo at Haakuwater@aol.com

S T A T E O F T H E N A T I O N S

Sandstone outcrop and basalt boulders inRinconada Creek

MODBRANCH was constructed; and planswere developed for a field monitoringprogram. In the second year of theprogram, field monitoring was initiatedthrough a partnership with New MexicoInstitute of Mining and Technology(NMIMT); two graduate students atNMIMT received funding to collect dataand conduct research in support of theNMISC program objectives; modeldevelopment continued; and an extensivedrilling program to expand the monitoringnetwork was planned and initiated.

During the first year of the monitoringprogram, data were collected from a networkof 32 existing wells, generally located alongseven transects across the Rio Grande andthe LFCC (see map, p. 6). Water levelelevations in the wells, the river, the LFCC,and adjacent irrigation and drainage canalswere monitored monthly beginning inOctober 2001. Water chemistry, including 2Hand 18O, has been monitored quarterly.NMIMT graduate students have initiatedcharacterization of the chemical and isotopicsignatures and have begun to assess spatialand temporal trends.

The field data presently being collected willsoon be augmented with data from theextensive array of new monitoring wellspresently under construction. This networkwill include more than 100 additionalmonitoring wells and 25 surface watergages. Many of the new monitoring pointswill be outfitted with continuous-recordingpressure transducers. Water quality sampling will continue for chemical andisotopic analysis.

Data from this monitoring network, alongwith aquifer test and other data, will be usedby the NMISC to refine the calibration oftheir surface water/groundwater model forthe Socorro reach of the Middle Rio GrandeBasin. Additionally, NMISC/NMIMT willutilize these data to construct a highresolution surface water/groundwater modelof a sub-reach of interest within the largerstudy area.

For more information contact Page Pegram atppegram@ose.state.nm.us

Middle Rio Grande, continued from page 6

The mist droplets are micron-sized andthe ULV application rate is less thanone ounce per acre.

The graph at right illustrates how themosquito population has been broughtunder control by using these regularabatement procedures since the springof 1998, when the wetland mosquitopopulation was essentially untreated.

Contact Bruce Prior at bprior1@ci.tucson.az.us

Mosquito Abatement, continued from page 7

Long Beach Water Signs Agreement with U.S.Bureau of Reclamation to Fund SeawaterDesalination Research and DevelopmentOn Sept. 9, the Long Beach Water Department signed aCooperative agreement with the U.S. Bureau of Reclamation tobegin design and construction of a $5.3 million prototypedesalination plant in Long Beach, California. The Long BeachWater Department has developed a process for desalting seawaterusing membrane technology and, for nearly one year, it has beentesting this patent-pending process on a small scale. The departmentis now ready to begin the next phase, which involves exhaustiveresearch into every aspect of desalting seawater with an eyetowards identifying the optimum sites and processes fordesalination in Long Beach. This phase will include the fabricationof a 100,000- to 200,000-gallon per day desalination plant at theLos Angeles Department of Water and Power Haynes powergeneration station. The desalted water from this test facility will berecombined with the salt water; it will not be placed into the city'sdrinking water system.

The desalination plant will be used to demonstrate the viability ofthe process, identify the optimum pretreatment process, optimizepower consumption, and address brine disposal issues, among other

things. In addition, thorough environmental studies will beconducted in order to comply with strict state and federalenvironmental quality regulations. Design of the plant wasscheduled to begin in October. It will be located at the Haynesgeneration station in southeastern Long Beach. The subsequent andfinal phase of the project will be to bring this optimized facility on-line, targeted for 2009, producing about 9 million gallons ofdrinking water per day for the city, or enough water forapproximately 20,000 Long Beach families.

For more information visit www.ci.long-beach.ca.us/water/

EPA Releases Demonstration Bulletin onEcomat, Inc.’s Biological Denitrification ProcessEcoMat, Inc., of Hayward, CA, has developed a two-stage, ex-situ,anoxic biofilter biodenitrification process. The fixed-filmbioremediation system employs biocarriers and specific bacteria totreat nitrate-contaminated water. The patented, mixed-bed reactorretains the biocarrier within the system, thus minimizing solidscarryover. Fixed-film treatment allows rapid and compact removalof nitrate with minimal byproducts. Methanol is added as a sourceof carbon for cell growth and for metabolic processes that removefree oxygen. The resulting oxygen-deficient environmentencourages the bacteria to consume nitrate. Methanol also isimportant to assure that conversion of nitrate proceeds to theproduction of nitrogen gas rather than to a more toxic nitrite intermediate.

A demonstration of the EcoMat biodenitrification system wasconducted in 1999 at the location of a former public water supplywell in Bendena, Kansas, in cooperation with the KansasDepartment of Health and Environment. The primary contaminant inthe water is nitrate from uncertain sources ranging from 20 to 130mg/L, with low concentrations of volatile organic contaminants,particularly carbon tetrachloride, posing a secondary problem.

During the study, EcoMat's main goal was to demonstrate that itssystem could reduce incoming nitrate-N in excess of 20 mg/L to acombined nitrate plus nitrite concentration below 10 mg/L. Asecond goal of the study was to demonstrate that the post-treatmentsystem would produce treated water that would meet applicabledrinking water standards with respect to nitrate-N and nitrite-N. Thefinal effluent would also have a pH between 6.5 and 8.5, and itwould not contain turbidity of greater than 1 NTU, detectable levelsof methanol (1 mg/L), increased levels of biological material orsuspended solids. Results from the EcoMat biodenitrificationprocess were encouraging when the entire system was operating atoptimal performance. In those instances where the final combinednitrate-nitrite effluent concentration was above the regulatory limit,operational problems (mostly mechanical) were suspected as theprimary cause.

For more information, visit www.epa.gov/ORD/SITE/reports/540mr01501.htm

R E S E A R C H A N D D E V E L O P M E N T

Colorado State ResearchersCreate Drought LabReasearchers at Colorado State University(CSU) have established DroughtLab, ajoint initiative of CSU’s Water Center andthe Climate Center. This research facilitybrings together the knowledge of morethan 100 researchers from 22 academicdepartments at CSU, as well as labs anddepartments at the University of Coloradoat Boulder. Disciplines contributing toDroughtLab’s efforts include atmosphericscience, civil engineering, watershedsciences, soil and crop sciences, rangelandscience, forest science, ecology, sociology,political science, and agricultural andresource economics.

DroughtLab will serve as a framework forresearchers to collaborate and developencompassing information that helps watermanagers reduce Colorado’s vulnerabilityto drought. Outreach education, statewideCooperative Extension efforts, technologytransfer and the communication of droughtknowledge to state and local officials andthe general public will compliment thelab’s research efforts. Research will beconducted on campus and across the stateat the university’s Agricultural ExperimentStation research centers located incommunities throughout Colorado.

DroughtLab researchers will initially focuson three key areas: drought analysis andcharacterization, drought impacts andconsequences, and drought response and management.

Visit cwrri.colostate.edu/ for more information.

Plant May Provide Key toMetal Distribution in StreamElizabeth Robbins and Martha Conklin, Ph.D.– University of Arizona Department ofHydrology and Water Resources

University of Arizona and U.S. GeologicalSurvey scientists are studying manganeseaccumulation in an aquatic plant to gaininsight into metal distribution in a mining-impacted stream in central Arizona. PinalCreek, in Globe, Arizona, receivedelevated concentrations of dissolvedmanganese and other metals due toseepage of contaminated groundwater

from copper mining operations. Thecontaminated groundwater has beenintercepted, but metals, includingmanganese, cobalt, nickel, and zinc,persist in the stream. Manganese is ofparticular interest because manganeseoxides combine with other, more harmfulheavy metals and thus may aid in theirremoval from the system.

Veronica anagallis aquatica, commonlyknown as water speedwell, is a commonemergent and submergent plant in the streamchannel of Pinal Creek. Roots and shoots ofthe plant were found to have much higherconcentrations of manganese and othermetals in them than the surrounding streamwater or sediment. The researchers set out toanswer the following questions:

• Where does water speedwell accumulate most of the metals?

• Can the metal uptake account for temporal and special variations in metals concentrations in the stream?

• What is the rate of metal removal by water speedwell from metal-spiked water?

Water speedwell was collected approximatelymonthly from Pinal Creek for one year,2001-2002. Roots and shoots were separated,and the external metal concentrations weremeasured. Water speedwell was found toaccumulate substantial manganese in its rootand shoot tissues. Submerged shoots andleaves tend to have slightly higherconcentrations of manganese oxide on theirexternal surfaces, but overall, more metalswere associated with the roots than theshoots. Median values of manganeseconcentrations were 22,000 mg/kg dry root

and 1,700 mg/kg dry shoot, respectively,compared to 7,000 mg/kg dry sediment and 1mg/L in surface water.

The root to shoot ratios of manganese andnickel were found to be highly correlatedacross different plant samples. However,zinc did not show the same trend; it wasnearly always found evenly distributedbetween roots and shoots, indicating adifferent uptake mechanism. Metalconcentrations in sediment and waterspeedwell did not correlate with surfacewater concentrations, thus, water speedwelland other local factors may control both therelease and reprecipitation of manganeseoxides in the stream.

To determine metal uptake rates, a knownmass of plants was placed in a container withartificial surface water spiked with knownmetal concentrations. The change in metalconcentration from solution was monitoredover time. Manganese, nickel, and cobaltfollowed similar trends of an initial rapiddecrease in metal from solution followed bya slower uptake rate. As much as 50 percentof the manganese and nickel were removedfrom solution over a five-day period.

Overall, the results suggest that the primarymechanism that water speedwell providesfor enhanced metal removal is to providesurfaces conducive for precipitation ofmetal oxyhydroxides. In that capacity, waterspeedwell may play a significant role inremoving metals from solution,accumulating metals at levels well abovesediment concentrations.

Contact Martha Conklin at martha@hwr.arizona.eduor (520) 621-5829 for more information.

An effective integrator of hydrologichistory, isotope hydrology is a key tounderstanding fundamental physical,chemical, biological, and climateforcing processes occurring in awatershed.

T he measurement of theconcentrations of isotopes ingroundwater and surface water can

be incorporated into models to predictfuture responses of the watershed totrends in land-use change, waterresource management decisions, andclimate variability.

Isotope methods are useful in regionswhere more traditional hydrologic tools– such as geologic mapping of aquifer

material, piezometric data, pump tests,hydraulic conductivity measurements,major ion chemistry, and hydrologicmodels – give ambiguous results orinsufficient information. Isotopes can beused to efficiently unravel water sourcesthat have combined at the samplinglocation, and they can accuratelydetermine residence time information,which has important implications forwater resources management. If a majorurban drinking water supply well from aSouthwest basin pumps thousand-year-old water, for example, then it is miningthe groundwater resource at a muchfaster rate than natural recharge.Likewise, a consultant might use isotopeages to prove that owner A, who boughtproperty in 1965, is responsible for a

contaminant leak rather than owner Bwho bought the property in 1980.

This article serves as an introduction toisotopes that are used to determineresidence time, sources for age-datingisotopes, and guides for assessing whichisotopes are appropriate with regard totheir age-range, sample volume size, andanalytical measurement. For moreinformation on this subject, see Clark andFritz (1997) and Cook and Herczeg (2000).

What is an Isotope?Isotopes of a particular element have thesame number of protons but a differentnumber of neutrons in the nucleus,resulting in a different atomic mass. Forexample, the most common element inthe universe, hydrogen, by definitioncontains one proton in its nucleus, but itcan contain none, one, or two neutrons.Some isotopes are stable, meaning theydo not decay to any other form overtime, and others are unstable, orradioactive, meaning they spontaneouslydecay at a predictable rate to form a newelement. For example, hydrogen withtwo neutrons is known as tritium, anunstable element. Tritium decays byemitting a radioactive beta particle andconverting into a stable helium element.

Sources of IsotopesBoth anthropogenic and natural sourcesexist for many isotopes. Anthropogenicsources are a result of the nuclear age ofweapons testing, nuclear powergeneration, fuel rod reprocessing, andnuclear medical waste. These activitieshave elevated many isotopes toconcentrations well above their naturalstate. Most became elevated on a globalscale, particularly in the northernhemisphere, after 1950.

Brenda Ekwurzel, Ph.D. – Department of Hydrology and Water Resources, University of Arizona

Natural isotopic sources are divided intothree broad categories: 1) cosmogenic,2) subsurface production, and 3)uranium decay series.

Cosmogenic isotopes arise from high-energy cosmic rays known as electronsand photons and lower-energy cosmicrays such as protons and other lightnuclei. These cosmic particles assailelements in the earth’s atmosphere,creating secondary particles, such asneutrons, that subsequently bombardother atmospheric nuclei and transforminto other isotopes.

Subsurface production occurs throughthe by-products of natural radioactivedecay series. These isotopes often mustbe accounted for when interpretingcosmogenic isotope transit times. They can also be directly used for age-dating groundwater.

The uranium decay series (238U) spawnsmany isotopes with long half-lives thathave been used in hydrologic studiesand are listed in Figure 1. Uranium-238is referred to as a primordial isotopebecause it was incorporated into theEarth during its formation. The 238U half-life is 4.47 billion years.

Understanding the various sources foreach isotope helps hydrologistsdetermine which isotopes are mostappropriate for hydrologic problems. Ifthe focus is on recharge or vadose zone

processes, then cosmogenic isotopes area good choice because they areincorporated into rain, snow, or drydeposition. On the other hand, if ahydrologist plans to study processes thatoccurred after 1950, anthropogenicisotopes are useful. For long-termprocess studies within a groundwatersystem, cosmogenic, subsurfaceproduction, and uranium decay-seriesisotopes all may be appropriate.

Figure 1 lists age-dating isotopescommonly used in hydrologic research,alongside the associated sources ofthose isotopes. Many of the sameisotopes are listed under severaldifferent categories; the multi-sourcepotential of these isotopes cancomplicate interpretation, but can oftenbe accounted for by multiple isotope orchemical measurements.

January/February 2003 • Southwest Hydrology • 17

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Age Dating FundamentalsBefore we delve into practical aspects ofage-dating isotopes, it is worth mentioninga common misconception. The term "age"sometimes creates the impression that thenumber represents a simple piston flowtransit time of a small water parcel.Despite the prevalent use of this term,isotope hydrologists understand that thewater sample measured represents theintegrated travel time information; "age"and "mean residence time" are usedinterchangeably.

Unstable isotopes periodically butpredictably emit a particle or break intotwo smaller nuclei. The time periodbetween emissions is known as the half-life for radioactive decay, and forms thebasis for most age-dating methods. Anideal age-dating isotope should behaveconservatively by not experiencing anylosses or additions during the transit timeof the water. This is rarely the case, butwe will discuss the ideal case to illustratethe straightforward age-dating technique.

We can calculate the time sincegroundwater recharged (left theatmosphere) if we know the originalrecharge concentration of a radioactiveisotope (No), its associated half-life (T1/2),and measure the number of atomsremaining in our groundwater sample atthe time of collection (Nt). T1/2 is related tothe decay constant (λ) by λ = ln2/T1/2.Assuming a single flowpath withoutmixing, losses, or additions of the isotope,we can calculate the approximate timesince recharge as t = -(1/λ)•ln(Nt/No).

For practical reasons, we might have tomake assumptions regarding the initialparent atom concentration, which createslarger uncertainties. Therefore, it is moredirect to measure the parent atomremaining (Nt) and daughter produced (Dt)at the sample collection time. Thisapproach is appropriate if the radioactiveparent isotope decays to a stable daughterproduct that remains with the water parcelcontaining the parent isotope. In this casethe age calculation is t = (1/λ)•ln(1+ Dt/Nt).

Another method to determine residence

time is to compare measuredconcentrations with the time-varyingconcentrations known as input sourcefunctions. Careful historical measurementsor reconstructions of the time-varyingglobal fluxes of anthropogenic isotopescan be exploited to derive fairlyinformative age determinations over thepast several decades. Precipitationmeasurements between 1950 and presentday record peak-shaped curves (such asfor 3H, 14C – see page 22 – and 36Cl) whileothers related to nuclear power facilities orfuel rod reprocessing have either increasedsteadily (such as 85Kr) or remain elevated(such as 129I). If only one anthropogenicisotope is measured, then theinterpretation may be limited to thedetermination that the water wasrecharged within the last 50 years.

Due to their varying concentrationsthrough time, if more than oneanthropogenic isotope is measured, thenmore precise age determinations may bepossible. Often the ratios of two isotopes(such as 85Kr/3H and 36Cl/129I) can becombined with each separate isotopeconcentration to create a unique timewhen all three factors match the historicalsignals. Tritium (3H), an anthropogenicisotope, has an advantage because itdecays to a stable daughter product (3He),and both can be measured in the watersample collected in the field. In this case,one can use the second age equationmentioned above as long as enoughtritium and 3He remains in the sample tobe measured in the lab. Also since 3H ispart of the H2O molecule it directly tracksthe movement of the water.

Consideration of Age Ranges The practical limit on the hydrologyresidence time age range is a function ofthe half-life, the laboratory detection limit,and the practical constraints regardinglocal evidence for the different sourcegeneration processes for each isotope.Figure 2 depicts both the natural andanthropogenic tracers and their respectivepractical age-dating ranges. The y-axis onFigure 2 is logarithmic due to theimmense range between several days forthe 222Rn isotope to the potential 80million-year maximum age for 129I.

Practical Limits of Field Sample VolumeThe required sample volume must also beconsidered when choosing an isotopicsystem. Figure 3 lists both the isotopesand their associated general labmeasurement category, which significantlyimpacts the required field sample volume.The y-axis on Figure 3 is also logarithmicdue to sample volumes that range betweena few milliliters to 3,000 liters. Fewhydrologists are willing to extract 81Kr gasout of 3,000 liters of water as was donefor Cyclotron measurements of ancientGreat Artesian Basin water in Australia. Ingeneral, required sample volumes havedecreased with mass spectrometer labsand especially accelerator massspectrometer (AMS) labs. However, thesample costs are higher for AMSmeasurements. Thus, many larger volumesamples are collected to be measured inlow-level counting labs in order to lowerthe cost.

Lately, there is a trend toward moreroutine use of isotope tools byhydrologists. The cost of analyses is quitereasonable for many isotopes (see page20), and a variety of commercial andresearch labs are available to perform theanalyses (see page 19). One couldpossibly spend a few thousand dollars onisotopic analyses of water collected fromexisting wells to produce a first orderanswer to a question that alternativelycould require several labor-intensive pumptests, additional borehole installations,and/or a groundwater model that reliesupon extensive water level data. As morehydrologists see the power of the isotopetechniques and learn to use themeffectively, we will ultimately gain animproved understanding of our waterresources and be better equipped tomanage them effectively.

Contact Brenda Ekwurzel atekwurzel@hwr.arizona.edu

ReferencesClark I. D. and Fritz P. (1997) Environmental

Isotopes in Hydrogeology, Lewis Publishers ofCRC Press, New York, 328 pp.

Cook P. G., and Herczeg A. L. (2000) EnvironmentalTracers in Subsurface Hydrology, KluwerAcademic Publishers, Boston, 529 pp.

Continued from previous page

This article presents a brief overviewof isotopic methods available fortracing and age-dating groundwater,

introducing the reader to the methods,typical applications, and assessments ofthe usability of these techniques. Most ofthese analyses can be completed withinone month, with more rapid turnaroundtimes available upon request and withappropriate surcharges.

The analytical techniques associated withthese methods are not typically foundamong standard U.S. EnvironmentalProtection Agency, American Society forTesting and Materials, and/or regulatoryagency protocols. However, the qualityassurance/quality control procedures forisotope analyses are rigorous products ofdecades of collaboration between researchinstitutions and the National Institute forStandards and Technology. These standardsinsure the quality of standard samples forinterlaboratory comparisons of data and amechanism by which the precision andaccuracy of isotope analyses could beimproved over time, to reach currentuncertainties of about 0.1 to 0.002 percent.

Groundwater GeochronologyCommercially available methods for age-dating groundwater rely on either tritium(3H) for qualitative ages or radiocarbondating (14C) if numerical ages are required.Both are cosmogenic – produced by nuclearinteractions in the atmosphere – and eachhas its place in age-dating of groundwater.

Tritium, with a half-life of 12.43 years,decays to Helium-3 (3He). Pre-atomic-bombbackground levels of tritium ranged fromabout 5 to 10 tritium units (1 tritium unit = 1TU =1 atom of 3H per 1018 atoms of 1H).Following atmospheric testing of nuclearweapons, levels of tritium rose to 500 tomore than1000 TU by the mid-1960s buthave been decreasing due to radioactivedecay, the cessation of atmospheric

detonations of thermonuclear devices, andremoval through rainfall.

General interpretations of groundwaterage based on TU levels are as follows: • Pre-1952, less than 0.8 TU. • 1960s, greater than 50 TU. • Young, less than 10 years old, about 5

to 10 TU.• Commingled old plus young

groundwater, 10 to 50 TU.

Although the decay of tritium to 3He hasbeen used to provide radiometric ages ofyoung groundwater (less than 30 yearsold), the analytical cost is high, themethod is only available through a fewresearch/government labs, and theturnaround times are lengthy since thesample must sit in order to accumulateenough 3He for analysis.

Radiocarbon, with a half-life of 5730years, is used to date groundwater up to50,000 years old. Recent advances, suchas accelerator mass spectrometry (AMS)have substantially reduced the amount ofsample required but not the uncertainty inages, which is a function of the amount ofcarbon analyzed. Applications ofradiocarbon dating are well known in thehydrologic community. (Seeaccompanying articles on pages 22-27.)

Other techniques used for datinggroundwater are not yet commerciallyavailable. Examples includechlorofluorocarbon compounds (forgroundwater 0-60 years old) and chlorine-36, which can date groundwater up to 2million years old.

Light Stable IsotopesThe light stable isotopes (LSIs) of carbon,hydrogen, oxygen, nitrogen, and sulfur(CHONS) are undoubtedly the best knownand most utilized isotopes in groundwaterhydrology. Their mass numbers are low and

Richard W. Hurst, Ph.D.— Hurst & Associates Inc. and California State University Department of Geological Sciences

Who Does the Analyses ?

The following laboratories are listed forinformation purposes only and representan incomplete list. Southwest Hydrologyintends no overt or implied endorsement oftheir services.

Commercial LabsGeochron LaboratoriesCambridge, MA(617) 876-3691www.geochronlabs.com14C, tritium, stable isotopes, and others

ISO AnalyticalCheshire, UK44 1 270 766771www.iso-analytical.comstable isotopes

ZymaXSan Luis Obispo, CA(805) 544-4696www.ZymaXusa.comstable isotopes, 14C preparation

University LabsUniversity of ArizonaLaboratory of Isotope Geochemistry(520) 621-1638www.geo.arizona.edu/researchers/mbaker/AustinLong/98prices.htmlstable isotopes, tritium, 14C, and others

University of Colorado INSTAARStable Isotope LaboratoryBoulder, CO(303) 492-7985mysticplum.colorado.edu/groups/sil/stable isotopes of oxygen, hydrogen, carbon

University of WaterlooEnvironmental Isotope LabWaterloo, Ontario, CanadaSciborg.waterloo.ca/research_groups/eilab/Stable isotopes, tritium, and others

For a listing of isotope laboratories in NorthAmerica and worldwide, visit the University ofVermont’s Web site at geology.uvm.edu/geowww/isogeochem.html#anchor559545

Continued on next page

all are stable – being neither radioactive nordaughter products of a radioactive parent(radiogenic). Large mass differences betweenisotopes in each system, such as 18O versus16O, allow separation (fractionation) ofisotopes by biogeochemical processes andexchange reactions associated with water-rock interactions.

Light stable isotope data are reported usingthe delta notation; the sample’s isotope ratiois measured relative to the lighter, lower massnumber isotope in the LSI system of interestand compared to a standard. For example, inthe case of oxygen isotopes:

δ18O={(18O/16O)SAMPLE – (18O/16O)STANDARD}x1000

(18O/16O)STANDARD

The resultant δ value, measured in parts perthousand (per mil), is termed heavy ifpositive (enriched in the heavier isotope), andlight if negative; however, these terms arerelative since a δ18O value of -3 is heavier

than a value of -10. The Meteoric Water Line(MWL), which depicts observed globalrelationships between H and O isotopes inprecipitation (δD - δ18O; Figure 1), is aclassic means of demonstrating how stable

isotope ratios are affected by biogeochemicaland physical processes.

Stable Radiogenic IsotopesStable radiogenic isotopes employed ingroundwater investigations include strontiumand lead. Although delta notations aresometimes employed, it is more common tosee actual isotope ratios (e.g. 87Sr/86Sr,206Pb/207Pb, 208Pb/206Pb) reported. With theexception of 210Pb, the isotopes of strontiumand lead are stable, however 87Sr and206Pb/207Pb/208Pb are also radiogenic, theirabundances increasing over geologic time dueto radioactive decay of rubidium anduranium/thorium isotopes, respectively. Unlikethe LSIs, strontium and lead isotopes are notfractionated by natural processes to anyappreciable degree, because mass differencesbetween their isotopes are small.

Strontium and lead isotopic analyses ofgroundwater are commercially available, buthave not been as widely used as the LSIsbecause groundwater hydrologists are notgenerally as familiar with these isotopicsystems, analytical costs are higher, and mostlead minerals are relatively insoluble.

Strontium isotopes, however, can be used toanswer the same questions posed ingroundwater investigations as the LSIs.Integrated Sr-LSI analyses have been effectivein assessing the effects of saline intrusion andfingerprinting sources of chlorinated solvents.Lead isotopes are also a powerful tool in age-dating and identifying sources of hydrocarbonreleases into groundwater.

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Figure 1. The Meteoric Water Line (MWL) of Craig (1961): Fractionation of D (deuterium) and 18O,heavier isotopes, due to evaporation and condensation varies as a function of latitude; both H and Oisotopes become lighter at higher latitudes. Hypothetical evaporation and water-rock interaction trendsare shown for reference.

What Does It Cost?(Information supplied by Richard W. Hurst – Hurst & Associates, Inc., and the University ofArizona’s SAHRA Isotopes and Hydrology Web Site(http://www.sahra.arizona.edu/programs/isotopes/))

Tritium: $80 to $300 per sample, depending on requested detection limit and method usedHelium: upwards of $1,000 per sample, available only through a few research/government labsRadiocarbon (14C): conventional dating--$300 per sample; AMS methods– $600 per sampleLight stable isotopes (carbon, hydrogen, oxygen, nitrogen, sulphur): $20-$235 per sampleStable radiogeneic isotopes (such as Sr and Pb): $325 per sample

Continued from previous page

Evaluating the Whole Story As a caution about the misinterpretation oftritium data, consider this case of a landslideat the base of a 400-foot high cliff. The slopeinstability was attributed to over-watering ofcrops by a farm on the cliff’s plateau.Plaintiffs’ experts in the ensuing lawsuitargued that high nitrate concentrations in localsprings originated from fertilizer, so liabilityfor property damage resided with farmowners. Tritium data from pore water sampledat depths of 10 to 30 feet below groundsurface at the top of the cliff ranged from 3-4TU; these results were used by plaintiffs’experts as evidence that young, 5- to 10-yearold irrigation water caused the landslide.

However, in addition to tritium analyses,groundwater 87Sr/86Sr and δ15N of nitrate werealso measured to evaluate nitrate sources andsupplement the hydrologic modeling. Theintegrated 87Sr/86Sr, δ15N, and tritium resultssuggested an alternative interpretation, whichwas consistent with hydrologic modeling. TheSr and N isotope characteristics of theirrigation water containing fertilizer differdramatically from those of local spring,surface, and pore water, indicating theirrigation water is not a likely source of nitrate(Figure 2). Furthermore, Sr-N ratios of highnitrate springs and surface water are identicalto those of organic-rich marine sediments –the bedrock in the region. So, in reality,

sources of nitrate are more likely the result ofgroundwater-organic rich marine sedimentexchange reactions, not overwatering.

In the absence of isotopic evidence forcommingling of irrigation with any surfaceor groundwater, combined with the fact thatSr-N-tritium data indicated pore watertritium was controlled by rainwater-marinesediment exchange reactions, not infiltrationof irrigation water over the last decade(Figure 2), the Court ruled to dismiss the suitagainst the farm.

Conclusions and RecommendationsProceed cautiously when interpreting isotopicdata. Experienced groundwater professionalsare competent and capable of performingmost of their own interpretations of isotopedata from the methods discussed. However,do your homework and do not step too faroutside of your comfort zone. Unfortunately,isotopic data are often treated independentlyof other geochemical and hydrogeologicaldata, which limits the effectiveness of thesevery powerful tools, and can lead to erroneousinterpretations. Remember too, that well-defined sampling plans should always be anintegral part of your investigation, and canmake or break the interpretations that follow. Richard Hurst has 34 years experience in isotopegeochemistry, focusing on applications of isotopegeochemistry to environmental problems. ContactHurst at www.hurstforensics.com

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Figure 2. Covariation of Sr and N isotopes of waters in the vicinity of a landslide. The large gapobserved between the respective 87Sr/86Sr – δ15N results of the irrigation water plus fertilizer and thoseof local waters indicate separate, distinct sources of nitrate for the two. Tritium results of the porewater, when viewed in light of the Sr-N data, are derived by rainwater-bedrock exchange reactions;local bedrock is comprised of organic rich marine sediments whose Sr-N isotopic characteristics arereflected in those of surface and spring waters.

Recharge to the upper 150 m of theregional aquifer in the alluvialsediments of the Tucson basin

appears to originate largely near majorwashes that convey water from watershedsaround the basin. Surface water in themajor washes visibly infiltrates flood-plainsediment and commonly does not leavethe basin. In order to understand the waterbudget of the basin, we need answers toquestions such as:

• Does the amount of infiltrating waterequal the amount of water reaching theregional aquifer?

• Does recharge to the regional aquiferoccur uniformly along the washes?

Groundwater isotope studies are useful inaddressing the second question. Surfacewater may be present in all of the majorwashes after heavy precipitation, and eachwash presumably contributes some water tothe regional aquifer. The question becomesone of relative rates of water movementbetween flood-plain sediment and theregional aquifer. We can determine the ratessemi-quantitatively using radioactiveisotopes with appropriate half-lives.

The radioactive isotopes tritium (3H) andradiocarbon (14C) have appropriate half-lives for the study of groundwatermovement. Both isotopes are generated asa result of interaction between cosmic raysand 14N in the upper atmosphere. Thelevels of both were also augmented byatmospheric testing of nuclear weapons,particularly between 1960 and 1972 (Fig.1). Tritium in the local atmosphere wasfurther augmented by releases from theAmerican Atomics factory in centralTucson between 1970 and 1982.

Properties of Tritium and RadiocarbonTritium, which has a 12.4 year half-life, isincorporated into water molecules in the

atmosphere. It is removed in rain, whichcurrently averages 5-7 tritium units nearTucson. One tritium unit (TU) correspondsto 1 tritium atom per 1018 atoms of 1H.Rain from years prior to 1955 wasprobably similar to present-day rain intritium content. "Bomb" tritium rose tolevels above 600 TU in rain during 1963and 1964 (Fig. 1), and had been strippedfrom the atmosphere by 1992. Tritium inwater that fell as rain or snow before 1955has decayed to levels below our detectionlimit of 0.6 TU. Consequently, we can usetritium in the Tucson area to distinguishgroundwater that precipitated prior to1955, on the one hand, from groundwatercontaining a significant fraction of post-1955 water, on the other.

14C is incorporated into CO2 molecules,some of which are removed from theatmosphere as plant material byphotosynthesis. Plant respiration and plantmaterial decomposed in soil contributes tosoil gas CO2, which has a 14C content closeto that of concurrent atmospheric CO2 .Soil CO2 dissolves in infiltratingrainwater, and is initially the principalsource of bicarbonate in groundwater.Subsequent dissolution of carbonateminerals in the subsurface addsbicarbonate containing "dead" carbon, i.e.carbon with no 14C, to groundwater.

A commonly-used unit of 14Cconcentration is percent modern carbon(pMC). Up until about 1955, the

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Fig. 1. A. Change in tritium content of Tucson rain since 1960. Model curve is from Doney et al.(1992). Annual means are data of the Laboratory of Isotope Geochemistry, University of Arizona.B. Change in 14C content of the atmosphere, unaffected by urban pollution, and 14C measurementson Tucson surface water. Data to 1985 from Burchuladze et al. (1989); subsequent data from theLaboratory of Isotope Geochemistry, University of Arizona.

The Tucson Basin ExampleC.J.Eastoe, Ph.D. – Geosciences Department, University of Arizona

atmosphere (disregarding industrial CO2

emission effects) contained 100 pMC.Bomb 14C increased to 190 pMC in theatmosphere in 1963-1964, and somebomb-14C persists in the atmosphere today.In 2001, southern Arizona air containedabout 109 pMC away from urban areas,and 106-108 pMC in Tucson.

The half-life of 14C is 5730 years, and pre-bomb 14C can be measured in naturalmaterial as old as 40-50 thousand years. Inthe case of groundwater, relating 14Ccontent to age is complicated by theaddition of "dead" rock carbonate that isinvariably present in the sedimentary fill ofTucson basin and other similar basins insemi-arid climatic zones. Nonetheless, 14Ccontent gives a useful indication of relativeages of groundwaters.

The process of adding "dead" carbonbegins before surface water undergoesinfiltration in Tucson basin. Surface waterwith as little as 85 pMC was collected in2000 (Fig 1B). Consequently, we interpretpMC values greater than 80 as potentiallyindicating water recharged in the last fewcenturies. The presence or absence oftritium in such water brackets the agemore closely. The mixing of older andyounger waters after infiltration alsocomplicates interpretations, and inparticular precludes the calculation of agesfrom tritium data alone.

Results and ConclusionsThree useful cases emerge from thediscussion above:

1. Water with measurable tritium andgreater than 80 pMC, containing asignificant fraction of water that fell asrain since 1955 is present in the regionalaquifer adjacent to a wash.

2. Water with tritium below detectionlevel, and greater than 80 pMC,containing a significant fraction of waterthat fell as rain potentially as recently asthe decade prior to 1955, is present.

3. Water with tritium below detectionlevel, and less than 80 pMC, containinglittle or no water that fell as rain in thefew centuries prior to 1955, is present.

Case 1 corresponds to the most rapidrecharge rates, with surface water reaching

the regional aquifer in less than 50 years. Incases 2 and 3, water that fell as rain prior to1955 is reaching the regional aquifer. Case2 corresponds to slower recharge than incase 1, and case 3 corresponds to very slowto non-existent recharge.

In the Tucson basin, tritium and 14C weremapped in the regional aquifer adjacent tomajor washes and examples of all three caseswere found (Fig. 2). Isotope maps showingall data points on which this figure is basedare available at www.geo.arizona.edu/researchers/mbaker/AusinLong/. Rapidrecharge occurs south of Rillito Creek andTanque Verde Creek, east of the Santa CruzRiver in the southern part of Tucson, andalso in a limited area near the confluence ofRincon Creek and Pantano Wash. Slowerrecharge (case 2) appears to occur north ofRillito Creek near its confluence with theSanta Cruz River. Recharge beneath PantanoWash downstream of Rincon Creek isextremely slow (case 3). In several intervalsof the major washes, not enough data wereavailable to constrain the recharge rate. Avery large data set would be necessary to

achieve full coverage.

At time scales relevant to the developmentof a city such as Tucson, recharge that takesmore than 50 years to reach the regionalaquifer is insignificant. As a consequence ofpumping, water-table levels are likely to befalling faster than the rate of advance ofwater infiltrating from the surface. Onlythose areas where tritium is present in theregional aquifer are receiving significantrecharge from the washes. Such rapidrecharge is clearly not occurring next toevery reach of wash in the basin. If gravity-driven artificial recharge is ever attemptedfrom Tucson washes, the number ofpotential sites will be limited.

Contact C.J. Eastoe at eastoe@geo.arizona.edu

ReferencesBurchuladze,A.A., Chudy, M., et al., 1989,

Anthropogenic 14C variations in atmosphericCO2 and wines. Radiocarbon, 31 (3), 771-776.

Doney, S.C., Glover, D.M., and Jenkins, W.J., 1992,A model function of the global bomb tritiumdistribution in precipitation. Jour. Geophys.Res. 97(C4), 5481-5492.

Santa Catalina Mts.

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Map of Tucson basin showing semi-quantitative recharge rates near the major washes

R = RillitoSCR = Santa Cruz RiverPW = Pantano WashRC = Rincon CreekTVC = Tanque Verde Creek

In 1993, the Orange County Water District(OCWD) was planning a comprehensivewater quality study of Santa Ana River

(SAR) water prior to and following rechargein the aquifers that comprise the 350-squaremile Orange County groundwater basin innorthern Orange County, California.Considering that more than 60 percent of theapproximately 200,000 acre-feet/year (af/yr)of SAR water that replenishes thegroundwater basin is composed of tertiary-treated wastewater from upstreamcommunities, OCWD wanted to evaluate theoverall quality of this important water source.In addition to SAR water, during the last tenyears OCWD has recharged an average of60,000 af/yr of imported water from theColorado River and northern California tomeet groundwater pumping demands.

Understanding the subsurface flowdynamics of the recharged SAR water wascritical to assessing changes in waterquality with distance from the rechargebasins. Of particular interest was thedelineation of the 1-year travel timeboundary of recharge water, as this criterionis being considered by California’sDepartment of Health Services in its draftrecycled water recharge regulations. Whilehistorical groundwater level measurementsand contour maps provided a reasonableunderstanding of general gradients inOCWD’s recharge area, determination ofdetailed groundwater flow paths andvelocities required more precisemeasurements. OCWD staff consideredusing existing geochemical data butconcluded that they were not sufficientlydistinctive to be useful in delineatinggroundwater flow paths and travel times. In1993, staff of OCWD and LawrenceLivermore National Laboratory (LLNL)met at a water conference and exchangedideas that resulted in a phased project thatused isotopes to characterize subsurface flowconditions in the vicinity of OCWD’s

recharge basins. This article summarizestheir methods and experiences, which aredescribed in more detail by Davisson et al.(1996, 1998, 1999) and Fujita et al. (1998).

Isotope Feasibility StudyAn isotope feasibility study was performedin 1995 by LLNL under contract to OCWD.The purposes of the feasibility study were to:

• Assess whether sufficient oxygen andhydrogen isotopic distinctions existed inthe recharge waters to serve as tracers.

• Develop a baseline groundwater agedistribution to identify potential "fast"recharge flow paths that should beprioritized for frequent monitoring duringthe subsequent tracer testing.

The scope of work consisted of sampling thesurface recharge water (SAR and importedwater) and the existing network of about 30wells for stable isotopes of oxygen (18O/16O)and hydrogen (2H) as well as age-dating the

groundwater samples using the tritium-helium-3 dating method.

Stable Oxygen Isotopic Tracers FingerprintColorado River Water

The 18O/16O ratio in Colorado River rechargewater can be distinguished from SAR waterand ambient groundwater because of thedepletion of 18O in Colorado River waterrelative to local waters (Williams, 1997).This depletion is caused by selectiveremoval or "rain out" of 18O relative to 16O asair masses containing ocean-derivedmoisture move inland. Because OCWD hadnot recharged Colorado River water inalmost two years, the groundwater samplescollected from wells close to the rechargebasins had an 18O/16O signature representativeof local water; however, groundwatersamples collected from a well approximatelyone mile downgradient of the rechargefacilities contained an 18O/16O signature thatwas clearly influenced by the last ColoradoRiver water recharge event. Based on the

Roy L. Herndon, R.G. and Greg D. Woodside, R.G. – Orange County Water District, and M. Lee Davisson and G. Bryant Hudson,Ph.D. – Lawrence Livermore National Laboratory

Figure 1. Groundwater ages (years) from 3H/3He age-dating (300-500 feet depth interval)

distinct oxygen isotopic character ofColorado River water, OCWD and LLNLstaff concluded that a tracer study usingColorado River water to determinegroundwater flowpaths would be feasibleand that this water could be reliably detectedto dilutions as low as 10 percent.

Tritium/Helium Method Provides Groundwater AgesPrior to initiating the tracer test usingColorado River water, groundwater ages atselected wells were estimated by measuringtritium (3H) and helium-3 (3He) concentrations(Schlosser et al., 1988). Because of its 12.4-year radioactive half-life, 3H is a goodchronometer for groundwater that wasrecharged within the last 40 years. Theproblem with attempting to age-dategroundwater using 3H measurements alone isthat atmospheric 3H concentrations havesteadily decreased over approximately thepast 40 years due to radioactive decay,making the estimation of the initial 3Hconcentration in the water at the time ofrecharge imprecise. This uncertainty wasaddressed by quantifying the amount of 3He,3H’s decay product, in each sample. Bysimultaneously measuring 3H and the daugherproduct 3He, known as tritiogenic helium, thetime, T, in years since the groundwater waslast in contact with the atmosphere wascalculated as follows:

T = 17.8 x ln(1 + 3He/3H)

Groundwater mixing within the screenedintervals of the monitoring and productionwells was found to be a major influence onthe age-dating results. Mixing ofgroundwaters that span the 40 years ofatmospheric tritium dispersal creates 3H/3Heages that represent a composite of the mixed"modern" waters. On the other hand, mixingof older, "pre-bomb" groundwaters devoid of3H and 3He with modern groundwaters doesnot affect the age estimate of the moderncomponent of groundwater, even if themodern component constitutes a smallpercentage of the total flow into a well. Formonitoring wells with screened intervals ofless than 20 feet in which mixing wasconsidered insignificant, the estimated 3H/3Hegroundwater ages were assigned anuncertainty of ±2 years. The resultantgroundwater ages were plotted and contouredwithin the study area (Figure 1). The

configuration of these contours indicatedpreferential flow paths of recharge water andhelped to establish a sampling plan for thesubsequent tracer tests.

Colorado River Water Tracer TestIn 1996, a tracer test was performed byrecharging 6,000 af of Colorado River waterat OCWD’s Anaheim Lake recharge basin.While the 18O/16O isotopes of the ColoradoRiver water were the primary "intrinsic"

tracer, LLNL utilized an additional tracer,xenon-124 (124Xe), to investigate the use ofthis stable noble gas as a conservative tracer.The 124Xe-spiked Colorado River water wasrecharged over a period of approximately 50days and then monitored for arrival at a seriesof downgradient wells. The test was repeatedin 1998 using a xenon-129 (129Xe) tracer andprovided results that were generally consistentwith the 1996 124Xe tracer test.

-1000

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Figure 2. Tracers introduced in Anaheim Lake demonstrate that recharge water moves deep as itmoves horizontally

See Groundwater Ages, page 36

From 1995 to 2001, the U.S.Geological Survey, together with otherfederal, state, and local governments,

agencies and tribes, conducted aninvestigation of the Middle Rio GrandeBasin (MRGB). The investigation wasdesigned to improve the understanding ofthe hydrology, geology, and land surfacecharacteristics of the MRGB and to providethe scientific information needed for water-resources management. One component ofthis investigation was a study usingchemical and isotopic data fromgroundwater to characterize groundwaterflow throughout the basin.

The MRGB, as defined for the study ofgroundwater chemistry, coversapproximately 3,060 square miles in centralNew Mexico’s Rio Grande Valley. It extendsfrom Cochiti Lake, about 40 miles north ofAlbuquerque, downstream to near SanAcacia about 55 miles south of Albuquerque.

Sampling and AnalysesAs part of this study, 280 wells —including 116 monitoring wells, 34domestic wells, 82 production wells, and

45 windmills — and eight springs weresampled throughout the MRGB during thesummers of 1996 through 1998.Concentrations of environmental tracersand other chemical and isotopic substanceswere measured in the groundwater samples.The analyses included major- and minor-element chemistry, tritium (3H), tritiogenichelium-3 (3He), chlorofluorocarbons(CFCs: CFC-11, CFC-12, CFC-113), sulfurhexafluoride (SF6), oxygen-18 (18O) anddeuterium (2H) in water; carbon-13 (13C)and carbon-14 (14C) of dissolved inorganiccarbon (DIC); sulfur-34 (34S) of dissolvedsulfate; and dissolved gases, includingoxygen, nitrogen, argon, methane, helium,neon, and carbon dioxide.

Most of the wells sampled intercept waterin the upper 500 feet of the Upper Santa Feaquifer. However, geochemical data from aseries of piezometer nests in the vicinity ofAlbuquerque provided additional data onvariations of the chemical parameters, todepths as much as 1500 feet below thewater table.

To gain information about potential sourcesof recharge to the aquifer system, waterfrom the Rio Grande and adjacent drainsand laterals, Tijeras Arroyo, Bear Canyon,the Rio Puerco and the Jemez River alsowas sampled and analyzed variously forCFCs, stable isotopes, tritium, and major-and minor-element chemistry on a monthlybasis. Samples of air and unsaturated zonegas were analyzed for CFCs, SF6, and 13Cof CO2 gas.

In addition, groundwater samples werecollected at all 91 operational City ofAlbuquerque production wells in thesummer of 1997 for analysis of stableisotopes. Archived groundwater samplesfrom City of Albuquerque productionwells, water from the Rio Grande, andprecipitation from the 1980s also were

analyzed for stable isotopes.

The geochemical data were used to:• Identify recharge areas.• Date the young (0 to 50 years) and old

(greater than 1000 years) water in the aquifer.

• Trace the movement of groundwaterthroughout the basin.

• Estimate recharge rates.• Trace seepage from the Rio Grande and

from the drains and laterals that hasentered the Santa Fe Group aquifer inthe Albuquerque area.

• Provide geochemical data to help refinethe USGS groundwater flow modeldeveloped for the MRGB.

Results Reveal PatternsThe results of the analyses show significantregional patterns that can be mappedthroughout the basin, many with a strongnorth-south component. These patternsappear to reflect recharge from the basinmargins and from the Rio Grande. Othermore local patterns appear to delineaterecharge from the Rio Puerco, the LadronPeak area to the southwest, Abo Arroyo,and Tijeras Arroyo.

Groundwater of the MRGB shows largevariations in the isotopic compositions ofhydrogen and oxygen. In the general areaof Albuquerque, variations ofapproximately 10 to 15 per mil in δDappear to separate groundwater derivedfrom the eastern mountain front fromgroundwater derived from the Rio Grande.Some stable-isotope values in a north-southstriking zone extending from the JemezRiver along the western half of the basin toareas southwest of Albuquerque aredepleted relative to water from the RioGrande. The isotopically depleted watersare also some of the oldest waters in thebasin and probably represent waterrecharged in the area of the JemezMountains during the last glacial period

Compiled from U.S. Geological Survey sources listed at the end of this article

Niel Plummer (USGS, Reston) collecting CFCsample in the Middle Rio Grande Basin (photo byF.E. Gebhardt, USGS, Albuquerque).

some 20,000 radiocarbon years ago.

Carbon-14 (14C, a radioactive isotope with ahalf-life of 5730 years) was used to dategroundwater recharged in the MRGBduring about the past 30,000 years.Because the chemical and isotopic dataindicate little effect of geochemicalreactions on radiocarbon activity alongflow paths in the primarily siliciclasticbasin-fill sediment, unadjusted radiocarbonages appear to provide reasonable ageestimates for most groundwater in thebasin. Preliminary unadjusted radiocarbonages suggest a bimodal distribution ofgroundwater ages throughout the basin.The 14C data indicate relatively youngwaters, about seven thousand years old,along most of the basin margins, and inapproximately the upper 200 feet of theinner valley sediment. Very old water, 18 to20 thousand years old, occurs through mostof the western half of the basin and atdepths greater than 500 feet below thewater table.

Chlorofluorocarbon, tritium, and heliumdata are being used to recognize areas thatreceived recharge within the past 30 to 50years. These tracers of modern recharge arefound in some groundwater and springs nearthe basin margins and arroyos and ingroundwater from the upper 200 feet of theinner valley. CFCs and/or tritium data arealso being used to recognize water sampleswith potential for contamination of old 14Cwith modern sources.

This study has demonstrated that chemicaland isotopic data can be used to improve theunderstanding of regional groundwater flowsystems such as that of the Middle RioGrande Basin. Sources of water to the basin-fill aquifer were recognized and were shown

to delineate groundwater flow paths.Radiocarbon ages were used to determinetravel times along flow paths, and toestimate modern and paleorecharge rates tothe aquifer. Modern recharge rates estimatedfrom the spatial- and depth-relatedradiocarbon ages were less than 20 percentof the previously-used recharge rate for thegroundwater flow model (Kernodle et al.,1995) for the basin. Recharge rates duringthe last glacial period were estimated to beat least 6-fold greater than the modernradiocarbon-based recharge rates. Thisimproved understanding of groundwatersources and ages is being used to furtherrefine the U.S. Geological Surveygroundwater flow model for the MRGB(Sanford et al., 2000).

Continued on next page

Sources compiled for this articlePlummer, L. N., 2002. Environmental tracers and

how they are used to understand the aquifer.In Bartolino, J.R. and J.C. Cole, eds.Ground-water resources of the Middle RioGrande Basin. U.S. Geological Survey

Circular 1222, pp. 82-83.

Plummer, L.N., L.M. Bexfield, S.K. Anderholm,W.E. Sanford, and E. Busenberg, 2001.Geochemical Characterization of GroundWater Flow in Parts of the Santa Fe GroupAquifer System, Middle Rio Grande Basin,New Mexico. In Cole, J.C., ed., U.S.Geological Survey Middle Rio Grande Basin

Study—Proceedings of the Fourth AnnualWorkshop, Albuquerque, New Mexico,February 15-16, 2000. U.S. GeologicalSurvey Open-File Report 00-488, Denver,CO, pp. 7-10.http://greenwood.cr.usgs.gov/pub/open-file-reports/ofr-00-0488/

U.S. Geological Survey Middle Rio Grande Basinproject home page:nm.water.usgs.gov/mrg/index.htm

U.S. Geological Survey Middle Rio Grande Basinenvironmental tracers and chemical andisotope study Web site:water.usgs.gov/lab/cfc/research/RioGrande.html#start

ReferencesKernodle, J.M., D.P. McAda, and C.R. Thorn,

1995. Simulation of ground-water flow in theAlbuquerque Basin, Central New Mexico,1901-1994, with projections to 2020. U.S.Geological Survey Water-ResourcesInvestigations Report 94-4251, 114p.

Sanford, W.E., L.N. Plummer, D.P. McAda, L.M.Bexfield, and S.K. Anderson, 2000.Estimation of hydrologic parameters for theground-water model of the Middle RioGrande Basin using carbon-14 and water-level data. In Cole, J.C., ed., U.S. GeologicalSurvey Middle Rio Grande Basin Study—Proceedings of the Fourth Annual Workshop,Albuquerque, New Mexico, February 15-16,2000. U.S. Geological Survey Open-FileReport 00-488, Denver, CO.

Continued from previous page

FOR INFORMATION ON WELLS ,

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W E L L WAT E R – N AT U R A L LY B E T T E R

Providing a little drink of water is a big responsibility.If you and your family are among the 23 million

Americans who have a well, your water comes

from safe, protected natural reserves within

the earth called aquifers. Protect your well and

family by having a well check up and testing

your water annually.

Web Sites on Isotope Hydrology Below are listed some comprehensiveWeb sites on the application of isotopesto hydrology. This list is by no meanscomplete or exhaustive, rather it isdesigned to highlight key portals thatprovide quick access to the most current information on the basics ofisotope hydrology.

Isotopes and Hydrology(www.sahra.arizona.edu/programs/isotopes/)

Developed by the University of Arizona’sSustainability of semi-Arid Hydrology andRiparian Areas program, this resourcecontains a clickable periodic table thatlinks useful isotopes to Web pages withbasic information about that isotopicsystem as well as important hydrologicapplications (Figure 1). Information alsoincludes cost of analysis, measurementtechniques, and links to print and onlineresources. The site also providesinformation on isotope types and origin,schematics and descriptions of the mostcommon instruments used in analysis, anda glossary of relevant isotopic terms.

USGS Isotope Interest Group Home Page(wwwrcamnl.wr.usgs.gov/isoig/)

This Web site is designed to serve the needsof the USGS but provides a wealth ofinformation on the application of isotopes(and related tracers) in hydrology, geologyand biology. The site contains shortsummaries on the natural variation andapplications of the most important isotopesystems. The publication page has excerptscovering the basics of isotope hydrology,taken from Clark and Fritz 1997 and Kendalland McDonnell 1998 (see below).

Isotope Hydrology Section - InternationalAtomic Energy Agency(www.iaea.or.at/programmes/ripc/ih/)

A division of the United Nations, the IAEAserves both as an intergovernmental forumfor scientific and technical cooperation in thepeaceful use of nuclear technology and asthe international inspectorate for theapplication of nuclear safeguards andverification measures covering civiliannuclear programs. This site details severalongoing international projects such as theassessment of groundwater resources inBangladesh, and provides access to severalglobal databases, including the GlobalNetwork of Isotopes in Precipitation.

Reference Texts on Isotope HydrologyClark, I., and P. Fritz, EnvironmentalIsotopes in Hydrogeology, LewisPublishers, Boca Raton, 1997

This text is designed for use in an upper-levelcollege course covering isotope hydrology. Itpresents essential material on environmentalisotopes in hydrogeology in plain languagefor nonspecialists. Topics include thetheoretical basis for natural isotopic variation,methods for measuring isotopic composition,tracing the hydrogeological cycle,groundwater quality, dating groundwaters,water–rock interaction, and methods for fieldsampling. The material is well-illustratedwith case studies and problems.

Kendall, C., and J.J. McDonnell, editors,Isotope Tracers in Catchment Hydrology,Elsevier, NY, 1998

This text is the first comprehensive synthesisof physical hydrology and isotopegeochemistry with a watershed (catchment)focus. The introductory chapters provide abasic treatment of the fundamentals ofcatchment hydrology, principles of isotopegeochemistry, and isotope variability in thehydrologic cycle. Most of the book presentscase studies in isotope hydrology that explorethe applications of isotope techniques forinvestigating modern environmentalproblems. Recommended for those interestedin the application of a particular isotopesystem in a watershed setting.

Cook, P.G., and A.L. Herczeg, editors,Environmental Tracers in SubsurfaceHydrology, Kluwer Academic Publishers,Boston, 2000

This text is a comprehensive synthesis ofphysical hydrology and isotope geochemistrywith a groundwater focus, recommended forthose interested in the application of aparticular isotope system to a groundwaterproblem. After the introductory chapters, themajority of the book examines specificisotope systems through a variety of casestudy applications for investigatinggroundwater problems.

James F. Hogan – University of Arizona SAHRA (Sustainability of semi-Arid Hydrology and Riparian Areas) and Department of Hydrology and Water Resources

Figure 1. Interactive periodic tableillustrating some of the information oncarbon isotopes that is available at theSAHRA Isotopes and Hydrology website.

Web and Print Resources

For more information on this article, contact James Hogan at jhogan@hwr.arizona.edu

approximately Nov. 15 and April 15 ofmost years. Seeding is only possible ifthere are clouds present that mightproduce rain. While the most effectiveseeding occurs during moderately wetyears, some level of cloud seeding isconducted most years.

Best Results in Wet YearsRecent statistical studies comparing rainfallnormals inside the target areas to thoseoutside them suggest that seeding results in amaximum increase in precipitation of about20% over one rain season. This statistictranslates to thousands of acre feet ofadditional water captured for storage in localreservoirs. In a moderately wet year withideal seeding conditions, which occurred in1992-93, approximately 20,000 acre feet ofwater was generated through cloud seeding.The moderate El Niño conditions predictedfor this winter may well result in ideal cloudseeding conditions.

The County has applied for a grant fromthe U.S. Bureau of Reclamation to performa chemical tracer study to better track thehuman-enhanced precipitation.

Controlling the Rainfall Santa Barbara County hydrologists use anetwork of rain and stream flow gagestogether with predictive computer modelsto prevent potential problems such asexcessive rainfall or rainfall occurring in

areas not intended. A set of suspensioncriteria is established every year thatspecifies conditions under which seedingmay be conducted. For example, all seedingis suspended in the areas recently burnedby wildfires, because those areas aresensitive to excessive soil erosion that canlead to landslides. Seeding can resumewhen hydrologists and others havedetermined that there is no longer anydanger of landslides or other adverseerosion impacts. The program is under theconstant supervision of a certifiedmeteorologist who uses real-time radar andsatellite imagery to monitor stormprogression and rainfall.

Cost Is JustifiedThe cost of the annual cloud seedingprogram is shared among the county andthe water districts that receive a benefitfrom it. The parties involved believe thecost is well-justified when compared to itsbenefits. The average cost of waterproduced by cloud seeding is less than$100 per acre foot. By comparison, the costof State-supplied water on the South Coastis roughly $1200 per acre foot. Desalinatedseawater costs approximately $1950 peracre foot. Groundwater and water fromLake Cachuma average between $75 and$250 per acre foot. Cloud seeding is one ofthe least expensive sources of wateravailable to the county.

Visit www.countyofsb.org/pwd/water for more infomation.

Cloud Seeding, continued from page 8

"However, that general formula issuperseded by the specific provision thatthe United States is entitled to an averageof at least 350,000 acre-feet annually incycles of five consecutive years," saidTCEQ Chairman Robert J. Huston. "TheTreaty provides Mexico no comparableminimum guaranteed entitlement."

Since 1992, Mexico has been inmaterial breach of the Treaty. For twoconsecutive five-year cycles (1992-1997and 1997-2002), it has fallen short ofminimum delivery obligations. The debtfor the two cycles is approximately 1.5million acre-feet.

"Mexico's argument that the 1992-1997deficit has been satisfied in thesubsequent cycle does not comport toany reading of the Treaty or lateragreements," Huston said. "Even undera tortured reading of the Treaty andMinute agreements, under whichdeliveries from sources other than theTreaty Tributaries are credited to the1992-1997 cycle, that cycle's deficit stillwould be more than 330,000 acre-feet.

"Since it is not a party to the Treaty,Texas has no legal remedy againstMexico for damage to its citizens,"Huston said. "But the United States hasextensive options, and we re-urge theState Department to consider those. TheUnited States can terminate the treaty.The United States can withhold itsperformance under the treaty, namely,deliveries of water from the ColoradoRiver to Mexico. The United States caninsist that Mexico pay the debt from anywater sources within Mexico's control."

Visit 163.234.20.106/AC/comm_exec/communication/media/mexico-treaty_position.html

Government, continued from page 11

DBS&A Receives Grant forArsenic Removal ResearchDaniel B. Stephens & Associates, Inc.(DBS&A) of Albuquerque, in associationwith Subsurface Technologies, Inc., wasrecently awarded a U.S. EnvironmentalProtection Agency (EPA) Small BusinessInnovation Research grant to testinnovative arsenic treatment technologies.The $100,000 grant will enable Dr.Gregory P. Miller, Senior Geochemist atDBS&A, to conduct a full-scale, on-sitedemonstration of subsurface arsenic-reactive barriers. The technology, referredto as Subsurface Treatment for ArsenicRemoval (STAR), is based onmodifications of proven subsurface (in-situ) iron control technology. On-sitedemonstration at the San Antonio, NewMexico well field will facilitate analysesand optimization necessary to make thistechnology commercially available towater systems seeking to comply with theEPA’s recently revised standard for arsenicin drinking water.

STAR offers significant advantages overconventional above-ground treatmenttechnologies in that it does not require theconstruction of above-ground facilities;generate large volumes of waste sludge,brine, or spent treatment media requiringdisposal; or require a skilled operator tomaintain the system. These advantagesposition STAR as a cost-effective optionfor both small community water systemsand large municipal providers.

Dr. Miller has conducted dozens of studieson chemical mobility in aquifers and is anexpert on geochemical barriers.Subsurface Technologies is a leader insubsurface microbiology and largemunicipal production well maintenanceprograms. They have successfullyimplemented the subsurface iron treatmenttechnology upon which STAR is based atover 50 sites around the world. SubsurfaceTechnologies has been working with thistechnology for more than 30 years.

Contact Dr. Gregory P, Miller atgmiller@dbstephens.com or (505) 822-9400.

Regenesis Receives Patenton Hydrogen ReleaseCompound (HRC®)Regenesis, based in San Clemente,California, was recently granted a patentfor its Hydrogen Release Compound(HRC®). HRC is a proprietary polylactateester used for the purpose of acceleratingreductive bioremediation processes thatdegrade chlorinated contaminants,nitroaromatics and oxyanions ingroundwater and saturated soils. HRC alsohas the capability to remove certain metalsfrom the subsurface through thefacilitation of precipitation reactions.

According to the company, a time-releasefeature of HRC allows relatively lowconcentrations of hydrogen to be releasedslowly, for periods of one to two or moreyears, optimizing biodegradation rates.The slow, low-concentration release ofhydrogen may also prevent unwantedbuildup of potentially dangerous gases,such as methane, in the subsurface.

HRC is applied with direct-push injection,and has been used on more than 350 sitesin the United States. According toRegenesis, HRC is effective oncontaminants ranging from PCE andexplosives to chromium and perchlorate.

Visit http://www.regenesis.com/

Cadiz Storage Project Vetoedby Metropolitan Water DistrictOn Oct. 8, the board of the MetropolitanWater District (MWD) of Californiaelected to forego the Cadiz Water Storageand Supply Project. This decision camejust over a month after the U.S.Department of the Interior gave its finalapproval on the project. According to apress release by the MWD, the action wastaken because of dramatically changedconditions on the Colorado River, makingit unlikely that there would be sufficientsurplus water to store as the proposedprogram anticipated in the near-term.

Visit www.mwd.dst.ca.us/

Knight-Piesold QuantifiesSouthwestern Water’sColorado ReserveSouthwestern Water ExplorationCompany’s engineering consultants, thefirm of Knight Piesold, has completed itsfull review of the large fresh waterreservoir discovered deep underground inColorado. The Knight Piesold estimate isthat the Southwestern Water reservoircontains at least 300,000 acre-feet ofwater. The reservoir can produce,according to the same engineeringanalysis, 3,000 to 6,000 acre feet ofwater per year, enough to supply thewater needs of a town of around 10,000people. At this rate of production, theSouthwestern Water reservoir will last fora minimum of 100 years.

The price of water in this region ofColorado is currently averaging $15,500per acre-foot for Colorado Big Thompson(CBT) delivery.

To bring this reservoir more rapidly intoproduction, Southwestern Water hasretained the services of independent waterappraisers and water brokers to sell theproduction on an annualized basis.

Southwestern Water is also now activelyinvestigating the potential of twoadditional aquifers the company haslocated underground in Colorado. Theseare expected to contain deposits of freshwater similar or greater in size to thediscovery in early 2002.

In addition, Southwestern Water alsorecently completed a private placement of100,000 shares of its treasury stock (Rule144) at a price of $1.50 per share. Thepurchaser also received warrants topurchase an additional 600,000 shares at$2.50 per share over the next three years.These funds will go toward SouthwesternWater's planned development of a largeunderground water aquifer in south Texas.

Contact Steven Misner or Thomas Lenney at (800) 661-9169 or www.southwesternwater.com

T H E C O M P A N Y L I N E

Business Directory

Clear Creek Associates Movesto Tucson LandmarkClear Creek Associates, an Arizonahydrogeologic consulting firm, hasexpanded its Tucson office space in thecity’s downtown area. Founding partnersDoug and Lori Bartlett, along with Tucson

office manager Mike Alter, invested in abit of old Tucson history by purchasingthe landmark Old Stork Building(sometimes referred to as “the Stork’sNest”), in the El Presidio Historic District.The adobe building was reportedly built in1882 as a private residence and acquiredits present-day name in 1922 after one of

its former owners turned it into Tucson’sfirst maternity ward. It remained amaternity ward until 1945. Clear Creekmoved into the new quarters on 221 NorthCourt Avenue in late August.

Visit www.clearcreekassociates.com

• Groundwater Development• Fractured Reservoir Systems• Groundwater Environmental• Geologic Mapping• GIS and Remote Sensing

Clay Conway, Ph.D., R.G. (AZ)790 W. 200 S. (52-4)Blanding, UT 84511435-678-7821conway@gaeaorama.com

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Coming Up: PHCs and OrganicChemicals in GroundwaterThe American Petroleum Institute andNational Ground Water Association aresponsoring a conference on theprevention, assessment, and remediationof petroleum hydrocarbons (PHCs) andorganic chemicals in groundwater, withspecial focus on gasoline oxygenates andlong-term site management. Scheduledtopics currently include sitecharacterization and monitoring, gasolineoxygenates, natural attenuation processes,remediation technologies, and cleanupgoals and site closures. The 4-dayconference will be held in Costa Mesa,CA Aug. 19-22; the deadline forsubmitting abstracts is Jan. 10.

For more information, visit www.ngwa.org/education

GRA Hosts Symposium onNitrate in Groundwater The status of nitrate in groundwater wasthe subject of the sixth symposium in theGroundwater Resources Association (GRA)of California’s series on groundwatercontaminants, held Nov. 12- 13 in Fresno.

"Nitrate remains one of [California’s] mostwidely-recognized groundwatercontaminants, and the problem may begrowing," said William V. Pipes, PrincipalGeologist of Geomatrix Consultants, Inc. ofFresno, and president of the San JoaquinValley Branch of GRA.

"Although wastewater management andagricultural land use practices havecontributed to successful nitratemanagement, recent investigations showthat nitrate contamination may be morewidespread and in deeper groundwater thanpreviously thought," said Pipes, who servedas the event co-chair.

The symposium featured collaboratorsfrom agriculture, public water supply,urban wastewater, academic, consultant andregulatory fields to share the most recentadvances and knowledge on the status ofnitrates in groundwater. The emphasis wason source identification, management,

basin-wide monitoring programs,discerning long-term trends, regulatoryframework, public health and land usepolicy issues.

Specific topics that were covered at thesymposium include: Overview ofLegal/Regulatory Framework, Impacts on

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Beneficial Use and Public Health, NitrogenCycling and Chemistry, OccurrenceTransport and Monitoring, Source Controlsand Treatment Strategies, CollaborativeApproaches to Achieve Source Management,and a panel discussion entitled "AManageable Threat or a Looming Disaster -Where do we go from here?"

Copies of the proceedings are available for$55 from the GRA Web site. Visit www.grac.org

NGWA Southwest FOCUSConference Scheduled forFebruaryThe National Ground Water Association(NGWA) has organized a conference tofocus on issues critical to groundwater inthe Southwest. Scheduled for Feb. 20-21 inPhoenix, the conference includes twoplenary sessions, plus focus sessions oninnovative remediation technologies,artificial and natural recharge, groundwatermodeling, emerging contaminants (1,4-

dioxane and perchlorates), and watersupply planning. In addition, a field trip toa TCE-remediation project site and anartificial recharge facility will be offered onFeb. 19. The list of speakers reads like aWho’s Who of Southwestern hydrology.This conference will be an excellentopportunity to find out what yourcolleagues throughout the Southwest are upto, and to learn from the experts.Registration ($350 for NGWA members, $500 for non-members) is available by mail, phone, fax, or on-line.Visit www.ngwa.org/education or call (800) 551-7379.

Hydrogeology PresentationsAbound at GSA Annual MeetingThe Geological Society of America (GSA)held its 2002 meeting in Denver inOctober, with a week-long program thatoffered 22 sessions, two short courses andthree field trips sponsored or co-sponsoredby the Hydrogeology Division. Sessionscovered all aspects of hydrogeology,including environmental issues related tomining, specifics of individual aquifers andregions, modeling karst terrain, science and

sensible public policy, soil and vadose zonehydrology, contaminant migration,watershed processes, and chemicalhydrogeology and geochemistry. The one-day short courses covered estimating ratesof groundwater recharge and methods inapplied contaminant geochemistry. Fieldtrips were led to the Summitville mine tolearn about Superfund activities there, toGlenwood Caverns for an introduction toCO2 and H2S speleogenesis, and to a localwell site to view borehole image logging.During the meeting, Dr. Thomas C. Winterof the U.S. Geological Survey in Denverwas awarded the O.E. Meinzer Award inrecognition of his outstanding contributionsto hydrogeology during the past 30 years,specifically with regards to the hydrologyof lakes and wetlands. Mary Jo Baedeckerof the U.S. Geological Survey in Restonreceived the Hydrogeology Division’sDistinguished Service Award for her manyyears of service to GSA and thehydrogeologic community.Visit gsahydrodiv.unl.edu to learn more about the GSA Hydrogeology Division.

Water Follies by Robert Glennon, Island Press, $20.00

Reviewed by Gary Woodard, Ph.D. – Assistant Director, NSF Center for Sustainabilityof semi-Arid Hydrology and Riparian Areas, University of Arizona

An environmental law attorney representingmining interests once noted that “Smokey theBear doesn’t give a darn what’s in thegroundwater.” But as Robert Glennon’s newbook, “Water Follies: Groundwater Pumpingand the Fate of America’s Fresh Waters”makes clear, groundwater pumping can haveprofound environmental consequences.

Glennon wears many hats in this book,including historian, legal scholar,environmental commentator, explainer ofbasic hydrologic principles, and policy analyst. He deftlyswitches hats throughout the book, but he is at his best as astory teller. Each chapter tells a tale of human desire – fordrinking pure spring water, mining rich gold deposits, eatingperfect French fries, pursuing economic development, orcreating the illusion of flowing water in the desert – and howthe pursuit of these desires has seriously impacted springs,streams, and rivers across the United States.

A historian and the Morris K. Udall Professor of Law andPublic Policy at the University of Arizona, Glennon shares hisbroad knowledge of the subject while keeping academictendencies in check. He eschews footnotes but providesencyclopedic bibliography, glossary and index. The larger andmore formidable challenge is providing technically correct andreasonably complete descriptions of complex hydrologic andsocial situations in a manner that can be understood by thegeneral public.

Glennon makes no bones about his environmental sympathies,even providing an index of “individuals fighting to make adifference” and organizations that “deserve our gratitude” and“need support.” Yet he never preaches, relying instead on humorand insight and consistently presenting all sides of the issues.Mixed with warnings of impending environmental disasters is anote of hope, almost optimism. Some of the stories are ofdisasters averted, or promising new approaches. Manyenvironmental consequences are avoidable, some reversible. Thefinal chapter outlines an approach for addressing these problemsand calls for a pragmatic balancing act between governmentalcommand-and-control approaches and market-based incentives.

The book’s jacket states “Quite remarkably, no books ormagazines have focused on this issue.” It’s a startling, seeminglyincredible claim. The literature is clogged with articles

describing aspects of particular groundwater -surface water interactions. Yet this is in factthe first publication to provide a thoroughoverview of these issues, and do it in a waythat is accessible to the general public.

Hydrologists and other water resourcesprofessionals may find some small nits topick with a specific technical description orexplanation. But overall, Glennon has pulledoff a most difficult task – penning a bookthat renders the obscure subject ofgroundwater understandable, evenentertaining. Water professionals will find ita fascinating read, and might considerpurchasing it for that friend or relative whohas never understood what your chosenprofession is all about.

“Water Follies” is sure to both widen and deepen the debate onhow we manage and mis-manage our groundwater resources.For that reason alone, this book is an enormous public service.

Visit www.islandpress.com. Contact Gary Woodard atgwoodard@sahra.arizona.edu

I N P R I N T

Tracer arrivals at shallow wells within 100feet of Anaheim Lake occurred withinapproximately two weeks, while arrivals atwells 3,000 feet downgradient occurred atabout four months, indicating averagegroundwater velocities of about 25 feet/day.The detections of Xe tracers and 18O/16O in therecharge water showed consistent arrivaltimes, demonstrating that the Xe isotopesacted as conservative tracers. Tracer arrivalsat depths of 800 feet indicated that recharge

flow paths have a significant verticalcomponent (Figure 2).

Summary of FindingsIsotopic measurements allowed OCWD todelineate groundwater flow paths andvelocities laterally and verticallydowngradient from its recharge basins in acomplex alluvial environment. These methodsprovided a level of detail of flow dynamicsbeyond that of conventional hydraulicgradient and geochemical interpretative

methods. The researchers’ findings aresummarized as follows:

• Stable oxygen isotopic signatures weredistinctive between imported ColoradoRiver water and local recharge water andgroundwater, making Colorado River watera viable tracer.

• Tritium/helium age-dating proved valuablein establishing general groundwater flowcharacteristics and ages prior to conductingthe tracer tests.

• Tritium/helium-derived ages wereestimated to within ±2 years when mixingwas minimal and represented compositeages when mixing of different "modern"waters occurred in long-screened wells.

• Noble gas isotopes such as xenon-124 canbe practically mixed with recharge watersand used as groundwater tracers; however,the manufacture and analyses of thesenoble gas isotopes can be performed byonly a few research laboratories, includingLLNL, making the common application ofnoble gas tracers less practical than thelower-cost oxygen isotopes.

Contact Roy Herndon at RHerndon@ocwd.com

ReferencesDavisson, M.L., G.B. Hudson, R.L. Herndon, S.

Niemeyer, and J. Beiriger, 1996. Report on theFeasibility of Using Isotopes to Source and Age-Date Groundwater in Orange County WaterDistrict’s Forebay Region, Orange County,California. Lawrence Livermore NationalLaboratory Isotope Sciences Division, May 1996(UCRL-ID-123953).

Davisson, M.L., G.B. Hudson, J.E. Moran, S.Niemeyer, and R.L. Herndon, 1998. IsotopeTracer Approaches for Characterizing ArtificialRecharge and Demonstrating RegulatoryCompliance. Annual UC Water Reuse ResearchConference, Monterey, California, June 1998.

Davisson, M.L., G.B. Hudson, R. Herndon, and G.Woodside, 1999. Report on Isotope TracerInvestigations in the Forebay of the OrangeCounty Groundwater Basin: Fiscal Years 1996and 1997. Lawrence Livermore NationalLaboratory, March 1999 (UCRL-ID-133531).

Fujita, Y., J. Zhou, E. Orwin, M. Reinhard, M.L.Davisson, and G.B. Hudson, 1998. Tracking theMovement of Recharge Water After Infiltration.Lawrence Livermore National Laboratory,March 1998 (UCRL-ID-130194).

Schlosser, P. Stute, M. Dorr, H. Sonntag, C.Munnich,O., 1988, Tritium/3He dating of shallowgroundwater. Earth, Planet. Sci. Lett., 89, 353-362.

Williams, A.E., 1997, Stable isotope tracers: naturaland anthropogenic recharge, Orange County,California. Journal of Hydrology, 201 230-248.

Groundwater Ages, continued from page 25

Software Review from theInternational Ground WaterModeling CenterPaula Jo Lemonds and John E. McCray,International Ground Water ModelingCenter, Colorado School of Mines

The Soil and Water Assessment Tool(SWAT) is a watershed-scale waterquality model developed by the USDAAgricultural Research Service (ARS)to predict the impact of managementpractices on water, sediment, nutrient,and chemical yields in watersheds thathave different soils, land uses, andmanagement conditions over longdurations. SWAT uses physically-baseddata. That is, instead of usingregression equations, it utilizes theory-based hydrologic and climateequations. Data from the watershed areused as input to these equations. Otherimportant attributes of SWAT includeits computational efficiency that allowsfor complex watersheds to be modeledin a straightforward manner, itsincorporation of easily accessible datathat is available for most watershedsfrom government agencies, and itsability to simulate long-term impacts ofpollutant buildup and downstreamimpact. SWAT can simulate manydifferent processes, including surfacerunoff, return flow, evapotranspiration,

pond and reservoir storage, cropgrowth, reach routing, nutrient andpesticide loading from point andnonpoint sources, chemicaltransformations, inter-basin watertransfers, irrigation, fertilization, andseveral types of tillage operations.Model development involves splitting abasin into sub-watersheds based ontopography from a digital elevationmodel (DEM). Model output is easilycompared to watershed data forcalibration with the built-in SWATcalibration tool. A limitation of SWATis that it does not rigorously simulategroundwater flow and transport. Modeldevelopment may require significanttime, depending on the user’s modelingbackground and knowledge of surfacewater and groundwater systems. SWATis available free of charge. It may bedownloaded from the SWAT Web page(www.brc.tamus.edu/swat/) or from theEPA’s BASINS web page(www.epa.gov/OST/BASINS/). Bothformats operate on a PC platform in anArcView GIS environment, but otherinterfaces have been developed.Technical assistance is available in theform of beginner and intermediatetraining workshops and a Web-baseduser’s forum from the SWATWeb page.

P R O D U C T A N N O U N C E M E N T S & S O F T W A R E R E V I E W

Visit www.mines.edu/igwmc

T H E C A L E N D A R

January 10 ABSTRACTS DUE! American Petroleum Institute and National Ground Water Association. Prevention,Assessment, and Remediation of Petroleum Hydrocarbons and Organic Chemicals in Ground Water. Aug.

19-22, Costa Mesa, CA. www.ngwa.org/education

January 21 ABSTRACTS DUE! Arizona Hydrological Society and others. 11th Biennial Symposium on GroundwaterRecharge. June 5-7, Tempe, AZ. Contact Jenny Bush at (602) 294-9600 or email

dbartlett@clearcreekassociates.com

January 23-24 CLE International. The Law of the Rio Grande. Albuquerque, NM. www.cle.com

January 28-29 National Ground Water Association. Design and Construction of Wells. Denver, CO. www.ngwa.org/education

January 28-31 Texas Groundwater Association. Annual Convention. Corpus Christi, TX. www.tgwa.org

January 29-31 National Ground Water Association. Environmental Geochemistry of Metals. Denver, CO.

www.ngwa.org/education

February 9-12 Colorado Mining Association. 105th National Western Mining Conference and Exhibition. Denver, CO.

www.coloradomining.org

February 10-14 CA-NV Section of the American Water Works Association. 2003 Education Symposium. Napa, CA.

www.ca-nv-awwa.org

February 18-19 National Ground Water Association. Economic Analysis for Ground Water Remediation: A Tool for DecisionMaking. Phoenix, AZ. www.ngwa.org/education

February 20-21 National Ground Water Association. Southwest FOCUS Conference: Water Supply and EmergingContaminants. Phoenix, AZ. www.ngwa.org

February 24-25 National Ground Water Association. Artificial Recharge of Ground Water. Phoenix, AZ. www.ngwa.org/education

February 24-28 International Erosion Control Association 34th Annual Conference. Las Vegas, NV. www.ieca.org/public/calendar/

February 24-28 Princeton Groundwater, Inc. The Groundwater Pollution and Hydrology Course. San Francisco, CA.

www.princeton-groundwater.com

February 26-28 Nevada Water Resources Association. Annual Conference: Growth vs. Supply. Sparks, NV. www.nvwra.org

March 1 ABSTRACTS DUE! Colorado State University and other sponsors. 10th Annual Conference on Tailings andMine Waste. Oct. 12-15, Fort Collins, CO. www.engr.colostate.edu/hsrc/

March 3-7 National Ground Water Association. Ground Water Geochemistry: Fundamentals (March 3-4) andApplications (March 5-7). Scottsdale, AZ. www.ngwa.org/education

March 4-5 National Ground Water Association. Application of Health Risk Assessment for Environmental DecisionMaking. Scottsdale, AZ. www.ngwa.org/education

March 17-21 Princeton Goundwater, Inc. The Remediation Course. Denver, CO. www.princeton-groundwater.com

March 19-21 National Ground Water Association. 3rd International Conference on Pharmaceuticals and EndocrineDisrupting Chemicals in Water. Minneapolis, MN. www.ngwa.org/education

April 1-4 UNESCO and HydroSciences Montpellier Maison des Sciences de l’Eau. Hydrology of the Mediterranean andSemi-Arid Regions. Montpellier, France. www.unesco.org/water/water_events/Detailed/127.shtml

April 6-10 Environmental and Engineering Geophysical Society. Annual Meeting/Symposium on the Application ofGeophysics to Environmental and Engineering Problems. San Antonio, TX. www.eegs.org/sageep/index.html

April 20 ABSTRACTS DUE! International Ground Water Modeling Center. MODFLOW and More 2003: Understandingthrough Modeling. Sept. 17-19, Golden, CO. www.mines.edu/research/igwmc/events/modflow2003/

Please submit event information to mail@swhydro.com

JANUARY 2003

FEBRUARY 2003

APRIL 2003

MARCH 2003