The gas station is located in the suburb of an economically developed city in North China, and the urban and suburban areas are connected at the northern end of the expressway. The station officially sold gasoline on February 1 2065438. The gas station covers an area of about 3.4 mu. See Figure 12. 1. There are offices, convenience stores, stationmaster's offices, warehouses, lounges, power distribution rooms and warehouses. There are two gasoline tankers (No.93 and No.97) and two diesel tankers (No.93 and No.0), two gasoline tanks and two diesel tanks.
Figure 12. 1 gas station layout
(2) Review of a gas station pollution accident.
In the process of daily profit and loss management, the gas station confirmed that the oil profit and loss of No.2 tank (15m3 reserve) was abnormal on March 5th, 20th13rd. On March 6, 20 13, the gas station pumped out all the remaining oil in No.2 tank, and checked the pressure. On March 6, 20 13, the static leak detection test of oil tank was carried out by water injection. After three days of water level measurement, it was found that there was obvious water level drop and water leakage, and it was confirmed that there was a water leakage point in No.2 tank.
20 13, 19, March 9, the gas station was officially closed. After the site was closed, a well-known engineering consulting company was hired to conduct on-site investigation, and a certain number of groundwater and soil samples were analyzed and tested. The test results showed that pollutants were detected in groundwater and no pollutants were found in soil in the northeast and eastern surrounding areas of the gas station.
On April 5, 20 13, the gas station excavated the tank farm. After all the four oil tanks were dismantled, it was found that only 1 and No.2 oil tanks had concrete impervious layers at the bottom, while No.3 and No.4 oil tanks had no impervious layers at the bottom. And there is an oil leakage point on the east side of No.2 tank, which forms a local oil-sludge mixture around the same area and extends outside the seepage control area. The excavation site shows that the leaked gasoline has bypassed the impervious layer and infiltrated into the soil layer to move downwards. After excavation, contaminated topsoil and storage tanks should be properly disposed of by gas stations.
The investigation found that the total profit and loss of No.93 gasoline in No.2 tank (leaking tank) and No.4 tank (non-leaking tank) was 28,600 L during the operating period from February 1 day to March 6, 2065438, including operating profit and loss, distribution profit and loss and leakage. The specific situation of refined oil leakage is unknown.
(3) Preliminary analysis of oil leakage.
1) The oil tank area of the gas station has not been effectively impervious. According to the field investigation, the underground oil tank pool has not been effectively impervious. At the beginning of the gas station, there were only two oil tanks (now No.65438+No.0 oil tank and No.2 oil tank). At that time, the oil tank was only treated with simple seepage control, with the side wall plastered with plain concrete paved with red bricks and the bottom plastered with plain concrete paved with red bricks, and a retaining wall was set between the two parties (Figure 12.2). In the later period, in order to expand its business scale, the gas station added two new oil tanks (now No.3 and No.4) and expanded the scale of No.2 oil tank. At the same time of expansion, not only did the additional oil tank area not undergo seepage control treatment, but the simple seepage control walls on the south and east sides of the original No.2 oil tank were also removed (Figure 12.3 ~ Figure 12.5). Only on the east side of the newly expanded oil tank farm, a simpler retaining wall was built, without relevant seepage control treatment, and there was no retaining wall between oil tanks.
Figure 12.2 Site photo of gas station oil tank area
Based on the above reasons, when the refined oil leaks from the No.2 oil tank of a gas station, the leaked oil can directly flow into the No.2 non-seepage area along the simple seepage control area, or even into the No.3 oil tank area, and directly penetrate into the unsaturated zone, polluting the soil and groundwater of the gas station.
2) The quality of the fuel tank is unqualified. According to the investigation (Figure 12.6), the original No.2 oil tank of this gas station is a steel single-layer tank with a volume of 15m3, which is a non-standard tank with a simple FRP protective layer outside, which is consistent with the existing 1 tank on site. At the end of 20 12, the original No.2 oil tank was replaced, and the replaced No.2 oil tank was a leaking tank. After investigation and visit, the replaced No.2 oil tank is an old tank (also a non-standard tank) bought in the second-hand market, and there is no anti-corrosion facility outside the tank.
After investigation, the leakage point of No.2 tank appeared at the eastern top of the tank, and the leakage point was the solder joint at the top of the original tank. The main reason is that the tank body of No.2 oil tank naturally corrodes after contacting with rainwater, and finally corrodes and penetrates its weakest solder joint, resulting in oil leakage. Therefore, the main reason for oil leakage is the unqualified quality of the fuel tank.
Figure 12.3 Site photo of No.2 oil tank in oil tank area of gas station
Figure 12.4 Site photo of the leakage point of No.2 oil tank in the oil tank area of gas station.
3) There is no rainproof facility at the top of the oil tank farm. According to investigation and interview, there is no effective rainproof facility at the top of crude oil tank farm in gas station. In rainy season, atmospheric precipitation will directly penetrate downward through the top of the tank farm, which will not only corrode the underground oil tank, but also accelerate the downward leakage and pollution of the leaked refined oil.
Figure 12.5 Site photo of simple cutoff wall on the side wall of No.2 oil tank in oil tank area of gas station.
Photo/KOOC-0/2.6 Gas Station/KOOC-0/Oil Tank Site Photo