Groundwater Geochemistry of the Nanaimo Group in the Yellow Point and Gabriola Island areas.

Groundwater Geochemistry of the

Nanaimo Group in the Yellow Point and

Gabriola Island areas

Environment Ministry evidence for elevated fluoride levels

Malaspina well-water sampling program was initiated in 2000

Focused on Yellow Point and Gabriola Island areas because they showed some particularly high levels, and are close to

Nanaimo.

~ 100 wells at Yellow Point (2000)

~ 75 wells on Gabriola (2001)

gabriola map

mudstone unitssandstone units

anion diagram

mudstone unitssandstone units

Proportion of water samples with fluoride levels above the MAC (maximum acceptable

concentration)

Yellow Point ~13%Gabriola ~8%

RDN Landfill Observation well data

Upper and lower samples at multi-piezo-meter sites

landfill Ca

representative n.g. g-waters

"Representative" Nanaimo Gp. water data from M. Env. website*

Location type Depth pH Ca Mg Na HCO3 Cl Cond.

    m   mg/L mg/L mg/L mg/L mg/L uS/cm

Denman recharge 3 6.3 16 2.9 7.9 71 4.1 150

Gabriola recharge 11 6.8 7 1.0 32 80 5.4 183

Hornby recharge 6 7.3 29 6.7 40 171 20 368

Mayne recharge 24 7.3 24 6.7 12 110 6.9 229

N. Pender recharge 55 6.8 55 14.0 33 244 25 523

Saltspring recharge 30 7.8 25 2.6 37 156 11 315

Denman discharge 18 8.5 11 0.2 313 189 390 1500

Gabriola discharge 27 8.7 21 0.0 170 109 223 911

Hornby discharge 24 8.0 30 4.9 1270 238 1890 6100

Mayne discharge 23 8.7 21 5.3 854 287 960 4900

N. Pender discharge 50 8.0 58 4.6 815 287 1130 4260

Saltspring discharge 62 9.0 2 0.2 354 510 220 1600

*Kohut, A, Foweraker, J and Hodge, W, Groundwater Resources of British Columbia, 9.13 Gulf Islands,

• According to the Le Chatelier principal, a decrease in the Ca content (because Ca is being removed from the water and adsorbed onto clays) will drive this reaction to the right, increasing the bicarbonate level, and resulting in a higher pH. This is base-exchange softening.

CaCO3 + CO2(g) + H2O = Ca2+ + 2HCO3-

owen drilling

Outcrop sampling at Yellow Point and Gabriola

f-b for rocks

mudstone units

sandstone units

ph-f

ca-f

na-f

so4-f

cl-f

b-f