Three Lakes Road Parcel
|Summary Date: October 2005||View detailed information from database on this site.|
|Status: Cleanup Complete - Institutional Controls||Database Name: Three Lakes Road Parcel|
|Location: Three Lakes Loop Road, Petersburg, AK||Latitude/Longitude: See database entry|
| DEC Contaminated Sites Contact: Bruce Wanstall, Project Manager – 907-465-5210
Local residents and foresters recall logging equipment storage and repair shop operations taking place on the property in the 1960’s when the site became known as the Falls Creek Shop. Similar operations in southeast Alaska have displayed incidental spillage from fuel handling and lapses in proper waste management practices. Alaska Department of Fish and Game expressed concern about the proximity of Falls Creek, an anadromous fish stream as well as an attractive recreational swimming site used by Petersburg residents.
The maritime climate supports a dense forest growth over the entire Pacific coastline, including Mitkof Island where the Three Lakes Road property is located south of Petersburg. Surface topography in the area is generally flat with irregular variations in soil and bedrock outcrops. Poor soil drainage results in peat bogs called muskegs where soil is heavily organic with a low pH that can leach tannin, a phenol, and terpene, an unsaturated hydrocarbon into water. These leachate compounds give water an orange color and non-petroleum sheen can appear on the surface of the water.
Public Health and Environmental Concerns
Environmental Investigation found that up to 5,000 mg/kg of diesel range hydrocarbons (DRO) was present in soil in the northwest quarter of the Three Lakes Road Land Parcel. The historical soil contamination is generally confined to the fill material that was imported to cover native forest soil root layer and muskeg to elevate the grade for operation of the vehicle repair shop. Concerns about migration of the petroleum soil contamination into the riparian habitat adjacent to the northern property line were investigated and are not supported by the environmental data. No floor drains or signs of petroleum spillage were associated with the building.
In May 2005, DEC approved a site cleanup workplan submitted by DMC Technologies, Inc., a qualified environmental consultant contracted to excavate soil from the property and conduct on-site active remediation of the petroleum contamination. Excavated clean material was segregated from oily soil by a combination of observation and field instrument testing known as field screening. Material with petroleum was immediately transferred to a bioremediation cell on the property directly adjacent to the cleanup site. Removal began at the former fuel storage area southwest of the shop building, continued across the rear of the shop building until clean soil was consistently found, then resumed again at the north edge of the property line where non-hazardous buried solid waste was recovered and transported off-site to the City of Petersburg Landfill. An estimated volume of 730 cubic yards of shot rock and native peat material was placed in the remediation biocell. The excavation was left open and bermed while remedial treatment of the contaminated soil was conducted.
Final confirmation analytical samples of undisturbed soil in the excavation received laboratory analysis to document the horizontal and vertical limits of hydrocarbon contamination. After DEC review and approval of the sample data, it is determined that the maximum concentration that remained in subsurface soil in the excavation was diesel range hydrocarbons (DRO) at 1,170 mg/kg and residual range hydrocarbons (RRO) at 2,530 mg/kg. The biocell soil received a nutrient and bacterial addition to promote accelerated chemical and biological breakdown of hydrocarbons bound in the soil particles and was tilled to promote aeration. DEC approved the biocell DRO statistically derived average concentration as just under 650 mg/kg and the RRO average as just over 3,225 mg/kg.
Assured that the confirmation sample analysis results were below the approved cleanup DRO concentration of 1,360 milligrams per kilogram mg/kg and RRO of 8,300 mg/kg, DEC approved backfilling the excavation with the biochemically activated soil from the treatment cell. The approved DRO cleanup concentrations are determined to be protective of the migration to groundwater pathway based on the site specific physical parameters of the property and the area.
Remaining On-Site Soil Contamination The portion of the property where soil was excavated, biochemically treated and tilled on-site, and then backfilled is located on the rear half of the northwest corner of the 2.2 acre property. The area begins at the former fuel storage area southwest of the shop building, continues behind the building to the north side where a stretch of clean soil was found, and then resumed for a short distance north of the shop near the north property line where buried solid waste was recovered and transported off-site.
The DEC is confident that concentrations of DRO in soil at the property are protective of ingestion, inhalation and migration to groundwater exposure risk scenarios for residential land use as long as the soil remains within the confines of the property. The DRO concentration in the remediated soil still exceeds most conservative Method Two Table B2 migration to groundwater cleanup levels that are required for unrestricted land use.
Natural attenuation will eventually reduce DRO concentrations in soil below Method Two Table B2 migration to groundwater cleanup concentrations that allow unrestricted placement of soil that has been impacted by oil. The biochemical breakdown of hydrocarbons is expected to continue in soil used to backfill the excavations on the property. The influence on soil surrounding the excavation is likely to enhance natural attenuation of petroleum that remains bound to soil in low concentrations.
After remedial action took place, DEC gave this site conditional closure status in October 2005. Institutional controls still apply to this site. See the glossary for more in formation on closure of sites. See the database entry (link at top of page) for specific controls placed on this property.