Well Drilling (C-57) · Lesson 1 of 6

Annular Seal: Depth, Hole Size, and Seal Volume

"Annular Seal: Depth, Hole Size, and Seal Volume" is lesson 1 of 6 in the Well Drilling (C-57) Learning Hub. It opens with "What the Annular Seal Is For" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. What the Annular Seal Is For
  2. Minimum Depth by Well Type
  3. Clay Layers Near the Bottom of the Seal
  4. Oversized Hole and Radial Thickness
  5. Seal Volume and Placement

The worked example in the course applies this lesson to a realistic job in 7 steps.

What you'll be able to do

  • Explain the main idea of "Annular Seal: Depth, Hole Size, and Seal Volume" in plain language you can use on the exam.
  • Apply this step with confidence: "Clay Layers Near the Bottom of the Seal".
  • Apply this step with confidence: "Oversized Hole and Radial Thickness".
  • Apply this step with confidence: "Seal Volume and Placement".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Annular Seal: Depth, Hole Size, VolumeGround surfaceCASING8.625 inODSEALSEALCLAY12 ftClay topat 47 ft50 ft min52 ftSeal depth 52 ftHole 12.625 inWORKED EXAMPLE: COMMUNITY WELLHole size8.625 + 4 = 12.625 inRadial seal(12.625 - 8.625) / 2 = 2.0 inMin depthcommunity supply = 50 ftClay rule47 + 5 = 52 ftRing areaπ/4 x (12.625² - 8.625²)= 66.76 sq in = 0.4636 sq ftVolume0.4636 x 52 = 24.1 cu ft24.1 cu ft x 7.48 = about 180 gal(7.48 gal per cu ft is a unit conversion)Seal 0 to 52 ft, bottom up, at least 24.1 cu ft (about 180 gal)Verify placed volume ≥ volume to be sealed (Sec. 9.F.6)Source: DWR Well Standards (Bulletin 74-90/74-81), Part II, Sec. 9.A, 9.B.2, 9.E, 9.F.6CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: What the Annular Seal Is For

The annular space is the space between the well casing and the wall of the drilled hole. The DWR Well Standards (Bulletin 74-81 as supplemented by Bulletin 74-90, Part II, Section 9) require it to be effectively sealed so it cannot become a preferential pathway for poor-quality water, pollutants, or contaminants. Secondary purposes are to protect the casing against corrosion and degradation and to stabilize the borehole wall. Everything else in this lesson comes down to three numbers: how deep the seal goes, how thick it is, and how much material it takes.

Step 2: Minimum Depth by Well Type

Section 9.A prints the minimum depth the annular surface seal must extend below ground surface: community water supply 50 ft, industrial 50 ft, individual domestic 20 ft, agricultural 20 ft, air-conditioning 20 ft, and all other types 20 ft. With the enforcing agency's approval a shallow well whose water is less than 20 ft deep may get a reduced seal, but in no case shallower than 10 ft below land surface or shorter than 10 ft (Item 1). A well approved at less than the Section 8 distance from a pollution source must be sealed from ground surface to the first impervious stratum if possible, and to at least 50 ft, whatever its type (Item 2).

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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