Stormwater Dry Wells as Class V Injection
A developer plans a 3-acre commercial parking lot. The city storm sewer is 1,100 feet away and undersized. The developer proposes two 48-inch diameter, 25-foot deep dry wells filled with washed rock, 60 feet apart, to receive parking lot runoff. The site has 40 feet of sandy loam over the High Plains aquifer, and the water table is at 65 feet. The lot will be salted in winter and will include a gas station with fuel dispensers. The developer asks you to drill the dry wells next week and says it is just rainwater and that the city has already looked at the plan. The site is outside the city limits but within a designated wellhead protection area for a nearby public water system.
1. Are the proposed dry wells UIC injection wells, and how would they be classified?
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Yes. A dry well that receives stormwater and places it below the land surface is a Class V injection well under the UIC program. The fact that the water is just rainwater does not exclude it; stormwater drainage wells are a classic Class V category. The design, with 48-inch diameter, 25-foot depth, gravel fill, and 60-foot spacing, is an infiltration system, not a simple surface drainage ditch. Because the site has sandy loam over the High Plains aquifer and a water table at 65 feet, contaminants from parking lot runoff, oil, fuel, deicing salt, and sediment can reach groundwater. The gas station and winter salting increase the risk. The wells are not exempt because they are small or because the storm sewer is inconvenient.
2. What approvals must be obtained before you drill, and who should be involved?
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Before construction, the developer must obtain UIC authorization from Nebraska's UIC program at NDEE, either a permit or rule authorization depending on the well category and state rules, plus any local stormwater, grading, and zoning approvals. The developer may need a stormwater pollution prevention plan and pretreatment, such as an oil-water separator, sediment basin, and shutoff valves, before runoff enters the dry wells. Because the site is in a wellhead protection area, the state drinking water program and local WHP committee should be consulted before approval. Do not drill on a verbal assurance that the city looked at the plan. Get written UIC approval and a design prepared by the appropriate professional. The driller's job is not to decide that the injection is harmless.
3. What construction and operational conditions would you require, and what would make you refuse the job?
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Conditions include pretreatment and a bypass or shutoff to prevent spills from entering the wells; clean washed rock and proper filter fabric; separation from the water table and confining layers; sealing where required; inspection and maintenance access; and recording the wells as UIC wells. The owner must have a spill response plan for the fuel dispensers and a deicing management plan. Refuse if the UIC program prohibits Class V wells at that location, if the site is in a WHP area where the contaminant source is inconsistent with the protection plan, if the water table is too close, or if the developer will not install pretreatment. A dry well that receives fuel or solvent-contaminated water may be a prohibited disposal practice, not a stormwater system.