Analysis of the Relationship Between Drilling Depth and Groundwater Level

Analysis of the Relationship Between Drilling Depth and Groundwater Level

Drilling depth and groundwater level are two closely related but entirely different concepts. Understanding their relationship is crucial for scientifically planning drilling, accurately estimating costs, and correctly assessing well potential.

I. Distinguishing Core Concepts

Groundwater Level: Refers to the depth of the free, stable water surface in the pores of soil or rock. It is usually measured downwards from the ground surface to the water surface (unit: meters). For example, a groundwater level of 5 meters means that water will be encountered at a depth of 5 meters.

Drilling Depth: Refers to the actual final depth reached during drilling, measured from the ground surface. It is usually much greater than the depth at which water is first encountered.

II. The Dynamic Relationship Between the Two

Drilling depth must exceed the groundwater level, but deeper is not always better. The relationship follows these principles:

Must penetrate the "first encountered water level": This is the minimum requirement. Drilling must first penetrate the first aquifer to reach the first encountered water level.

The key is to reach a "stable aquifer": The water above the first encountered water level (called "perched water") is often small in quantity, unstable, and easily contaminated. Therefore, drilling needs to continue downwards, penetrating the impermeable layer to reach a deeper confined aquifer or stable unconfined aquifer. This aquifer has a more abundant water supply, better water quality, and a more stable water level.

In short: Drilling depth = Depth of first encountered water level + Additional depth to penetrate the impermeable layer and reach a high-quality aquifer.

Relationship between "water line" and well depth: After the well is completed, the stable water surface in the well is called the "static water level." It is usually higher than the top of the aquifer but lower than the first encountered water level. The deeper the well is drilled, the thicker the aquifer penetrated, and the more reliable the water yield usually is, but this increase is not unlimited. After penetrating the main aquifer, further deepening may not significantly improve the water yield.

III. Core Factors Determining Drilling Depth

How deep to drill is mainly determined not by the first encountered water level, but by the following factors:

Burial depth of the target aquifer: This is determined through geological data or local experience. This is the decisive technical factor.

Water demand requirements: The greater the water demand, the thicker the aquifer or the larger the water-bearing cross-section is usually required, which may necessitate deeper drilling. Water Quality Requirements: Deep groundwater is generally of better quality than shallow water and less susceptible to surface contamination.

Geological Structure: If the shallow layers are water-poor, it is necessary to search for aquifers at greater depths.

IV. Practical Advice for Homeowners

Do not stop drilling solely based on the "depth at which water is found": Stopping drilling as soon as water is encountered may only result in a shallow well with low water yield and seasonal drying.

Refer to local experience: Consulting the depth and water yield of existing wells in the surrounding area is the most valuable reference.

Clearly define objectives with the contractor: The contract should specify a "target depth range" (e.g., expected to drill to 30-40 meters) based on local experience, rather than a fixed shallow number.

Understand the risk of "dry wells": Even if the predetermined depth is reached, an ideal aquifer may not be found due to geological anomalies. This is unrelated to construction techniques and is a geological risk; the handling of such situations should be clearly defined with the contractor beforehand.

Summary: Depth is for finding quality water, not just any water

The fundamental purpose of drilling a well is to obtain a stable, sufficient, and high-quality water source. Therefore, the drilling depth should be aimed at meeting these conditions, not just reaching the initial water level. As a homeowner, you should focus on the common depth of stable aquifers in your area and develop a reasonable drilling plan and budget accordingly, understanding the scientific relationship between depth, water yield, and water quality.