There are approximately 420,000 septic systems in Maryland. Of these, 52,000 systems are located within the “Critical Area,” [land within 1,000 feet of tidal waters]. A conventional septic system does not remove much nitrogen, instead delivering about 23.2 pounds of nitrogen per year to the groundwater. An upgraded, nitrogen-removing Best Available Technology (BAT) unit reduces a system’s nitrogen load in half.
The Maryland Department of the Environment has upgraded over 12,000 conventional septic systems by either hooking the dwelling to a public sewer connection or installing a nitrogen removing BAT through the Bay Restoration Fund (BRF) Onsite Sewer Disposal System (OSDS) grant program and regulatory requirements.
In accordance with Maryland State Law, the Bay Restoration Fund prioritizes upgrades as follows:
- Failing OSDS in the Critical Areas
- Failing OSDS outside the Critical Areas
- Non-conforming OSDS in the Critical Areas
- Non-conforming OSDS outside the Critical Areas
- Other OSDS in the Critical Areas, including new construction
- Other OSDS outside the Critical Areas, including new construction
On November 24, 2016, Maryland Department of the Environment finalized a regulatory action which reforms the universal requirement that Best Available Technology for Removal of Nitrogen (BAT) septic systems be installed outside the Chesapeake Bay and Atlantic Coastal Bays Critical Area (Critical Area) for all new construction. Instead, the final regulation would allow the installation of conventional septic systems outside of the Critical Area. Under the regulation, BAT is still required for large septic systems with design flow of 5,000 gallons per day or greater. Additionally, local governments would not be preempted from requiring a BAT system outside the Critical Area in order to protect public health or waters of the State.
For more information on grant implementation, please visit the following links:
Best Available Technology (BAT) Classifications
- Class I Technologies - Field Verified, Grant Eligible BAT technology listing and contact information. These systems are capable of reducing TN within the final effluent to 30mg/L or better.
- Class II Technologies - Currently undergoing Field Verification, Not Grant Eligible BAT technology listing and contact information. These systems claim they are capable of reducing TN within the final effluent to 30mg/L or better
- Class III Technologies - NSF 40 Certified, Grant Eligible BAT technology listing and contact information. These systems are capable of reducing TN within the final effluent to 48mg/L and must be paired with a Class IV system for eligibility to be used as a BAT .
- Class IV Definitions- Soil distribution systems that are capable of reducing TN by 20%-30% without pretreatment. With pretreatment, the combination may reduce TN upwards of 75%. These systems can be paired with a Class I or III for eligibility as a BAT. Each has slightly more requirements to enhance the TN reduction.
The following checklists may be used while doing site inspections and operation and maintenance of BAT Class IV. These are for reference to use when onsite. These checklists were copied from the Consortium of Institutes for Decentralized Wastewater Treatment, Residential Onsite Wastewater Treatment Systems: An Operation and Maintenance Service Provider Program, Second Edition.
Waterless Toilet Systems Application Process and information
Best Available Technology (BAT) Information
Chesapeake Bay States - Data Sharing
On April 16, 2015, the states of Delaware, Maryland, Pennsylvania, Virginia and West Virginia signed a Memorandum of Cooperation to share data developed to document the performance of advanced onsite pretreatment units for nitrogen reduction and, therefore, to simplify and expedite the approval processes for these technologies in each individual state, as well as reduce costs to residents and manufacturers. Prior to this MOC, all states nationwide approved systems on an individual basis and many did not take into account data collected by other state programs. To learn more about data sharing, visit the
Chesapeake Bay Program website
OWTS Expert Panel
The On-Site Wastewater Treatment Systems (OWTS) Nitrogen Reduction Technology Expert Review Panel was tasked with identifying and recommending on-site wastewater treatment systems that would reduce total nitrogen (TN) loads to the Chesapeake Bay watershed. For more information on the recommendations of the panel, please visit the link below.
Field-verified Sampling Results
If you have additional questions or would like more information, please contact the Wastewater Permits Program, Bay restoration Fund Program, 410-537-3599.
The Maryland Department of the Environment thanks you for your continued interest and support of this important program!