Arsenic in the Water?

Elevated arsenic levels result in a groundwater management strategy

In April 1993, a family living near Powell River had their water tested because family members failed to recover from an extended period of illness. To their astonishment, along with the residents of the rural communities and the Sunshine Coast and the staff of Coast Garibaldi Health, the water test results confirmed arsenic levels 13 times greater than the recommended interim standard in the Guidelines for Canadian Drinking Water Quality (GCDWQ). This set off a series of events that cumulated in a management strategy for future groundwater sources in the region.

Shortly after the water test results, the staff of Coast Garibaldi Health (CGH) responded by sampling wells in the neighbourhood. Initial results were under the maximum acceptable concentration (MAC) interim standard, but subsequent results from wells sampled by broadening the sampling area, found elevated results and the extent of the problem quickly broadened to include the Sunshine Coast.

It was soon determined that the wells drilled into bedrock presented a higher risk of elevated arsenic levels. (Groundwater with arsenic is found within fractures, fissures, joints, and faults of weathered igneous rocks containing sulphide minerals).

"The fractures and fissures act as conduits for water. The exposed surface rocks were formed deep below the surface of the earth and were uplifted by tectonic activity and erosion. The environmental conditions that influence the rock today are very different from the conditions that the rock was subjected to in the past. While magma was cooling and forming the rock, superheated water circulated through the fissures. The various chemicals and metals that were dissolved in this geothermal water formed precipitates in the fissures as the rock cooled. Many different minerals may have crystallized from the magma into the rock that now forms the bedrock through complex physical and chemical processes. These minerals can include arsenopyrite (FeAsS), and other minerals that may also contain traces of arsenic. Today, when water circulates through the fissures, it has a different chemical composition and weathers the material in and around the fissures. The weathered material dissolves into the water which is then intercepted by the wells." (Mattu and Schreier 1999 Study)

In March of 1994, the Ministry of Health responded by funding a survey that allowed property owners in the area to have their well water tested for the detection of arsenic. A total of 199 wells in the Powell River area and 259 wells on the Sunshine Coast were sampled in the survey and the results were startling. (See Fig 1 and Fig 2)

In 1999, CGH contracted with the Institute for Resources and Environment at the University of British Columbia to further evaluate arsenic issues and develop options for assisting with management strategies for future groundwater sources in the region. The study was funded by the Ministry of Transportation and Highways, the Ministry of Health, the Sunshine Coast regional District, North Shore Health Region and Coast Garibaldi Health.

The 1999 Institute for Resources and Environment (Mattu and Schreier) study revealed:

There is no significant seasonal variation in arsenic concentrations. There was significant variability at 4 of 21 sample sites over one year. Analytical variability may account for at least some of the annual differences.
The present IMAC under the CCDWQ (25 ppb) may be subject to reconsideration in view of the standards in other jurisdictions. The current World Health Organization (WHO) standard is 10 ppb. The US EPA has also recently set a new MAC of 10 ppb.
The speciation results indicate that both trivalent (As +3) and pentavalent (As +5) forms are present. The differential toxicity between these forms is not well understood. However, performance of various treatment technologies may be affected.
Water treatment technology for point of entry and point of use (POE/POU) removal devices has not significantly altered since the 1995 report (Carmichael) recommendations.
Due to the emerging importance of arsenic in other regions of the world, a concerted effort has been made to develop new treatment technologies, which are anticipated to become available in future years.
Laboratory error can normally be expected to be within 25% of the true value, from laboratories that participate in an internal QA/QC audit. Statistically, error can exceed the 25% range in 5% of the samples.
Other sources of error can also exist, including sampling error. Additionally, the quality of ground water in recently completed wells can change over time as the well develops a draw down depression cone, drawing groundwater from greater distances over time.
No correlation was found between well depth and arsenic concentration. The location of arsenic bearing fissures within the bedrock aquifer cannot be determined. Accordingly, the likelihood of a well intercepting one of these contaminated fissures also cannot be determined

Groundwater Management Strategy

In response to the report, the GBH have developed a guideline for assisting homeowners to select appropriate treatment devices. The guideline empowers the homeowner to make informed decisions on issues including treatment costs, removal efficiency, maintenance requirements, water use efficiency, difficulty in retrofitting, independent rating and approval, disposal of waste materials, and other important criteria.

In association with the Ministry of Transportation and Highways, CGH is also developing an assessment guideline for proposed subdivisions with individual wells or parcels potentially affected by elevated arsenic concentrations. The management strategy proposes to evaluate groundwater supplies prior to the subdivision of property.

At this time, due to the unreliability of treatment and the likelihood that the IMAC will be lowered, the CGH recommends that the subdivision Approving Officer (AO) not approve subdivisions with private wells with arsenic exceeding the IMAC of 25 ppb. Laboratory error is normally + or - 25% from laboratories that participated in an internal QA/QC audit. The quality of water at initial pump out may not be indicative of eventual quality. And due to these uncertainties, it is recommended that initial sample results exceeding 10 ppb, but less than 25 ppb, require additional sampling and professional assessment. In these cases, the subdivision proponent would be required to retain the services of a professional hydrogeologist to further sample the wells and provide the AO and Medical Health Officer (MHO) with sufficient data and advise to assure the AO and MHO that the ground water quality is safe and will not likely exceed 25 ppb in the foreseeable future.

The CGH also recommends that if arsenic concentrations exceed 10 ppb, but below 25 ppb, and the subdivision is to be issued a preliminary approval, that the approval be conditional on the registering of restrictive covenants. The covenants should express cautionary advise, that includes: annual testing, the potential need for treatment in the future due to changed standards and health risk knowledge, and potential changes in the concentration of arsenic from the well, due to the development of a depression cone and migration of ground water from greater distances over time.

From a public health perspective, CGH still prefers to see new land development serviced with approved community water systems. In the case of existing development already supplied by groundwater containing arsenic, a different approach is recommended. For the short term, homeowners may elect to employ a POE/PUE treatment devise, or to utilize bottled water for domestic purposes.

CGH concludes the best long-term resolution to this problem would be to foresee the extension of community water mains to retrofit municipal services to those affected. This may include developing smaller regional water systems where the distance to service in impractical.

Fig 1. Results of the 1994 survey are as follows:

In the Powell River area (the number and percentage of wells exceeding the GCDWQ by community:

33% in Lang Bay to Saltery Bay(6 wells)
19% in Black Point/Kelly Creek (18 wells)
2% in Powell River South (1 Well)
None of the wells in Powell River North

If only the wells with reported depths greater than 20 metres are considered for the Powell River area:

75% in Lang Bay to Saltery Bay
46% in Black Point/Kelly Creek
3% in Powell River South

On the Sunshine Coast (the number and percentage of wells exceeding the GCDWQ by community:

13% on Gambier/Keats Islands (2 wells)
8% in Roberts Creek (4 wells)
13% in Sechelt and area (4 wells)
27% in Halfmoon Bay (7 wells)
67% in Secret Cove (8 wells)
51% in Middlepoint (21 wells)
33% in Madeira Park (1 well)
26% in Kleindale (7 wells)
22% in Garden Bay (6 wells)
5% in Eqmont/Ruby Lake (1 well)

None of the wells in Gibsons and area

Fig 2.

Based on the wells sampled in 1994 and the results obtained, the following table shows the number of samples exceeding various standards (MAC).

MAC for Arsenic (pph) Powell River Sunshine Coast
GDCWQ interim 25 25 61
World Health Org. 10 33 107
Proposed EPA 5 42 123