Water-quality assessment of the Indiana Dunes National Lakeshore, 1973-74

The Indiana Dunes National Lakeshore is underlain by unconsolidated lake and glacial deposits which have been divided into three units. Unit 1 is comprised mostly of sand and, in the western part of the National Lakeshore, is capable of yielding more than 500 gallons per minute (32 litres per second) to properly constructed wells. Unit 2, a silt till below unit 1, has little potential as a source of water for public supplies within the National Lakeshore area. Unit 4, a clay till under unit 2, is capable of yielding from 10 to 65 gallons per minute (0.6 to 4 litres per second) throughout the National Lakeshore.

Precipitation samples collected at the National Lakeshore had average inorganic ion concentrations ranging from 0 to 7.0 milligrams per litre. Streams in the National Lakeshore generally had a specific conductance ranging from 300 to 600 micromhos, a pH ranging from 6.5 to 8.1, and a dissolved oxygen concentration near saturation (7.7 to 12.9 milligrams per litre). The hogs and marshlands generally contained water with a specific conductance ranging from 40 to 150 micromhos, a pH ranging from 5.0 to 6.5, and dissolved oxygen ranging from 0.2 to 4.0 milligrams per litre. Most surface waters tended to have calcium and bicarbonate as the dominant ion pair. Exceptions include some inter-dunal ponds and certain watercourses and areas of Pinhook Bog. Ground-water chemical quality varied with depth and location but not with time during a 6-month interval. Ground water was usually a calcium magnesium bicarbonate type and moderately to very hard (71 to 390 milligrams per litre).