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With a combined total of over 80 years of remediation experience, StoneHill employees have selected and applied remediation strategies to address numerous contaminant types in many different substrates including soil, surface water, groundwater, sediment, structures, and indoor air. StoneHill employees have extensive experience with remediation of sites impacted with various petroleum distillates including gasoline, diesel fuel, No. 2 fuel oil, No. 6 oil, waste oil, and mineral oil dielectric fluid, as well as individual petroleum compounds including benzene, methyl tertiary-butyl ether (MTBE), polynuclear aromatic hydrocarbons (PAHs), and naphthalene. In addition, StoneHill has experience remediating dense non-aqueous phase liquid (DNAPL) and dissolved chlorinated solvents in bedrock and unconsolidated formations. StoneHill also has designed and implemented remedial plans for soils, sediments and urban fill sites impacted with lead, arsenic, chromium, polychlorinated biphenyls (PCBs), and PAHs.

The remediation technology implemented is based on site-specific chemical and physical characteristics, the nature of the contaminant and migration pathways, regulatory requirements, insurance coverage considerations, and optimal time frames. In light of these considerations, StoneHill has experience with both traditional methods and new innovative treatment methodologies which may be appropriate in various scenarios. The traditional extraction technologies for soil and groundwater include excavation of contaminated soils, groundwater pumping and treatment, soil vapor extraction, air sparging, high volume/low vacuum sub-slab vapor collection systems, and interceptor/recovery trench collection systems. These technologies may be coupled with standard treatment technologies including oil/water separators, settling tanks, granular activated carbon (GAC), air stripping, and UV irradiation systems, all of which have been employed by StoneHill. StoneHill owns a customized mobile trailer equipped with product recovery and water treatment equipment for rapid and cost effective deployment to spill sites where groundwater has been impacted.

In some cases monitored natural attenuation (MNA) or enhanced MNA is a more appropriate response action than implementing one of the above techniques. MNA includes the regular monitoring and testing of dissolved phase groundwater contaminants to ensure natural in-situ degradation processes are reducing the contaminants of concern. In an enhanced MNA program, biological degradation processes are enhanced to more rapidly degrade the contaminants. Enhancement technologies include nutrient injection, oxygenated water infiltration, oxygen releasing products, and oxygen diffusion systems.

Selected Project Summaries

Fuel Oil Spill Cleanup

A release of heating oil throughout the basement impacted air, soil and
groundwater at this residence. Severe winter weather worsened some conditions and made completion of response actions very difficult in this case. As the spill occurred in the early winter, the air inside the home was quickly heavily impacted with fuel oil vapors as the
forced hot air heating system intake was in the basement, forcing the owners to move out of the home. This situation was resolved owners to move out of the home. This situation was resolved within a few days by installation of a vapor barrier in the crawl space and redesign of the heating system to collect exterior air rather than recycle indoor air. In doing so, oil vapors were eliminated from the living space of the home. Fuel oil floating on water in the basement and outside the residence was removed using a vacuum truck and the fuel oil impacted soil floor of the basement was removed using a vactor truck. The owner’s bedrock water supply well and a neighbor’s dug well were located 50 feet downgradient of the release location. Therefore, groundwater impacted with fuel oil product and dissolved phase fuel oil constituents was pumped to prevent impacts to the water supply wells and minimize the movement of contamination. Contaminated water was treated using StoneHill’s mobile groundwater treatment trailer. An emergency discharge permit was obtained from the U.S. EPA and treated groundwater was discharged to a catch basin located in the street. Despite nature’s repeated attempts to freeze the trailer treatment system, approximately 175,000 gallons of contaminated groundwater were treated over a four month period. Groundwater quality improved to meet Massachusetts groundwater quality standards within six months.


Soil and Sediment Remediation

A 62-acre property formerly used as part of a farm homestead, apple orchard, saw mill, and pig farm since 1910, was impacted by the on-site
burial of solid wastes, farm waste, and 55-gallon drums containing waste paint during the 1970's and 1980’s. The primary contaminants of concern at the Site included arsenic in on-site stream sediments, polynuclear aromatic hydrocarbons (PAHs) in large a volume of fill
soils, and waste paint residuals in soil. A Massachusetts Phase II Comprehensive Site Investigation completed by StoneHill identified that the arsenic in sediment was the result of decades of natural arsenic precipitating with iron oxides, and the PAHs in soil were associated with coal and wood ash. As such, both of these contaminants were considered local background and exempt for Massachusetts Contingency Plan response action requirements. However, due to the possible future residential use of the property, voluntary remedial measures were undertaken to eliminate or minimize the potential for direct human contact with PAHs in soils or arsenic in sediments. The response actions were completed as a continuation of Immediate Response Actions (IRAs) initiated by consultants previously involved with the site. In the case of the PAH impacted soils, large rocks and cobbles were screened from the soil to reduce the total soil volume and the soil was used to reclaim an on-site gravel pit area. Several feet of clean fill were then placed over the PAH impacted soils to complete the reclamation. In the case of the arsenic in sediment along the brook, the material exhibiting the highest arsenic concentrations was selectively removed by vacuuming the sediment, thereby avoiding the need to enter the brook area with heavy equipment, minimizing the impacts to the stream environment. The former waste paint drum disposal area was remediated by excavation and off site disposal of soil exhibiting paint residuals. Finally, groundwater quality data collected from an extensive network of overburden and bedrock groundwater monitoring wells did not detect exceedances of applicable groundwater standards. Therefore, a condition of no significant risk was achieved at the site and a Class A-2 Response Action Outcome (RAO) Statement was filed with the MADEP. The most significant feature of this project was that StoneHill’s common sense approach, combined with comprehensive data collection, allowed the successful closure of the site at a cost significantly less than projected by other parties previously involved with the site. A MADEP representative indicated that they were impressed by the level of data collection used to decipher contaminant origins and subsequently support the selection of remedial alternatives.

Fuel Oil Spill Cleanup

Approximately 200 gallons of No. 2 fuel oil leaked from an above ground residential fuel tank onto the concrete basement floor and seeped into the ground beneath the residence. Following an initial site visit on behalf of the homeowner’s insurance company, StoneHill conducted a Geoprobe™ investigation to assess whether the release threatened to impact third party or adjacent properties. The investigation identified a lens of fuel oil migrating towards the property boundary and a significant threat of third party impacts. Subsequently, StoneHill was contracted by the homeowner

to manage the remediation of the fuel oil release which included the removal of 300 tons of oil contaminated soil, recovery of fuel oil floating on the water table, and pumping and treatment of contaminated groundwater. Contaminated groundwater was pumped
through two activated carbon drums and discharged to the Whitman sanitary sewer system under an emergency discharge permit. Background soil conditions were achieved in all but a small area where removal of residually impacted soil beneath and adjacent to the residence foundation was not reasonably feasible. Field activities were completed and the disturbed areas landscaped within four weeks of project initiation.




600 State Street, Suite 2
Portsmouth, NH 03801
Telephone: 603-433-1935
Toll Free: 1-800-639-4503
Fax: 603-433-1942

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