The Halma-Lake Bronson area covers about 80 square miles in the northwestern corner of Minnesota. It is a relatively featureless poorly drained glacial drift plain which slopes gently to the west about 10 feet per mile. The plain is interrupted by sand dunes and by beach deposits of Glacial Lake Agassiz. In the northeastern part of the area, the glacial drift rests on Preeambrian crystalline basement rock; throughout the rest of the area the drift is underlain by shale, limestone, and sandstone of Ordovician age, and probably by shale and limestone of Cretaceous age.

Information from 75 test holes showed that, except for minor amounts of surficial swamp sediments, eolian sand, and alluvium, the area is underlain by a'bout 320 to 420 feet of glacial drift. The most important aquifers are the relatively coarse-grained glacial outwash deposits that constitute part of the drift. The principal aquifer is a series of outwash deposits, ranging in thickness from 0 to about 280 feet, that fill a north-south trending valley cut in the underlying relatively impermeable drift. The deposits in this buried valley have an average thickness of about 130 feet in an area about 8 miles long and 3 miles wide, and are considered as a hydrologic unit.

The main source of ground-water recharge is precipitation on the part of the area underlain by the principal series of outwash deposits; evapotranspiration accounts for most of the discharge. The sandy texture of the soil and the flat topography are particularly conducive to recharge, and there is extremely little surface runoff. The average depth to the water table is about 8 feet below land surface. Although the regional slope of the water table is probably to the west, locally the gradient is toward Lake Bronson and South Branch Two Rivers.

Pumping tests of the outwash deposits in 2 parts of the buried valley indicate that the average coefficients of transmissibility were about 80,000 gpd per ft and about 50,000 gpd per ft. The field coefficients of permeability were about 800 and 300 gpd per sq ft, respectively.

About 65 billion gallons of ground water is estimated to be in storage in the area underlain by the principal aquifer.

There are no large ground-water developments in the area. The average depth of farm wells and the few municipal wells is about 25 feet.

Chemical analyses of water from the principal aquifer show that the water is primarily of the bicarbonate type. The water is hard, and contains high iron Concentrations. Most wells yield water that is softer and less mineralized than ground water from the adjacent area to the west.

Large quantities of water suitable for most industrial purposes are available in the Halma-Lake Bronson area. Yields of 1,000 to 2,000 gpm could probably be obtained from wells located by an adequate program of exploratory drilling and test pumping.