Ralph Vasquez, Senior Regulatory Compliance Specialist

Avoiding water quality violations from property dewatering

The process of dewatering a property is a vital step in the course of many new construction projects. A procedure carried out by environmental engineers, dewatering is a process in which groundwater contained within the site’s soil is extracted, ensuring a stable foundation for the intended structure.

Note that not all construction projects require dewatering. If, for instance, the property owner is simply building slab on grade at the site, dewatering most likely is not necessary since, chances are, builders would not need to dig the foundation deep enough to reach groundwater. However, if excavating for an underground parking structure, groundwater may become an issue which will effect the flow of construction phase.

During new construction, as well as after construction is completed, it is vital that owners know how to properly dispose of the excess groundwater they have accumulated throughout the construction process. There are several options property owners may consider when contemplating what is the most cost, time and energy efficient way to dispose of groundwater which may include discharging to a storm drain, the city sewer system, or using the water for irrigation purposes after construction has been completed.

Additionally, everyone involved in the construction/development process needs to remain updated on the newest legislation and requirements for disposing of wastewater in order to avoid unnecessary penalties. Recently, new policies from the City of San Diego have been enacted, such as, changes to the application process, testing criteria, pretreatment process, flow-metering requirements, and permit renewal authorization.

DEWATERING METHODS

There are two different methods for dewatering: construction dewatering and dewatering through the use of an underground foundation drain system. After considering the type of development that will occupy the site, the best method is chosen for each project. 

Construction Dewatering

When deep excavation reaches groundwater, the groundwater must be extracted from under the development to provide a stable foundation during construction. To do so, pumps are inserted into the soil, which remove the excess water. A dewatering system is designed for the construction project to remove excess groundwater. This system consists of multiple pumps set within wells to pump out the groundwater and may include a treatment process before discharging the water.

Underground Foundation Drain System

In contrast to construction dewatering in which water is removed before and during construction takes place, using an underground foundation drain system collects groundwater only after construction. This process prevents an underground structure, like a parking garage, from filling up with excess water. The water that collects is directed toward a drainage system that leads to a sump, which then is pumped to some discharge point. If this dewatering process is chosen, it is essential that a sump and pump system is designed that is large enough to hold the amount of water that will be removed from the structure, and can handle excess during an unusually wet rainy season.

WHERE DOES THE EXCESS WATER GO?

After extracting the excess groundwater from the site, developers need to determine the best way for it to be legally discharged. There are three main choices for groundwater discharging: into the storm drain, through the sewer system, or for use in irrigation. The best method of discharging is chosen based on the site’s location and irrigation needs.

Storm Drain Discharge

This process discharges excess groundwater into storm drains, which then empty into inland surface waters, such as rivers and lakes. This is one of the more expensive options, since the water needs to be thoroughly tested before it is cleared for discharge. Additionally, the water may need to be treated, continuously monitored and reported, and developers may be subject to fines if it doesn’t meet discharge requirements. A permit for storm drain discharge is required, which may be time consuming and costly. This option may be used during construction and post-construction, based on location of the project.

Sewer System Discharge

Although not allowed post-construction, discharging water to the sewer system is a quicker process during the construction phase, which requires much less analysis than storm drain discharge. After a permit is attained, water can be discharged to the sewer system. Based on the water quality, pre-treatment may sometimes be required, even though the water is already headed to a treatment facility. The main challenge with this type of discharge is that property owners need to find a system near the site’s location that can handle the volume of water that will be discharged.

Irrigation 

Due to its sustainability aspect, using excess groundwater, post-construction for use in irrigation systems recently has been increasing in popularity. After the excess water is extracted from the site, property owners may use it for their landscaping needs, based on acreage and plant type.

The important thing to keep in mind when thinking about using this process for water discharge is that the volume required for irrigation needs to exceed the amount of water that is collected during dewatering. If the irrigation needs are not large enough, the property owner may need to attain a permit to discharge the leftover water to the storm drain or sewer system. Using the excess water for irrigation is a money-saving and environmentally friendly option that will earn the project some sought-after LEED points.

NEW LEGISLATION

Due to an increasing concern over the environment, discharging requirements continue to change. For instance, the City of San Diego recently passed legislation that changes the requirements for discharging to the sewer system. Additionally, there is proposed legislation that changes the requirements for discharging to the storm drain. The Regional Water Quality Control Board (RWQCB) has issued a tentative order with new requirements for any discharge of dewatering, remediation activities, to inland surface water (except San Diego Bay). A majority of the new requirements are procedural, however, if not addressed completely or correctly, application review will take longer to process and will extend the time period for permit issuance.

CONCLUSION

In addition to the many considerations that must be taken when working on a development project, property owners and the people working for them need to be aware of the importance of dewatering, as well as what to do with the water that has been extracted from the site. To ensure the smoothest and least expensive discharging process, be sure to stay informed of any new groundwater discharge policy changes.