How do we know on-site wastewater is NOT contaminating a shallow aquifer if we do not monitor groundwater downgradient of private sewage disposal systems?
August 26, 2015 – Bryer Manwell M.Sc. P.Eng, Hydrogeological Engineer, Partner at Western Water Associates Ltd. and Director for WCOWMA-BC.
In the on-site wastewater industry we know that if there is breakout (daylighting) of wastewater effluent down slope of a dispersal field there could be an immediate risk to health. If a breakout is identified and a Provincial Heath Officer becomes involved, system upgrades or system replacement will likely occur. However, if septic systems are operating, seemingly without failing (without effluent daylighting) but are not adequately removing nitrate and/or pathogens before entering the groundwater, contamination of our province\’s shallow groundwater aquifers can occur. Unfortunately, there is no mandate within the Standard Practice Manual or the Sewerage System Regulation to ensure operations of private sewage disposal systems do not contaminate shallow aquifers with nitrates or pathogens.
Nitrate, a drinking water parameter of concern at concentrations above 10 mg/l, is not specified as parameter to be monitored at the point of application, even with a Type 3 system. Further, with no mandate for the Ministry of Health to test groundwater wells which supply water to individual homes, the burden of responsibility to ensure safe drinking water falls on well owners.
At older developments, prior to the 1 hectare minimum lot size requirement, we often see high density lots where both disposal of on-site wastewater and sourcing of shallow groundwater occur within the same shallow unconfined aquifer. I have seen situations where home owner wells are down slope of wastewater dispersal fields operated by their neighbours or themselves. In locations where the groundwater table is shallow, this situation can create water quality problems in the aquifer, even when the down slope water wells are more than 30 m from dispersal fields (the SPM horizontal setback). In one case, I have tracked the plume from on-site wastewater systems for over five kilometers within a shallow river connected aquifer. I have heard of other cases where septic plumes have migrated over 10 km within sand and gravel aquifers. Further, the cumulative effect of operating multiple on-site wastewater systems above a shallow aquifer can create long term contamination, requiring point-of-use treatment to improve water quality.
Often, I find when I am asked to investigate potential impacts from operation of on-site wastewater systems on groundwater and surface water receptors, home owners are not routinely sampling their groundwater well. As on-site wastewater practitioners, we are the point-of-contact with home owners. We can help educate the home owners on the need for routine sampling of their well water to ensure they are providing their families with safe drinking water. Routine sampling can help home owners understand if operation of their own or neighbouring on-site wastewater systems are having a perceivable impact on their drinking water.
WELL OWNER RESPONSIBILITIES
In November 2005, a regulation was enacted in British Columbia with the intent of improving the safety and quality of groundwater in the Province. The Groundwater Protection Regulation (BC Reg 299/2004) established standards to protect groundwater supplies by requiring all water wells in British Columbia be properly constructed, maintained and at the end of their service, properly deactivated. More specifically, wells constructed after November 1, 2005, must meet minimum construction standards including incorporation of a surface annular seal, a minimum of 30 cm casing stickup [above existing or modified ground surface], appropriate drainage away from the well, and completion with a secure well cap plus well identification plate. Once drilled, responsibility for the well transfers to the owner to maintain the casing stickup, surface drainage away from the well, secure cap and well identification plate. This includes maintaining the surface annular seal, if a pitless adapter is installed.
With regard to water quality and private well water treatment, as noted above, this is the homeowner’s responsibility as the Ministry of Health does not regulate private water sources.
Finally, the Groundwater Protection Regulation says that all work on the well must be undertaken by a qualified well driller (QWD) or qualified pump installer (QPI). Registered QPI and QWD have identification cards issued by the BC MNRO and a list of such qualified professionals in maintained on line by the MNRO at:
http://www.env.gov.bc.ca/wat/gws/applications/pdfs/
Routine sampling of the following parameters will provide a low cost method for determining if the well is being impacted by operation of nearby on-site wastewater systems:
- Nitrate, chloride, electrical conductivity, fecal coliforms, E.Coli, and total coliforms.
I recommend that well owners sample for these parameters at least once a year. If fecal coliforms or E.Coli are ever detected, the well should immediately be put out of service until it is assessed by a qualified professional and actions are taken to make the water safe to drink again. If total coliform bacteria are detected in the absence of fecal coliforms or E.Coli, the well should be disinfected and resampled. Guidance on the disinfection of private domestic wells can be found at:
If you have questions or concerns about the potential contamination of aquifers from operation of on-site wastewater systems, contact me, Bryer Manwell – bmanwell@wcowma-bc.com.
