1. One sample from each end of the tank |
a. From outside the tank within 6" of the ends and between
12” and 24” below the tank bottom
b. From inside the tank, beneath each end of the tank within
1' of the tank bottom
2. Samples are to be placed in clean jars and refrigerated at less than 42 degrees F.
3. Samples are transported under chain of custody to a licensed laboratory
4. To be valid, samples must be analyzed within 14 days of collection,
using method NWTPH-Dx
|Please note that Oregon Law does not require soil samples, except for purposes of registering a tank with the Oregon DEQ's Voluntary Heating Oil Tank Registration Program.|
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Dana Thompson Tanks & Soil installs all ASTs consistent with the building codes established by the City of Portland. These codes have been strengthened to address seismic concerns. We construct a 6” thick concrete slab with 3/8” steel reinforcement bars on 12” centers, measuring 39” x 72” for a 275 gallon tank. The tanks are bolted to stands, which in turn are fastened to the slab with expansion bolts. Lines are typically protected in aluminum conduit.
The most difficult part of an AST installation is establishing the location. The tank must be no closer to any retaining wall than the distance between the two elevations separated by the wall. In other words, if the ground level outside your basement wall is five feet above the basement floor, the tank must be placed no closer than five feet from the wall. This holds whether the tank is installed inside or outside. If a tank is installed inside, then it can be place no closer than seven feet to the furnace fire box unless it is separated by a code fire wall. There must also be a reasonable way to route the 2” fill pipe and 1.5” vent pipe. In any installation, routing the heating oil supply and return lines can be problematic.
Generally, the price for installation of a new, 275 gallon tank runs between $1,950 and $2,600, but a firm price can only be established when the tank location is finalized.
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A tank is decommissioned when it is pumped of remaining oil, cleaned and either filled completely with solid, inert material or removed and recycled. On decommissioning, the tank’s vent and fill pipe should be removed. Oregon law does not require soil samples when a tank is decommissioned. In order for a tank to be certified under the DEQ’s voluntary registration program, valid initial site assessment soil samples must be collected no more than 90 days prior to, or at any time after decommissioning, and laboratory analysis must show concentrations of less than 50 parts per million diesel hydrocarbons.
Standard In-Place Decommissioning
Usually, when a tank is located under a lawn or garden area and is not buried too deep, decommissioning is performed by digging a large hole over the top of the tank to allow access for cleaning and filling. Typically a tank is filled completely with pea gravel or sand. After decommissioning the excavated soil is returned to the excavated area and compacted to grade.
In-Place Decommissioning With Control Density Fill (CDF) Material
There are many situations which do not allow the standard approach. When the tank is buried too far beneath ground surface, excavation to the top of the tank can be impractical or dangerous. When the tank is covered by a driveway, patio or building, gaining access to the top of the tank may cause unacceptable damage to finished surfaces or may be to costly. In these cases all decommissioning work can be cleaned through the fill pipe. We use a garden hose detergent infusion device attached to a ½” pvc pipe with a 90° pressure nozzle at the end to wash and emulsify oil and solids from the walls of the tank. The wash material is pumped and recycled. When the tank is clean, a concrete pump is employed to pump control density fill material into the tank via the fill pipe. Control density fill is a lean concrete product using sand, cement and other cementious materials, which sets up to 100 psi.
Decommission By Removal
After a tank has been cleaned it can be decommissioned by removing it from its location and delivering it to a steel recycling location.
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Environmental Cleanup Defined Environmental cleanup involves performing whatever work may be necessary to demonstrate to the Oregon DEQ that environmental conditions at a site where an oil tank leak is discovered do not pose a threat to human health or the environment. This may or may not involve excavation and removal of petroleum impacted soil.
When a release of heating oil from an underground tank has been reported, the DEQ assigns a file number to the property. The objective of a cleanup is contractor certification that the site meets DEQ cleanup requirements, thus allowing the DEQ to close the file, and removing any environmental cloud from the property.
Most leaking oil tank sites in the Portland metro area can be DEQ Certified without removal of the tank or disposal of contaminated soil.
The Oregon DEQ provides three options for cleanup of sites where a release of petroleum has occurred. The following is a brief description of these options. For more detailed information, consult the DEQ's website, where the guidance documents for these cleanup approaches may be found.
Soil Matrix Cleanup
The DEQ developed a matrix scoring method which applies a point value to site specific conditions. Any site with a score of 40 points or lower, qualifies for Level II Soil Matrix Cleanup. Most homes in the Portland metro area are Level II Soil Matrix Cleanup sites. Level II Soil Matrix Cleanup is achieved if the most contaminated soil on a site contains less than 500 ppm TPH. When a soil sample collected before or during tank decommissioning on a Level II site contains more than 50 ppm TPH, but less than 500 ppm TPH, the release must be reported, but usually the site will meet cleanup standards without further site work.
Risk Based Decision Making
The Oregon DEQ allows sites to be closed where contaminated soil exceeding soil matrix cleanup levels still remains on site if it can be shown that the contaminated soil does not pose a threat to human health or the environment. The Risk Based Decision Making process requires that:
1. The source of contamination is removed (the tank is properly decommissioned)|
2. There is no “free product” (puddles of oil)
3. The full vertical and horizontal extent of petroleum impact has been delineated.
4. A representative sample of contaminated soil is analyzed for
BTEX and PAH constituents.
5. Exposure pathways for constituents of concern (known carcinogens
present in heating oil) are explored and no risk to human health or the
environment is present.
The Generic Remedy cleanup option is a simplified Risk Based Decision Making process . The unique features of the Generic Remedy are:
1. No groundwater is encountered |
2. Soil sampling demonstrates that no more than 65 cubic
yards of contaminated soil remains on the site.
3. All contaminated soil is located at least 3’ below
4. The most contaminated soil remaining on site contains
less than 10,000 ppm TPH and less than 0.0083
5. No PAH analysis is required
6. If the most contaminated soil samples shows petroleum concentrations
below 2500ppm no BTEX analysis is required.