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Dewatering
Dewatering is a critical SWPPP requirement because excavation during construction sometimes meets groundwater and/or rain, rainfall, and surface runoff. In order for construction to proceed, muddy waters need to be removed from the site; however, such water can contain sediment, oils, chemicals, etc. The UPDES dewatering permit ensures this discharged water is properly managed and treated using a specific plan and Best Management Practices (BMPs) before it enters local waterways. This prevents water contamination, protects aquatic ecosystems, and safeguards our water resources from the direct impacts of construction activities.
Understanding Construction Site Dewatering
In most construction projects, particularly those with excavations for foundation, basement, or utilities, contractors usually have an uninvited visitor: water. Regardless of whether it is the groundwater rise, rain accumulation, or seepage from adjacent sources, this surplus water must be removed to establish a firm and safe working environment. This is referred to as dewatering.
However, it is not simply a matter of pumping water out of a hole. Water taken from a construction site can be full of pollutants such as sediment, oils, chemicals, and trace metals that would have disastrous effects on our local rivers, streams, and groundwater if released untreated. That is why the State of Utah, through the Utah Department of Environmental Quality (UDEQ) and its Utah Pollutant Discharge Elimination System (UPDES) program, permits dewatering.
What is a Dewatering Permit?
Utah construction dewatering activities typically need to be covered under the UPDES Construction Dewatering / Hydrostatic Testing (CDHT) Permit (UTG070000). The permit is for discharge of:
Clean Water Obtained from Excavations, Trenches, or Sumps.
Water utilized for hydrostatic testing of pipelines, tanks, or any other liquid containers.
Other comparable construction-related water discharges, e.g., wheel wash water (where there are no additives) or drinking water pump testing.
There is also a separate permit (UTG790000) for the discharge of treated groundwater from pollution sites, a distinct category.
What Is Covered by a Dewatering Permit?
A dewatering permit in Utah is not a formality, but an extensive plan for accountable water management. It addresses a number of crucial aspects:
Dewatering Control Plan (DCP): Prior to the start of any discharge, the permit mandates the preparation of a comprehensive Dewatering Control Plan. The plan consists of:
The origin and approximate amount of water to be dewatered.
The suggested treatment measures (i.e., sedimentation basins, weir tanks, filter bags, flocculants) for the removal of impurities such as suspended solids, oil and grease, and to pH adjust.
The point of discharge and how the water will be discharged in order to avoid erosion or scouring of the receiving environment.
Contingency planning for unexpected situations or equipment breakdown.
Identification of waters receiving the discharge and whether those waters are impaired, possibly resulting in more restrictive discharge limits.
Discharge Limits: The permit defines specific effluent limits for the water being discharged. The limits generally consist of parameters such as:
Total Suspended Solids (TSS): To restrict the amount of sediment and soil released.
Oil and Grease: To prevent toxic sheens and petroleum product contamination.
pH: To make sure the water's alkalinity or acidity is at a desirable level for aquatic organisms.
Other parameters such as chlorine (if hydrostatic testing) or certain metals (if relevant).
Monitoring and Reporting: Permitted dewatering activities must be regularly monitored. This generally involves:
Daily routine visual inspections of the treatment system and discharge location.
Weekly sampling and laboratory testing of the discharged water for parameters given in the permit.
Monthly Discharge Monitoring Reports (DMRs) to the UDEQ that detail the amount of water discharged and the results of all monitoring.
Best Management Practices (BMPs): The permit focuses on the application of the appropriate BMPs to treat and control the discharge from dewatering. Typical BMPs include:
Sedimentation Basins/Tanks: To allow solids to settle.
Filter Bags/Chambers: To eliminate fine sediment.
Weir Tanks: To slow flow and aid in settling.
Flocculants: Chemicals that enable small particles to stick together for more convenient removal (used cautiously and frequently with special authorization).
On-site reuse or infiltration: Discharging dewatered water to a land area with vegetation to infiltrate, to the degree possible, or reusing it on site (e.g., for dust control) can eliminate the necessity for direct discharge permits.
Why is this so Important to Utah?
Utah is an arid state and, as a result, places an extremely high value on its water resources. Having these waters free from pollution is vital for drinking water supplies, agriculture, recreation, and allowing ecosystems to remain healthy.
Dewatering permits are an important mechanism to help ensure that essential construction activities do not inadvertently cause damage to these valuable resources. By following dewatering permit regulations, builders are helping to keep waterways healthy across Utah.