Practical Steps to Prevent Pollution of Wells (Detailed Analysis)

Acknowledgement: Modified after Donal Daly, G.S.I.

Potential pollution hazards in rural areas.

INTRODUCTION
Practical pollution prevention approaches depend on a variety of factors, as described below:- Understanding your well, Vulnerability assessments, Hazard surveys, Proper siting of wells and hazards,¨ Monitoring of well water quality, Assessments of water quality data, Well construction and sanitary protection, Disinfection, Public awareness.

UNDERSTANDING GROUNDWATER FLOW TO WELLS
Prior to the start of pumping, water will have been flowing to and by the well from the up-gradient side, perhaps from a long distance - several kilometres in some instances, but usually at least tens of metres and frequently hundreds of metres. During pumping of a well groundwater flowing by the well is drawn into the well as the nearby flowlines are directed towards the well (see Cone of Depression in diagram below). Pumping of the well causes some of the flowlines on the down-gradient side to reverse their direction and flow back towards the well. The entire land surface area contributing water to a well is called the zone of contribution (ZOC). Contamination of a well can only occur from potentially polluting activities or hazards in the ZOC; consequently, a knowledge and understanding of this area is a vital part of pollution prevention.

Conceptual drawing of the Zone of Contribution (ZOC) at a pumping well.

RECORDING WELL DETAILS
The GSI receives at least 200 queries every year from householders and engineers concerning problems with wells, e.g. pollution, high iron, silting, caving-in, pump getting stuck. Assisting with these queries is frequently made more difficult by the lack of information available on the well. For householders, it is recommended that the following information should be collected and filed: ¨ Depth of well ¨ Diameter ¨ Depth of lining ¨ Diameter of lining ¨ Details on sealing/grouting ¨ Depth to bedrock ¨ Type of subsoil ¨ Type of bedrock ¨ Water entry levels ¨ Depth to any cavities met in drilling ¨ Static water level below ground ¨ Measured pumping rate ¨ Drawdown during pumping ¨ Estimated maximum safe yield ¨ Chemical and bacteriological analyses ¨ Drilling Contractor ¨ Date of drilling ¨ Drilling method. This may seem a very comprehensive list to a householder at first glance, in fact the driller will provide most of the information, and in any case it is basic information that will assist if a problem arises. If a householder is buying a house with an existing well, it is worthwhile checking on the precise location of the well, the well details and water quality information. If the existing water quality information is inadequate, insist on having the well tested, chemically and microbiologically.

VULNERABILITY ASSESSMENTS
A vulnerability assessment of an area provides:

For example, a well located in an area with <1 m of soil and subsoil over bedrock, i.e. an extremely vulnerable area, is at risk from nearby septic tank systems, landspreading, etc. In contrast, a well in an area with >10 m of low permeability subsoil, i.e. low vulnerability, is well protected from contamination, and hazards such as septic tank systems and landspreading are unlikely to contaminate the well (provided surface water does not enter directly into the well). It is advisable for householders to check for outcropping bedrock and enquire about the depth to bedrock prior to buying a site, if they need to drill a well. Local authorities are advised to carry out a preliminary assessment of vulnerability prior to choosing sites for public supplies. Vulnerability maps have been completed for 9 counties - Offaly, Waterford, Tipperary (SR), Limerick, Meath, Wicklow, Clare, Laois, South Cork - and mapping has commenced in Kilkenny, Tipperary (NR), Monaghan, Roscommon and Kildare. However, a vulnerability assessment can be carried out, using the national guidelines (DELG/EPA/GSI, 1999a) on any site or area. The GSI can provide advice on this, if requested.

HAZARD SURVEYS
Local authorities are advised to identify and map existing hazards in the higher risk areas, particularly in zones of contribution of significant water supply sources. This would involve conducting a survey of the area and preparing an inventory of hazards. Prior to purchasing a site or a house, householders should look at existing developments and potentially polluting activities nearby and, together with consideration of the vulnerability, assess the likely risk to the well. The treatment system on the site may be located a good distance downhill of the well, but the neighbour's system might be over the hedge, 10 m away!

PROPER SITING OF WELLS AND HAZARDS
The location of wells and hazards, in a way that minimises the probability of contamination, depends on the following: * Hazard contaminant loading (for example, the contaminant loading from a single house on-site wastewater treatment system is less than from a landfill); *Vulnerability of the site/area; *Hydrogeology of the site/area; *Whether the hazard is inside or outside the ZOC of the well; *Distances (often called 'setback' distances) between wells and hazards; *The density of hazards; *The planning control measures for hazards; *Risk assessment and management. For regulatory bodies, such as local authorities, all these aspects are encompassed in the source protection component of groundwater protection schemes and the groundwater protection responses. Groundwater Protection Schemes and appropriate groundwater protection responses incorporate these above aspects and are detailed in Joint EPA and GSI Department of Environment publication 'Groundwater Protection Schemes' For everyone involved, use of 'common sense', based on some knowledge of groundwater flow, in locating wells is essential. So, choose the site carefully. Be wary of using diviners. As a general rule, a well should be located up-slope and as far as possible from potential pollution sources, such as farmyards and on-site wastewater treatment systems.

Monitoring of Groundwater Quality
Monitoring for contaminants provides direct information on contamination, and a lot of emphasis and perhaps even over-emphasis is given to monitoring of groundwater in EU countries. However, monitoring, while desirable and useful, only provides an indication of the presence or absence of contamination, and is inadequate by itself to ensure protection.

ASSESSMENT OF WATER QUALITY DATA
Water quality data, whether from a monitoring programme or once-off sampling, enable not only a check on the presence of contamination but also an assessment of the likely source of contamination. In assessing groundwater quality, the approach taken in the GSI is to distinguish between the terms 'contamination' and 'pollution'. Groundwater becomes 'contaminated' when substances enter it as a result of human activity. The term 'pollution' is reserved for situations where contaminant concentrations are sufficiently high to be objectionable e.g. above the EU maximum admissible concentration (MAC). As human activities have impacted on a high proportion of groundwater in Ireland, there are few areas where the groundwater is in pristine condition. Faecal coliforms, nitrates, ammonia, high K/Na ratio and chloride indicate contamination by organic waste. The high K/Na ratio helps distinguish between septic tank effluent and farmyard wastes. The analyses can show potential problems and indicate likely sources but other information is needed to complete the assessment. Regular assessment is required to prevent pollution and major incidents occuring. Parameters can be used to help indicate situations where significant contamination has occured and action can be taken to prevent pollution.

Well Construction and Sanitary Protection Role
This is a means of preventing pollution that is within the control of the well owner. Even if the well has already been drilled, improvements can usually be made including:

1. The annular space outside the casing should be filled with a suitable sealant, such as cement or cement/bentonite grout to prevent surface water runoff or shallow groundwater seeping directly into the well.

2. No unsealed openings should exist in the wall or along the joints of the casing.

3. A concrete slab, 150 mm thick, should be keyed in around the casing to a distance of at least 0.5 m from the casing.

4. The casing should protrude above the surface of the concrete slab. 5. A secure, watertight well cap should be fitted to prevent foreign matter or small animals from falling into the well 6. The wellhead should be housed, preferably in a manhole with a manhole cover. 7. If the general land surface around the well is depressed or susceptible to flooding, it should be raised and regraded so that it slopes away from the well. 8. If the well is in a field used by farm animals, it should be enclosed so that animals cannot get close - a distance of 10 m from the well is recommended. It is suggested that a relatively high wall should be used rather than a fence, which tends to attract farm animals with the consequent concentration of faeces and urine in the area of the well.

It is recommended that borehole headworks are completed above groundlevel, where possible, as diagram above suggests, particularly in high risk situations eg., farm, industrial sites etc. Below ground completion requires exceptionally high standards of headwork design, good natural drainage, good construction and on-going maintenance and protection.

Dig area 2' around pipe and 2' deep.
Using poured concrete or 4" solid blocks construct a manhole with a "u" on one side to allow pipe / cable passage to pressure vessel and electrics as appropriate.
Make concrete floor at a slope with corner piece in lower corner funnelled through with drainage pipe to allow water lodging in manhole to drain. Leave outer steel liner pipe 4" above concrete apron.
Consider secure lock on placing of concrete slab / reinforced steel cover over manhole.

Inspect the well at regular intervals. Good advice on well construction is given in Briody (1995 Manhole Construction), Ball (1995) and NSAI (1992).Well Construction Standards In Ireland. A borehole is one of the most important feature of a house which is not governed by any regulations or standards (Wright, 1995; Ball, 2000). A modern house requires planning permission and must be built in accordance with detailed Building Regulations which ensure that certain minimum standards are observed. Mains services - electricity, gas, water and sewerage - are all constructed to national standards by certified installers. On-site sewage treatment systems, where required, must also conform to planning conditions and, to the guidelines of S.R.6 and Agrement Certificates, and in the future, to the EPA Manual (2000) and the Groundwater Protection Responses (DELG/EPA/GSI, 2000). However, a private well does not have to conform to any "official" standards, regulations or planning conditions. It is therefore not surprising that many rural boreholes are contaminated and that this is often due to faulty well construction. In other developed countries some or all of the following are fairly closely regulated: · Licensing of well drillers: qualifications, experience and health of drilling personnel · Construction of wells: notification/permission to drill at a given site · standards of construction and of materials used · sealing of abandoned wells. It is recommended that new national regulations should:

¨ Require well drilling contractors to be registered and set minimum standards for well drillers

¨ Set minimum standards for well construction, including procedures for sealing abandoned wells

¨ Require completion of well records for new water wells and submission to an appropriate authority.

WELL DISINFECTION;
is an important means of protecting human health, but it should not be considered as a solution to groundwater contamination: ¨ it is not a sustainable strategy for managing groundwater in that it is merely treating the symptom of the problem; ¨ The EU Water Framework Directive aims to reduce dependence on purification and pre-treatment of drinking water. Procedure regarding well disinfection is as follows:

1. All new wells should be disinfected after drilling.

2. Existing wells should be disinfected on a regular basis (each Autumn is suggested).

3. Drilling equipment should be cleaned and sterilised prior to drilling.

4. Householders with private wells in karst areas and extremely vulnerable areas should install a disinfection system such as an ultra violet (UV) light to reduce the incidence of microbiological contamination.

TAKING RESPONSIBILITY, PUBLIC AWARENESS AND "COMMON SENSE".
'The primary responsibility for groundwater protection rests with any person who is carrying out an activity that poses a threat to groundwater'. This is the first sentence in 'Groundwater Protection Schemes' (DELG/EPA/GSI, 1999 (a)); it is a powerful principle that needs to be more widely accepted and followed. "Command and Control" regulations are unlikely on their own to ensure successful prevention of contamination. Therefore other alternatives, such as public education, must supplement good planning regulations and enforcement. Greater awareness of the significance of hazards, such as septic tank systems and farmyards, as a source of water pollution and as a health risk is required. Also, a greater appreciation and understanding of groundwater, which is 'out of sight, out of mind' for many people, is needed. Improved awareness would lead to a more responsible approach to environmental issues and the use of 'common sense' in dealing with wells and the possible impacts of human activities.

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