City Council Workshop, Jun 3, 2026

Great Bay Water Quality Update

In Brief

The estuary’s health is influenced by nitrogen loads, stormwater runoff, and light availability, with adaptive management guiding regional collaboration among municipalities and environmental agencies.

Key Points

• The city’s wastewater treatment plant has reduced nitrogen discharges significantly since upgrades in 2015, now averaging 3–5 mg/L during warm months.
• Stormwater contributes 80% of nitrogen and other pollutants to the estuary via non-point sources, with impervious surfaces increasing runoff.
• Dover operates under a National Pollutant Discharge Elimination System (NPDES) permit for wastewater and a separate MS4 stormwater permit, both administered by EPA Region 1.
• The Municipal Alliance for Adaptive Management (MAM) includes 13 communities and coordinates regional efforts to monitor and reduce nutrient loading.
• Dover’s annual MAM contribution is $138,000, based on wastewater plant size, funding shared research and modeling initiatives.
• Inflow and infiltration (I&I) in sewer lines are monitored using cameras and smoke testing to prevent overloads during heavy rain events.

Council Inquiry

• Questions focused on the discrepancy between declining nitrogen levels and continued eelgrass loss, prompting discussion on sediment resuspension, water clarity, and climate effects.
• Council members inquired about monitoring practices for stormwater outfalls and whether increased sampling could identify illegal discharges.
• Concerns were raised about the cost-effectiveness of further reducing point-source nitrogen when non-point sources dominate pollution.
• Questions addressed homeowner and developer roles in stormwater management and whether current regulations ensure adequate infiltration.

Toland Road Landfill Remediation Update

In Brief

The landfill, an EPA superfund site, continues to release persistent contaminants into groundwater, requiring hydraulic control rather than source removal due to site conditions.

Key Points

• The landfill operated from 1960 to 1978 without a liner or cap, leading to groundwater contamination with VOCs, 1,4-dioxane, and PFAS.
• A remediation system installed in 2012 intercepts the eastern plume moving toward the Cocheco River; the southern plume toward Bellamy Reservoir was identified later.
• 1,4-dioxane and PFAS are the primary contaminants of concern in the southern plume due to their solubility and resistance to degradation.
• Monitoring includes shoreline wells, pore water sampling, and surface water testing in tributaries and the Bellamy Reservoir.
• No VOCs have been detected in the reservoir; 1,4-dioxane levels remain low (1–3 µg/L) but exceed the 0.32 µg/L drinking water threshold.
• A new $2.7 million remediation system will be built to intercept the southern plume, consisting of 12 stations with three wells each, designed to operate at 20–25 GPM.
• The system will connect to the existing treatment infrastructure and is projected to begin operation in October 2027.
• The design prioritizes consistency with the existing system to ensure reliable operation and maintenance.

Council Inquiry

• Council members asked why the landfill was not excavated or capped, receiving clarification that natural attenuation governs degradable compounds, while persistent chemicals require active interception.
• Questions addressed the timeline of plume migration and whether new contamination is emerging, with confirmation that the southern plume is long-standing but only recently monitored for emerging contaminants.
• Inquiries were made about municipal well safety, with confirmation that no city wells are impacted due to groundwater flow direction.
• A question confirmed that the project is funded through an existing city budget line item for landfill remediation.

Financial/Strategic Outlook

• The Great Bay adaptive management program requires sustained annual funding and inter-municipal coordination, with no major budget changes anticipated.
• The Toland Road remediation project has completed 100% design, with bidding underway as of June 1, 2026; construction is planned in two phases — earthwork in late 2026 and infrastructure installation in mid-2027.
• Full operation of the southern plume system is expected by October 2027, with long-term monitoring to continue indefinitely.
• City leadership emphasized that current decisions in development and stormwater management aim to prevent future liabilities similar to the Toland Road legacy.