Page 270 - Hydrogeology Principles and Practice

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Jet fuel clean-up at Heathrow International Airport
7. 2

This case study concerns hydrocarbon contamination of ground- kerosene was about 100 m in diameter and at its thickest point
water adjacent to Technical Block L at Heathrow Airport. Heathrow measured a depth of 0.95 m in borehole 5, with further ‘free
Airport is built on the Taplow Terrace adjacent to the River Thames product’ measured in boreholes 1, 11 and 13 and in Well 1 (Fig. 1).
floodplain. The geology is formed by 4.5 m of coarse clean gravels Odour was reported during the drilling of boreholes 3, 9 and 10,
overlying low permeability London Clay. The water table is shallow, indicative of kerosene. No kerosene was detected in the outlying
about 2.5 m from the surface, with groundwater flow southwards observation boreholes, including borehole 12.
beneath the airport towards the River Thames at Shepperton. A leak The basic remediation structures used included large diameter
of jet fuel (kerosene, a light non-aqueous phase liquid, or LNAPL) wells lined with perforated concrete rings about 1.5 m in diameter
occurred from a cracked fuel pipe leading to an engine mainten- (Fig. 2). Wells 1 and 2, installed close to borehole 1 where a consid-
ance facility, the leak having occurred over a number of years. The erable thickness of fuel was shown to be floating on the water table,
leak was discovered when fuel was observed floating on drainage were used to begin recovery of the floating kerosene. The kerosene
water in a manhole north of Technical Block M (Fig. 1). In response, was removed by floating oil-skimmer pumps. Surface-mounted cen-
a large concrete-lined well (Well 1), about 1.5 m in diameter, was trifugal pumps, installed with their intakes in the two wells, were
installed close to the manhole and revealed about 10 cm of kero- also used to lower the water table and encourage the kerosene to
sene floating on the water table. As a first step in remediating the move towards the recovery wells. The waste water pumped from the
contaminated site, the leak was traced to the cracked pipe and the wells was discharged to the drainage system of the airport, which
fracture repaired. leads to a balancing reservoir before flowing into the River Thames.
A detailed site investigation, including the installation of 14 The balancing reservoir provided settlement and dilution of the
monitoring boreholes, showed that the ‘pancake’ of floating remediation waste water.

Fig. 1 Site of a jet fuel leak adjacent to Technical Block L at Heathrow Airport showing the estimated extent of the kerosene ‘pancake’
resting on the gravel aquifer water table. After Clark and Sims (1998).