Sewage disposal system

The sewage disposal system is secluded in the south eastern corner of Tweedsmuir across the stream that runs along the camp's eastern border. At the time of writing 63 years have elapsed since its construction. When the camp closed, substantial parts of the sewage disposal complex were demolished and are now overgrown by trees, grass and moss. Although these factors place constraints on one's understanding of exactly how the system functioned, we have developed a theory to show how contaminated water may have been cleansed during the camp's occupaton. As seen today the system comprises a primary septic tank, a secondary septic tank, a flat roof brick structure and two concrete discs.

The primary septic tank, part of which had been artificially elevated, was positioned on raised ground (first image).

The secondary tank was built on lower ground (second photograph). The top of the secondary tank is at ground level. In this photograph a blue arrow shows the position of the stream along Tweedsmuir Camp's eastern boundary, an orange arrow indicates the location of what once was part of the camp and a purple arrow points to an escapement (or drain) through which purified water ran into the stream via a 250mm wide earthenware gully (third image).

The primary septic tank differs in construction to the secondary septic tank in that the former has deep, sloping sides whereas the latter has shallow, vertical sides. This suggests that the primary tank was designed to deal with heavily contaminated water where the slopes on each side reduced the likelyhood of sludge clogging up corners. Cross sections of each tank are shown to the right. In the insert below a red arrow points to one of the primary tank's sloping sides and a yellow arrow to its central separation wall.

Details of the primary septic tank are shown in the labelled drawings below (Primary Septic Tank). They are not made to scale.

The remains of the three cast iron inlet pipes drawn in the last sketch are shown in the photograph opposite. Although it is not too easy to determine the origin of these pipes, in the knowledge that a sewage pump existed on the disposal site, our preferred theory is that they orginated at the pump.

Elements of the secondary tank are shown in the labelled drawings above (Secondary Septic Tank), which again are not made to scale. From observation, it's function would have been to further cleanse water and release it into the stream via a gully. In the insert to the right a red arrow points to the escapement into which water entered through two under ground, earthenware pipes, and a blue arrow to the escapement from which cleansed water left the system.

Before the water left the
system, castellated brickwork in front of the upper water shelf (see Secondary Septic Tank graphic and the photograph to the right) would have agitated the water as it flowed into the secondary tank thereby aerating it in the process.

Each septic tank includes one pair of shafts on either side of the central separation wall. In the photograph to the far right an orange arrow points to one of the shafts in the primary tank, and in the picture to the near right two arrows point to shafts in the secondary tank.

At the visible end of each shaft is a reduced threaded section. This suggests that at the top of each shaft there once existed a turning wheel that was held in place by a washer and nut. The purpose of the turning wheel would have been to rotate the shaft, which in turn opened and closed a gate valve during the periodic removal of sludge.

Each of the gate valves, one of which is shown in the picture to the right, is engineered to be bolted into place at the end of a gully inside the tanks.

There were four gate valves
per tank, two in each of half. They would have been used to empty the water from the tanks to aid the process of removing the scum and the sludge, which would have been transported away by tankers.

The flat roof brick structure stands close to the secondary septic tank the position of which is indicated by a yellow arrow in the photograph to the above left, and shown in the foreground of the photograph above right.

Inside this somewhat pragmatic structure are the remains of electrical switch gear. Below ground level is a space accessed by a steel ladder cemented into the wall immediately under an entrance hole in the floor.

From the Canadian Works Directorate War Diaries we know that a pumping system (mentioned previously) was installed on the sewage disposal site in 1941. The remains of steel pipes inside the underfloor space suggests that this simple building was the heart of a pumping system that moved effluent from waste digester tanks, where organic matter would have been broken down, to the septic tanks. The orange and blue arrows in the two pictures immediately below (note that the blue arrows are pointing to the same pipe) indicate the remains of pipes that are in direct line with the primary septic tank.

The smaller of the two pipes, indicated by the blue arrow in the above two photographs, passes under a manhole (image below left) that is situated immediately outside the entrance to the flat roof structure.

At ground level, in front of the primary septic tank and on land between it and the secondary septic tank, are two concrete discs each of 10 metres in diameter. These are the remains of two trickle filter beds. The outline of these structures is accentuated by coloured dots in the next image, which comprises two butted photographs taken just in front of the primary septic tank.

On the periphery of each concrete disc is a circular gully (one of which is marked by a blue arrow in the photograph on the left below) that measures 300mm in width and 100mm in depth. Each is packed with two layers of filtering material, one of flint stones and the other of clinker. The discs are conical in form, sloping downwards from their centres to their outer edges. On the outer edge of each concrete disc is a layer of roughly textured cement (indicated by a red arrow) on which stood retaining walls (probably of brick) when the filter beds were in use. The space within the retaining walls would have been filled with clinker.

At the centre of each disc there once existed an arrangement of bricks as illustrated by the marks left behind in the concrete (see image to the right above). The bricks would have provided a level base for seating a steel plate that was anchored to the disc by 4 bolts. A section of tubular steel welded vertically to the plate would have supported 4 rotating booms.

These are typical design features of a trickle filter bed associated with older sewage disposal systems.

The appearance of each filter bed would have resembled the graphic to the right. Brick columns reduced the likelihood of the retaining walls bursting outwards.

Each rotating boom would have delivered soiled water from the primary tank (presumably via the two cast iron pipes identified by yellow arrows in the picture to the right) onto the clinker where, as it percolated downwards, the water was filtered. Drains at the base of each filter bed allowed the cleansed water to escape into circular gullies where it was treated further. The drains also generated an upward draught, creating aerobic conditions for films of bacteria, protozoa and fungi to form on the clinker surface. These biological films digested organic material in the water. Two under ground earthenware pipes collected the filtered water and directed its flow into the secondary septic tank from where it was discharged into the stream. This description is illustrated by the graphic below, which is not made to scale.

An entry in the Works Directorate War Dairy for 17 May 1941 reads "... a new road to service sewage disposal is being surveyed now." To the right is a photograph, which shows the start of the road as seen today. Beyond the gate in the background, what was once part of the service road, is a private garden. In 1941, however, this was a vehicular thoroughfare that provided access for haulage tankers responsible for removing sludge from the septic tanks.

On the other side of the private garden is a second gate, which leads directly into the field where the septic tank remains are located.

The last photograph on this page shows clearly how, in 1941, British contractors made use of the land's natural contours in the design of the sewage disposal system.