In　North　America,　numerous　aquifers　as　fresh　drinking　water　supply　sources　have　been　contaminated　from　various　sources　such　as　septic　systems,　leaking　underground　storage　tanks,　spills　or　improper　disposal　of　industrial　chemicals,　and　leachate　from　solid　and　hazardous　waste　landfills.　A　major　task　associated　with　the　contamination　of　aquifers　is　to　develop　effective　tools　to　assess　and　determine　the　health　risks　to　individuals　potentially　consuming　the　water　from　these　aquifers.　This　poses　many　obstacles　due　to　the　complexity　of　the　environment　that　the　contaminant　is　spilled　in　and　the　population　consuming　the　water.　This　paper　presents　a　Monte　Carlo　simulation　based　methodology　which　is　capable　of　considering　many　variations　present　in　the　natural　environment　and　human　populations.　The　methodology　is　tested　using　a　hypothetical　aquifer　and　population　case.　Downgradient　contaminant　concentrations　resulting　from　a　leaking　underground　storage　tank,　containing　petroleum,　are　calculated　using　an　analytical　solution　to　the　two-dimensional　advection-dispersion　transport　model.　Contaminants　under　consideration　include　benzene,　toluene,　and　ethylbenzene　(BTE)　which　can　cause　deleterious　health　effects.　Parameters　and　variables　in　the　model　are　considered　as　random　numbers.　Contaminant　ingestion　dose　is　calculated　using　the　stochastic　exposuredose　model.　Random　population　variables　are　used　to　give　a　distribution　for　contaminant　ingestion　dose　for　each　contaminant.　The　chronic　non-cancer　hazard　index　is　used　to　determine　the　risk　associated　with　the　ingestion　of　non-carcinogenic　contaminants.　The　cancer　risk　is　calculated　using　the　slope　factor,　given　by　the　USEPA,　for　the　carcinogenic　contaminants.　Results　of　the　case　study　indicate　that　environmental　health　risks　can　be　effectively　analyzed　through　the　developed　methodology.　They　are　useful　for　supporting　the　related　risk-management　and　remediation　decisions.　©　2012　by　Nova　Science　Publishers,　Inc.　All　rights　reserved.