Protocol for the Derivation of Environmental and Human ... - CCME

Appendix D
during spring snowmelt. Many of these factors vary greatly on local rather than regional scales. In the
absence of a systematic data summary, surface runoff is assumed to average 15% of the total amount of
recharge and surface runoff:
R = 0.85 (P - ET) [13]
Precipitation data were obtained from Environment Canada (1982) and actual evapotranspiration data
taken from small scale maps prepared by Fisheries and Environment Canada (1978). Where more than
one precipitation monitoring station was available for a given location the mean of all observations was
used.
Results
Recharge calculated from equation [13] for a rqange of locations spanning most climatic types common
to populous areas of Canada are presented in Fig. D.3. Estimates range from nearly 1 m in maritime
regions to near zero in some prairie locations. Small, negative values of drainage occur in some arid
locations. These likely are caused by underestimation of precipitation by standard gauges (Fisheries and
Environment Canada 1978) and, in any event, deviate from more direct estimates of drainage in these
locations by only a few mm (C. Maulé 1993, pers. comm.).
Extreme values of recharge (>1 m) occur, or are expected to occur, in maritime regions of high rainfall -
- particularly exposed coastal areas of British Columbia and Newfoundland. However, in these areas
groundwater protection concerns are in part mitigated by:
• the relatively infrequent occurrence of potable, unconfined, shallow aquifers (related to the
preponderance of porly permeable igneous and metamorphic bedrock types); and
• low human population densities, which should indicate low contaminated site frequency.
Recharge in high precipitation regions is likely overestimated in equation [13] because surface runoff and
interflow is increased by:
• the generally greater relief existing in these areas of Canada, and
• the frequency and duration of precipitation can exceed the soil infiltration capacity.
Recharge in populated areas of Quebec surrounding the St. Lawrence river has been estimated to range
to about 0.3 m (L. Martel 1994, pers. comm.).
For the screening purposes here recharge was taken to vary between 0.005 and 0.5 m yr -1 . A modal
recharge of 0.2 m yr -1 was chosen to reflect the abundance of contaminated sites in the Windsor to
Quebec City corridor.
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