Subdivision Water Main and Sewer Separation Review
A developer submits plans for a 240-lot subdivision served by a new 8-inch PVC water main 2,300 feet long, connecting to an existing 12-inch main. Static pressure is 62 psi; the fire-flow requirement is 1,000 gpm at 20 psi. The same plans show a 10-inch gravity sewer paralleling the water main for 600 feet with 8 feet of horizontal separation, and one crossing where the water main is 6 inches above the sewer. A 300-foot segment of water main lies in a private lot with no recorded easement. Hydrants are spaced about 600 feet apart. The plans are sealed by an engineer, but the DEQ construction permit application is incomplete and no separation waiver is included. The reviewer must decide whether to approve, deny, or approve with conditions, and what field changes could be accepted.
1. Identify the permit-blocking deficiencies and explain which ones are technical versus administrative.
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Blocking issues: the 8-foot horizontal separation is less than the usual 10-foot minimum for a water main parallel to a sewer, the 6-inch vertical clearance at the crossing is below the usual 18-inch requirement unless the sewer is encased or the water main is relocated, and the 300-foot segment lacks a recorded easement. The incomplete DEQ application and missing separation waiver are also permit-blocking. Hydrant spacing of 600 feet is not necessarily a failure, but the 1,000-gpm fire-flow requirement must be supported by a hydraulic calculation that includes the 2,300 feet of 8-inch main and the connection to the 12-inch main. The reviewer should not approve as-is; require a sealed revision, easement or condemnation documentation, and either compliance or an engineered waiver with justification. Field changes that do not restore separation should not be accepted by verbal instruction.
2. How should the reviewer handle the parallel separation, the crossing, and the missing easement?
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For the parallel section, the designer can relocate the water main, lower or relocate the sewer, or use a restrained and encased sewer with a waiver; the choice depends on groundwater, bedding, and maintenance access. At the crossing, 6 inches is not enough; require 18 inches or a full encasement of the sewer with joints away from the water main. The easement must be recorded before construction, not promised at close-out. A waiver request needs a seal, soil and corrosion information, and a maintenance plan showing how the utility can repair either line without compromising the other. The reviewer role is to protect the public water system and document the basis, not to design the fix. Approve only with conditions that are enforceable and inspectable.
3. What approval path and conditions would you recommend, and how should field changes be controlled?
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Issue a deficiency letter rather than a denial if the project is otherwise sound. Conditions should include revised sealed plans, recorded easement, separation waiver or relocation, hydraulic fire-flow calculation, and a preconstruction meeting. The DEQ construction permit should not be issued until the application is complete. Field changes can be accepted only through revised drawings and engineering justification; the inspector can stop work if separation is not restored. The reviewer should also confirm that the 8-inch main can deliver 1,000 gpm at 20 psi with the actual C-factor and elevations; if not, upsize or loop the main. This is a judgement call because some deficiencies can be conditioned and others go to the core of public health protection. The test is whether the condition is verifiable before burial and whether the utility can maintain the system afterward.