Monroe County is on the eastern border of Pennsylvania and includes much of the area popularly called the Poconos. It is an area long used for outdoor recreation and includes a part of the Delaware Water Gap National Recreation Area.

Water resources in the county are derived from precipitation. The Lehigh and Delaware Rivers, bordering the northwestern and southeastern parts, respectively, are the drains for surface-water and ground-water discharge and are essentially unused for water supply.

Water budgets were calculated for average conditions when annual precipitation is 45 in. Sixty percent of this or 27 in. runs off and 65 percent of that runoff or 17 in. moves through the ground-water reservoir. Evapotranspiration varies little between wet and dry years and averages 18 in.

Bedrock consists of Silurian and Devonian sedimentary rocks, which are intensely deformed by folding in the southeastern third of the county and are moderately deformed in the remainder. During the Pleistocene Epoch, glaciers repeatedly advanced across most of the county. The last of these advances deposited a terminal moraine that extends across the southwestern part of the county. The glaciers eroded pre-existing deposits, veneered the upland, and filled valleys with unconsolidated deposits that changed surface-water drainage and altered ground-water gradients.

Water occurs in fractures and solution openings in the consolidated rocks and in intergranular openings in the unconsolidated rocks and weathered calcareous sandstones. Water that reaches the water table moves down the hydraulic gradient to points of discharge, moving both laterally and vertically away from ground-water divides and toward streams. The thickness of the fresh-water system is 800 ft or more, but little water is yielded to wells by aquifers more than 500 ft below land surface. Ground-water recharge is 600 to 650 (gal/min)/mi²; and about 1.6 billion gallons per square mile is stored in the ground-water reservoir.

Currently the most productive wells are in consolidated-rock aquifers; however, specific-capacity data suggest that wells in the unconsolidated deposits have potentially larger yields. Well yield is affected primarily by the distribution, size, and interconnection of the water-bearing openings and by topographic location, available recharge, well-depth, location within the flow system, pumping rate and duration of pumping, and interference from other pumping wells. Potential yields of properly located, drilled, and developed wells have been calculated for the aquifers. The median yields calculated from specific capacity data from the unconsolidated deposits, are 200 gal/min; from the Bloomsburg Formation, 100 gal/min; and from the Poplar Gap Member of the Catskill Formation, 70 gal/min. Median yields of the other units range from 15 to 40 gal/min. In general, enough water for domestic use can be obtained throughout the county. Large-scale development and consumptive use of the ground water will diminish baseflow of the streams.

The temperature of water measured in wells ranges from 44° to 57°F and is largely dependent on altitude of the land surface and depth to the producing zone. Hardness of water in the noncarbonate rocks averages 3 to 4 grains per gallon, or about half that of the carbonate rocks. Water from most of the bedrock aquifers is low in dissolved solids, acidic, and soft. In carbonate rocks, the water tends to be hard and slightly alkaline. Excessive amounts of iron and manganese are encountered in water from the unconsolidated deposits and, locally, from the Catskill and Shawangunk Formations.