Grease Trap Regulations in Delaware

Overview of Delaware FOG Compliance Framework

If you run a restaurant or any food service business in Delaware, you sit under three rule layers: state environmental rules, the state plumbing code, and the local sewer ordinance for your city or county. Fats, oils, and grease (FOG) cool inside the sewer main, choke the pipe, and cause sanitary sewer overflows. The U.S. EPA calls these overflows a top cause of surface-water pollution under the Clean Water Act 40 CFR Part 403. The state baseline comes from the Department of Natural Resources and Environmental Control (DNREC) under Title 7, Chapter 60 of the Delaware Code. Grease interceptor installs are handled through the state plumbing code and the sewer rules in Wilmington, Dover, and Newark.

This guide pulls together the rules every Delaware FSE needs to know: who governs you, how to size and install the trap, how often to clean it, what records to keep, and what fines apply. Treat the rules below as the floor. Cities and county sewer districts can add tighter permit terms. EPA Region 3 in Philadelphia keeps federal oversight of the state pretreatment program under 40 CFR Part 403.

Delaware has three counties: New Castle, Kent, and Sussex. Each has a mix of city sewer utilities and county sewer districts. A downtown Wilmington restaurant follows one set of rules. A Dover deli follows another. A beach kitchen in Sussex County may answer to the county sewer code under Sussex County Code Chapter 110. Across all three counties, the same two things matter most to inspectors: a properly sized grease interceptor that gets cleaned, and a clean folder of pump-out manifests.

Governing Authorities

DNREC's Division of Water is the lead state agency for water quality, groundwater, and NPDES permits under Title 7, Chapter 60. You can reach the Division of Water at 302-739-9949. Program guidance is on the agency portal at dnrec.delaware.gov. DNREC sets water-quality standards, licenses liquid waste haulers, and works with city pretreatment programs that feed Publicly Owned Treatment Works (POTWs).

Grease trap installs are governed by the Delaware State Plumbing Code under Title 16, Chapter 79. The code adopts the International Plumbing Code (IPC) by reference IPC 2024. A licensed plumber must do all plumbing work, including any grease interceptor install or change. You also need a permit before any work starts.

At the federal level, EPA Region 3 in Philadelphia oversees Delaware's pretreatment program EPA Region 3. Region 3 can audit local programs, review POTW data, and step in directly when a Control Authority fails to enforce against repeat violators under 40 CFR 403.10.

Installation and Sizing Requirements

Delaware adopts the IPC by reference under Title 16, Chapter 79. So your trap must follow the rules in IPC §1003. The IPC says a grease interceptor must catch wastewater from any fixture that puts out grease. That includes pot sinks, pre-rinse sinks, soup kettles, dishwashers, hood wash units, and floor drains in food prep areas. Hand-washing sinks, residential dishwashers, and lavatories must not feed the grease trap, per IPC §1003.3.4.

For hydromechanical grease interceptors (HGIs), the IPC sizes units by flow in gallons per minute (gpm) and by grease retention in pounds. Units must meet PDI G101, ASME A112.14.3, or ASME A112.14.4 testing standards under IPC Table 1003.3.5.1. Where a city uses the Uniform Plumbing Code instead, gravity grease interceptors are sized by Drainage Fixture Units (DFUs) on a 30-minute retention period under UPC §1014.2.1. Your local Authority Having Jurisdiction (AHJ), usually city public works or the county sewer department, can require bigger sizes or longer retention when the receiving sewer is grease-impaired.

Gravity interceptors of 750 gallons or larger usually go outside the building. That gives the vacuum truck room to work and keeps sewer gas out of the kitchen. Inlet baffles or sanitary tees, two-compartment construction, and accessible cleanout covers are all standard. The AHJ checks them at plan review and final inspection. New builds and major remodels in Wilmington, Dover, and Newark also need plumbing permits before any grease trap work under Title 16, Chapter 79.

If you are replacing an undersized trap, ask the AHJ for a written sizing review before you buy the new unit. A few common cases force an upsize: adding a wok station or fryer bank, switching from quick-service to full-service, or adding pre-rinse sinks. The IPC also says combination waste-and-vent or food-grinder connections need a separate review. Food grinders push more solids into the trap, which speeds up grease buildup, per IPC §1003.3.4.

Cleaning and Maintenance Frequency

Across Delaware cities, the standard cleaning rule is the "25% Rule." You must fully pump the trap before the floating grease layer plus the bottom solids layer hits 25% of the trap's liquid depth. EPA technical guidance backs the 25% threshold. Past 25%, the trap loses retention time and lets emulsified grease pass through to the public sewer EPA SSO/FOG fact sheet.

The City of Wilmington runs a formal Industrial Discharge Pretreatment Program under Wilmington Code Chapter 11 (Sewerage System). The Commissioner of Public Works issues wastewater discharge permits, sets pump-out schedules, and inspects for compliance. Article V covers pretreatment. Article VI bans illicit discharges to the city's storm sewer system (MS4).

The City of Dover regulates FOG under Dover Code Chapter 110 (Utilities), Article IV (Sanitary Sewer Service). FSEs in the Dover service area also follow Kent County Code Chapter 180, Article III, § 180-13 for sanitary standards. Newark FSEs follow city Public Works rules that line up with DNREC. Get your permit-specified pump-out interval in writing. If the trap hits 25% before the next scheduled service, pump sooner.

Two more habits matter to Delaware inspectors. First, the hauler must fully empty the tank, not skim or partly decant it. Partial pumping leaves emulsified grease that re-coats the baffles fast. Second, do not flush hot water through the trap to "clear" it. Hot water melts trapped FOG, pushes it past the outlet, and the FOG re-hardens downstream in the lateral or main.

In coastal Sussex County, pump-out frequency often needs to tighten in summer. Seasonal restaurants in Rehoboth Beach, Lewes, and Bethany Beach can triple their daily covers in tourist season. Plan a service in May, then another in July or August, instead of one off-season pump-out. The Sussex County sewer code lets the Engineering Department require extra pump-outs whenever an inspection shows grease over the 25% threshold under Sussex County Code Chapter 110.

Record-Keeping and Manifest Requirements

Federal pretreatment rules require industrial users (which includes commercial FSEs that discharge to a POTW) to keep monitoring records, pump-out manifests, and self-monitoring data for at least three years under 40 CFR §403.12(o). The retention period extends if the records relate to active enforcement or a lawsuit. Records must be open for review by the Control Authority, the state, and EPA.

Each pump-out should produce a service manifest. The manifest should show the FSE name and address, the date and time of service, the volume removed, the licensed hauler's name and registration number, and the disposal facility that took the waste. Wilmington pretreatment permittees also send periodic compliance reports to the Department of Public Works as a permit term under Wilmington Code Chapter 11, Article V. False statements in those reports trigger higher penalties under 40 CFR §403.12(e).

Keep service manifests, hauler invoices, internal inspection logs, and any letter from DNREC or your city in one binder or shared digital folder on site. Inspectors from Wilmington Public Works, Dover Public Utilities, Newark Public Works, and DNREC's Division of Water can ask to see these records during a routine visit or after a complaint.

Fines and Penalties

Delaware enforces on two parallel tracks. State environmental violations are pursued by DNREC under the civil penalty rules of Title 7, Chapter 60. That covers administrative orders, civil penalties, and injunctions for unpermitted discharges, NPDES violations, and waste-hauler infractions. Plumbing code violations (no install, no permit, or improper changes to a grease trap) are pursued under Title 16, Chapter 79. That track has its own penalty schedule run by the Division of Public Health and the local AHJ.

At the city level, Wilmington has the most clearly published FOG penalties in Delaware. Under Wilmington Code Chapter 11, Article V, a commercial user who breaks an individual wastewater discharge permit, a general pretreatment standard, or a city pretreatment rule faces civil penalties of $1,000 to $10,000 per violation, per day. When the violation involves a long-term average discharge limit, fines can add up for every day of the violation. Repeat non-compliance can also lead to permit revocation, sewer-service shutoff, and criminal referral.

The City of Dover enforces sanitary sewer service violations under Dover Code Chapter 110, Article IV. The penalty amounts and cure periods come from the city's general penalty rules and the Department of Public Utilities. Sussex County FSEs outside city limits fall under the county sewer code. Sussex County Code Chapter 110 contains the county's grease-control rules and the penalties for unpermitted connections or discharges.

Federal penalties act as a backstop. Under the Clean Water Act, EPA can assess civil penalties for pretreatment violations. EPA can pursue both the industrial user and the POTW Control Authority when local enforcement falls short, under 40 CFR 403.10. Stack it all up (DNREC civil penalties, Wilmington's $1,000 to $10,000 per-day pretreatment fines, Title 16 plumbing penalties, and federal Clean Water Act exposure) and proactive trap maintenance plus clean records is the cheapest path for any Delaware FSE.

The fine itself is often not the worst cost. A documented pretreatment violation can trigger costlier knock-on effects. Wilmington can suspend or revoke the wastewater discharge permit of a chronic violator under Wilmington Code Chapter 11, Article V. In practice, that forces the kitchen to close until pretreatment is restored. Insurance carriers may decline renewal after a sewer-backup claim tied to grease. Landlords often add FOG-compliance clauses to commercial leases. Franchise contracts for national brands typically make the operator indemnify the franchisor for environmental cases. The takeaway for a Delaware FSE is simple. Confirm the trap is sized for current flow. Schedule pump-outs that keep the unit under 25%. File every manifest. Reply fast to any notice from DNREC, the city Department of Public Works, or the county sewer engineer.