Managing Risks Associated with Industrial Impoundments

R. Kent Nilsson, P.E.Senior Consulting Engineer

TRC Environmental Corporation

Drawbacks of learning by trial and error…

Industrial Impoundments in their Current Context

Recent highly-publicized releases of residuals or chemicals from industrial structures into public waters.

New attention on treatment basins and impoundments located on rivers and waterways.

By nature of facility locations, the forest products industry is expected to be under increased regulatory and public scrutiny.

Industrial Impoundments in their Current Context

Impoundments are being monitored using current and historic web-based aerial photographs.

Unmanned aerial vehicles (drones) touted for their ability to access remote areas. Being used by researchers, regulators, and NGOs to monitor impoundments and river conditions.

Impoundments in the Forest Products Industry

Used to retain wastewater, process residuals, or storm water Frequently located adjacent to or near waterways, natural

surface water bodies, or wetlands Typically cut/fill earthen construction – perimeter dikes built

from soil borrowed from pond interior Impoundments may be lined (clay or geosynthetic materials)

or unlined May have a variety of discharge structures (weirs, spillways,

channels, pipelines, river diffusers) More than “just an engineered hole in the ground”

Industrial Impoundments – an Analogy

“All ships leak, but it is the system that keeps it afloat.” (i.e., Risks are managed through an engineered system.)

Industrial Impoundments – an Analogy

Even the most watertight and well-maintained ship requires alert and competent operation.

Industrial Impoundments as a System

“A dam system should be considered in terms of the physical, operational, and management infrastructure that is responsible for safe retention of the reservoir and reliable system performance.”-National Performance of Dams Programs (NPDP), Stanford University

Industrial Impoundments as a System

Performance criteria: Provide containment of fluids and/or solids Provide protection of human health and environment

Industrial Impoundments as a System

Owners of dams, impoundment, and containment systems must evaluate risk. Hazards defined as: High hazard potential — A dam failure

would likely result in the loss of at least one human life.

Significant hazard potential — Loss of human life is possible but unlikely in the event of a dam failure. However, significant loss of property or environmental destruction would likely occur.

Low hazard potential — Loss of human life and property and/or environmental damage is unlikely in the event of a dam failure.

System Components

An impoundment SYSTEM is typically comprised of some or all of the following components: Physical infrastructure Operations Monitoring Maintenance Emergency action planning

Physical Infrastructure

System may include perimeter dikes, clay or synthetic liner, water conveyance structures, pipelines, access roads, piezometers/groundwater monitoring wells, weirs, emergency spillways

Know the construction:– Design or as-built drawings– Construction Quality Assurance reports– Documentation of modifications or repairs– Stability evaluations– Subsurface investigations

Applicable regulatory requirements (State Dam Safety rules)

Understanding the System - Geotechnical Investigation

Monitoring Mill Impoundments

What does an incipient or potential problem look like? From 1975 – 2001, 82% of dam failures were due to flooding/overtopping and seeping/piping.

Monitoring

Dike seepageIt is important to note seep location, flow volume, changes in flow, and presence of sediments or suspended solids (color).

Monitoring

Evidence of slope movement – recent or historic

Monitoring

Outlet structure condition: Material of construction deterioration/corrosion Clogging of pipes Blockage of openings Structural support

Monitoring

Erosion due to: Storm water run-off Overtopping of dike River flow

Mechanics of Dike Erosion and Failure

Mechanics of Dike Erosion and Failure

Monitoring

Vegetation and animal burrowsA post-Katrina study cited animal burrows as a “pervasive problem” in levees in New Orleans.

Monitoring

Soil PipingInternal erosion of soil that seeps through a dam. May have no or subtle external evidence.

Operations Pitfalls

Routine dredging from the perimeter that progressively removes the liner or inside face of dike

Liner puncture due to deployment of pump intake hoses

Operations Pitfalls (continued)

Dramatic raising or lowering or water levels in adjacent ponds or water bodies

Operations Pitfalls (continued)

Seemingly “minor” modifications to the impoundment– Improving freeboard through raising the dike elevation– New pipe penetrations– Introduction of additional storm water drainage

Installation of aerators or mechanical equipment that induce wave action, scour or erosion

Operations Pitfalls (continued)

Allowed grazing of livestock on dike face creates trails that are susceptible to erosion

Routine Impoundment Maintenance

Repair of surface erosion (re-seed, replace rip rap) Clear outlet structures and emergency spillway of

debris Replace corroded or deteriorated structures Remove or properly abandon unused structures/pipes Mow dike surface, cut trees Remove burrowing animals/ provide buffer to

potential habitat Maintain access roads (can all areas be accessed in the

middle of heavy rain?)

Emergency Action Plan (EAP)

“One should not believe that periodic state safety inspections are sufficient to prevent failure of the dam and harm to those located downstream. This is not the case. Safety inspections and EAPs are very different.” Association of State Dam Safety Officials (ASDSO)

An EAP is a written document that identifies potential emergency conditions at a dam and specifies pre-planned actions to be followed to minimize property damage or loss of life as a result of failure or mis-operation of a dam.

Emergency Action Plan (EAP)

EAP Components typically include: Dam characteristics EAP Overview Roles and responsibilities Event Detection Emergency level determination Notification/communication Expected Actions Termination EAP maintenance Appendices (Inundation map)

Summary

An impoundment is a SYSTEM that is typically comprised of some or all of the following components: Physical infrastructure Operations Monitoring Maintenance Emergency action planning

Questions/Comments?