By the end of the year, the state Department of Hawaiian Home Lands expects to be ready to hire a contractor to remediate a hazardous waste site on its lands in `Ewa.
When the state bought 1,100 acres of former sugarcane and pineapple plantation land — “as is” — from Campbell Estate in 1994 for nearly $32 million, it didn’t know that a small portion of that land was heavily contaminated with dioxins, simazine, ametryn, pentachlorophenol, arsenic, atrazine, and trifluran. And to this day, the state leases land surrounding that site — a former O`ahu Sugar Company pesticide mixing and loading (PML) site — for agriculture. The primary tenant, Aloun Farms, grows fruits and vegetables on the leased land.
In September 2004, the Department of Land and Natural Resources approved the transfer of 318 acres of that land, including the contaminated site, to the Department of Hawaiian Home Lands, which plans to build 1,000 affordable single-family homes and 1,000 multi-family units there.
Although the PML site has not been used since 1994 and has been fenced off for several years, the fencing has not prevented stormwater runoff and truck movement from carrying contaminated soil offsite. A June 2010 memorandum by DHHL consultant Enviroservices & Training Center, LLC, notes that high levels of dioxins have been found in soil that is three feet deep in a nearby ditch, and arsenic has also been found outside the 0.6-acre site in concentrations that exceed what the federal government has determined to be acceptable levels.
Last year, the DHHL received a $200,000 brownfields cleanup grant from the Environmental Protection Agency and also secured a $1.97 million Hawai`i Brownfields Cleanup Revolving Loan Fund to remediate the site. The June draft Response Action Memorandum laid out five possible remediation alternatives, ranging from no action to complete excavation. The preferred alternative is to place an impermeable cap over the entire site.
The public comment period ended July 31, and according to DHHL community outreach coordinator Darrell Ing, Enviroservices and the state Department of Health are preparing a final Response Action Memorandum. Once it receives DOH approval, Enviroservices will prepare a work plan, Ing says, adding that he expects the project will go out to bid by the end of the year.
He says the department received about a half dozen comments from the public, most of which were in support of the preferred alternative, although a couple of comments favored complete excavation and offsite soil treatment.
According to the draft memo, the proposed alternative is the cheapest (aside from no action), while excavation is the most expensive. Capping the site would cost an estimated $1,695,000 with annual operation and maintenance costs of $15,000. Excavation, on the other hand, could cost anywhere from $6.8 million to $16.8 million with annual O&M costs of $10,000.
While excavation would best protect human health and the environment over the long term, the short-term effects (handling large volumes of soil, contaminated runoff and fugitive dust during excavation) and exorbitant costs make capping the site a better option, the memo concludes.
Before capping, the DHHL plans to excavate the contaminated soils that have been found outside the project area and place them inside. The total volume of dioxin- and arsenic-contaminated soil within the site is approximately 2,830 cubic yards. The total volume of dioxin-contaminated soil in the ditch is approximately 311 cubic yards.
According to the draft memo, capping the site will involve much more than slapping on a thick liner, covering it with soil and planting shrubs on it. Once all of the contaminated soils are in one place and compacted, a visual barrier will be placed on top, followed by clean, low permeability soil, which will be compacted again to form a two-foot thick layer. Geotextile fabric would then be installed, followed by a 60-mil geomembrane liner, and another layer of compacted, low-permeability soil.
A metallic barrier tape grid would then be placed across the filled areas, followed by yet another layer of low-permeability soil that, when compacted, will be another two feet thick. Finally, a 6-inch layer of top soil would be placed on top and possibly vegetated.
“Various geomembrane industry sources have suggested that, with good periodic
maintenance practices, the life expectancy of a HDPE geomembrane liner in buried applications can be up to 200 years,” the draft memo states.
Ideally, the cap will eliminate the possibility that contaminants will leach into the groundwater and be drawn into downgradient wells, where they could then pose a threat to human health and any marine life that live where that groundwater discharges into the sea.
According to the memo, existing data indicate that the groundwater beneath the site has not been affected by the contaminants at the spill site. Also, no drinking water wells are located within one mile of the site and the nearest surface water body, the West Loch of Pearl Harbor, is approximately 1.6 miles away.
(For an in-depth look at this site, read the cover story and sidebars in our July 2001 issue and the “Board Talk” item in our November 2004 issue. All are available at www.environment-hawaii.org For more information on the project, see the DHHL fact sheet at hawaii.gov/dhhl/publications/ekii/FINAL_Jun10_FactSheet_4pgs_11x17.pdf)