Drilling a Water Well in Southwest Idaho: What Homeowners Should Know

When you watch a well driller at work, it might look like just another machine punching a hole in the ground. But in reality, water well drilling in Southwest Idaho is a highly technical process, guided by Idaho Department of Water Resources (IDWR) statutes, deep knowledge of local aquifers, and a science called lithology.

At Hydro, we specialize in bringing that science and regulation together to safely and legally access the Treasure Valley’s groundwater. Here’s what the process looks like and why geology matters.

Step 1: Permitting & IDWR Rules

Before the first bit hits the ground, drilling a well requires:

• A well drilling permit filed with IDWR (Idaho Code Title 42, Chapter 39; IDAPA 37.03.09 – Well Construction Standards).

• A licensed driller – only contractors with valid IDWR licenses may legally drill wells.

• Site compliance – rules govern how close wells can be to septic systems, property lines, and other wells to protect groundwater quality.

These statutes exist to make sure every well is safe, properly sealed, and protective of Idaho’s aquifers.

Step 2: Understanding the Aquifers of Southwest Idaho

The Treasure Valley and surrounding basins sit atop a layered aquifer system—think of it as stacked underground reservoirs of water, separated by layers of clay or rock.

• Shallow aquifer (0–200 ft)

  Found in sandy and gravelly deposits near the Boise, Payette, and Snake Rivers. Commonly used for irrigation and some domestic wells, but water levels can fluctuate with seasons and pumping.

• Intermediate aquifer (200–600 ft)

  Often tapped for rural domestic wells. Provides more stable water levels but may require deeper casing and careful sealing to prevent mixing with shallow water.

• Deep aquifer (600–1,200+ ft)

  Confined beneath thick clay and basalt layers. This is where many municipal and community wells draw from. Water is generally higher quality, but drilling costs and technical challenges increase significantly at these depths.

Because these aquifers are layered, IDWR requires proper well seals to keep water from one zone from leaking into another. This prevents contamination and preserves water quality.

Step 3: Lithology—Reading the Earth Like a Book

As drillers cut deeper into the ground, they record the changing layers of soil and rock. This record is called a lithologic log (or litholog).

A litholog shows:

• Depth of each layer (sand, gravel, clay, basalt, silt, etc.)

• Thickness of water-bearing zones

• Where casing and seals were set

Think of it as the “biography” of your well—an official record required by IDWR and submitted with the driller’s well report.

Why it matters: lithology tells us whether your water is in clean, coarse sand and gravel (ideal for yield), or in fine silts or clays (lower production). It also guides how we size your pump, protect your aquifer, and design your well for decades of reliable use.

Step 4: The Drilling Process

Drilling isn’t one-size-fits-all. Here’s how Hydro typically approaches a well in Southwest Idaho:

1. Set surface casing & seal

   A steel casing is installed through the upper layers and sealed with bentonite or cement grout—per IDWR rules, seals must extend at least 18–38 feet depending on geology.

2. Advance the borehole

   Our rigs cut through layers of sand, gravel, clay, and basalt, carefully monitoring lithology as we go.

3. Well casing & screen installation

   Once water-bearing zones are identified, we install casing and well screen to keep the borehole open and allow water in, while keeping sediment out.

4. Sealing aquifers

   If multiple aquifers are encountered, we isolate them with grout to prevent cross-flow between zones—an IDWR requirement that protects both you and your neighbors.

5. Well development & testing

   High-capacity pumps surge water through the well to clean out fines and improve yield. We then test pumping capacity to size your permanent pump system.

Why Drilling Here Requires Expertise

Southwest Idaho isn’t easy ground. A single borehole might pass through:

• Topsoil & alluvium (river-deposited sands and silts)

• Gravel & cobble lenses that produce high-yield zones

• Sticky blue clays that can collapse without proper casing

• Basalt flows from ancient lava fields that require powerful rigs and hardened bits

Every layer requires a driller who understands geology, IDWR standards, and how to adapt equipment on the fly.

The Big Picture

Drilling a well in the Treasure Valley isn’t just about hitting water. It’s about:

• Protecting aquifers through proper sealing

• Following IDWR statutes for safety and compliance

• Recording lithology for transparency and future reference

• Navigating complex geology with the right equipment and experience

At Hydro, we bring together licensed drillers, advanced rigs, and deep knowledge of Southwest Idaho geology to ensure your well is built to last—and built to code.

Thinking about drilling a new well on your property? Hydro can walk you through permits, aquifer conditions, and design options to make sure your water source is reliable and compliant with Idaho law.

-Jenae Sexton, owner of Hydro Drilling