Groundwater Study on Hornby Island

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EARTH SCIENCES 
SIMON FRASER UNIVERSITY 
 
 
 
 
 
Results of the Groundwater Geochemistry Study  
on Hornby Island, British Columbia 
 
 
Final Report 
 
 
 
 
Prepared by: 
 
D.M. Allen and G.P. Matsuo 
Department of Earth Sciences 
Simon Fraser University 
Burnaby, B.C.  V3Y 2L4 
 
 
 
Prepared for: 
 
Islands Trust 
Victoria, B.C. 
 
 
 
 
 
 
 
 
 
 
April 2002 
 

 
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EXECUTIVE SUMMARY 
 
Because  groundwater  supplies  the  majority  of  potable  water  in  many  coastal  
communities  and  islands  in  British  Columbia,  more  attention  is  being  paid  to  its  
quality  and  quantity,  and  to  the  processes  that  potentially  threaten  this  valuable  
resource.  This  study  benchmarks  the  current  groundwater  chemistry  on  Hornby  
Island,  characterizes  the  general  evolution  of  groundwater  on  the  island,  and  
provides  data  for  future  studies  involving  the  chemical  evolution  of  groundwater  
on the Gulf Islands.   
 
Water  samples  were  collected  from  wells  volunteered  by  local  residents  under  
the  auspices  of  a  joint  pilot  project  between  the  B.C.  Ministry  of  Environment,  
Lands and Parks, the Islands Trust and Simon Fraser University. Water samples  
were analyzed for dissolved ionic species (i.e., metals and common anions) and 
were interpreted in the context of the local geology in order to provide information 
on  the  chemical  character  of  groundwater  (including  the  spatial  distribution  of  
dissolved  metals  and  anions),  the  evolution  of  groundwater  within  different  flow  
regions, and the location of recharge and discharge areas. 
 
Groundwater on Hornby Island is recharged locally, typically at high elevation in 
areas  corresponding  to  Mount  Geoffrey  and  the  Crown  Land.  However,  the  
relatively   immature   chemical   composition   of   many   well   waters   (calcium-
bicarbonate  type  water)  situated  at  lower  elevations  suggests  that  recharge  
occurs   over   a   significant   portion   of   the   island.   Many   groundwaters   have   
undergone  extensive  cation  exchange,  a  process  whereby  sodium  replaces  
calcium  during  and  following  the  dissolution  of  calcite.  It  is  suggested  that  
groundwater  flow  through  fractured  mudstone  units  may  be  the  cause  for  the  
high  occurrence  of  cation  exchange.  Mature  groundwaters,  characterized  by  
higher   concentrations   of   chloride,   result   from   mixing   between   the   Na-rich   
groundwater and seawater. Several wells in the Whaling Station Bay area show 
significant  salinization,  and  suggest  that  saltwater  intrusion  may  be  prevalent  in  
that area. 

 
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ACKNOWLEDGMENTS 
 
Financial  support  for  this  study  was  provided  by  the  Islands  Trust,  and  the  
research   was   undertaken   by   Gregory   Matsuo   in   partial   fulfillment   of   the   
requirements  for  a  B.Sc.  Honours  degree  in  Earth  Sciences  at  Simon  Fra

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