Merit Engineering provided a complete Level 2 ESA study for a project which involves 3 separate areas in a warehouse facility complex. The facility is located in downtown Bellingham central commercial zone. The company has been being at this location since early in the century. The three areas were known to have USTs removed before 1986 with:
- area 1 contained a crude oil tank and diesel tank;
- area 2 contained a gasoline tank; and
- area 3 contained diesel fuel.
Therefore, the objective of this study was to
- investigate the subsurface conditions at the removed tank sites;
- determine the approximate extent of the contamination; and
- provide recommendations for site remediation.
Merit Engineering conducted a field subsurface investigation by executing 10 test borings with continuous sample collections to the depth of 10′ where either groundwater or geologically impermeable clayey soils were encountered.
The subsurface investigation revealed that the native soils at the site were predominantly clayey soils and glacial marine drift deposits (Bellingham Drift). This soil is fine grained with a very low permeability which practically can be considered as impermeable. With our strong knowledge and extensive experience in local geology and soil conditions, we successfully determined, with a limited amount of test borings, the extent of the areas where UST had been removed and backfilled with imported materials. The collected soil samples were delivered to a local analytical laboratory for analysis. The laboratory analysis was focused on diesel, gasoline, and crude oil.
From this study, we concluded that
- soil contamination is primarily limited to the fill materials which were backfilled to the areas excavated for removing the tanks;
- contamination is apparently due to either non-thorough cleanup or lack of cleanup action when the underground storage tanks were removed;
- the native firm clay appears to have played a role as an earth barrier, lining the contaminated fill soils so that the contaminated soils are confined to the limited tank-removal area;
- no seasonal high water marks such as mottled soil were observed from this investigation;
According to the test results, the silty and clayey soils both above and below the groundwater are not contaminated. Therefore, it may indicate that the groundwater is not contaminated because the clayey and silty soils are practically impermeable materials and blocked the transport of the hazardous materials.
We recommended the owner to cleanup the site with three possible methods which were determined most economical for the project area at the time:
A. Soil Bioremediation
B. Aeration; and
C. combination of the above two methods
Merit Engineering was also retained to investigate the cause for the building settlement. It was suspected that the settlement was due to a “sinkhole” cave-in of an abandoned coal mine. MERIT conducted several test borings around the building including a deep one at the location of a “sinkhole” and analyzed the results and compared with literature documentation. We concluded that the sinkhole had occurred due to the cave-in of the abandoned coal mine before the building was constructed. The sinkhole was backfilled with “uncontrolled” fill and the building was built after the fill took place. The soft compressible nature of the uncontrolled fill in the sinkhole caused differential settlement of the building which further induced cracking of the building.