Identifying The Origin Of Tap Water Across The Western United States Based On Stable Isotopic Composition S Good1, L Chesson2, L Valenzuela3, M Beasley4, J Ehleringer5, and G Bowen1 1Department of Geology and Geophysics, University of Utah, Salt Lake City Utah, USA (contact email: s.good@utah.edu) 2IsoForensics Inc., Salt Lake City, Utah, USA

3Consejo Nacional de Investigaciones Cientificas y Tecnicas, Buenos Aries, Argentina

4Department of Anthropology, California State University – Chico, Chico, California, USA 5Department of Biology, University of Utah, Salt Lake City Utah, USA

Project State Flow (afy) Length (mi)

Completed

1 Central Utah Project UT 218,000 200+

2 Central Arizona Project AZ 1,500,000 350

3 Colorado River Aqueduct CO 1,200,000 481

4 Los Angeles Aqueduct CA 254,000 360

5 California Sate Water Project CA 2,400,000 700

6 Central Valley Project CA 5,300,000 500

7 Hetch Hetchy Aqueduct CA 165,000 160

8 Mokelumne Aqueduct CA 364,000 91

9 Portland Water Bureau OR 132,000 26

10 Cedar River WA 103,500 56

Future Projects

11 Lake Powell Pipeline Project AZ, UT 100,000 158

12 Gallup-Navajo Pipeline Project NM 35,893 260

13 Narrows Project UT 5,400 17

14 Easter Nevada to Las Vegas NV 84,000 300

15 Cadiz Valley Water Project CA 50,000 43

16 Peripheral Canal/Tunnel CA Uncertain 37

17 Weber Siphon WA 30,000 337

Major water projects in the west

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HUC6 region boundaries

A B A B

FIGURE 2: Isotopic composition of tap waters across the west. Tap water hydrogen isotope values (A) and deuterium excess (B) at the 612 sampled locations in the western United States.

FIGURE 3: Isotopic composition of precipitation and surface waters. Estimated δ2H isotopic composition in (A) precipitation and (B) surfaces waters. Only cells with a flow rate greater then 1000 m3/year are shown.

OVERVIEW

FIGURE 1: Major water transfer projects in the west. Locations are approximate, flows are expressed in acre-feet per year (afy) and lengths are in miles (mi). White lines denote USGS hydrologic basins west of the continental divide.

INTRODUCTION    In   the   western   United   States,   the  

spa2al   mismatch   between   public   water  demands   and   the   distribu2on   of   water  resources   necessitates   large   inter-­‐basin  transfers  of  water  (Fig  1).  The  convoluted  nature   of   local,   state,   and   federal   inter-­‐basin   transfer   projects   obstructs   the  direct  compila2on  of  water  transfer  data  into  a   regional  assessment,  with   the   last  federal  inventories  completed  in  1986.  B e c a u s e   t h e   s t a b l e   i s o t o p i c  

composi2ons   of   rainfall   (Fig   3A)   and  surface   water   (Fig   3B)   exhibit   a   well-­‐  understood   spa2al   structure,   an   isotopic  comparison  between  a  water  sample  (Fig  2)   and   poten2al   local   water   resources  can   determine   the   likelihood   of   local  origin.  

BASE  DATA  SETS  Public  Tap  Water  612  individual  samples  from  7  states,  collected  from  2002-­‐2003.  Bowen,  G.,  J.  Ehleringer,  L.  Chesson,  E.  Stange,  and  T.  Cerling  (2007),  Stable  isotope  ra2os  of  tap  water  in  the  con2guous  united  states,  Water  Resources  Research.  43  (W03419)      

Local  Precipita2on  Interpolated  values  based  on  the  IAEA  ‘Global  Network  of  Isotopes  in  Precipita2on’  database.  Bowen,  G.,  and  J.  Revenaugh  (2003),  Interpola2ng  the  isotopic  composi2on  of  modern  meteoric  precipita2on,  Water  Resources  Research.  39  (10),  1299.      

Local  Surface  Water    Surface  water  balance  model  used  to  predict  runoff  isotope  composi2on.    Bowen,  G.,  C.  Kennedy,  Z.  Liu,  and  J.  Stalker  (2011),  Water  balance  model  for  mean  annual  hydrogen  and  oxygen  isotope  distribu2ons  in  surface  waters  of  the  con2guous  United  States,  Journal  of  Geophysical  Research,  116,  (G04011).    

 SPATIAL PATTERN IN ISOTOPIC DISTRIBUTIONS

A B

METHODOLOGY

RESULTS

FIGURE 4: Schematic of calculation of likelihood of local origin. Both the local tap water sample (blue) and local water (red) are characterized by multivariate normal probability distributions. Random realizations of the local water composition (δ18O,   δ2H) and evaporation slope are generated (gray lines) and the line integral of the tap water distribution is then calculated (dark shading on lines) and averaged.

CONCLUSIONS  We   find   that   a   majority   (55%,   Fig  

5A)   of   collected   tap   water   samples  a r e   i n cons i s t en t   w i th   l o ca l  precipita2on   isotopic   composi2on  while   a   smaller   percent   of   samples  (29%,   Fig   5B)   are   inconsistent   with  loca l   sur face   water   i sotopic  composi2on.  These  samples  that  are  not  of  local  origin  are  predominately  clustered   in   southern   California,   the  San   Francisco   bay   area,   and   central  Arizona,   regions   known   to   import   a  majority  of  their  tap  water.    A  simple  mul2ple   linear  regression  

(Fig   5D)   between   likelihood   of   local  surface  water  origin  that   includes   (i)  rainfall,   (ii)   popula2on   density,   (iii)  basin   eleva2on,   (iv)   basin   size,   and  (v)  average  household  income  is  able  to  model  the  observed  pafern  well.  

Specifica2on   of   the   probability   of   obtaining   a   tap   water   sample   given   a   loca2on’s  water   distribu2on,   P(ds|dl),   is   accomplished   by   integra2ng   each   sample’s   probability  distribu2on   along   possible   evapora2on   lines,   g(t),   where   t   is   the   δ18O   isotopic  enrichment  of  a  sample  due  to  evapora2on.  The  expected  value  of  the  likelihood  of  local  origin   is   then   calculated  by  mul2plying   these   integrated   values  by   the  probability  of   a  specific   local   water   source   and   evapora2on   line   occurring.   For   the   local   water   and  collected   tap   water,   we   assume   standard   mul2variate   normal   distribu2on,   f(...),   with  mean   and   covariance  matrix   based   on   previous   studies   (Bowen   et   al   2007,   Bowen   &  Ravenaugh   2003,   Bowen   et   al   2011).   This   approach   is   represented  mathema2cally   in  equa2on  (1)  as        (1)      

where   x,   y,  m,   are   the   local   source  water   δ18O,   δ2H,   and   local   evapora2on   line   slope  respec2vely.     This   generalized   approach,   as   represented   in   equa2on   (1),   provides   a  quan2ta2ve  framework  for  assessing  the   likelihood  of   local  origin   for  a  sample  given  a  specific  source  distribu2on  (as  shown  in   in  fig  4),  and   is  applicable  to  a  wide  variety  of  ques2ons  of  provenance.    

FIGURE 5: Likelihood of local origin. Relative likelihood of local tap water originating from (A) local precipitation and (B) local surface waters. Circled locations have a likelihood of less then 0.05 (C), and are deemed inconsistent with local sources. A simple multiple linear regression (D) using 5 correlates is able to represent the spatial pattern observed in the west (r2=0.60).

A B

A B

C

D