Groundwater Pollution Groundwater and Groundwater Pollution Lecture by Dr. Ken Galli, Boston College EESC116301 Environmental Issues and Resources July 26, 2016 Please do not distribute beyond the EESC116301 Class.

1 m = 100 cm = 1000 mm. ----- Meeting Notes (7/10/12 07:33) ----- 76cm = 30inches per year 1 m = 100 cm = 1000 mm.

AVERAGE PRECIPITATION OF THE UNITED STATES https://upload.wikimedia.org/wikipedia/commons/d/d3/Average_precipitation_in_the_lower_48_states_of_the_USA.png accessed 3/18/16.

U.S. average annual precipitation Note: 20 inches = 51cm 100th meridian >20 in/yr <20 in/yr (inches) (Understanding Earth, 2004)

Semi-arid to Humid Arid 20in =51cm Two Major Soil Types in the United States as result of Average Precipitation Pedocals—soils formed in semi-arid to arid areas. Rich in Calcium. Made of thin A horizon with underlying calicite-rich B horizon called Caliche Pedalfers—soils formed in humid areas. Rich in Aluminum and Iron Oxides. Made of organic-rich (humus) A horizon (zone of leaching), B-horizon rich in Al and Fe-oxides (zone of accumulation), and C-horizon—Regolith/slightly decomposed bedrock or parent material. Semi-arid to Arid Humid 20in =51cm

Chemical weathering makes soil (Understanding Earth, 2004)

Mechanical Weathering increases Surface Area available for Chemical Attack!

U.S. average annual runoff: lots of water evaporates and infiltrates (inches) (Understanding Earth, 2004)

Global Water Cycle Cyclic nature Global distribution Global movement of water between different water storage compartments Global distribution Abundance not a problem Distribution in space and over time a problem Supply vs. Use a problem

Global Water Cycle Water’s vertical movement Upflow: Evaporation, transpiration Downflow: Precipitation and infiltration Water’s horizontal movement Surface runoff Shallow subsurface through flow Groundwater flow

t = Global Water Supply Residence Time (t) V q is the average amount of time that a particle spends in a particular system. V {The capacity of a system to hold a substance} t = q {The rate of flow of the substance through the system}

Idealized diagram showing the hydrologic cycle’s important processes and transfer of water. (Modified after Council on Environmental Quality and Department of State. 1980. The Global 2000 Report to the President. Vol.2)

505,000 Units are thousands of cubic kilometers (km3) per year. (Data from Gleick, P. H. 1993. An introduction to global fresh water issues. In Water in Crisis, ed. P. H. Gleick, pp. 3–12. New York: Oxford University Press)

Map shows Two Drainage Basins Drainage density is controlled By underlying Bedrock.

Porosity and permeability (Understanding Earth, 2004)

Joints- fractures without movement Faults- fractures with movement Hawk Mountain, Pennsylvania (2004)

Water table (Understanding Earth, 2004)

Discharge of groundwater from Fern Spring at the southern end of Yosemite Valley, California. This spring emerges at the base of a hill slope, as do many springs. The small stream emerging from the spring pool in a short cascade or falls is about 2 m (6.6 ft) wide. (Edward A. Keller)

Perched aquifer (Understanding Earth, 2004)

Water rises in homes because of pressure created by the water level in the tower. If there is only a small amount of friction in the pipes, there will be little drop in pressure. (b) The pressure surface, or water table, in natural systems declines away from the source because of friction in the flow system, but water may still rise above the surface of the ground if impervious particles such as clay create a confining layer and cap the groundwater.

Cone of depression in the water table, resulting from pumping water from a well.

Groundwater Movement (1) Hydraulic gradient: The gradient of water table, generally following the topographic gradient Hydraulic conductivity: Ability of rock materials to allow water to move through (m3/day/m2) Porosity: Percentage of void (empty) space in sediment or rock to store water Permeability: Measuring the interconnection of pores in a rock material

Groundwater Movement (2)

Hydraulic Gradient is the inclination of the water table surface.

439 -15 feet = 424 feet

This amount is temporarily (seasonally) stored, but it will be given up to plants and streamflow and lakes.

Groundwater Use and Supply (1) Available GW estimated above the total flow of the Mississippi during the last 200 years GW as primary drinking water source for ~50% of the U.S. population GW overdraft problems (extraction rate exceeding recharging rate) in many parts of the country, particularly some states in the Great Plains region Estimated 5% of GW depleted, but water level declined more than 15 m (50 ft) in some areas

Ogallala Aquifier Groundwater overdraft for the contiguous United States. (b) A detail of water level changes in the Ogallala aquifer, Texas-Oklahoma-High Plains area. (U.S. Geological Survey)

Interactions b/w SW and GW Overdraft of GW: Leads to lower water levels of streams, lakes, reservoirs, etc. Overuse of SW: Yields lower discharge rates of GW Effluent stream (in GW discharge zone): Tends to be perennial Influent stream (in GW recharge zone above the water table): Often intermittent or ephemeral Special linkage area: Sinkholes and cavern systems in the karst terrains

Interceptor wells create Cone of depression which Can change direction of Flow of contaminated Groundwater.

Sinkhole

The Colorado River basin, showing major reservoirs and the division of the watershed for management purposes. The delta, once a large wetland area, at the head of the Gulf of Mexico has been severely degraded as a result of diversion of water for various uses.