Groundwater Contamination at the Carp Rd. Landfill Site

Sept 28, 2006 

Groundwater Contamination at the Carp Rd. Landfill Site 

Report prepared on behalf of 

The Coalition of Citizen’s Groups Opposing the Expansion of the Carp Rd. Landfill 

Abstract: Water quality data related to the Carp Road Landfill Site contained in the 

official 2005 groundwater assessment report have been critically examined. The 

report was prepared by Water and Earth Sciences Associates Ltd. (WESA) and 

submitted to the Ontario Ministry of the Environment (MoE) on behalf of the operator, 

Waste Management of Canada Corporation (WM). The chemical analysis of samples 

from groundwater monitoring wells on the Carp Road Landfill Site and adjacent 

down-gradient properties shows concentrations of typical landfill leachate 

contaminants in excess of MoE Reasonable Use Guidelines (RUG). The authors of 

the report argue that those exceedances are not valid indications of off-site migration 

of leachate and conclude that the data supports WM’s claim that the leachate control 

measures currently in use are effective. 

The analysis of the same data, as presented here, leads to a different conclusion. 

Introduction: 

The WM Ottawa Landfill Site is located at 2301 Carp Road, in the former township of West 

Carleton, which is now part of the City of Ottawa. The landfill site is bounded on the east by Carp 

Road (Regional Road 5), on the south by Highway 417 (the Queensway), on the west by William 

Mooney Road and on the north by privately owned agricultural and commercial properties. The 

main access to the site is from Carp Road and for that reason it is locally known as the Carp 

Road Landfill. 

Historically the site was operated as a commercial gravel pit and since the 1970’s various owners 

have intermittently used sections of the property for waste disposal. In 1994 a 34.59 ha area on 

the site was licensed by the MoE under Certificate of Approval (CoA) 461002 for landfilling of 

solid non-hazardous waste. That landfill area is approaching its estimated capacity of 8,744,400 

cubic meters: documentation 1 supplied by the operator in 2006 in conjunction with EBR 

IA06E0345 estimates landfill closure in 2009. 

Under the terms of the CoA, the landfill operator is required to submit an annual report including, 

among other required data, a review of surface and groundwater monitoring results. The purpose 

of surface and groundwater monitoring is to assess compliance with the Ontario Environmental 

Protection Act R.S.O. 1990 chapter E.19 section 6(1) and the sections 4 to 7 of Ontario 

Regulation 347, which applies the Act to Waste Management. The essence of these statutes is to 

prohibit the discharge of contamination into the environment in excess of an amount or 

concentration stipulated by law, and to specifically prohibit the egress of contamination that might 

lead to water pollution. 

It is worth noting that there have been reports of off-site contaminant egress as early as 1987 2 . 

Figure 1 shows the extent of leachate migration estimated in 1986 and 1987. In response, the 

landfill owners undertook to mitigate the potential impact on groundwater wells down-gradient 

from the landfill. They designed a system of purge wells to draw leachate-impacted groundwater 

from a series of wells along the eastern edge of the landfill site. It is well established that, if 

groundwater can be extracted at a rate sufficient to locally lower the water table below the levels 

Sept 28, 2006 - Groundwater Contamination at the Carp Rd. Landfill Site 

Report prepared on behalf of The Coalition of Citizen’s Groups Opposing the Expansion of the Carp Rd. Landfill

on either side, then, to first approximation, the flow of groundwater across this line is blocked. The 

system was fully commissioned in 2001. In 1997, the landfill operators also introduced the use of 

leachate containment liners 3 . The MoE estimates that one third of the current active landfill area 

is lined. 4 These measures are expected to reduce leachate migration. 

Since the initial discovery of offsite 

leachate, no new survey of 

the size of the leachate plume 

has been made public to our 

knowledge. In order to determine 

if there have been any changes in 

the degree of off-site migration 

arising in the intervening years 

and to assess the effectiveness of 

the purge well system, a copy of 

the latest groundwater monitoring 

report was requested under the 

auspices of the Freedom of 

Information and Protection of 

Privacy Act. 

Figure 1 - Estimated Leachate Plume Position: 

solid line – Richards 1986 

dashed line – WESA 1987 

(extract from a 1987 WESA Report 5 ) 

The near vertical line through the center of the figure is Carp Road; the pair of horizontal lines 

through the center is the two lanes of Highway 417. 

Data Source: 

The latest off-site groundwater assessment report 6 on the public record related to the operation of 

this site is dated February 14, 2005. It was prepared by WESA on WM’s behalf. It presents a 

review of the surface and groundwater monitoring data (current as of November 2004) and is 

augmented by historical groundwater monitoring data going as far back in some cases as 1983. 

The report covers two distinct sets of measurements: the first relating to the hydraulic properties 

of the wells and the second to water quality. The former establishes the general features of 

groundwater flow, while the second checks the groundwater for traces of leachate contamination. 

The water quality data tracks 22 separate properties in selected surface, shallow and deep 

groundwater sites on the Carp Landfill Site and adjoining properties. These properties are 

sensitive indicators of groundwater contact with leachate 7 . Tests for the presence of volatile 

organic compounds (VOCs) were included for a subset of the down-gradient sites. These include 

anthropomorphic compounds with no natural source that are sometimes associated with landfills. 

The MoE approved the choice of wells, the monitoring parameters and the sampling interval. The 

analysis in this report focuses on the shallow ground water data in the WESA report. 

Data Analysis: 

The WESA report divides the monitoring wells into three categories: background, leachate and 

down-gradient (also called monitoring). The basic premise is that contaminants will predominantly 

spread in the direction of groundwater flow (i.e. down-gradient). Additional assumptions are: 


Report prepared on behalf of The Coalition of Citizen’s Groups Opposing the Expansion of the Carp Rd. Landfill 

2

- the 14 background wells, chosen to be up-gradient or cross-gradient from the landfill foot 

print, are representative of the groundwater quality existing prior to landfill operation. 

- the leachate wells, drilled adjacent to unlined portions of the landfill area, are representative 

of the highest concentration of contaminants. 

- the contaminants in the down-gradients wells, if any, will exhibit a monotonic downwards 

trend with distance from the landfill if their source is landfill leachate. 

As part of the groundwater quality assessment, the authors of the WESA report compared the 

concentrations of the leachate indicators to the Reasonable Use Guideline (RUG) limits. The 

latter are calculated from the concentrations of each contaminant found in the background and 

the concentrations found in the table of Ontario Drinking Water Standards (ODWS), using the 

equation from Ontario Regulation 232/98 s 10.2: 

[C]RUG = [C]background + X * ( [C]ODWS – [C]background ) 

where: X is 0.25 for a contaminant with a health related drinking objective 

0.5 for a contaminant with an aesthetic drinking water objective 

The underlying concept for the multiplicative factor is that there may be multiple sources of 

contamination affecting a shared groundwater resource, and greater care must be taken when 

the contaminant has a health impact, hence a smaller value for X. 

Note that some leachate indicators have no ODWS and therefore no RUG. Also note that when 

no amount of a specific contaminant is found in the background, the detection limit of the analysis 

technique is used in the calculation of [C]RUG. 

The list of leachate indicators and the ODWS and RUG limits if relevant are given in Table 1. 

Table 1: 

Indicator [C]background mg/L [C]ODWS mg/L [C]RUG mg/L 

Alkalinity 210 ---- ---- 

Conductivity 597 ---- ---- 

Potassium 2 ---- ---- 

Ammonia 0.02 ---- ---- 

Total Kjeldahl 

Nitrogen 

Chemical Oxygen 

Demand 

0.23 ---- ---- 

5 ---- ---- 

Calcium 62 ---- ---- 

Magnesium 20 ---- ---- 

Iron 0.07 0.3 (AO) 0.19 

Boron 0.05 5 1.29 

Barium 0.12 1 0.34 

Sodium 6 200 (AO) 103 

Chloride 9 250 (AO) 130 

Sulphate 24 500 (AO) 262 

Fluoride 0.16 1.5 0.49 

Nitrate 0.10 10 2.58 

Nitrite 0.10 1 0.33 

Manganese 0.02 0.05 (AO) 0.04 



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Lead 0.001 0.01 0.003 

Chromium 0.001 0.05 0.01 

Cadmium 0.005 0.005 0.005 

Cyanide 0.005 0.2 0.05 

The same approach is used with the 37 VOCs tracked in a subset of the main monitoring wells. 

Since these are anthropogenic compounds, the author of the report assumed that they would not 

be detected in the background and chose to use the detection limit of the analysis technique for 

calculating [C]RUG. 

Results: 

As noted in the WESA report, concentrations in excess of the RUG limits were found in 2004 in 

the off-site down-gradient wells for the following primary leachate indicators: 

• barium • fluoride • nitrite 

• boron • iron • sodium 

• chloride • manganese • sulphate 

• chromium • nitrate 

The authors of the WESA report discount the exceedances of barium, iron, manganese, sulphate 

and fluoride by virtue of having a highly variable background, routinely exceeding RUG limits. The 

exceedances in the case of chromium are excused on the basis of that the levels in the leachate 

wells are not elevated with respect to the background. The excessive sodium and chloride are 

attributed to road salt. They also note landfills are not the sole sources of nitrite and nitrate: these 

have other sources such as septic tanks and farm operations. Finally, an analysis of 

concentration vs. distance from the purge well line is presented. If the trends are not 

monotonically decreasing then the author concludes that the source is not the landfill. 

The report also notes that no VOC was found in excess of [C]RUG in the year 2004 and that the 

only VOC detected was cis-1,2-dichloroethylene at a concentration very close to the detection 

limit. 

Analysis: 

Profiles were created from the raw data in the WESA report for each leachate indicator as a 

function of distance from the landfill. The purge well line is taken as the zero point for distance. 

The concentration of sodium is shown as an example in Figure 2. Unlike the data selected for the 

WESA analysis coming from a single year, the data used in this plot averages each well’s data for 

the years 2000 to 2004, and all monitoring wells were plotted. This reduces some of the intrinsic 

scatter and makes the underlying downwards trend more readily discernable. Similar trends were 

observed for chloride, conductivity, iron and potassium; less clear trends were observed for 

magnesium and manganese. Chemical Oxygen Demand, ammonia and Total Kjeldahl nitrogen 

also drop with distance from the landfill, but much more rapidly. Alkalinity, calcium and sulphate 

concentrations were elevated in the leachate wells and also in the down-gradient wells, but no 

downwards trend was observed. 

Some intrinsic scatter in contamination concentration is to be expected due to the variations in 

amounts of precipitation, monitor well depths, inhomogeneities in the percolation paths followed 

by the groundwater (especially given the prevalence of fractured limestone in the shallow aquifer 

as noted in the report). Variation in the background is not justification for disqualification of a set 

of exceedances, especially those clearly above the background. Where the differences are less 

noticeable to the eye, statistical techniques can be applied to test whether off-site data is higher 

than might be expected from natural variation. Additional data would improve the statistics. 

The expectation of a point-by-point monotonic trend in the off-site data is also unrealistic, given 

this degree of variation. The disqualification of a set of exceedances, especially those clearly 



4

above the background, based on a single outlier should be questioned. Even if a local source of 

contamination is found to be responsible for the outlier that does not imply that the source is 

responsible for all of the exceedances. It clearly cannot explain those up-gradient for that point. 

The prudent response to an outlier would be to substitute another well for the contaminated one 

so that the close monitoring of possible leachate contamination can continue. 

These plots also call into question the assumption that the leachate wells should exhibit the 

highest concentrations. It is frequently the case in this data set that the purge wells adjacent to 

the landfill have the higher concentration. This may be due to changes in leachate chemistry as 

decomposition proceeds, or due to groundwater flow from east to west, or merely the fact that 

leachate sampling points are to one side of the active landfill zone. 

Sodium Concentration (mg per litre) 

350 

300 

250 

200 

150 

100 

50 

Background Well 

Leachate Wells 

Down-gradient Wells 

RUG limit 

0 

-1500 -1000 -500 0 500 1000 

Distance from Purge Well Line (m) 

Figure 2 - Average sodium concentration (2000-2004) along a line parallel to Highway 417 and 

perpendicular to Carp Road: The down-gradient data is clearly above the background for 

approximately 500 meters from the edge of the Landfill Site, and is above the RUG limits for more 

than 300 meters. A substantial number of the data points are above the Ontario Drinking Water 

Standard for sodium which is 200 mg per litre. 

Sodium is one of the leachate indicators that can also come from other sources. The authors of 

the WESA report suggest that there is a trend for less sodium (and chloride) the further the 

monitor point is from Highway 417. This is explored using the pooled data approach by Figure 3, 

which plots average sodium concentration as a function of distance from the Highway 417. 

Rather than a rapid drop in concentration with distance as expected for a road salt origin 8 , the 

levels are elevated until the right hand side of the graph – which corresponds to the northern 

edge of the landfill footprint. Also shown on the plot are the background wells, up-gradient of the 

landfill. These wells are as close, if not closer, to Highway 417 and yet they show no road salt 

effect. It maybe posited that the fact higher traffic level on Carp Road as compared to those on 

William Mooney is contributing to the higher levels seen in the vicinity of the purge well line, 

however that seems unlikely since well data for homes and businesses elsewhere on Carp Road 

do not exhibit the elevated sodium (or chloride) levels as seen in these monitoring wells. 



5

A more consistent explanation for this data is that leachate from the older closed sections of the 

site and possibly the active fill zone has crossed the boundary of the landfill property. This leads 

to elevated levels on contaminants in the purge wells and down -gradient wells from the southern 

edge of the old fill zone (~200 m north of Highway 417) to the northern edge of the active zone 

(~800 north of Highway 417). 

Sodium Concentration (mg / litre) 

350 

300 

250 

200 

150 

100 

50 

0 

Up-gradient Wells 

Purge Wells 

0 200 400 600 800 1000 

Distance from Highway 417 (m) 

Down-gradient Wells 

Figure 3 - Average sodium concentration (2000-2004) along lines perpendicular to Highway 417 

and parallel to Carp Road. The concentrations at the purge well line and a transect ~100 m downgradient 

from the purge wells are high relative to the up-gradient transect. The curve is a guide 

for the eye. 

The data for many of the other leachate indicators show similar trends. The consistency of the 

patterns allows estimated contamination contours to be drawn. These are shown in Figure 4 

where the figure of merit is the percentage of RUG exceedances measured between 2000 and 

2004. This is not the only set of contours that can be drawn through the data but these do take 

into consideration the previously established groundwater flow direction from west to east. More 

data would be required to map out the distribution more precisely. 

The pattern is consistent with a landfill leachate source. It is similar to the leachate plume 

mapped out in the late eighties (c.f. Figure 1). It seems to have expanded to the north, as one 

might expect with new landfill activity to the north of the original landfill zone (now closed). 

There is little that can be said whether there have been the changes in the severity of the 

contamination, since there is no quantitative data presented in this report from the off-site downgradient 

wells prior to the year 2000. Over the following four years, however, the leachate 

indicators in each well vary significantly. There is no consistent downwards trend to support the 

conclusion of the author of the WESA report that the purge well system has been effective. That 

conclusion was based on improvements in the surface water quality. On the contrary, many of the 

indicators in the groundwater increase over this time frame. 



6

Figure 4 – Location of groundwater monitoring wells. Green: up-gradient wells or background; 

Purple: leachate wells; Light blue: purge wells; dark blue: monitoring wells. The coloured areas 

indicate different levels of groundwater contamination in excess of RUG limits. The red 

encompasses the test wells where limits were most frequently exceeded. The boundaries are 

estimates: more closely spaced monitoring sites would be required to locate them precisely. 

Note also, that the borders of the older fill sections are inferred from comments in the WESA 

report and not to be taken as being definitive. 

The analysis of the VOC data in the WESA report is problematic. Of the 37 compounds tested, 11 

of them were detected in monitoring wells between 2000 and 2004, including 6 off-site locations. 

The difficulty arises in that the detection limit for some of these compounds is very close to the 

ODWS limit. In the case of vinyl chloride, a known carcinogen, it is actually higher than the 

ODWS limit. If a RUG is calculated using the detection limit as a substitute for the background, 

then even the valid data between the detection limit and the ODWS may not be registered as an 

exceedance. Table 2 lists the VOCs detected in the on-site and off-site monitoring wells, the 

maximum level detected (2000-2004), the detection limit and the current ODWS limit for that 

compound. This table shows that 1,4 Dichlorobenzene and vinyl chloride have been detected at 

levels in excess of the ODWS. Benzene has been detected at levels in excess of one half of the 

ODWS. Trichloroethene has been detected at levels in excess of one half of the new Canadian 

Drinking Water Standards (CDWS). All of these would fail RUG limits, if the limits were set to the 

detection limit or the usual fraction of the ODWS or CDWS which ever is the highest. 



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Table 2: 

VOC onoff- [C]max ppb [C]detection ppb [C] ODWS ppb 

sitesite 1,1 Dichloroethane yes yes 5.7 3.5 none 

1,4 Dichlorobenzene yes no 5.9 2.4 1 

Benzene yes yes 4.2 1.3 5 

Chlorobenzene yes yes 8.9 2 none 

Chloroethane yes yes 7 1 none 

Cis 1,2 

Dichloroethene 

yes yes 14 1.2 none 

Monochlorobenzene yes yes 8.9 0.2 30 

Toluene yes yes 5.2 1.5 24 

Trichloroethene yes yes 4.8 1.9 50 * 

Vinyl Chloride yes no † 25.8 4.9 2 

Xylene yes no 4.8 3.4 300 

Notes: 

* The Canadian Drinking Water Standard for trichloroethene is now 5 ppb 9 

† According to court documents 10 , vinyl chloride at the level of 19.2 ppb was 

measured in a domestic water supply well on one off-site property and 23.5 ppb 

in another, both adjacent to the Landfill Site. 

Conclusions: 

The groundwater data has been independently analysed and the interpretation proposed by the 

WESA consultants critically examined. We find that the data does not support the conclusion that 

there is no off-site leachate migration. 

Specifically, flaws have been shown in the criteria used to discount certain exceedances and thus 

reject the landfill as a unique source of certain contamination, namely: 

- high and variable background levels sometimes in excess of the ODWS limits 

- down-gradient levels in excess of those in the leachate wells 

- a non-monotonic trend in concentration with distance from the landfill 

The hypothesis that road salt is the source of high sodium and chloride levels in the downgradient 

wells has been challenged. This is particularly significant since the levels are in excess 

of the health based ODWS criterion. The claim of other sources for other contaminants has not 

been substantiated. 

On the contrary, the data taken as a whole is consistent with on-going off-site leachate migration. 

Off-site levels are frequently above RUG limits for considerable distances from the landfill. They 

are not consistently decreasing with time, which calls into question the effectiveness of the 

leachate containment system. 

The presence of VOCs in the off-site wells is disturbing regardless of the source. These are 

known leachate contaminants and include known and suspected carcinogens. In addition, there 

has been literature published that suggests the primary path for groundwater contamination is 

through contact with landfill gas in the vadose zone. If so, the VOC monitoring points should not 

be restricted to the down-gradient side of the site. It also seems prudent to us to improve the 

detection limit of the analyses used to quantify these compounds and re-visit what is an 

appropriate RUG for anthropogenic contaminants where the detection limit approaches or 

exceeds the drinking water standard. 



8

References 

1 

Application for a Provisional Certificate of Approval for a Waste Disposal Site, EBR Registry 

Number IA06E0345, filed by M. Walters, (March 2006) 

2 

Regional Municipality of Ottawa Carleton Interdepartment Correspondence, “Newill Realty Ltd. 

Sanity Landfill”, R.O. Pickard, July 8, 1987 

3 

Canadian Waste Services Community Newsletter (1999) 

4 

e-mail Greg Davies, Regional Officer, MOE 

5 

WESA drawing attached to reference 2 (undated) 

6 

Off-Site Groundwater Assessment Report, Ottawa Landfill Site, Water & Earth Science 

Associates Ltd., File No. C-B1572, (February 2005) 

7 

“Present and Long-Term Composition of MSW Landfill Leachate: A Review”, Peter Kjeldsen, 

Morton A. Barlaz, Alix P. Rooker, Anders Baun, Anna Ledin, and Thomas H. Christensen, Critical 

Reviews in Environmental Science and Technology, 32(4):297–336 (2002) 

8 Priority Substances List Assessment Report: Road Salts, a joint publication of Health Canada 

and Environment Canada, (2001) www.hc-sc.gc.ca/ewh-semt/alt_formats/hecssesc/pdf/pubs/contaminants/psl2-lsp2/road_salt_sels_voirie/road_salt_sels_voirie_e.pdf 

9 Guidelines for Canadian Drinking Water Quality, Summary Table, (2006) 

www.healthcanada.gc.ca/waterquality 

10 

Notice of Action between Newill Corporation and Canadian Waste Services, Court File 98-CV- 

5120, (March 1998) 



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Groundwater Contamination at the Carp Rd. Landfill Site

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