The Governing Framework

Delaware regulates onsite wastewater under:

• 7 DE Admin Code 7101 — Regulations Governing the Design, Installation and Operation of On-Site Wastewater Treatment and Disposal Systems. The substantive Delaware rule.
• 7 DE Admin Code 7101-5.0 — Small Systems (less than 2,500 gpd).
• Delaware Department of Natural Resources and Environmental Control (DNREC) — state-level administrator. DNREC Groundwater Discharges Section.
• Class D Licensed Soil Scientist — performs site evaluation.
• Licensed System Designer — designs the system and obtains permit.
• Class E System Contractor — installs the system.

Septic Tank Requirements

Delaware mandates specific tank construction that differs from many states:

The Three-Step Process

1. Class D Licensed Soil Scientist site evaluation. Soil profile, percolation assessment, site restrictions per 7 DE Admin Code 7101.
2. Licensed System Designer design and permit. Based on soil scientist's findings, designer prepares system plan and obtains DNREC permit.
3. Class E Licensed System Contractor installation. Constructs the system per approved design.

Each step is performed by a state-licensed professional. Temporary licenses may be available under certain circumstances. Verify license status on DNREC's professional registry before hiring.

Setback Distances

Delaware setbacks vary by system size, soil conditions, and local factors. General framework covers:

• Private wells (typical baseline 50–100 feet depending on system type and soils)
• Surface water features
• Property lines and structures
• Wellhead Protection Areas (where applicable)

Specific distances in 7 DE Admin Code 7101. Your Licensed Designer applies the correct setbacks. Coastal and inland Bay watershed locations may have additional requirements.

Regional Considerations

• New Castle County (Wilmington metro): Largely on municipal sewer. OWTS remaining on exurban fringe. Coastal-plain sandy soils.
• Kent County (Dover): Mix of sewer (Dover city) and rural septic. Agricultural parcels, varied soils.
• Sussex County (Rehoboth, Lewes, Ocean View, inland): Highest OWTS density. Sandy coastal-plain soils work well for conventional septic. Inland Bays (Rehoboth, Indian River, Little Assawoman) watershed concerns drive nitrogen-reduction attention on coastal and near-coastal parcels.
• Beach resort communities: Mix of municipal systems (ocean resorts) and OWTS (inland). Post-Hurricane Sandy floodplain elevations affect design.
• Agricultural Sussex County: Large-parcel agricultural operations common. Standard systems typical, with occasional commercial-scale installations for poultry and other ag facilities.

Inland Bays Watershed Considerations

Delaware's Inland Bays (Rehoboth Bay, Indian River Bay, Little Assawoman Bay) are designated watersheds with heightened attention to nutrient loading from OWTS. Within the Inland Bays watershed, additional system standards may apply, particularly for new construction and significant system upgrades. Nitrogen-reducing technology may be specified for parcels closer to the Bays. Confirm with your Licensed Designer whether your parcel falls within Inland Bays watershed additional requirements.

Frequently Asked Questions

Do I really need three different licensed professionals?

Yes for standard onsite systems. Class D soil scientist for site evaluation, Licensed Designer for permit/design, Class E contractor for install. Some firms employ professionals with multiple licenses, but the roles remain distinct. Budget $2,000-$5,000+ for professional services on top of system construction cost.

Why the two-compartment + effluent filter mandate?

Delaware prioritizes treatment effectiveness and downstream system protection. Two-compartment improves solids settling. Effluent filters further reduce solids reaching the absorption field, extending absorption-field life. The mandate is stricter than many states where these features are preferred but not required.

Are polyethylene tanks accepted in Delaware?

Yes, when meeting IAPMO/NSF listings, 7 DE Admin Code 7101 requirements, configured as two-compartment with effluent filter. Major OEM rotomolded polyethylene tanks from Norwesco, Snyder, and others include Delaware-compliant two-compartment models. Your Designer will specify accepted options.

What happens if I need a larger system (>2,500 gpd)?

Larger systems fall outside the "small systems" track (§7101-5.0) and require additional engineering review. Commercial and institutional installations typically require extended permitting and may invoke Groundwater Discharge Licenses.

What's Delaware's Inland Bays program?

State and federal partnership addressing water quality in Rehoboth, Indian River, and Little Assawoman Bays. OWTS in the watershed may have additional nutrient-reduction requirements. If your parcel is inland-Bay-watershed-affected, your Licensed Designer will specify the applicable standards.

Source Citations

• DNREC Residential Septic Systems
• Delaware Regulations Title 7 7101
• 7 DE Admin Code § 7101-5.0 Small Systems
• Delaware On-Site Regulations PDF with Exhibits
• DNREC Groundwater Discharge Licenses

Agricultural Tank Regulations — DE Dept of Agriculture

The Delaware Department of Agriculture (DDA) regulates pesticide, fertilizer, and feed bulk storage under the Delaware Code and Delaware Administrative Code:

• 3 DE Admin Code 501 — DDA Pesticide Rules and Regulations: applicator licensing, RUP recordkeeping, bulk storage, repackaging.
• 3 Del. C. Ch. 12 — statutory authority for the Delaware Pesticide Law.
• 3 Del. C. Ch. 22 — Commercial Fertilizer Law: registration, tonnage reporting, labeling.
• 7 Del. C. Ch. 60 / 7 DE Admin Code 5101 — Nutrient Management Law and regulations administered by the Delaware Nutrient Management Commission under DDA.

Delaware is small but agricultural intensity is disproportionate: Sussex County is one of the highest-density broiler-producing counties in the United States, supplying major integrators (Perdue, Mountaire, Allen Harim) and forming the southern anchor of the Delmarva poultry complex that also spans eastern Maryland and Virginia's Eastern Shore. Kent and New Castle counties run grain, vegetable, and dairy operations. Bulk liquid fertilizer and pesticide retail storage build secondary containment to 110% of the largest tank with impermeable liners, rinsate recovery, and documented inspection. Poultry growers above animal-unit threshold operate under DNREC CAFO permits (general permits under the Delaware Pollutant Discharge Elimination System) with dry-litter storage buildings, NRCS-aligned nutrient management plans filed with the Delaware Nutrient Management Commission, and annual implementation reports. The Sussex broiler concentration drives most of Delaware's ag-environmental regulatory activity.

Petroleum Storage Tanks (UST & AST) — DNREC

The Delaware Department of Natural Resources and Environmental Control (DNREC) administers petroleum-tank programs through its Division of Waste and Hazardous Substances — specifically the Tank Management Section:

• 7 DE Admin Code 1351 — Underground Storage Tank Regulations: design, installation, corrosion protection, spill/overfill prevention, release detection, operator training, closure, financial responsibility.
• 7 DE Admin Code 1352 — Aboveground Storage Tank Regulations: registration, construction, spill prevention, release reporting for petroleum AST facilities.
• 7 Del. C. Ch. 74 — statutory authority for the Jeffrey Davis Aboveground Storage Tank Act and Underground Storage Tank Act.
• Delaware Underground Petroleum Storage Tank Response Fund — state trust fund for UST corrective-action reimbursement for eligible facilities.

Delaware is distinctive in maintaining both a mature UST rule (1351) and a state AST rule (1352), driven largely by the state's petroleum-industry concentration: the Delaware City Refinery (PBF Energy, one of the major East Coast refineries), the Port of Wilmington, major pipeline and bulk-terminal infrastructure, and the I-95 / I-495 fuel-distribution corridor. DNREC registers petroleum tanks, inspects facilities, certifies operators, administers the state response fund for UST cleanups, and runs 24-hour spill response. The Tank Management Section coordinates with the Delaware Environmental Response Team (DERT) on significant releases.

Septic Systems — 7 DE Admin Code 7101

DNREC's Division of Water regulates on-site wastewater treatment and disposal systems under 7 DE Admin Code 7101 Regulations Governing the Design, Installation and Operation of On-Site Wastewater Treatment and Disposal Systems. Residential design flow is 150 gpd per bedroom:

Delaware soils are Coastal Plain throughout: sandy loams, sands, and areas of high water table especially in Sussex County and along the Inland Bays. Inland Bays (Rehoboth Bay, Indian River Bay, Little Assawoman Bay) watershed carries TMDL-driven nitrogen-reduction requirements; septic systems in designated Pollution Control Strategy (PCS) areas must use advanced treatment units or connect to central sewer where available. Alternative systems common in DE: aerobic treatment units (ATU), drip dispersal, and pressure-dosed drainfields for shallow-water-table sites. Coastal zones require elevated drainfields and anti-flotation considerations in flood-prone parcels.

Chemical Storage Secondary Containment & Spill Reporting

Federal SPCC (40 CFR 112) applies at 1,320 gallons aggregate aboveground oil. Delaware layers on:

• 7 DE Admin Code 1352 — AST containment and release reporting.
• 7 Del. C. Ch. 63 — Regulated Substances; release reporting and corrective action.
• 7 DE Admin Code 1375 — Hazardous Substance Cleanup Act Regulations.
• DNREC 24-hour spill response: 1-800-662-8802.
• 7 DE Admin Code 1302 — Regulations Governing Hazardous Waste (RCRA Subtitle C delegation).

Report federal-RQ releases to the NRC at 1-800-424-8802; report state releases to DNREC. Secondary containment at 110% of the largest tank is the SPCC and 1352 default. Delaware's compact geography places almost every significant petroleum or chemical facility within miles of tidal waters or the Inland Bays — release response is correspondingly rapid.

Permit Pathways at a Glance

• Residential OWTDS: DNREC Ground Water Discharges Section under 7 DE Admin Code 7101.
• Nutrient management plan: Delaware Nutrient Management Commission (under DDA) per 7 DE Admin Code 5101.
• Pesticide applicator: DDA under 3 DE Admin Code 501.
• Poultry CAFO: DNREC under Delaware PDES general permit with NMP filed to the NMC.
• Petroleum UST: DNREC Tank Management under 7 DE Admin Code 1351 with state response fund.
• Petroleum AST: DNREC Tank Management under 7 DE Admin Code 1352.
• SPCC > 1,320 gal oil aggregate: Federal SPCC plan; DNREC state spill reporting.
• NPDES industrial stormwater: DNREC Surface Water Discharges Section (Delaware is a delegated NPDES state as DPDES).
• Delaware City Refinery / port facilities: DNREC multiple divisions coordinate (Air, Waste & Hazardous, Water).

Current fees change; verify with DNREC, DDA, or the Delaware Nutrient Management Commission before budgeting.

More Delaware FAQs

How does the Inland Bays PCS affect my septic system?

Pollution Control Strategy areas within the Inland Bays watershed impose nitrogen-reduction requirements on new and replacement septic. Advanced treatment units, drip dispersal, or central-sewer connection where available are typical compliance pathways. Check DNREC's Inland Bays PCS designation for your parcel before septic design.

Do I need to register my poultry-house manure shed with the Nutrient Management Commission?

Most Delaware poultry operations above small-flock threshold hold or are covered by a nutrient management plan filed with the Delaware Nutrient Management Commission. Bulk litter storage buildings, stormwater exclusion, and annual implementation reports are standard. Integrators typically provide template documentation that growers adapt.

Does DE have its own AST rule beyond SPCC?

Yes — 7 DE Admin Code 1352 is Delaware's state AST regulation. It imposes registration, construction, spill-prevention, and release-reporting requirements on petroleum AST facilities, supplementing federal SPCC. The presence of the Delaware City Refinery and port-area terminal volume drove the state's comprehensive AST rule.

What is the Delaware City Refinery's regulatory framework?

The refinery operates under a stack of DNREC permits spanning Air Quality (synthetic-minor/major source), Water (DPDES discharge), Waste & Hazardous (RCRA, UST/AST), and coastal-zone regulation. Federal SPCC, FRP (Facility Response Plan under 40 CFR 112.20), and Risk Management Plan under 40 CFR 68 all apply. The refinery is one of the most heavily regulated individual facilities in Delaware.

Who runs my county septic permit?

DNREC's Ground Water Discharges Section runs septic permitting statewide — Delaware does not delegate to county health departments the way Maryland or Virginia do. Contractor licensing is also DNREC-administered. One-stop-shop workflow with the state agency.

Is Delaware a delegated NPDES state?

Yes — Delaware Pollutant Discharge Elimination System (DPDES) permits are issued by DNREC Surface Water Discharges Section under EPA NPDES delegation. Industrial stormwater, municipal stormwater (MS4), and wastewater treatment discharges all route through DNREC DPDES.