Hart Crowser Hawai‘i Office He‘eia Work Day

He‘eia Stream Estuary

The Hart Crowser Hawai‘i team working at He‘eia Stream Estuary. In the area in the right half of this photo we’ve removed the invasive knot grass. The remaining akulikuli is looking a bit trampled, but will recover quickly and thrive.

On Wednesday, June 27, the Honolulu staff each dedicated a vacation day to volunteer with Hui Ko‘olaupoko (HOK) at He‘eia, O‘ahu. HOK is a non-profit watershed management group established in 2007 to work with communities to improve water quality through ecosystem restoration and storm water management, focusing specifically in the Ko‘olaupoko region on windward O‘ahu. HOK’s mission is to protect ocean health by restoring the ‘āina: mauka to makai (land: mountain to sea).

HOK implements innovative projects that effectively manage and protect water quality and natural resources. Projects have included storm water low-impact development projects such as rain gardens, and other watershed focused projects.

The He‘eia estuary restoration project is a collaboration with several other non-profits to restore the ecosystem of He‘eia Stream. This project is aimed at improving water quality and increasing habitat for native aquatic animal species by removing invasive plants and replanting native Hawaiian species. In the past 3 years, about 4 acres of mangrove have been cleared and native species planted. Our work for the day consisted of removing invasive “knot grass” from the estuary flats where it was overwhelming the native vegetation that was planted following removal of the mangrove.

For the plant nerds among us, the predominant native vegetation we protected in the estuary flats were:

  • Akulikuli (Sesuvium portulacastrum), an indigenous coastal succulent ground cover that has been very successful in the estuary
  • Mau‘u‘aki‘aki (Fimbristylis cymosa), a sedge that forms short, rounded tufts of light green narrow, stiff, erect blades
  • Ahuawa (Mariscus javanicus), a greenish blue rush with beautiful brown spiky umbrella flowers/seed pods

We also got to see many native and rare species that have been planted along the stream bank, including Ilima with its tiny flowers that need about 500 to make a lei!); Lama; Ohai; and Mao hau hele. All of these plants have interesting cultural uses and significance, well explained at these website links by our friends at Hui Kū Maoli Ola, an amazing native plant nursery in upper He‘eia.

One of the delights of working on this project was getting to visit the adjacent He‘eia Fishpond. Paepae o Heeia, another non-profit, has been restoring the 88-acre, 800-year-old fishpond since 2001. He’eia Fishpond was likely constructed by hundreds, if not thousands, of Hawaiians who passed and stacked rocks and coral for approximately 2-3 years to complete the 1.3-mile wall. Fishponds helped Hawaiians practice sustainable aquaculture long before western contact. There are only a few fishponds remaining of the approximately 100 that are known to have existed on O‘ahu, as most have been destroyed by development. Restoration of remaining fishponds has been a big part of the Hawaiian cultural renaissance over the past 25 years. While we didn’t work on the fishpond itself, we were able to cross the stream to walk on the fishpond walls (which are dry stacked!), to view the functioning sluice gates, and to learn more about fishponds.

We had a fun team-building day that successfully cleared invasive species from a large area, and learned a bit more about native plants and Hawaiian culture around fishponds. Thanks to HOK for hosting us, and kudos to our Hawai‘i team for being adventurous and volunteering their own time to take on this project!

Ko‘olau mountains

The beautiful Ko‘olau mountains in the distant background, a portion of the fishpond wall and sluice hale in the midground, and our team working hard in the foreground.

Walking on Fishpond Wall

Walking on the fishpond wall after a long day of work; the enclosed fishpond is to the left, with the open waters of Kāne‘ohe Bay to the right.

Hawaii team

Our Hawaii team is all smiles visiting He‘eia Fishpond after a long day of work helping to restore He‘eia Estuary.

Sluice gates

The working mākāhā (sluice gates) of He‘eia Fishpond.

Ilima,official flower of O‘ahu

The beautiful native Ilima, the official flower of O‘ahu. The little flowers are treasured for lei – it takes more than 500 of these flowers to make a delicate and special lei.

 

You Shall Not Pass

Chinook Salmon

Removing Fish Barriers

In 1969, a burning river helped draw attention to the polluted state of many United States waterways. Since then, much progress has been made to clean them up, allowing wildlife to thrive in habitats that were once dead. It’s only more recently that attention has migrated (pun intended) to fish passage problems.

According to NOAA, In the United States, more than 2 million dams and barriers block fish from migrating upstream to spawning and rearing habitat. The Washington State Department of Transportation (WSDOT) says that a little under two thousand culverts block fish passage along Washington highways. As of last year, WSDOT completed 319 fish passage projects, but there is still much to accomplish.
Read on for an example of a recent project, what services are needed to clear the way, and information about Washington, Oregon, Hawaii, and Alaska organizations that are trying to make a difference.

Example of a Fish Passage Project—Rue Creek

Before construction

Rue Creek before construction.

After construction

Rue Creek after construction.

The Pacific Conservation District received a Washington Coastal Restoration Initiative grant from the Washington State Recreation and Conservation Office. Hart Crowser supported the Pacific Conservation District with design and development of two culvert replacements on Rue Road in Pacific County.

Fish passage and flow conveyance capacity were restored by removing the existing culverts and overlying fill, and installing a 50-foot bridge that met design requirements in the Washington Department of Fish and Wildlife’s Water Crossing Design Guidelines and Washington State Department of Transportation’s Standard Specifications for Road, Bridge and Municipal Construction and Design Manual. Staff then used the stream simulation approach (one of the methods to size and design culverts that is an option in the Washington Department of Fish and Wildlife’s Water Crossing Design Guidelines) to design the pattern, dimensions, and other features of the stream channel at the crossing, which would enable safe passage of juvenile and adult salmonids both upstream and downstream. An added benefit was that the replacement should prevent the creek from flooding Rue Creek Road and nearby residences.

Services Needed for Fish Passage Projects

These projects can require:

  • Hydraulic engineering
  • Geotechnical engineering
  • Stream reach assessment
  • Wetland delineation
  • Permit applications to comply with Section 404 of the Clean Water Act, Section 7 of the Endangered Species Act, and other federal, state, and local permit requirements. For the Rue Creek example above, this included preparation of a JARPA, SEPA checklist, ESA Section 7 Biological Assessment, Essential Fish Habitat assessment, and Stewardship Plan.

Action on the Local Level

Washington

In 2014, the Washington State Legislature created the Fish Passage Barrier Removal Board to develop a coordinated barrier removal strategy and provide the framework for a fish barrier grant program. Its stated mission is to “identify and expedite the removal of human-made or caused impediments to anadromous fish passage in the most efficient manner practical through the development of a coordinated approach and schedule that identifies and prioritizes the projects necessary to eliminate fish passage barriers caused by state and local roads and highways and barriers owned by private parties.”
The board has monthly meetings; agenda and meeting handouts are available on its website. It advanced its first project list to the legislature, which has been funded.

Oregon

The Oregon Department of Fish and Wildlife has a nine-member Fish Passage Task Force, which “advises the Oregon Department of Fish and Wildlife and the Fish and Wildlife Commission on matters related to fish passage. These matters include, but are not limited to, rulemaking to implement statutes, funding and special conditions for passage projects, and exemptions and waivers.” The most recent agendas and minutes are at the link above; older ones are here.

Hawaii

The Pacific Islands Fish and Wildlife Office of The US Fish and Wildlife Service says that the Hawaii Fish Habitat Partnership “is composed of a diverse group of partners that have the capacity to plan and implement a technically sound statewide aquatic habitat restoration program. The partnership is committed to implementing aquatic habitat restoration in the appropriate landscape scale to achieve conservation benefits.”

They list “instream structures and barriers including stream diversions, dams, channel alteration, and road crossings” as one of eight key threats to freshwater species and habitat.
See the Pacific Islands Fish & Wildlife Office annual report for fiscal year 2017 for more information.

Alaska

The Alaska Department of Fish and Game has a fish passage inventory database with information about 2,500 stream crossings. They have partnered with other organizations to complete at least 33 culvert replacements.

You Shall Pass

A blocked river isn’t as dramatic as a burning river, which makes it harder to draw attention to the plight of the remaining blocked fish. But the hope is that continued effort will forward the progress that is already being made.

Performance-Based Seismic Design for Safer High-Rises

F5 Tower

The City of Seattle knows that building codes for downtown Seattle are not safe for tall buildings in a strong earthquake. That’s why it now requires performance-based seismic design for all buildings over 240 feet tall.

What is Performance-Based Seismic Design?

Seismic design usually follows a prescriptive code, sort of like following a cookbook. Performance-based seismic design is a more rigorous seismic analysis, performed by a team of experienced geotechnical and structural engineers. Because the design doesn’t follow the cookbook code, this alternate design procedure must be done by top engineers, so that it meets the intent of the code while also going beyond the code in certain respects. It must also be peer-reviewed by experienced engineers—often the people who participated in developing the code in the first place.

Doug Lindquist, a principal geotechnical engineer with Hart Crowser, describes it this way: “Performance-based design is a design method where the geotechnical and structural engineers proactively evaluate the performance of a structure in terms of displacements, forces, moments, and damage level. Performance-based design often results in a more resilient, constructible, and valuable structure compared to prescriptive/reactive methods.”

In the early 2000s, Hart Crowser was the first local geotechnical firm to use modern performance-based seismic design methods in the Pacific Northwest. Our engineers have incrementally improved on our proprietary methods and procedures over the last 18 years.

When and Where is Performance-Based Seismic Design Used?

Performance-based seismic design is used for buildings taller than 240 feet—around twenty-four stories or higher. It is used in areas zoned for high-rises, and only when allowed by the local permitting jurisdiction (e.g., Seattle and Bellevue).

Examples of our 20+ performance-based seismic design projects include:

  • Rainier Square Tower, Seattle (850 feet tall)
  • F5 Tower, Seattle (660 feet tall)
  • Russell Investments Center, Seattle (598 feet tall)
  • Lincoln Square Expansion, Bellevue (two towers, 450 feet tall)
  • Cirrus, Seattle (440 feet tall)
  • Midtown 21, Seattle (322 feet tall)

Major western United States cities allowing performance-based seismic design include Seattle, Bellevue, Portland, San Francisco, San Jose, Oakland, Los Angeles, and San Diego.

Advantages

Safer Design

Typical building design following the International Building Code (IBC) is based on the Design Earthquake (DE), which is defined as two-thirds of hazard level of the Risk-Adjusted Maximum Considered Earthquake (MCER). Using performance-based seismic design, the geotechnical engineer works closely with the structural engineers to analyze the building under both the DE and the MCER hazard levels. Because the building is analyzed under the higher MCER loading, the engineers have a better understanding of how the building will behave when subjected to strong ground motions. After review of many performance-based design projects, the City of Seattle identified deficiencies in the typical building design methods and now requires performance-based seismic design for all buildings taller than 240 feet.

Faster Construction and Lower Development Costs

When a building is so tall, the building code requires a dual seismic restraint system. This is like wearing both a belt and suspenders. If it’s a good belt, you don’t need the suspenders, and vice versa. Using performance-based seismic design allows you to build using one or the other. Just as it’s faster and more economical to dress donning only one fashion accessory, it’s faster and more economical to build only one structural system. This is allowed when the design engineers perform detailed analyses showing that the single system achieves the desired performance goals of the structure.

Improved Views and Higher Building Value

Eliminating cross-bracing or other exterior seismic restraint systems improves the building’s views, allowing floor-to-ceiling windows, which make the building more desirable to tenants.

Recent Advances

ASCE 7-16

Although it will not be required for use until 2020, improved methods in ASCE 7-16 have been used by Hart Crowser engineers since 2015. Certain provisions of this new code document allow for the removal of some of the extra conservatism built into the current building code. Hart Crowser was the first to use these methods in the Pacific Northwest, which result in reduced construction costs compared to older methods.

Ground Motions

Horizontal pairs of ground motions are provided by the geotechnical engineer to the structural engineer, who simulates the seismic response of the building subjected to these motions using a building model in the PERFORM 3D. There are thousands of ground motions in multiple public databases for geotechnical engineers to choose from to give to the structural engineer for design. Over the last 18 years, Hart Crowser has developed tools and techniques to identify, select, and scale the optimum ground motions that meet the source characteristics (e.g., magnitude, mechanism, spectral shape, site conditions, and source-to-site distance) and reduce the error between the target spectrum and ground motion spectra. This eliminates unnecessary conservatism and reduces construction cost compared to using less ideal ground motions.

Seattle Basin Amplification

The Seattle Basin amplifies ground motions compared to motions outside of a basin. Hart Crowser has been at the forefront of the practical implementation of research on the Seattle Basin into building design. Doug Lindquist has presented at both the 2013 and 2018 workshops on the subject organized by USGS and the City of Seattle.

Future Improvements

Future improvements will include enhanced scenario modeling to determine the strength of shaking at a building site (e.g., the M9 project) and additional advancements on incorporating basin amplification into design.

Lincoln Square Expansion

Lincoln Square Expansion in Bellevue, Washington.

Stream Restoration Certification Program Fills Pressing Need

Case Study Presentation

Brad Hermanson and Timmie Mandish present a stream restoration case study.

Fish habitat across the country has been seriously impacted from years of human activity.  There is considerable effort now being made to repair the damage done and improve the chance for fish survival. There is a pressing need for professionals trained and certified in stream restoration.

To meet the need, Portland State University (PSU), in concert with several resource agencies, created a stream restoration certification program.  The one-year program, with five core and a number of elective courses, is the only one of its type in the country.  Started in 2006, the stream restoration program has certified over 160 students in advanced concepts of stream restoration.

Brad Hermanson, Hart Crowser’s Manager of Environmental Sciences and Engineering, co-leads the three-day core course “EPP 225 – Restoration Project Management” with Timmie Mandish of USDA-Natural Resources Conservation Service.  EPP 225 covers topics ranging from fundamentals of project management and project risk management, to contracting strategies, regulatory permitting, construction options, and real-life case studies. Besides co-leading the course, Brad teaches the first half-day kickoff portion, introducing the students to concepts on project management and project risk management.

This year’s EPP 225 course was offered at PSU December 5-7.  There were 32 students, most employed by state and federal natural resource agencies, but also several independent consultants and contractors.  Review comments from the students were very positive.  One student noted “Definitely exceeded my expectations. I’m a scientist.  I tend to underestimate how essential project management is.  The class gave me crucial skills that will probably be serving me in the future.  I learned a ton!  Thank you so much.”  Another stated “…was great to combine project management with the river restoration lens.  I have a PM background and this helped to hone those skills – reminders and tools to communicate, evaluate risk, prepare for unique (project) changes – all are very useful and will strengthen me in my career.”

Course participants

32 students, including state and federal natural resource agency employees, attended the 2017 course.

STEM for Future Generations

Jessica teaching about salmon

Science, Technology, Engineering, and Mathematics (STEM) schools in our area and across the country are working to improve the way our students learn in these subject areas. These STEM-focused schools offer a more hands-on approach to teaching, from using objects students can physically manipulate to working with resources and companies in the area to bring in experts to teach the students more about these fields.

This is why Jessica Blanchette, a marine biologist at Hart Crowser, volunteered her time to educate the 4th graders of Odyssey Elementary on the life cycle of salmon, a crucial element of the ecological community of the Pacific Northwest.

Using multiple instructional strategies, including hands-on activities and colorful presentation materials, Jessica captivated Mukilteo School District students with her knowledge of fry, parr, and smolt—the salmon life cycle. Students had many questions and Jessica had plenty of answers!

Jessica led a thoughtful discussion about the human relationship with salmon, our impacts on them, and ways in which we can promote a successful co-existence. There was excitement in the classroom as the lesson wrapped up: not only because of the activities and new knowledge, but also because the students were beginning to see that one day they, too, can be scientists.

When scientists like Jessica share their time to promote STEM, it has a positive and lasting impact in the community. Hopefully, with more endeavors such as this, local scientists will make a positive difference in our world and for future generations.

Salmon Life Cycle

Mussels Reveal Impact of Puget Sound Stormwater

Bay Mussels

Native mussels (Mytilus trossulus) like these were used to evaluate the degree of contamination in Puget Sound nearshore habitats. Photo: Brewbooks

The mission of the Washington Department of Fish and Wildlife (WDFW) is to preserve, protect and perpetuate fish, wildlife and ecosystems while providing sustainable fish and wildlife recreational and commercial opportunities. An important initiative is evaluating the impacts to nearshore aquatic areas from stormwater discharges. Mussels sieve the water as they feed, and their tissues absorb and retain chemicals and pathogens, so the WDFW led a study using mussels as an indicator organism. They got help from so many organizations and volunteers, the list fills nearly an entire page. It includes the Snohomish County Marine Resources Council (Mike Ehlebracht, Hart Crowser geochemist, volunteers for the MRC), the Washington State Department of Ecology, other governmental agencies, native American tribes, and various non-governmental organizations. The work was funded under the new Stormwater Action Monitoring (SAM) program that is paid for by municipal stormwater permit holders.

How Was the Study Done?

As part of this study, the WDFW and volunteers placed “clean” caged mussels at over seventy locations across Puget Sound, including highly industrial areas (such as Smith Cove and Salmon Bay), urban areas like the Edmonds waterfront, and rural areas (such as the San Juan Islands). They left the caged mussels in the water for several months, then retrieved them, often in the dark, in cold and blustery weather. They tested them for stormwater-related contaminants including PAHs (produced by burning coal, fossil fuels, wood, and garbage), PCBs (used in electrical apparatuses, surface coatings, and paints; banned in the US in 1979), metals, PBDEs (used in flame retardants), DDTs (insecticides; banned in the US since 1972), and others.

And the Results…

The study showed that stormwater discharges continue to impact the nearshore aquatic environment, particularly in industrial and highly urbanized (paved) areas. PAHs and PCBs were the most ubiquitous, problematic chemicals detected in the mussels, with some of the highest concentrations found in Elliott Bay (particularly Smith Cove).

Puget Sound is a large, complex, and diverse estuary. This data will be critical in determining best management practices and providing recommendations for environmental remediation. The next round of sampling will occur this fall, with updated data available in another year or two.

Download a copy of the Stormwater Action Monitoring 2015/16 Mussel Monitoring Survey: Final Report.

Questions? Contact Mike Ehlebracht.

Placing caged mussels

Snohomish County Marine Resources Council volunteers and staff place caged mussels.

Recent Guidance on Vapor Intrusion – EPA, Washington State, Hawaii, and Oregon

Vapor intrusion occurs when there is a migration of vapor-forming chemicals from any subsurface source into an overlying building. The vapors can enter buildings through cracks in basements and foundations, or through conduits and other openings. Examples of vapor-forming chemicals that are hazardous to human health include methane (from landfills), tetrachloroethene (PCE) and trichloroethene (TCE) from dry cleaners, benzene (from petroleum products), and radon.

Soil Vapor Migration

Migration of Soil Vapors to Indoor Air
This figure depicts the migration of vapors in soil gas from contaminated soil and groundwater into buildings. Vapors in soil gas are shown to enter buildings through cracks in the foundation and openings for utility lines. Atmospheric conditions and building ventilation are shown to influence soil gas intrusion. (source: EPA)

 

Since 2000, research has shown that exposure to toxic vapors has much greater health risks than previously known. Long term exposure to even very low concentrations can result in cancer. In response, the federal and state governments have lowered the safe exposure limits, and regulators have recently updated guidance for assessing vapor intrusion.

EPA published new guidance for assessing vapor intrusion in June 2015. (OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air; OSWER Pub 9200.2-154). The document provides guidance on conducting investigations, including collecting samples; interpreting risk assessments; and mitigating vapor intrusion.

Washington State subsequently updated their guidance for vapor intrusion in February 2016 (Washington State Department of Ecology, Guidance for Evaluating Soil Vapor Intrusion in Washington State: Investigation and Remedial Action, Pub 09-09-047). This document describes Tier I Screening assessments and Tier II sampling assessments.

Hawaii published their VI guidance in 2014 (Technical Guidance Manual for the Implementation of the Hawai’i State Contingency Plan, Section 7: Soil Vapor and Indoor Air Sampling Guidance). This document provides good information on different types of sampling equipment, with photos.

The state of Oregon is using vapor intrusion guidance published in 2010 (Guidance for Assessing and Remediating Vapor Intrusion in Buildings).  The guidance describes how to perform risk-based evaluations, and the state periodically publishes updated risk-based concentrations for chemicals.

In the state of Minnesota, vapor intrusion concerns have significantly affected the real estate market. Starting in 2017, if a building is suspected of having contaminated soil below or around it, the state has asked the owners to test for vapors and fix vapor problems before the property can be sold. This can significantly add to the costs of property transfers and delay sales or even scare off buyers.

Here in the Pacific Northwest, the states are not requiring soil vapor testing, although near landfills methane vapor testing is often required.  Also, areas with known radon often require vapor mitigation systems. But your environmental consultant should be considering vapor intrusion risks during Phase I Environmental Site Assessments, and might recommend soil vapor tests during Phase II investigations. Vapor intrusion is complicated – vapors move more easily than soil or groundwater contamination. It takes careful evaluation and interpretation of the guidance and test results to help property owners and purchasers make knowledgeable decisions.

Questions? Contact Anne Conrad, (425) 775-4682

There’s a Volcano on our Project Site

Water is the life blood of any city, but its systems are not always pretty. So the two-million-gallon Forest Park Low Tank was embedded into the hillside to preserve the natural character of the area and leave unfettered views. However, this presented engineering challenges. Overcoming those challenges helped us win a 2017 Grand Award from the American Council of Engineering Companies (ACEC).

Wait—What’s Down There?

The subsurface conditions were quite unusual. Maps showed them as hard volcanic rock, but our geotechnical explorations discovered a new volcanic vent, as yet unmapped. Although of great interest to geologists, volcanic vents are rarely built on. A search of case histories did not find any information to guide the process. We embarked upon an exploration and laboratory testing program to determine if the 100-foot plus pile of cinders would support the tank. We determined that the cinders were fairly uniform across the area, resulting in uniform support for the tank. Our testing further determined the magnitude of loading the cinders could support. With this information we were able to design a foundation that did not require expensive subgrade improvements or pile foundations.

Our high-tech analyses confirmed a low-tech approach would work.

Burying Infrastructure to Preserve the Natural Beauty

In many places, water tanks are constructed within large cuts that many may view as eyesores and which permanently remove natural habitat. This has been accepted over decades as a necessary compromise to provide a robust water supply to our cities. However, this compromise does not need to be accepted. Much like the trend of burying power, communications, and other utilities that were once also overhead, the Forest Park Low Tank demonstrates that water infrastructure can be adapted similarly.

Making the Water Supply Safe

Water is a critical resource in any disaster that disrupts our infrastructure. It’s common knowledge that we cannot survive for more than three days without water. During any natural disaster, it is imperative that our water remain safe and accessible. We completed a site specific seismic hazard (SSSH) as part of our work, so the tank and appurtenant facilities will withstand the next “Big One.”

Defining Ingenuity

Sometimes ingenuity is not devising something new, but applying simple methods to solve a problem. We used performance-based results to guide changes in shoring design, and confirmed landslide mitigation approaches during construction. We avoided designing expensive foundation alternatives, installing bulletproof (and expensive) secant shoring walls, and over-analyzing slope stability prior to construction. And then we buried our best work.

The one thing to remember about this project is that we did not blow our top over an unexpected volcanic vent; instead, we persevered and worked with the design and construction teams to build a successful project…and then buried it out of “site.”Finished project

Preserving Eelgrass While Remediating Legacy Contamination

Eelgrass

What do you do when the State requires you to take action, yet prohibits that action? It’s a conundrum that takes imagination and determination.

The Setup

For over 100 years, several companies used the nearshore at the former Custom Plywood site for processing and manufacturing wood-related materials that would be used nationwide. They filled the tideland with wood, ash, bricks, metal, and sediment. They left a tug, boiler ash, scrap metal, barrels and drums, aluminum cans, scrap wood, paper, sawdust and creosote-treated pilings. As if that wasn’t enough, in 1992 a fire destroyed the mill, adding dioxin (a carcinogen) to the sediment.

The Conundrum

The Washington State Department of Ecology and Hart Crowser removed most of the contamination from the property and tidelands. Despite this, there are many acres of tidelands that are still peripherally contaminated with dioxins, much of which contains healthy eelgrass habitat. The eelgrass is not affected by the dioxin contamination; the problem is that it serves as a potential pathway for human exposure (i.e., shellfish consumption). By State mandate eelgrass must be protected. (See our earlier post about the importance of eelgrass). This means that the State requires that something be done about the contamination but not at the expense of the valuable eelgrass habitat. Our current options for dealing with dioxin contamination are to either dig up the contaminated material, or immobilize/cover it to prevent the exposure to the benthic community. Either action would potentially destroy the eelgrass. What to do?

The New Approach

The solution? Remediate the sediment in place by covering the eelgrass habitat, but not burying it. Eelgrass, unlike other species of seagrass, can only tolerate a very small level of burial. We needed to determine if the eelgrass at the former Custom Plywood site could withstand deposition of very fine layers of sand that would act as a barrier (cap) to the contamination in order to protect the benthic community and the habitat overall. Our team conducted a two-year pilot study to see whether the eelgrass could tolerate a four- or eight-inch layer of sand (applied two inches at a time), rather than a single layer application that would ordinarily be used for remediation. As part of this study, our team also investigated if adding a layer of carbon could increase the cap performance so that the cap could be as thin as possible.

Diver

Diver with eelgrass/sediment sample. Photo courtesy of Research Support Services.

The Result

The data clearly showed that eelgrass at the former Custom Plywood site can survive a four-inch cap if implemented in multiple thin layers. This means that the preferred alternative for cleaning up the residual contamination is potentially feasible. The next step is to design a large scale application using the information and data gathered from the pilot study. Eventually we hope to finally cleanup the former Custom Plywood site while leaving the existing eelgrass habitat in place and functioning.

 

The Game of Thrones Wall—An Engineering Perspective

Game of Thrones Wall

Photo: HBO

The Game of Thrones (the HBO series based on George R. R. Martin’s books, A Song of Fire and Ice) features a giant wall made of ice. Seven hundred feet high. It’s an imposing structure, but it has to be, in order to keep out the terrifying dead people who inhabit the north.

According to Martin, “You could see it from miles off, a pale blue line across the northern horizon, stretching away to the east and west and vanishing in the far distance, immense and unbroken. This is the end of the world, it seemed to say.”

Such an extraordinary structure couldn’t help but draw attention from our geotechnical engineers and staff, who responded to some of the quotes from the books.

“The wall is a hundred leagues long.”

A league was supposed to be the distance that a person could walk in one hour. An English league, once upon a time was about three miles long, which would make the wall three hundred miles long.

“The wall is 700 feet high.”

This is almost as tall as the 1201 Third Avenue Building in Seattle, a 55-story building, which coincidentally has beautiful blue coloring as well. Certainly it takes a lot of work to design and build a high-rise—imagine building so many adjacent high-rises that they would stretch for 300 miles. That’s never been done.

At a height of 700 feet and a unit weight of 57.4 pounds per cubic foot (pcf) for fresh water ice, the base contact pressure on the underlying soil/rock would be on the order of 40,000 pounds per square foot (psf). (Compare that to a high-rise on glacial till at 14,000 psf).

“The wall has stood for, what, eight thousand years?”

Assuming a coefficient of secondary compression, C-alpha, of 0.02 and assuming that the base upon which the wall is built is comprised of some reasonable thickness of compressible organic muskeg (say ten feet), and assuming the wall was built over a period of one hundered years, the wall will likely have settled about three to five feet under its own weight.

“The top wide enough for a dozen armored knights to ride abreast.”

How wide is an armored knight? Say five feet? 5 x 12 = 60 feet wide? To safely travel, there would need to be at least three feet between riders so the total width (including four feet on either side for shoulders and jersey barriers) would be 101 feet.

“The gaunt outlines of huge catapults and monstrous wooden cranes stood sentry up there, like the skeletons of great birds, and among them walked men as small as ants.”

To anchor the catapults and cranes, it is likely that the overturning and uplift forces on the catapults and cranes would control the design. The overturning forces associated with the action of the catapults and the wind loads on the structures (resulting from the unobstructed exposure to the predominant winds due to the height of the wall) could be resisted by using high-capacity drilled micropiles.

“It was older than the Seven Kingdoms and when he stood beneath it and looked up, it made Jon dizzy. He could feel the great weight of all that ice pressing down on him, as if it were about to topple, and somehow Jon knew that if it fell, the world fell with it.”

One of the Seattle-Tacoma International Airport Third Runway walls (135 feet tall) was built stepped in, in order to avoid this feeling when you stand at the base of it. However, typically, a tall wall looks shorter when looking up than when it does when looking down. Jon is a weenie.

“Eight hundred feet above the forest floor, a good third of that was earth and stone rather than ice.”

It seems that people got creative over the years, sometimes making use of on-site materials, a good practice to save cost, time, and the environment. It also makes sense, when you are building a structure with a contact bearing pressure equal to 40,000 psf, to do overexcavation and replacement with densely compacted (i.e., 95 percent of the maximum dry density, within two percent plus or minus of optimum moisture content, as determined by ASTM D1557 Test Procedure) well-graded sand and gravel with less than five percent passing the U.S. No. 200 sieve based on the minus three-quarter-inch fraction.

Have questions about the geotechnical design of other giant structures? Need a dragon or two? Contact Garry “the Hound” Horvitz.