with 19th century alterations. Reid's Bridge carries the drive for Brook Farm, after which a ridge of higher ground separates the valley from that of the River Loddon, and so the river turns to the north. The hamlet of Lambwoodhill Common is on the left bank, with Foudry Bridge to the south and Gravelly Bridge to the north. Just before it reaches the M4 motorway Burghfield Brook joins on its left bank, and after the bridge, the stream passes between the Green Park Business Park and the Madejski Stadium and football centre west of Whitley, where it provides the water for the meadow-landscaped lakes. It then passes under a large roundabout on the A33 road, carries on between Thames Water's Reading sewage treatment works to the west and the Brunel Retail Park to the east, before discharging into the River Kennet, here canalised as part of the Kennet and Avon Canal, just downstream of Fobney Lock and Bridge 8A, which carries the A33 over the Kennet. The Kennet weaves its way through Reading passing through County Lock and Blake's Lock to join the River Thames downstream of Caversham Lock. Geology and hydrogeology Chalk is the major aquifer in the catchment area of the River Kennet and its tributaries, including the Foudry Brook. Whereas the chalk is on the surface in the west of the catchment, it is covered by a layer of clay and sand to the east, where the Foudry Brook is located. This gives it the typical characteristics of a clay catchment river, where the flow rates can be quite variable, with the low base flow rising rapidly after heavy rainfall, as surface water cannot pass through the impermeable clay, and quickly finds its way into the river. Ecology In 2004, Foudry Brook had a grade of ‘c’ to ‘d’ on the Environment Agency General Quality Assessment (GQA) scheme for biological and chemical quality (with ‘a’ being the highest quality and grade ‘f’ the lowest). This was thought to be a result of the discharge of treated effluent into the lower reaches from sewage treatment works. The GQA scheme has since been replaced as a way of recording the water quality of the river systems in England. Each is given an overall ecological status, which may be one of five levels: high, good, moderate, poor or bad. There are several components that are used to determine this, including