Question

please answer this question!!!

4)

Describe how scale influences the estimation of hydraulic parameters obtained from core samples, slug tests and pumping tests. which method tends to produce the most reliable estimates? why?

Answer 1

A slug test is a controlled field experiment performed by groundwater hydrologists to estimate the hydraulic properties of aquifers and aquitards in which the water level in a control well is caused to change suddenly (rise or fall) and the subsequent water-level response (displacement or change from static) is measured through time in the control well and one or more surrounding observation wells. Slug tests are frequently designated as rising-head or falling-head tests to describe the direction of water-level recovery in the control well following test initiation. Other terms sometimes used instead of slug test include baildown test, slug-in test and slug-out test.

Besides slug tests, other types of aquifer tests used to determine aquifer properties include pumping tests and constant-head tests.

the following slug test topics:

• rising and falling head slug tests
• overdamped vs. underdamped response
• wells screened across water table
• well construction details and field data you'll need
• initiating a slug test
• taking water-level measurements
• normalized head
• test duration
• The saturated thickness of the aquifer under investigation may not be known from direct measurement at the control well in certain groundwater studies (e.g., LNAPL monitoring). In such cases, the thickness must be be estimated from other data sources such as nearby wells, published reports, geologic maps, geophysics, etc. Another strategy is to perform a sensitivity analysis for a range of aquifer thickness values and observe how varying the thickness affects your estimate of hydraulic conductivity.Pressure transducers are available in vented and nonvented models. Vented transducers measure pressure relative to the ambient barometric pressure. Nonvented transducers measure absolute pressure including the pressure of the air column above the sensor. A barometric sensor is required to correct readings from nonvented transducers for changes in barometric (air) pressure.=

procedure:

1. Measure the ``static'' depth to water from your benchmark, before any water is removed from the well
2. Remove the beeper tape from the well.
3. Remove the desired volume of water from the well using the bailer (one liter for each group)
4. Record water level recovery slug test data form.

Subtract the measurements you collect as the pump is running from the static water level. The difference is the drawdown. For example, if the static water level is 1 foot below the top of the casing and the water level after one hour is 3 feet below the top of the casing, the drawdown at one hour of pumping is 2 feet.

Slug tests may be initiated in a number of ways including the following methods:

• solid slug
• bailer
• pneumatic pressurization

Of these initiation methods, the pneumatic technique is often preferred for its ability to reduce noise immediately after the start of a test especially in high-hydraulic conductivity (high-K) aquifers (Butler 1998). For slug tests in wells screened across the water table, however, the pneumatic method is not viable and an alternate method of test initiation is required.