Single installation company can design, construct and install a bespoke Sewage Treatment Plant, Water Supply Borehole, Open-Loop Ground Source Heating System and Surface Water Soakaways. 


At a site in Hertfordshire, H.D. Services Ltd. was instructed to install a Sewage Treatment System, Water Supply Borehole, Open-Loop Ground Source Heat Pump and Surface Water Soakaways for use by a single domestic dwelling.  The idea was for the property to be as self-sufficient as possible.  Utilising water from the chalk aquifer to provide a grey water supply, a potentially potable supply and the heat source for an open-loop heat pump, this project offered many interesting challenges.

Spring House 3In January 2011, H.D. Services Ltd were approached to quote for cleaning a failed soakaway at the site.  During the site visit the client outlined the project details which comprised the construction of a new domestic property.  It was mentioned that H.D. Services Ltd. could provide a water supply, sewage treatment system, heating system and surface water soakaways by drilling into the chalk aquifer and utilising the groundwater contained within it.

Following this discussion H.D. Services Ltd. were asked to quote for the Sewage Treatment System; a complete heat pump installation (water supply borehole with pumps, heat pump, harvesting tank and soakaway); and a surface water soakaway. Using the postcode of the site we were able to confirm the hydro-geology and a quotation was submitted.

Water Supply Borehole and Surface Water Soakaways:

The water supply borehole was drilled using a cable-percussion rig – the method preferred by the Environment Agency when drilling into the chalk aquifer.  This method is also used to drill our soakaways.  A duty/standby dual pumping system was adopted in the borehole, meaning there is always a standby pump to act as backup should one pump fail.  This method is always recommended by H.D. Services Ltd. as it means that any pump issues can be addressed without disruption to the water supply and hence the heating system.

Water was pumped from the supply borehole to the soakaway to prove the worthiness of both.  Borehole logs were submitted to both the British Geological Survey and Environment Agency to protect the abstraction from derogation by a third party.

Sewage Treatment System:

photoA bespoke HD-SM Sewage Treatment System (STS) was designed based upon the number of people that could live at the property.  The final effluent from an HD-SM STS is designed to achieve a discharge standard of 20:30:10 (BOD:SS:NH4) but increased standards can be accommodated by internal adjustments or additional chambers.

Three months after this system was commissioned a courtesy visit was conducted to confirm compliance with the design standard.  All HD-SM’s are covered by a full 12 month extendible warranty and an annual service contract.  Our expertise covers not only the design, supply, installation, commissioning and servicing of sewage treatment systems but also septic tank installation and modification.

Open-Loop Ground Source Heat Pump:

Plant Room HedgelryWorking from detailed floor plans and SAP reports, H.D. Services Ltd. sized the heat pump and designed the water supply borehole and soakaway. The efficiency of both the water supply borehole and soakaway was proved by pumping from one to the other.

Upon completion of construction of the property, the heat pump was installed and commissioned.  All H.D. Services Ltd. installations are covered by a 5 year workmanship warranty and an annual maintenance contract is offered.  We assisted the client in applying for the Renewable Heat Premium Payment (RHPP) in anticipation of implementation of the Renewable Heat Incentive (RHI) in Spring 2014.

Apart from the environmental and economical advantages to an Open-Loop Ground Source Heat Pump, an additional benefit is that the discharge water can feed a harvesting tank, from where it can be pumped for garden irrigation or other ‘grey-water’ uses.  Unlike rainwater harvesting tanks which only replenish when it rains and empty very quickly in dry weather, a harvesting tank fed from a heat pump will replenish whenever the heat pump is in operation, meaning that the garden can be irrigated throughout the summer regardless of hosepipe bans.  It is an option we advise and which was adopted in this installation.


Work commenced in June 2011 when the water supply borehole was drilled and a pump left in situ to provide the construction site with a water supply during the building process.  In November 2011, we returned to site to construct trenches for the pumping mains and installed the bespoke HD-SM Sewage Treatment System.  Work was completed in June 2012 when both the Sewage Treatment System and the Open-Loop Ground Source Heat Pump system were commissioned successfully before the client took up residence.