Construction Dewatering Groundwater Discharge Permitting
Written by: Kyle Hansen, CEM
Groundwater is one of the most precious natural resources in Southern Nevada as about 10 percent of our public water supply system relies upon groundwater. The Nevada Division of Environmental Protection (NDEP) – Bureau of Water Pollution Control (BWPC) is tasked with protecting the waters of the State from the discharge of pollutants by issuing and regulating different types of permits.
Construction projects in many portions of the Las Vegas Valley may require some amount of construction dewatering to get the job done. Projects that involve underground utility construction that is in close proximity to an established watercourse such as the Las Vegas Wash will commonly deal with design and implementation of a construction dewatering system. There are several factors that will determine which type of groundwater discharge permit will be required for the permitting of construction-related dewatering discharge.
- Clean Water Act De Minimis Permit– authorization for discharge to surface waters for certain types of activities/discharges, each with their own discharge limits and water quality restrictions.
- NV/NPDES Permits– regulates surface water discharges to “waters of the US”. The US EPA has delegated responsibility to the State of Nevada to implement the National Pollutant Discharge Elimination System (NPDES) Program authorized by the Clean Water Act. All NPDES permits are sent to the EPA for review.
- Temporary Groundwater (TNEV) Discharge Permits– authorized for temporary discharges to groundwater; maximum 6 month term, but can be extended for additional 6 months in certain cases. Typically used for shorter-term construction projects that require dewatering, and there is land surface availability for storage/infiltration/settling, with ultimate discharge back to groundwater.
- NEV Permits– for long term discharges that will infiltrate into the ground like unlined ponds, reuse or treated effluent (gray water), individual or commercial sewage disposal systems and lined ponds or tanks (“zero” discharge permits).
Which Permit Do You Need?
There are primarily 4 questions that need to be answered to determine which type of permit will be:
What is the water quality?
Groundwater can be affected by both naturally occurring and man-made constituents, and varies from one location to another. Naturally occurring metals such as Molybdenum and Selenium common to groundwater in the southwest are harmful above specific concentrations and must be monitored at periodic frequencies during discharge. Perchlorate, a compound used to make rocket fuel, is also found in various concentrations in the southeast part of the Las Vegas Valley and must be tested prior to and during discharge so that the receiving waters are protected from increasing concentrations. Groundwater that contains constituents in excess of the established maximum concentration levels (MCLs) will likely require treatment prior to discharge. Data on groundwater quality is typically submitted with any type of discharge permit application and should be provided by a State of Nevada certified analytical laboratory.
What is the quantity of the discharge?
For groundwater discharge the flow rate is not a parameter that can typically be looked up in a book, but is typically calculated by a hydro-geologist using software that can model the subsurface soil and groundwater conditions. Poorly graded, course-grained soils yield larger amounts of groundwater than well graded, fine-grained soils. The anticipated flow rate is also dependent on the geometry of an excavation (long narrow excavations are usually more productive than square ones of the same cubic yards) and other elements (i.e. existing utility corridors).
What is the duration?
The duration of construction dewatering is also another factor in determining what permit is appropriate. In general, for projects less than 6 months in duration, a different permit will be required than for projects longer than this period.
What is the location the discharge is going to?
Where the water is being discharge to also is also a factor in determining what type of permit is required. Surface water conveyances, including lakes, streams, storm sewers, dry washes have more of an immediate impact to the receiving water body’s quality and each body often has unique limits, standards or restrictions. Discharges to groundwater are often just returning groundwater of similar quality back into the same aquifer and thus additional latitude can be given in the pre-discharge requirements.
Working with the State Regulators
The BWPC is an advocate of protective progress…not adversarial impedance. Every area of the valley is different with respect to quantity and quality of the groundwater. The State employees are invaluable resource as to where to start and what the most cost and time effective options that should be considered. Important: Call them up front!
If you are in need of groundwater discharge permitting support or you would like GES to present information about dewatering groundwater discharge permitting, give GES a call.
Las Vegas, NV
7150 Placid Street
Las Vegas, NV 89119
530 Commerce Street
Mesquite, NV 89027
5301 Longley Lane, Suite 116
Reno, NV 89511