Regina is situated on the Assiniboine River Plain approximately 30 km south of beautiful Qu'Appelle Valley, a huge glacial meltwater channel whose 1 to 2 km wide floodplain lies some 100 m below the adjoining upland.

To the southwest of the Assiniboine River Plain lies the Missouri Coteau Upland, a hummocky ice- disintegration terrain. To the east, seemingly stretching away forever, is the rolling Moose Mountain Upland (Fig. 1). Our city of about 187, 600 population is located on the bed of glacial Lake Regina, a 6000 km2 extinct ice-marginal lake whose waters reached 50 m in depth about 14,000 years ago (Fig. 2).

Up to 12 m of sticky montmorillonitic clay was deposited on the bottom of Lake Regina (Fig. 3). Up to 200 m of complexly interlayered till and stratified sediment (Fig. 4) overlies Upper Cretaceous Bearpaw Formation

bentonitic marine shale. Testhole drilling in the city suggests this formation is cut by vertical faults associated with collapse following dissolution of underlying Prairie Evaporite strata (Fig. 5).

Reginans' most common and troublesome geotechnical problem is the swelling and shrinking of expansive clay, which each year inflicts hundreds of thousands of dollars damage to light buildings, city pavements, and underground utilities. The Regina clay has over 90% silt and clay, more than 75% montmorillonite in the clay fraction, and a liquid limit of

about 90 (Fig. 6). Testhole drilling along a section of Albert Street shows the thickness variation of this clay over till and the irregularities on underlying, erosional surfaces (Fig. 7).

For over 70 years, beginning in the 1880s, Regina residents relied on groundwater for their water supply, obtaining water from well fields tapping intertill sand aquifers (Fig. 8). These same groundwater sources are now supplemented by surface water diverted down the Qu'Appelle Valley from Lake Diefenbaker. At present, aquifers north and east of the city are said to supply roughly 10 million m3 of well water annually to the city. The Zehner and Northern aquifer systems, as well as most of the Regina aquifer system, are protected from contamination by layers of relatively low permeability Regina clay and clay-rich till. However, the aquifer

underlying the Condie Moraine, which trends WNW-ESE a short distance north of the city ( Fig. 9), is vulnerable to contamination because it is located nearer ground surface and includes a highly permeable stratum (Fig. 10 underlying Regina's industrial and waste-disposal areas.

Over the past 120 years Regina residents have faced a variety of geoenvironmental challenges in addition to the destructive effects of soil moisture change and frost activity on buildings, streets and pavements constructed on

Regina clay. The Regina Plain has a history of flooding (Fig. 11); the evidence of thismay be seen in the high dikes constructed in the area west of Wascana Lake

Q. Fig. 12a - Why is the block of light-colored stratified sand more or less intact and little-deformed in what looks like till? Fig. 12b - How did the block of till get deposited in clean, well-stratified sand? In the early '50s a novel test, called the Inner Lip Test, was designed to confirm the identity of popout-prone, moisture-imbibing opaline shale in concrete aggregate mixes. Can you describe and demonstrate how this test works? What makes this siliceous shale so deleterious in concrete?