PROJECT A-2
In Situ Sub-Surface Soil and Groundwater Treatment
Gasoline Station, Brockton, MA
PROBLEM:
High concentration of volatile organics and MTBE in soils
At an oil company in Brockton, MA, three underground storage tanks
(kerosene and gasoline) were removed in June 1997 as part of the
required upgrading program of the state and federal
governments. During the removal process, screening of soils indicated
total organic vapor concentrations in excess of 1,000 ppm in some of
the soils. This triggered a reportable condition as part of the
Massachusetts Contingency Plan. Sidewall samples of the tank
excavation indicated that the highest concentrations of organic vapors
were located in the east sidewall. Further excavation of these soils
was precluded due to the presence of a 7,200- gallon diesel fuel tank
just beyond the east sidewall. An estimated 80 cubic yards of soil
were excavated as part of the tank removal process.
Prior to backfilling, soil samples for laboratory analysis were
collected from the four sidewalls of the excavation. Each sample was
tested for volatile organic compounds by EPA Method 8020 and for
petroleum hydrocarbons (TPH) using the hydrocarbon fingerprinting
method (GC/FID). The analytical results are presented below with their
respective reportable concentrations (RCS-2):
| |
Benzene
(ppb) |
Toluene
(ppb) |
Ethylbenzene
(ppb) |
Xylenes
(ppb) |
MTBE
(ppb) |
THP
(ppm) |
| RCS-2 |
60,000 |
500,000 |
500,000 |
500,000 |
200,000 |
2,500 |
| North Wall |
BRL |
58 |
BRL |
67 |
BRL |
BRL |
| East Wall |
27,000 |
500,000 |
88,000 |
1,160,000 |
10,000 |
6,000 |
| South Wall |
92 |
200 |
80 |
620 |
BRL |
560 |
| West Wall |
BRL |
BRL |
BRL |
BRL |
BRL |
BRL |
BRL= Below Reporting Limit
The laboratory results confirm the headspace readings with the east
wall showing significant levels of contamination. However, previous
assessment activities (monitoring well installations) around the
former tank location area indicated that the extent of the east wall
contamination was limited. Groundwater sampling from these monitoring
wells did identify up to 50,000 ppb of MTBE in the groundwater.
SOLUTION:
Bio treatment program with MicroSorb® Microbes, Nutrients, Biocatalyst
Because the soils could not be removed due to neighboring tanks, an in
situ bioremediation program was begun as the best remedial
alternative. After the underground storage tanks were removed from the
excavation, the contaminated stockpiled soil was treated with
MicroSorb products (Microbes, Nutrients, and Biocatalyst) and returned
to the tank excavation as temporary back fill. Also, the native soils
near the east wall of the excavation were inoculated with MicroSorb
products with a hand auger.
RESULTS:
MicroSorb products reduce contaminant levels of soils to well within clean-up standards
Two months after treatment (August 1997) as part of the new tank
installation, samples were obtained from the re-excavated soil and the
results indicated non-detect conditions for volatile organic compounds
(including MTBE). In October 1997, soil samples were obtained from
the area of the east wall by hand auger. The results indicated a
significant reduction in the contaminant levels (MTBE was non-detect),
well within clean-up standards for S1 soils (see table below).
| |
Benzene
(ppb) |
Toluene
(ppb) |
Ethylbenzene
(ppb) |
Xylenes
(ppb) |
MTBE
(ppb) |
THP
(ppm) |
| S-1/GW-3 |
40,000 |
500,000 |
500,000 |
500,000 |
100,000 |
500 |
| S-3/GW-3 |
200,000 |
2,500,000 |
500,000 |
2,500,000 |
200,000 |
5,000 |
| Boring-1 |
1,700 |
13,000 |
18,000 |
120,000 |
BRL |
1,100 |
| Boring-2 |
3,700 |
11,000 |
16,000 |
77,000 |
BRL |
1,300 |
BRL= Below Reporting Limit
Groundwater sampling (October 1997) from the wells in the vicinity of
the tank excavation indicated levels of volatile organic compounds
(including MTBE) to be within clean-up standards as well - although
MTBE was at the upper limit (50,000 ppb), indicating that a small
release from the former gasoline tank may have occurred. However,
within one year (November 1998) MTBE levels dropped to 5,000 and other
volatile organic compounds were significantly reduced (see table
below).
| Well |
Benzene
(ppb) |
Toluene
(ppb) |
Ethylbenzene
(ppb) |
Xylenes
(ppb) |
MTBE
(ppb) |
THP
(ppm) |
| GW-3 |
7,000 |
50,000 |
4,000 |
50,000 |
50,000 |
50 |
| MW-6 (10/97) |
4,400 |
140 |
1,400 |
3,040 |
50,000 |
5.6 |
| MW-6 (11/98) |
2,000 |
92 |
870 |
1,437 |
5,000 |
0.5 |
| MW-7 (10/97) |
290 |
27 |
38 |
176 |
720 |
3.2 |
| MW-7 (11/98) |
7 |
BRL |
BRL |
6 |
130 |
BRL |
BRL= Below Reporting Limit
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