Warmhouse Beach Dump Remediation - Hydrological Engineering Team

Client Information:

Bruno Ridolfi

Principal Engineer, PE

Ridolfi Inc.

1011 Western Ave # 1006

Seattle, WA 98104-1085

Steve Pendelton

Makah Indian Tribe

P.O. Box 115

Neah Bay, WA 98357

Team Name:

Warmhouse Beach Hydrological Engineering Team

Team Members:

Jeffrey Collins jdc237@nau.edu

Whitney Koester wik2@nau.edu

Kevin Davenport ktd7@nau.edu

Kirstie Englis ke252@nau.edu

From left: Kevin Davenport, Kirstie Englis, Whitney Koester, Jeffrey Collins

Project Description:

The goal of the Warmhouse Beach Hydrological Engineering Project is to mitigate the transport of contaminants via the surface water and subsurface water migration pathways that transport leachate contamination from the Warmhouse Beach Dump into the surrounding environment. The engineering project work will include a hydrological analysis of the site in order to determine the volume and rate of leachate production by the Warmhouse Beach Dump as well as to determine the amount of runoff that enters the dump from the uncontaminated slopes located adjacent to the dump site. This analysis will consist of a watershed delineation, a hydrological analysis of the Warmhouse Beach Dump, and a hydrological evaluation to determine the runoff and leachate production volumes/rates for the site. The results of this analysis will be used to design engineered leachate containment structures to mitigate the flow of leachate from the Warmhouse Beach Dump in the surface and subsurface contaminant migration pathways. In addition, runoff collection and diversion structures will be implemented up gradient from the dump in order to divert the flow of runoff from the uncontaminated slopes adjacent to the dump from entering the dump.

Scope of Services:

The project work for the Warmhouse Beach Hydrological Engineering Project has been divided into eight tasks. The tasks that make up the scope of services are listed below.

Task 1 – Project Management

Task 2 – Watershed Delineation

Task 3 – HELP Model Analysis

Task 4 – Contaminant Migration Pathway Analysis

Task 5 – Summary of Technologies

Task 6 – Engineering Solution Selection and Final Design

Task 7 - Plans, Specs and Estimate

Task 8 – Public Outreach/Awareness

Task 1- Project Management

The purpose of the project management task is to keep all team members, the client, and the technical advisor apprised to the current status of the project as well as to help keep the project work on schedule. These goals will be accomplished by conducting a series of meetings throughout the project duration. Team meetings will be conducted regularly to inform all team members of the current status of the project work and to discuss any questions and concerns. Client meetings will be conducted when needed to inform the client of the project status, request any additional information or clarification that the team may require or to address any concerns or comments that the client may have.

Task 2 – Watershed Delineation

The team will conduct a watershed delineation of the Warmhouse Beach site in order to determine the total volume of expected surface and runoff infiltration. The analysis will provide runoff estimates for the 10, 25, and 100-year storm events as well as for an average condition. In addition, the delineation will provide separate estimates of “uncontaminated runoff” and “contaminated runoff” as well as a map of areas in which they occur. Uncontaminated runoff is defined as runoff water that has not come in contact with the dump, waste materials, contaminated sediments, or any sources of contamination from the Warmhouse Beach Dump. Contaminated runoff is defined as runoff water that has come in contact with any source of contamination from the Warmhouse Beach Dump.

The watershed area will be determined using AutoCAD software and a USGS topographic map of the site. The Hydrological Evaluation of Landfill Performance (HELP) model will be used along with local precipitation data and slope incline characteristics to determine the volume of expected runoff and the partition of runoff between surface and infiltration runoff.

Task 3 – HELP Model Analysis

The team will perform a hydrological analysis of the Warmhouse Beach Dump in order to determine the volume and rate of leachate generation from the dump. This analysis will be performed using the Hydrological Evaluation of Landfill Performance (HELP) Model. This analysis will be performed on the current open dump condition as well as for the engineered cap proposed in the Makah Dump Closure Assessment. These two cases are outlined further below.

HELP Model Analysis of Open Dump Condition

A HELP model analysis will be performed on the Warmhouse Beach Dump in its current open condition. This analysis will provide a leachate production volume/rate for the dump in its current condition. These values will be used to size the engineered leachate collection systems to be designed for the dump prior to closure of the landfill. In addition, the leachate production volume/rate will be a necessary input during the design of a leachate treatment system. The design of the treatment system is to be completed by the Treatment Design Team.

The leachate production analysis of the open dump condition will be conducted using the HELP model, a USGS topographic map of the site, and local soil data. The soil data will be sourced from the United States Department of Agriculture’s Web Soil Survey.

HELP Model Analysis of Capped Dump Condition

A HELP model analysis will be performed on the Warmhouse Beach Dump in its capped dump condition. This modeling will provide a leachate production volume/rate for the engineered cap and closure plan proposed in the Makah Dump Closure Assessment by Ridolfi Engineering Inc. These leachate production values will be used to determine the size of the leachate treatment system as well as any additional engineered leachate collection systems for post closure dump conditions. In addition, the analysis will provide a runoff volume/rate draining from the engineered cap. These runoff quantity values will be used to determine the size of the runoff collection and management structures to be used in the post closure conditions.

This leachate production analysis of the capped dump condition will be conducted using the HELP model, the engineered cap specifications provided by Ridolfi Engineering Inc., a USGS topographic map of the site, and local soil data. The soil data will be sourced from the United States Department of Agriculture’s Web Soil Survey.

Task 4 - Contaminant Migration Pathway Analysis

The team will conduct an analysis of the surface water and groundwater contaminant migration pathways. This analysis will serve to determine the locations of the contaminant migration pathways in order to facilitate the engineering of leachate collection and contaminant mitigation systems.

Groundwater Migration Pathway Analysis

Analysis of the groundwater contamination pathway will include study of the local subsurface geological stratigraphy in order to determine the location and depth of the subsurface runoff below ground surface. Additional analysis will be performed to determine the potential points of entry (PPEs) of the leachate from the Warmhouse Beach Dump into the groundwater migration pathway. This information will be used to design subsurface hydraulic control structures.

The analysis will be performed using preexisting stratigraphic profiles, groundwater data, and topographic site maps provided by Ridolfi Engineering Inc. These data will be used in conjunction with the resulting leachate production values from the HELP model analysis of the open and capped dump conditions.

Surface Water Migration Pathway Analysis

Analysis of the surface water contamination pathway will be performed to determine the PPEs of the leachate streams into East and West Creeks. This information will be needed in order to engineer a leachate collection system to mitigate the flow of leachate into the two creeks.

The analysis will be performed using preexisting stream flow data, maps of East Creek and West Creek, and topographic site maps provided by Ridolfi Engineering Inc. These data will be used in conjunction with the resulting leachate production values from the HELP model analysis of the open and capped dump conditions.

Task 5 – Summary of Technologies

As per client request, the team will conduct a comprehensive study of the state of the art technologies used for mitigation of both groundwater and surface water runoff control. These technologies include cutoff walls, slurry walls, runoff collection channels and diversion berms. The team will discuss the feasibility of each of these technologies to the specific requirements of the Warmhouse Beach Site. The team will draw from these options during the engineering design phase of the project once the hydrological analysis has been completed.

Task 6 – Engineering Solution Selection and Final Design

The team will select from the State of the Art Technologies Memorandum the most desirable engineering design solution for the mitigation of the groundwater and surface water contamination pathways for the Warmhouse Beach Dump Site. This determination will be made using decision matrices and based on the background research performed in Task 5. The decision matrices will consider criteria pertinent to the selection of the best design. These criteria may include runoff capture effectiveness, ease of construction, construction cost, total design costs and operation and maintenance costs. The criteria will be weighted according to the relative importance of each parameter to the final design. These criteria include input from the client.

Once the final design technology has been selected, the team will develop an engineering design for mitigation of the groundwater and surface water contaminant pathways at the Warmhouse Beach Dump Site. This design will serve as a preliminary design and will be documented in a technical design report prior to the termination of the project. This report will consist of preliminary design information including the results of the HELP hydrological analysis, design calculations and plans for the runoff and leachate control structures.

Task 7 – Plans, Specifications and Estimate

Throughout the course of the project, the team will prepare a design report detailing the proposed engineering work and remediation plans. This report will include all relevant deliverables from the individual project tasks. In addition, a set of engineering plans and specifications for the final design will be provided with the report. The final design will not include a full build design, but design specifications that can be used in a full scale build design.

Task 8- Public Outreach/Awareness

The team will develop a website that presents an overview of the project. This website will include background information, current project status, a description of the project engineering work, and graphics and photographs pertaining to the project. Meeting agendas and minutes will be available for review. In addition, pertinent bulletin material, educational documents and articles will be presented on the website.

Description of final products:

The final product of the Warmhouse Beach Hydrological Engineering Project is a conceptual design of the necessary engineered runoff control/diversion structures to successfully mitigate the transport of contamination from the Warmhouse Beach dump to the via the surface water and groundwater migration pathways. The final design will consist of the design of leachate collection and containment structures such as engineered slurry walls, cut-off walls, diversion channels, or diversion berms. Other additional designs may include uncontaminated surface and subsurface runoff collection and diversion structures which may comprise of slurry walls, cut-off walls, diversion channels, or diversion berms.  The design of subsurface leachate pumping wells may be required if it is determined the subsurface leachate must be extracted for a pump and treatment scheme.

The final design will be presented to the client, Ridolfi Inc., in a final design report. Accompanying this report will be a plan set detailing the design of each of the engineered control structures as well as the locations where they are to be implemented.