SUMMARY OF REPORT

• Structure & hazard class: Glass Lake Dam is a masonry dam/earthen dike (built 1916, 108-acre impoundment on Wynants Kill, Sand Lake, NY), classified Class B “Intermediate Hazard.” Glass Lake Road (with a bridge) runs across the top of the spillway.
• Recent structural discovery: In March 2026, part of the downstream stone façade failed, revealing that the dam is actually granular earthfill with stone facing — not solid masonry as previously assumed. This required a revised stability analysis with lower-weight material assumptions. Repairs are in design.
• Façade failure limit: Analysis found the dam remains stable if no more than 24 feet of material is lost from the downstream face.
• Spillway capacity is inadequate: The spillway cannot safely pass the SDF (150% of the 100-year storm) — the earthen dike and Glass Lake Road east of the dam would overtop by about 1.1 feet during such an event.
• Dike stability shortfall: The 2016 slope stability analysis shows the earthen dike fails to meet minimum safety factors under normal, design-flood, and rapid-drawdown loading conditions.
• Other capacities are adequate: The spillway meets NYSDEC drawdown requirements, and the low-level outlet meets its drawdown requirement too.
• General condition: Overall in serviceable-to-good condition with minor issues (seepage, erosion, rodent burrows, deteriorated culverts); vegetation limited full inspection. The bridge deck underside shows notable concrete spalling and exposed rebar.
• Bottom line: No life-safety loss is predicted even in a dam failure scenario, but real deficiencies exist — inadequate flood capacity and a dike that doesn’t meet stability standards — needing follow-up engineering work and likely construction (dike raising, spillway improvements, façade repair).

KEY RECOMMENDATIONS:

• Evaluate options to increase spillway capacity to safely pass the SDF (Spillway Design Flood).
• Conduct subsurface borings on the earthen dike (none have ever been done) and redo the slope stability analysis with updated surveys.
• Raise the dike to meet NYSDEC flood freeboard requirements, with a new stability analysis for the modified embankment.
• Revise the Emergency Action Plan’s inundation maps (currently hard to read/interpret) and verify/update notification contacts at least annually.
• Continue routine maintenance per the existing Inspection & Maintenance Plan.