Ministry of Environment
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Report: Groundwater Quality Survey of Aquifers in South Cowichan, Vancouver Island

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A survey was conducted of groundwater quality in samples from wells constructed in the Cobble Hill (AQ197) and Cherry Point (AQ198) aquifers in the South Cowichan area. Samples were collected from 82 wells (70 private domestic and 12 water supply systems). Water quality in the region was excellent overall. Naturally occurring contaminants, manganese and arsenic were widespread. Nitrate concentrations below drinking water above background at some sites was linked to human land use.

Author:  Sylvia Barroso, Cali Melnechenko

Date Published:  Dec 2019

Report ID:  58351

Audience:  Government and Public

A snap-shot survey of groundwater quality in wells in South Cowichan, Vancouver Island was conducted in November 2013 to March 2014. Samples of untreated groundwater were collected from 82 wells. Samples were analyzed for 60 parameters including general chemistry, metals and bacteria. Samples with nitrate-nitrogen above 2 mg/L were analyzed for nitrate isotopes. Groundwater quality was found to be excellent overall. Naturally occurring contaminants arsenic and manganese were widespread and exceeded health related water quality guidelines in samples from 2 (2%) and 24 (38%) of sites respectively. Iron was above aesthetic drinking water quality guidelines ins samples from 14 (17%) wells. Nitrate, associated with land use such as pollution discharges and agriculture, was undetected in samples from 27 (33%) wells and below health related guidelines at all sites sampled. A present background concentration of 0.5 mg/L nitrate was estimated using all available data (261 samples) from wells in aquifer 197 collected over a period from 1979 to 2019. In comparison, within the 2013-2014 study, 27 (42%) of samples, had concentrations above a 0.5 mg/L nitrate background. Nitrate isotope analysis indicated that organic materials such as human or animal waste (manure) was the predominant nitrogen source. Elevated nitrates were observed within areas that were highly vulnerable, based on the aquifer vulnerability index (AVI) or DRASTIC ratings; however, intrinsic vulnerability of the aquifer in the area of a well was one of several factors apparently influencing nitrate in groundwater. Nitrate concentrations also varied according to spatial proximity to either point‐source or non‐point sources of pollution. Thus, while the presence of confining sediments overlying an aquifer may provide some protection from contaminant hazards, management and reduction of contaminant inputs is key. Well maintenance concerns such as missing or broken well caps, flooded well pits, buried well heads or low casing stick‐ups were identified at 41% sites and well owners were provided with information on how to fix and protect their wells.

Report Type
  Region - Vancouver Island
  Watershed Groups - 920 - Vancouver Island (East) Rivers
  Water Information - Groundwater
  Water Information - Water Management
  Water Information - Water Quality

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