| 7/28/2010 |
Document, Report, or Work plan Review - other |
Reviewed the Shannon & Wilson, Inc. “UST Closure Assessment, Municipality of Anchorage, Fire Station No. 9, 1148 Huffman Road, Anchorage, Alaska” dated August 1997. A 500-gallon waste oil UST and associated piping, installed in 1982, were removed on 7/16/97. The subject UST was located in a paved area beneath about 4 feet of soil. The tank showed signs of moderate corrosion, but no holes were observed. Approximately 41.5 c.y. of soil was excavated during removal of the UST, 39 c.y. of which were deemed as potentially clean soil via screening. After analytical results confirmed their cleanliness, these soils were used to backfill the excavation. Soil samples collected from the UST and piping excavation and the stockpile were selected for analytical testing based on highest PID headspace readings. All samples were submitted to the laboratory to be analyzed for GRO, BTEX, DRO, and RRO. Additionally, one sample each from the stockpile, UST excavation, and piping trench excavation were tested for PCBs, HVOs, and total metals, including arsenic, cadmium, chromium, and lead.
The soil encountered in the UST excavation consisted of a brown, silty, gravelly sand throughout the depth of the excavation. The soil observed in the tank excavation would provide little resistance to lateral or vertical migration of liquids if a release from the UST system had occurred.
Groundwater was not encountered in the UST excavation. Based on previous work in this area, we estimate the depth to groundwater to be approximately 8.0 to 13.5 feet bgs. The nearest known private well is within a 500 foot radius of the site and the nearest public well is within ¾ mile of the site.
Since this UST system was used to store waste oil, soil samples were analyzed for GRO, DRO, RRO, and BTEX and selectively analyzed for PCBs, HVOs, and total metals, including arsenic, cadmium, chromium, and lead. The site is subject to ADEC Category B cleanup levels based on site information. A maximum concentration of 0.94 ppm GRO and non-detectable concentrations of DRO, RRO, benzene, total BTEX, PCBs were detected in the UST and piping excavation. The halogenated compound methylene chloride was reported in Sample S1 at a concentration of 0.34 ppm. This concentration is above the most conservative ADEC proposed risk base criteria of 0.008 ppm in soil. The 0.34 ppm methylene chloride is probably a laboratory contaminant. With the exception of methylene chloride, the concentrations of hazardous substances in the soil are below the appropriate ADEC cleanup criteria.
A maximum concentration of 0.84 ppm RRO and non-detectable levels of DRO, GRO, BTEX, PCBs, and HVOs were detected in the stockpiled soils placed back into the excavation. With the exception of total chromium, the concentration of metals detected in the stockpile samples are within background levels for the Anchorage area. The concentration of chromium is above the typical background concentration of less than 50 ppm. The EPA regulatory guideline for leachable chromium is 5 ppm by the toxicity characteristic leaching procedure (TCLP) method. The TCLP dilutes the sample 20 times. Therefore, even if the entire concentration of chromium in the sample is leachable the sample would yield 2.8 ppm leachable chromium which is below the EPA regulatory guideline. The-allowable total chromium level in soil is 390 ppm. The concentration of petroleum hydrocarbons and hazardous substances detected in the stockpile are below the ADEC cleanup guidelines appropriate for this site.
|
Bill Petrik |
