Groundwater Monitoring and Protection at the Closed Landfill
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2007-01-12
Ernst Zaltsberg David Grant Smith
The Glenridge Quarry Landfill Site is located in the southern part of the City of St. Catharines and surrounded by residential and institutional areas. The Landfill is situated in a former quarry and bounded by the Niagara Escarpment and Glenridge Avenue to the north, institutional properties to the west, St. David’s Road (Regional Road 71) to the south, and Brock University’s property to the east. The residential area is located north of the landfill, at the base of the Escarpment. The total site area is 44.6ha including the 17.4ha landfilling area (Fig.1). The landfill was operational for 25 years until 2001, when it reached the approved contours and was closed.
The bedrock geology at the site consists of several rock units of Silurian age. They include the dolostone Lockport and Decew Formations and shaly Rochester Formation. All three Formations are fractured and contain ground waters. Under natural conditions, groundwater flows north towards the Escarpment. There are several groundwater seeps on the slope of the Escarpment immediately north of the landfill, which indicate the groundwater discharge areas. Shallow ground waters are of the relatively good quality, which rapidly deteriorates with the increasing depth.
The close proximity of the site to the residential and institutional areas emphasized the need to minimize, or even eliminate deterioration of groundwater and surface water resources due to landfilling operations. To achieve this goal, the Landfill was heavily engineered. The 0.6m thick compacted clay liner, clay sidewalls and a leachate collection system were constructed at the site prior to accepting waste. When landfilling operations commenced, leachate (toxic liquid originated from infiltration of precipitation through the waste pile) was collected by the leachate collection system and directed to the local sanitary sewer.
In order to address potential contaminant migration through the clay liner into shallow groundwater and as a pro-active contingency measure, the “T” shaped Groundwater Collector Trench was constructed in 1991 immediately west of the landfilling area. The trench was excavated into the upper portion of the Rochester Formation and caused 3m to 4m drawdown in the water table near the trench. As a result, shallow groundwater from beneath the site flows into the trench, which discharges by gravity to a sewer north of the site.
There was the unexpected “side effect” associated with trench installation – an increase in the salinity of seeps and groundwater at the base of the Escarpment. It was assumed that this increase was caused by the trench collecting relatively fresh shallow groundwater, which initially discharged at the base of the Escarpment. The main concern associated with this increase was the health of the trees on the slope and base of the Escarpment. In order to minimize this negative impact, trench operation was modified by installing two valves, which could reduce groundwater inflow into the trench and, therefore, increase flow of relatively fresh water towards the Escarpment. Even operating with partially closed valves, the trench still could act as a contingency collector. This strategy was not entirely successful, and the salinity of some seeps still increased. Further study of seeps determined that this increase is due to not only trench installation, but also to natural climatic factors and road salt runoff. Extensive tree sensitivity study conducted at the Escarpment indicated that trees adopt this new environment and remain healthy. The Groundwater Collector Trench is monitored for groundwater flow and its quality after the site closure.
During the landfill operational life, several monitors were installed into the waste. Many of them remain operational during the landfill post-closure period. They provide leachate levels within the capped landfilling area, which indicate the efficiency of the leachate collection system. They also provide the data on leachate quality, which are used in the assessment of the adverse impact of past landfilling operations on groundwater and surface water resources.
Prior to commencing landfilling operations and during the operational period, more than 100 piezometers were installed in the bedrock and overburden within the landfill, and beyond the landfill boundaries. Almost all of them are monitored during the post-closure period. Groundwater level measurements are conducted at all monitoring locations in order to confirm direction of groundwater flow and the efficiency of the Groundwater Collector Trench performance. Groundwater samples taken from piezometers are analyzed for a variety of inorganic and organic parameters. The sampling frequency ranges from quarterly, at the strategically important trigger locations, to every other year at some less important stations.
Trigger monitors are located along the northern and southeastern site boundaries and will trigger contingency plan implementations if concentrations for any of the trigger parameters exceed their trigger valves. For trigger monitors along the northern site boundary, the leachate related trigger parameters are chloride, iron, and chlorinated volatile organics. The historical range of concentration for each of them was established at each trigger location, and this range should not have been exceeded during three consecutive sampling rounds.
For trigger monitors at the southeastern boundary, the trigger parameters are chlorinated volatile organics, which apparently originate from the landfilling gas dissolving into groundwater. Based on the long term monitoring results, trigger concentrations for these parameters were established as well.
During the landfill operational and post-closure periods, exceedances of trigger concentrations for three or two consecutive sampling events have never been detected at either the northern or southeastern landfill boundaries. Trigger mechanisms implemented provide assurance that groundwater exiting the landfill do not adversely impact groundwater and surface water resources beyond the landfill boundaries.
Along with groundwater and leachate monitoring, surface water, air quality, the landfill gas and tree health are also monitored at the closed Glenridge Quarry Landfill to insure that there is no adverse impact on the environment due to past land filling operations. All monitoring and reporting are conducted by Gartner Lee Limited on behalf of the site owner, the Regional Municipality of Niagara.
After the site closure in 2001, the Regional Municipality of Niagara conducted the ambitious program of rehabilitation and converting the former landfill into a naturalization site. In a few years, this site was established and became the gorgeous parkland within the City of St. Catharines (Fig 2). Its main attractions include the visitor’s pavilion, trail system, pond boardwalk, impressive overlooks, children’s science and nature area, and a heritage arboretum. The park was open to the public in September 2004.
The Glenridge Quarry Landfill site is a good example of how the landfill could be properly monitored, maintained and rehabilitated during the post-closure period.
E. Zaltsberg, PhD, P.Geo. is with AGRECOM Inc. in Toronto-Waterloo, Ontario
D. Smith, P.Eng. is with the Regional Municipality of Niagara, Thorold, Ontario