able below shows basic information needed for ground water vulnerability assessment and mapping. This is the most comprehensive list; not all information can be easily collected nor entered into a Ground Water Information System (GWIS). The table serves as a reminder for data collection and data base design. Table is modified from the Guidebook on Mapping Groundwater Vulnerability. IAH, 1994.

TOPOGRAPHY	�Elevation, slope variability of land surface; surface runoff paths, stream network density.
VEGETATIVE COVER	�Land use, subsurface water pathways, recharge and discharge areas, fracture traces and lineaments, contaminant potential.
CLIMATOLOGY	�Long records of precipitation, average temperature, humidity, solar radiation, evaporation, evapotranspiration; effective precipitation assessment.
SOILS	�Thickness, structure, texture, mineralogy, chemical and physical properties, porosity, permeability, moisture, infiltration capacity.
HYDROLOGY	�Streamflow discharge, hydrograph analysis, baseflow, flow ratio, water exchanges with underlying ground water systems.
HYDROGEOLOGY (Unsaturated zone)	�Depth to water; thickness, lithostratigraphy, mineralogy, geometry, fracture index, karst index, effective porosity, and saturation ratio of surficial deposits; vertical effective permeability, effective flow velocity, infiltration rate index, net recharge.
HYDROGEOLOGY (Saturated zone)	�Lithostratigraphy, geological structure, geometry, effective porosity, permeability type (primary or secondary), transmissivity, storativity, and hydraulic conductivity of an aquifer; aquifer type (unconfined, semiconfined, confined); water level fluctuations, hydraulic gradient, flow directions, effective flow velocity and discharge, ground water divides, exchanges with surface water bodies or/and adjacent aquifers.
WATER USE	�Water-discharge points (spring, wells) and location of ground water extraction works; surface and ground water sources, distribution, and usage; yield and drawdown of pumping/dewatering plants, location and inflow rate of recharge systems.
HYDRO-CHEMISTRY	Physical and chemical properties of surface and ground water, chemical markers, isotope content, age and residence time of water, characteristic ratios; natural surface and ground water quality distribution.
CONTAMINANT FEATURES	�Changes in water quality; contaminants present and their physical and chemical characteristics, concentration, half-life, persistence, mobility, dispersivity, cation exchange capacity, biodegradability, etc.
HUMAN IMPACT ON ENVIRONMENT	�Extent of urban areas, location and type of industrial complexes, existing and potential contamination sources, potential contamination entries, main objects of protection.

• Sea water intrusion: closeness to the coast, intrusion already advanced, too much ground water development.
• Soil cover: thickness, permeability, filtration and sorption capacity.
• Land use: agriculture with fertilizers (nitrates, phosphates, etc.).
• Depth to ground water.
• Ground water gradient, velocity of flow, residence time.
• Alluvial deposits near rivers, rivers recharging aquifers, local cones of depression created near rivers.
• Industrial developments, waste water ponds, industrial canals.

Sea Water Intrusion

• More than 5 km from the coast.
• Within 2 and 5 km distance.
• 2 km coastal belt in pumped area.

Soil Cover

• Zero cover thickness. Permeable materials (sand, gravel, limestone) exposed at the surface.
• Clay, marl, mudstone, shale, and like, between 0 and 10 m thick, clean, impermeable; or more than 10 m thick but with sandy or loamy content.
• Clay, marl, mudstone, shale, and like, more than 10 m thick; w/out sand, loam, or rock.

Land Use

• Intensive agricultural developments, land fertilized with manure and industrial fertilizers.
• Sporadic agricultural development, rain fed, use of industrial fertilizers only.
• No agricultural developments.

Depth to Ground Water

• Ground water normally less than 5 m below ground surface. This refers to unconfined aquifers.
• Ground water between 15 and 5 m deep. Unconfined aquifers only.
• Confined aquifers or ground water more than 15 m deep.

Ground Water Gradient, Velocity of Flow

• Slow ground water flow, gradient less than 0.001 m/m; alluvial plain. Already established local cones of depressions due to heavy abstraction belong to this category.
• Medium fast ground water flow; e.g. limestone at the slope break, within a plain.
• Rapid natural ground water flow, short residence time. E.g. limestone, fractured, fissured, cavernous.

Alluvial Deposits near River

• Aquifer receives water from the river during most of the year. A local abstraction has already created cones of depression below the river water surface.
• River under flood stage may affect nearby aquifers.
• River not affecting alluvium and shallow aquifers.

Industrial Developments, Waste Ponds

• Aquifer development near existing waste ponds or established industries.
• Industry remote, but an extended cone of depression may reach the places of industrial effluents, waste ponds, or local damping sites.
• No industry within possible ground water development.

oastal belt.

The quality of ground water near the coast is not good. Electrical conductivities above 3000 microS/cm result from (a) tidal effects, (b) high abstraction in the past along the coast and/or several kilometres inland. One map shows the sites with increased electrical conductivities:

To fight back the sea water intrusion, one would have to cut back on abstraction - a highly unpopular and difficult to implement measure. Higher, "historic" ground water levels could be restored only by reducing the pumping from many kilometres back inland. The "protective" steps should be taken from the highway May Pen - Mandeville all the way down to the coast.

mproper Well Construction.

Many wells drilled in alluvium have been completed by improper placing of well screens. In some wells the screen has been set opposite clayey materials rather than permeable sand and gravel. Examples are:

ells Near Rio Minho

• The Rio Minho enters the Clarendon Plain NNE of May Pen at North Hall. The Rio Minho looses all of its dry season flow to the limestone aquifer between North Hall and Alley - an average of 20 MCM/Y (source: FAO, 1974; Rio Minho -Milk River Basin, Jamaica. AGL:DP/JAM/70/512 Technical Report 1.).
• The map of the Rio Minho between North Hall and Alley shows that there are many wells drilled near the river for domestic use (big circles), and many more more agricultural and industrial uses (small circles).
• The dry river bed serves as a recharge area after heavy rains. It must be kept under sanitary controlled conditions to prevent any surface contaminant entering the limestone system underneath the river bed.

ndustrial Waste Ponds

• One large industrial waste pond is identified in the map. This is a "red mud" deposit obtained as a by product of processing bauxite to alumina. Normally, due to technological process used, the waste water is characterized by very alkaline conditions (pH>11). If there is a connection between the pond and the ground water, the latter's pH would be expected to be high.
• There is a well nearby, used for domestic (including drinking) purposes. The well, RM-022 or Hayes Primary School, is located not more than 150 m from the edge of the waste pond. Its lithology favours hydraulic connection with the surface, but its chemical analyses taken over the period between 1983 and 1992 does not indicate any deterioration of the quality with respect to electrical conductivity, TDS, Cl and Na. Water's pH value is not increased, neither is its Na content. (A hydraulic connection with bauxite-processing-produced waste water ponds would be indicated by high Na values and pH values greater than 9.)

epth to Water

Depth to water in wells shows the following:

oil Cover

Soil cover, soil texture, permeability and storage capacity are important parameters in a study of vulnerability of aquifers. The limestone aquifer in the Rio Minho Basin is particularly vulnerable, considering poor filtration capacity of limestones and their karstic nature.

A map is prepared for a limestone area between May Pen and Mandeville showing thickness, in feet, of more or less impermeable soil overlying permeable limestone. One may select one of 27 wells to display their lithological logs and check the thickness and characteristics of soil.