Bauneg Beg Lake — Long-Term Passive Phosphorus Reduction, Maine

Project type: Passive in-water phosphorus reduction system

Client: Bauneg Beg Lake Association (North Berwick/Sanford, Maine)

Location: Bauneg Beg Lake, Maine

Installed: 2018 — continuously operational

The Challenge

Bauneg Beg Lake is a 188-acre lake in the Towns of North Berwick and Sanford, Maine, with a direct watershed of 14.8 square miles. The watershed includes active agricultural areas and high-density residential and commercial development in downtown Sanford. Over 200 seasonal and year-round homes line its shores, along with a summer camp and year-round facility serving children and families. The lake is an impounded segment of the Great Works River.

Phosphorus loading from a watershed of this character arrives through multiple pathways: runoff carrying suspended sediment, particle-bound phosphorus transported in fine material, and dissolved phosphorus moving through the water column. Addressing only one pathway leaves the others unmanaged. The lake association needed a system that could be left in place year-round, require minimal active management, and demonstrate measurable improvement over time — not a one-time treatment, but a durable, passive approach.

System Design

Mackworth-Enviro designed and installed a three-barrier system at a wetland inlet to the lake, targeting phosphorus across its principal transport forms.

Barrier 1 — Debris and sediment interception

A coarse barrier positioned to capture larger debris and settleable sediment before it enters the main lake system. This extends the service life of the downstream barriers and reduces direct sediment loading.

Barrier 2 — Particle-bound phosphorus capture

A fine filtration barrier targeting the particle-bound fraction of phosphorus — the dominant transport form from agricultural and developed catchments — using Mackworth-Enviro's composite filter material technology. Water passes through; the phosphorus-bearing particles are retained.

Barrier 3 — Dissolved phosphorus capture (experimental)

A third barrier designed to address dissolved phosphorus, a fraction that bypasses conventional sediment control. This element represents an active area of development in passive in-water treatment and reflects Mackworth-Enviro's ongoing investment in expanding the performance envelope of barrier-based nutrient management.

The three-barrier configuration was designed to work within the natural hydraulics of the wetland inlet — low-velocity, diffuse flow — without requiring pumping, chemical dosing, or active operation.

Performance

The system has been continuously installed and operational since 2018. Measurable phosphate reduction has been observed throughout the monitoring period. Annual maintenance requirements have been minimal, consistent with the system's design intent as a low-intervention, long-duration installation.

The lake association has maintained the installation as part of its ongoing commitment to the health of the lake and its watershed.

Why This Approach

Passive in-water phosphorus reduction is well-suited to lake systems where:

• The phosphorus source is diffuse across a large watershed rather than a single point of discharge

• Active treatment infrastructure (pumps, dosing systems, dredging) is either too costly or too disruptive for the community managing it

• Long-term, consistent reduction is more valuable than a large one-time intervention

• The managing organization — a lake association, a municipality, a watershed district — needs a system they can maintain without specialist operators on site

The Bauneg Beg installation has now accumulated more than seven years of continuous operation. That duration is itself the performance record: a system that degrades, clogs, or fails under real watershed loading conditions does not remain in service for seven-plus years.

Mackworth-Enviro designs, fabricates, installs, and monitors passive nutrient reduction systems, including experimental approaches to dissolved phosphorus management not available from barrier manufacturers alone.

Managing phosphorus loading in a lake or reservoir watershed? Contact Mackworth-Enviro.