05/18/2026
Date: May 18, 2026
The Board of Directors and Interested Members of the Lake Wynonah Community
Lake Wynonah Property Owners’ Association
406 Navajo Drive
Auburn, PA 17922
Re: Preliminary Engineering Report
Conceptual Rehabilitation Plan for Lake Wynonah Dam Without Reservoir Drawdown
1. EXECUTIVE SUMMARY
This report presents a conceptual engineering approach for the rehabilitation of the Lake Wynonah Dam without requiring a long-term reservoir drawdown. The report relies heavily upon the findings and conclusions contained within the:
• 2014 Gannett Fleming Seepage Evaluation Report;
• 2022 Schnabel Engineering Review of Seepage Evaluation Report;
• Historic as-built construction documents and seepage monitoring data.
Based upon review of the available documents and field observations, ALTA Design Associates, Inc. (“ALTA”) believes that the principal seepage issues at Lake Wynonah Dam are associated with:
1. Incomplete and ineffective bedrock grouting during original construction;
2. Widely spaced grout curtain holes that left substantial untreated fractured rock;
3. Seepage through highly fractured bedrock near the right abutment and spillway contact zones;
4. Aging spillway waterstops and deteriorated concrete joints;
5. Long-term migration of seepage through transmissive bedrock discontinuities.
Importantly, neither the 2014 Gannett Fleming report nor the 2022 Schnabel report conclusively established that catastrophic internal erosion is currently progressing. Instead, the reports indicate a dam that has experienced long-term seepage conditions, which require remediation and modernization.
ALTA believes that the Lake Wynonah Dam can likely be rehabilitated through a phased engineering program consisting primarily of:
• Completion of a modernized grout curtain;
• Pressure grouting of fractured bedrock zones;
• Localized seep remediation;
• Spillway rehabilitation;
• Installation of a new auxiliary emergency spillway;
• Continued instrumentation and seepage monitoring.
In ALTA’s opinion, it may be possible to accomplish these repairs without a multi-year reservoir drawdown and potentially within the approximate $4,000,000 currently held in LWPOA dam reserve funds, depending upon final design parameters and subsurface conditions encountered during construction.
2. BACKGROUND
Lake Wynonah Dam is an earthen embankment dam located in Schuylkill County, Pennsylvania. Historic reports indicate seepage concerns have existed since shortly after the reservoir was initially impounded.
The 2014 Gannett Fleming report and subsequent 2022 Schnabel review documented:
• Seepage emerging from multiple weirs and toe drain systems;
• Highly fractured and transmissive bedrock beneath portions of the dam and spillway;
• Historic boils and seepage outbreaks;
• Deterioration of portions of the spillway system;
• Evidence that portions of the original grout curtain were ineffective or incomplete.
Measured seepage quantities reported by Schnabel in 2022 approached approximately 525 gallons per minute, equivalent to roughly one Olympic-size swimming pool per day.
Although this seepage is significant and should not be ignored, seepage alone does not establish imminent structural failure. Many embankment dams experience measurable seepage, particularly where fractured rock foundations exist.
3. ORIGINAL CONSTRUCTION DEFICIENCIES
3.1 Incomplete Grouting of Bedrock Foundation
The 2022 Schnabel report specifically notes that the original grout curtain consisted primarily of grout holes spaced approximately 10 feet on center, with limited tertiary holes.
Schnabel further stated:
“When comparing the highly fractured rock to the original grout hole spacing, it becomes apparent that the amount of rock fractures that are likely ungrouted is significant; therefore, the grout curtain was likely largely ineffective in reducing seepage.”
Historic documentation further suggests that portions of the north shoulder and right abutment bedrock were never fully treated to modern grouting standards.
The available records indicate:
• Highly fractured bedrock conditions existed during original construction;
• Tertiary grout holes at 5-foot spacing were not comprehensively installed;
• Portions of the grout curtain may never have been closed to refusal;
• Subsequent seepage patterns strongly correlate with incompletely treated foundation rock.
In ALTA’s opinion, the available evidence suggests that the seepage problem is fundamentally associated with an incomplete and ineffective grout curtain rather than failure of the embankment itself.
4. RECOMMENDED FOUNDATION REPAIRS
4.1 Completion of Modern Grout Curtain
ALTA recommends the installation of a new modern grout curtain utilizing:
• Primary grout holes;
• Secondary grout holes;
• Tertiary grout holes;
• Split-spacing methodology;
• Verification drilling and pressure testing.
Unlike the historic construction program, ALTA recommends grout spacing at approximately 5 feet on center in the highly fractured bedrock zones.
This recommendation is directly supported by the conclusions of the Schnabel review and by modern dam foundation grouting practices.
4.2 Pressure Grouting Operations
The fractured bedrock beneath the spillway and abutments can likely be treated through pressure grouting utilizing:
• Cementitious grout;
• Low mobility grout mixes;
• Stage grouting procedures;
• Lugeon testing;
• Controlled injection pressures.
The objective of the grouting program would be to:
• Reduce permeability of fractured bedrock;
• Re-establish hydraulic cutoff conditions;
• Reduce seepage gradients;
• Reduce discharge through the toe drain systems and seepage weirs.
Importantly, these repairs can generally be performed while maintaining the reservoir near normal operating elevation.
Temporary localized lowering of the lake by several feet during specific construction operations may be beneficial, but a complete long-term drawdown does not necessarily appear technically required based upon presently available information.
5. SPILLWAY REHABILITATION
5.1 Existing Spillway Repairs
The existing concrete spillway shows signs of deterioration including:
• Failed or displaced waterstops;
• Joint leakage;
• Rotated spillway wall sections;
• Deteriorated concrete fillets;
• Seepage entering slab joints.
ALTA recommends:
• Concrete repairs;
• Joint reconstruction;
• Replacement of deteriorated waterstops;
• Localized underpinning and stabilization;
• Sealing of seepage pathways adjacent to spillway walls.
The existing spillway structure appears repairable.
5.2 Auxiliary Emergency Spillway
One of the primary deficiencies identified in prior reports involves probable maximum flood (“PMF”) capacity.
ALTA recommends evaluation and construction of a new auxiliary emergency spillway designed to safely pass the PMF event.
Potential alternatives include:
• Vegetated earth emergency spillway;
• Roller compacted concrete (“RCC”) spillway;
• Fuse plug spillway system;
• Labyrinth weir spillway.
Installation of a properly designed auxiliary spillway would:
• Significantly improve hydraulic safety;
• Reduce overtopping risk;
• Allow continued use and rehabilitation of the existing spillway;
• Potentially avoid the need for full spillway replacement.
6. POTENTIAL COST RANGE
Based upon conceptual-level review and comparison to similar dam rehabilitation projects, ALTA believes it may be possible to engineer and perform the following work for much less than the $27 million proposed by the LWPOA BOD:
• Exploratory drilling and geotechnical investigation;
• Modernized grout curtain installation;
• Pressure grouting operations;
• Spillway concrete rehabilitation;
• Emergency spillway installation;
• Instrumentation and monitoring upgrades;
• Engineering and permitting.
Final costs would depend upon:
• Actual subsurface conditions encountered;
• Final spillway design;
• Extent of concrete deterioration;
• Regulatory requirements;
• Construction sequencing.
Nevertheless, the currently available data does not conclusively establish that a multi-year reservoir drawdown and complete dam reconstruction are the only feasible alternatives.
7. REGULATORY CONSIDERATIONS
Under Pennsylvania dam safety regulations, emergency stabilization work may generally proceed on an expedited basis with DEP coordination.
Additionally, phased rehabilitation work can often be permitted while maintaining reservoir operations.
ALTA recommends:
• Preparation of a focused geotechnical investigation program;
• Performance of a phased seepage remediation program;
• Continued monitoring during rehabilitation.
8. CONCLUSIONS
Based upon review of the available engineering reports and historical data, ALTA Design Associates, Inc. believes:
1. The principal seepage issues at Lake Wynonah Dam are likely associated with incomplete and ineffective foundation grouting during original construction.
2. The original grout curtain was not completed at modern closure spacing standards and significant fractured bedrock likely remains untreated.
3. A modernized grout curtain utilizing approximately 5-foot spacing in highly fractured zones could substantially reduce seepage.
4. The existing spillway appears repairable.
5. A new auxiliary emergency spillway can likely be constructed to address PMF deficiencies.
6. The presently available data does not conclusively demonstrate that a multi-year reservoir drawdown is technically necessary to rehabilitate the dam.
7. It may be possible to substantially rehabilitate the dam without the significant assessment recently proposed by the LWPOA BOD.
Further geotechnical investigation and engineering analysis are recommended to refine the conceptual repair program outlined herein.
DISCLAIMER
This report constitutes a preliminary conceptual engineering opinion based solely upon review of available reports, drawings, and publicly available information. Additional field investigation, drilling, testing, surveying, and detailed engineering analysis would be required prior to final design or construction.
Respectfully submitted,
ALTA DESIGN ASSOCIATES, INC.
/s/ Timothy Maurice Brouse
Timothy M. Brouse, P.E.
Principal Engineer
