Tight Lot, Two Setbacks, and a Fractured-Rock Completion
A Frederick County homeowner needs a replacement for a 28-foot brick-lined dug well that goes dry each August. The lot is 0.45 acre. The proposed 6-inch drilled well site is 38 ft from the septic tank, 72 ft from the drainfield, 15 ft from the property line, and 25 ft downslope from a neighbor’s horse paddock. The owner wants to start there because the drill rig can reach it without crossing the driveway. Soil is 18 ft of silty clay over 10 ft of weathered schist, then fractured schist; the driller expects water at about 95 ft and 180 ft. A fuel-oil tank is 18 ft from the proposed location. The owner asks you to 'just drill it and grout the top 20 feet' to keep the price down. You are the licensed driller responsible for the permit and the well log.
1. Evaluate the proposed location against Maryland well-siting requirements. What must happen before a permit is issued, and what alternatives would you present to the owner?
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The proposed site fails the usual Maryland separation table on at least three counts: 38 ft from a septic tank is less than the 50-ft minimum; 72 ft from the drainfield is less than the 100-ft minimum; and a well 25 ft downslope of a horse paddock is too close for a site that can receive animal waste. The 18-ft fuel-oil tank is another concern. A local property-line rule may also apply, so the 15-ft distance must be checked with the Approving Authority.
Do not start drilling. The permit application must show a compliant location, and the local health department is the approving authority for a domestic well. Present alternatives in this order: (1) relocate upslope and as far from the tank, drainfield, paddock, and fuel tank as the lot allows; (2) if no compliant site exists, ask the Approving Authority about a variance or alternative construction before drilling; (3) if a variance is not available, discuss another water-supply option. A drilled well cannot cure a failed setback simply by adding grout.
2. Assuming a compliant site is found, design the casing and annular seal for the expected geology. Explain why grouting only the top 20 ft is unacceptable here.
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The casing must pass through 18 ft of silty clay and 10 ft of weathered schist and seat into competent schist, not stop in the clay. A practical design is 6-inch steel casing set at least 10 ft into competent rock, with the annulus grouted from the casing shoe to the surface with neat cement or an approved bentonite grout. The casing top should be at least 12 inches above finished grade and fitted with a sanitary seal and pitless adapter.
Grouting only the top 20 ft leaves the weathered-rock interval and the upper fractures open to surface water, insects, and shallow contamination. In fractured schist, water can move vertically along the outside of the casing and enter the well below the seal. A continuous annular seal forces water to enter through the intended open-rock interval and protects the well from the septic system and paddock. The well log must record casing depth, grout volume and method, and the water-bearing zones.