Thorpe Row Farm-Domestic supply

Site history

In 2013 we were asked to investigate the private water supply at the above location, both treated water quality and pressure into the property were poor.

The system comprised of:

  • Borehole with submersible pump
  • Break tank and sparge bar
  • Jet pump and 100 litre horizontal PV
  • 1252 vessel with early 5600 control valve Iron removal filter
  • Autotrol 255 water softener

System appraisal

Ground water is pumped up from the BH and into the break tank. This is controlled by a float switch. A sparge pipe (a pipe with multiple small holes along its length) across the surface of the water at the top of the tank sprays the water into the tank.

The water is then drawn from the break tank and pressurised by the Jet pump, pressure vessel and associated controls.

When a drop in pressure is detected in the property the Jet pump runs and the water passes through the iron removal filter and water softener.

There are a number of inherent problems with this type of installation which effect performance and reliability:

The iron removal process relies on aeration of the incoming water. This is achieved by using the sparge pipe to encourage and agitate the water into taking on oxygen from the atmosphere.

This it does and the oxygen starts to react with the iron. The majority of the iron changes from the Ferrous (dissolved, Fe 2+) state to the Ferric (precipitated, Fe 3+) state and starts to deposit in the tank.

The iron deposits build up in the tank, pipe work, Jet pump and pressure vessel.

With the majority of the iron in the Ferric state the iron removal filter is acting as a mechanical filter trying to hold on to the iron deposits. What it couldn’t remove passed through and into the water softener.

The water softener probably did reasonably well, for a time, removing the remaining iron. However, it was no longer able to cope with this level of iron and the resin inside the water softener was fouled with iron.

The inherent problems above were always going to be this systems downfall, however the quality of the installation itself left little to be desired.

Starting at the borehole, this had been poorly finished without a sealed wellhead which could allow surface water, insect and rodent ingress.

The break tank’s lid and side had large holes drilled in it for a float switch and inlet pipe. Neither was sealed.

The copper pipe work was poorly configured with too few isolating valves and no concern for accessibility or future service work. The weight of the pipe work was taken by the back of the control valves. Drain hoses were undersized and the use of vacuum breakers caused leaks and iron staining on the surrounding equipment.

Alternative solution

Although this system was installed circa 1990’s, with all its limitations and inherent faults, it is still installed by some treatment suppliers today! It is often used on high iron level private water supplies in a belief that it helps the iron removal filter work better. This is not the case.

A proposal was put forward to improve the system:

Starting at the borehole the pump was lifted and inspected. The top of the borehole was cleaned and a compression flange adaptor fitted.

The pump was in good order, so this was reinstalled on MDPE pipe along with a new flange complete with cable gland and new fittings.

To provide a treated pressurised supply a Shakesby ET1665 iron removal filter was installed. This was followed by a 100 litre pressure vessel and then the refurbished water softener.

Treated, soft water goes into the cleaned storage tank. Hard water is taken from before the water softener directly to the kitchen tap. The Jet pump was refurbished and used to supply the rest of the property.

A short time after the installation a new potable water storage tank replaced the old glass fibre tank. The noise from the Jet pump could be heard within part of the property, so a submersible pump was installed with a constant pressure controller.

With excellent water quality and more than adequate pressure the water supply has been transformed. The first service was 2 ½ years after installation and it was determined that 3 years would easily be achievable at current usage levels.