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Nitrate loading from an intensively managed commercial red raspberry field to groundwater in the Abbotsford-Sumas Aquifer, British Columbia was estimated over a 1 yr period and compared with the nitrogen surplus calculated using a simple nitrogen budget. Nitrate loading was estimated as the product of recharge (estimated from climate data as total precipitation minus potential evapotranspiration (PET)) and monthly nitrate concentration measured at the water table. Most nitrate loading occurred when nitrate, accumulated in the root zone over the growing season, was leached following heavy autumn rainfall events. Elevated groundwater nitrate concentrations at the water table during the growing season when recharge was assumed to be negligible suggested that the nitrate loading was underestimated. The estimate of annual nitrate loading to the water table was high (174 kg N ha−1) suggesting that the tools currently available to growers to manage N in raspberry production are not adequate to protect groundwater quality. The calculated nitrogen surplus from the nitrogen budget (180 kg N ha−1) was similar to the measured nitrate loading suggesting that simple nitrogen budgets may be relatively effective indices of the risk of nitrate loading to groundwater.

Groundwater contamination of the Abbotsford aquifer by 1,2-dichloropropane (1,2-DCP) was reported previously. The purpose of the present study is to quantify groundwater contamination by other chlorinated hydrocarbon compounds which are present in fumigant formulations containing 1,2-DCP. Widespread contamination of 1,2,2-trichloropropane (1,2,2-TCP) was measured consistent with a non-point source. 1,2,2-TCP concentration generally decreased with depth suggesting a surface source. Localized contamination by 1,2,3-trichloro-propane, 2,3-dichloropropene and 1,3-dichloropropane was detected. Detection of these compounds was associated with higher concentrations of 1,2-DCP suggesting contamination by these compounds may have been from the same fumigant sources. The lack of a decrease in the concentration of most of these compounds over time suggests that the measured contamination will persist for some time. The results highlight the potential for persistent trace impurities in chlorinated fumigant formulations to contaminate groundwater in vulnerable aquifers.

Forty piezometers at 13 sites in the Canadian portion of the Abbotsford aquifer were tested for 1,2-dichloropropane (1,2-DCP) and 1,3-dichloropropene (1,3-DCP) on an approximate monthly interval from July 1991 to June 1994. Detectable levels of 1,2-DCP were found in 32 of the 40 piezometers. Average 1,2-DCP concentrations within a piezometer ranged up to 2.23 µg/L and a maximum concentration of 7.07 µg/L was recorded in one piezometer. 1,3-DCP was detected for only a short period of time in one piezometer and at a maximum concentration of 0.23 µg/L. 1,2-DCP contamination in the aquifer is attributed to application of fumigants containing this compound as an active ingredient or as an impurity for the control of root nematodes in red raspberry crops. The nature of the contamination is consistent with a non-point source that is highly variable in space and time. Although soil fumigants containing 1,2-DCP as an active ingredient are no longer used in the Abbotsford area, fairly constant values of 1,2-DCP would indicate there is still a contaminant source providing input to the groundwater. 1,2-DCP has apparently accumulated on the soil sediments above the water table and is slowly being released to the groundwater. In the top 15 m of the saturated zone, concentrations generally decreased with depth below the water table to near nondetectable levels. Correlation between contaminant levels and rainfall or other environmental factors that might affect the distribution of 1,2-DCP could not be established. More detailed soil measurements and controlled laboratory experiments are needed to determine 1,2-DCP movement as well as rates of dissipation in the Abbotsford aquifer.