Megan Surrette

Two drilled wells completed in fractured quartzite bedrock at sites in East Dartmouth and Waverley were tested to determine aquifer properties and well yields. Tests were conducted at different rates for various durations to determine aquifer response. The data was analyzed by a number of different analytical methods. The current short term test required by Canada Mortgage and Housing Corporation (CMHC) for mortgage purposes was also assessed for its applicability in determining well yield.

The two wells showed a very different type of response. The East Dartmouth well behaved in a manner reflective of an ideal confined. The Waverley well behaved in a non-ideal manner more reflective of an unconfined aquifer with a single water-bearing fracture at very shallow depth. Functionally, the Waverley drilled well was more similar to a shallow dug well completed in fractured bedrock.

The transmissivity values obtained from the analytical methods (excluding the slug tests) range from 0.5 to 0.7 m2/d for the East Dartmouth well and are reasonable for the performance of the well. Values for the Waverley well showed a much wider range, from 0.2 to 1.2 m2/d.. Short term (30-60 minute) well yields based on transmissivity and available drawdown ranged from 0.2 to 0.3 L/s for the East Dartmouth well, and from 0.1 to 0.6 L/s for the Waverley well. Rough estimates based on casing storage rather than traditional analytical methods gave comparable results. The Waverley well gives a higher apparent transmissivity and yield under low rate pumping that does not result in fracture dewatering. In order to optimize yield from similar wells, it may be more appropriate to pump at a lower rate for a longer period of time. In practical terms, this would require additional storage capability in a home, which would increase the cost of the water system. The slug test method is a fast, simple and inexpensive method for determining aquifer properties compared to pumping methods. However, the transmissivities obtained were too high, reflective of areas that are very close to the well and of fractures with the highest hydraulic conductivity. The CMHC test is not very useful in determining aquifer properties under non-ideal conditions. Estimates of well yield based on casing storage methods are probably just as applicable under conditions such as those in the Waverley well. The wide range of results for the Waverley well illustrate the difficulty of determining aquifer properties under non-ideal, low yield, shallow single fracture conditions.

Although the CMHC test is not really amenable to aquifer parameter determination under non-ideal conditions, it is useful as a practical tool to evaluate well response under possible usage conditions. Its test rate is also more typical of typical submersible domestic pumps. Recommendations for further work include consideration of cyclic and step drawdown methods, longer recovery periods, and assessment of other short term yield tests if a database were compiled. Longer term tests should consider use of the derivative method to determine the period during which radial flow is applicable for traditional methods.

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Pages: 222
Supervisor: Heather Cross