Underground Infiltration Systems and Dry Wells Registration

Dry wells and other sub-surface stormwater infiltration practices/technologies serving uses other than single-family homes are considered Class V wells, subject to US Environmental Protection Agency (US EPA) regulations. Typically, Class V wells are shallow wells used to place a variety of fluids directly below the land surface. By definition, a well is “any bored, drilled, driven shaft, or dug hole that is deeper than its widest surface dimension, or an improved sinkhole, or a subsurface fluid distribution system” and an “injection well” is a “well” into which “fluids” are being injected (40 CFR §144.3). A guide can be found here: Class V Well Guide.

Stormwater dry wells and other sub-surface stormwater infiltration practices/technologies may be authorized to operate as long as they are registered with the US EPA, and only inject uncontaminated stormwater. The County of San Luis Obispo currently requires Class V Well registration as part of permitting new development.

What is the process?

Review Guidelines and Finalize Plans

Review the requirements for underground infiltration systems and dry wells within the County's Post-Construction Stormwater Guidebook. The applicant finalizes their plans based on applicable codes and ordinances and any direction received from staff during the optional pre-application meeting.

Submit Plans

The applicant submits a completed application and pays initial application fees for a construction permit or grading permit.

Review by Staff

Staff in Planning & Building and Public Works review the application to verify that the plans comply with all applicable codes and ordinances, determine remaining application fees, and ensure that the application is complete.

Public Works will add a Condition to the building permit that requires federal registration of the system prior to final of permits.

Register System

Complete the EPA online registration for the Class V System while the well operating status is ‘Planned/under construction’.

Satisfy Conditions

The applicant satisfies the building permit condition by provide evidence of system registration to Public Works. A confirmation email and registration number from the US EPA are sufficient evidence of registration.

Who is eligible?

Anyone who has applied for a County construction permit or grading permit can use this service.

When and where is this service offered?

This service is available throughout the year during regular business hours except during scheduled holidays.

FAQS

Are underground stormwater infiltration chambers covered by this designation?

Yes. Subsurface fluid distribution or infiltration systems (i.e. ADS, Stormtech, or Contech chambers) are included in the Class V well designation.

Do I need to register my septic system?

Only large-capacity septic systems must complete registration as a Class V well. A septic system is considered a large capacity septic system (LCSS) if it receives solely sanitary waste either from multiple dwellings or from a non-residential establishment and the system has the capacity to serve 20 or more persons per day. Please review the US EPA guidance on when a septic system is regulated as a Class V well.

Do infiltration systems serving single-family homes need to register?

No. EPA Region 9, which oversees California, does not require registration of dry wells or other buried infiltrative devices that serve lots with single-family homes.

How do I register a Class V system with the US EPA?

Registration is competed by filling out an online form. The form fields will ask for specific information about ownership and design of the Class V system.

If I need to install a dry-well within an existing stormwater basin, do I need to register the well?

Yes. Any bored or driven shaft whose depth is greater than the largest surface dimension must be registered. The well should be registered, but the basin does not require registration.

What are the County's guidelines for construction of new Class V systems?

In California, Class V wells are overseen by the US EPA’s Region 9 office. After an inventory form is submitted, the Underground Injection Control (UIC) Program will determine if the well is authorized to “inject”.

The County of San Luis Obispo has adopted requirements for underground infiltration systems and dry wells, which are detailed in the Post-Construction Stormwater Guidebook. Project plans will be checked against the requirements during drainage and flood hazard review of new construction permits.

Why is the County requiring new systems to meet these guidelines?

There are no detailed State or Federal requirements for the design or approval of new Class V systems. However, the County is the local authority responsible for ensuring that new Class V wells do not endanger underground drinking water supplies. The County’s guidelines are intended to ensure that new systems meet the minimum requirements set forth by the US EPA to and protect underground drinking water supplies.