Procedure for Conducting Pumping Tests part (2)
Designing and planning a pumping test is critical prior to testing. Lack of planning can result in delays, increased costs, technical difficulties and poor or unusable data.
Some things to consider in the pre-planning stage are:
1) time of year the pumping test should be done
2) natural variations in the groundwater levels that occur during the test
3) informing others who may be affected
4) depth of pump setting and type of pump
5) pumping duration
6) pumping rate
7) control and measurement of the pumping rate
8) frequency of measurements of the water levels
9) measuring water levels in neighbouring wells and/or streams
10) discharge of pumped water
11) collection of water samples for water quality analysis
special conditions to be aware of e.g., salt water intrusion in coastal aquifers
Materials required for conducting pumping tests:
For conducting pumping tests and analysing the data, the following items may be required:
1) generator
2) submersible pump
3) discharge pipe, connections
4) flow measurement device(s)
5) tape measure(s), steel tape(s) and carpenter's chalk
6) pressure transducer(s), cables, data logger(s)
7) electric water-level sounder(s) and batteries
8) watches/stopwatches
9) barometric sensor/ thermometer
10) pH and conductivity meters
11) sample bottles
12) toolkit, , wires
13) data collection forms, log book, permanent-ink pens
14) computer, calculator
15) graph paper (semilog, log) and/or computer software
16) references, standard operating procedures
17) manufacturer's operating manuals for equipment
18) maps (site, geologic and topographic), cross section(s).
Well-Inventory analysis:
Well-inventory is one basic step. Well inventories are also conducted as part of most of the environmental investigations.
Different types of wells are studied for recording their yielding capacities, main aquifers contributing to yield, etc. The nature and period of their use and sustainability are also recorded. The hydrostatic heads of the aquifers are monitored on a monthly basis through shallow dugwells (monitoring stations), piezometers, deep wells, etc, in the areas. Water samples are collected from selected wells and analysed to determine the variation of water quality over time and space.
Before conducting a pumping test the geological and hydrological information of the area should be collected.
1. The geological characteristics of the subsurface (i.e. all those lithological, stratigraphic, and structural features that may influence the flow of groundwater).
2. The type of aquifer and confining beds. 3.The thickness and lateral extent of the aquifer and confining beds.
4. The aquifer may be bounded laterally by barrier boundaries of impermeable material in the lithology (e.g. the bedrock sides of a buried valley, a fault, or simply lateral changes of the aquifer material);
Data on the groundwater-flow system: horizontal or vertical flow of groundwater, water table gradients, and regional trends in groundwater levels.
Details of any existing surrounding wells in the area.
Well should be suitable for the test.
1) The hydrogeological conditions should not change over short distances and should be representative of the area under consideration, or at least a large part of it;
2) The site should not be near railways or motorways where passing trains or heavy traffic might produce measurable fluctuations in the hydraulic head of a confined aquifer;
3) The site should not be in the vicinity of existing discharging wells;
4) The pumped water should be discharged in a way that prevents its return to the aquifer.
The gradient of the water table or piezometric surface should be low;
Manpower and equipment must be able to reach the site early and easily.
New Exploratory and observations wells:
If there is no existing well in a region, bore wells are drilled for pumping test purpose. Sometimes, bore well drilled for drinking water supply purpose are tested to know the hydrological properties, by conducting pumping tests.
Before conducting the pumping test the dimensions of the well should be measures.
Radius for circular wells. length and width for rectangular wells.
The depth also should be measured. if it is new well, during the drilling operations, samples of the geological formations that are pierced should be collected and described lithologically.
Records should be kept of these lithological descriptions, and the samples themselves should be stored for possible future reference.
Well screen: for bore wells, the casing pipe length should be measured.
END OF PART 2
No comments:
Post a Comment