Investigation and Remediation of Groundwater Contamination at by sanmelody

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Investigation and Remediation of
Groundwater Contamination at a
        Pesticide Facility
• Carter et al., 1995. Water Quality
  Research Journal of Canada, pp. 469-
  491.
                                         2


            Site History
• Since 1972 Ciba-Geigy Canada has
  operated an agrichemical formulating
  and warehousing facility in
  Cambridge, Ont.
• In 1991 soil impacted with Dinoseb
  was discovered.
                                         3


     Preliminary Investigation
• Wells installed just below the water
  table confirmed that dinoseb was
  present in groundwater at about 400
  mg/L (40 times the ODWO).
• Other organic compounds were also
  found.
                                         4


 Environmentally Sensitive Site
• About 30% of Cambridge drinking
  water is pumped from 8 wells located
  between 600 and 2200 m from the site
  in the underlying bedrock.
                                        5

    Location of Site and Municipal
            Supply Wells
           Hiway 401




Hiway 24
                       Franklin Boulevard
                                       6


       Further Investigation
• Two pesticides (metolachlor and
  dinoseb) have been measured above
  ODWO in deep groundwater in the
  bedrock about 30 m below the site.
                                            7


     Pesticide Characteristics
• Significant impacts to groundwater are
  not expected under typical agricultural
  use.
• Recent well surveys indicate that deep
  migration of pesticides is uncommon.
                                            8

 Ciba initiated a four-phase soil and
 groundwater remediation program.
• Phase 1: Background information
  review.
• Phase 2: Remedial investigation.
• Phase 3: Remedial alternative analysis.
• Phase 4: Remedial action plan
  implementation.
                                           9


All 4 Phases have been initiated.
• Localized excavation of impacted soils
  and implementation of interim
  measures to control and treat
  contaminated groundwater.
• Site remediation for 10-20 years.
                                       10


   Investigation Methodology
1 Process and Waste Management Audit
2 Private Well Survey
3 Soil Vapour Survey
4 Drilling Program
                              11


         Methodology...
5 Geophysics
6 Groundwater Flow Modeling
7 Regional Well Testing
8 Monitoring Program
                                 12


           Methodology...
9 Treatability Studies/Interim
  Groundwater Control
1 0 Regulatory/Public Liaison
                                            13

Process and Waste Management Audit

• Current and historical site operational
  practices.
• Interviews with current and former
  employees.
• Records of all chemical compounds
  handled at the site.
                                           14


        Private Well Survey
• Review water well records on file with
  MOE.
• Door-to-door survey within a 1 km.
  radius.
• Only two private wells discovered,
  neither were registered with MOE.
                                           15


        Soil Vapour Survey
• Volatile organic solvents were used at
  the plant.
• Shallow soil vapour survey conducted
  and information used to identify areas
  for drilling and soil sampling.
                                           16


          Drilling Program
• 87 monitoring wells installed as of
  Aug. 1994.
• Using mainly 10.8 cm hollow stem
  augers with continuous coring.
• Wells constructed of 5 cm PVC pipe
  and slotted well screens set in silica
  sand filter pack.
                                       17


         Drilling Program...
• Shallow wells near water table are
  constructed with 3m screens.
• Deeper wells have 1.5 m screens
  sealed with bentonite grout.
• Measure K in situ.
                                          18


  Groundwater Flow Modeling
• Used a 2-D model (FLOWPATH) to
  estimate groundwater flow velocities,
  regional groundwater flow conditions
  in the bedrock, and the potential
  effectiveness of a groundwater pump
  and treat system.
                                         19


 Regional Well Testing Program
• How to use nearby municipal wells?
• Shut-down municipal wells for 48
  hours and measure water level
  response in on-site wells.
• Measurable drawdown of 0.1 to 1 m at
  a distance of 1 km.
                                         20


       Monitoring Program
• Wells sampled up to 4 times per year
  until 1994.
• Use Waterra foot valve samplers.
• Sample protocol according to MOE
  standards.
                                          21


        Treatability Studies
• Interim groundwater pump and treat
  facility with two granular activated
  carbon units in series.
• Alternatives are ultraviolet-peroxide
  destruction and in situ /ex situ
  bioremediation .
                                            22


    Regulatory/Public Liaison
• Regular meetings with municipal,
  regional, and provincial regulators and
  the general public.
• Major technical reports in the local
  library.
                                              23
    Results: Hydrogeologic Setting
Unit Description Thickness (m) K (cm/s)
1   Silty sand/sandy silt 10    10-2 - 10-5
2   Silty clay/clayey silt 3    10-5 - 10-7
3   Sand                   12   10-3 - 10-4
4   Silt till               4   10-4
5   Sand, gravel            1   not tested
6   Dolomite              100   10-2 - 10-5
                                       24
           Summary
      Surficial Sand Aquifer
      Clay and Silt Aquitard
      Lower Sand/Till Aquifer*
      Bedrock Aquifer
* Unit 3 is confined, semi-confined,
  and unconfined on site.
                                        25


  Pesticide Distribution on Site
• Metolachlor has the greatest
  exceedance of ODWO (50 mg/L).
• Up to 10,000 mg/L in surficial sand
  aquifer.
                                          26
      Pesticide Distribution...
• Maximum concentration in bedrock is
  14 mg/L.
• Mixing/dispersion is suspected as the
  principal process of reduction.
• Some metabolites are present.
• Ciba-derived compounds have not
  been detected in the municipal wells.
                                            27


   On-Site Groundwater Flow Patterns

• Shallow groundwater flow from east to west.
• Velocities from FLOWPATH 0.4 to 75 m/yr.
• Maximum migration distance of 250m.
                              28
Water Table Configuration




                        306
                  305
302   303   304
                                            29


 Groundwater Flow Directions...
• Lateral flow direction in lower aquifer
  and bedrock is south and
  southwesterly.
• Dilute concentrations of pesticides in
  bedrock south and southwest of the
  site.
                                30
Equipotential Lines: Bedrock


                          299

                         298


             297
       296
                                         31


 Results from Shut-Down Tests
• Water levels in bedrock and lower
  aquifer are influenced by municipal
  pumping.
• Vertical gradients in lower aquifer
  increased up to a factor of about 2.
                                        32
 Municipal Wells that Influence Water
  Levels in Bedrock Wells on Site
           Hiway 401




Hiway 24
                       Franklin Boulevard
                                       33

       Interim Groundwater
        Control/Treatment
• Install pumping wells in upper and
  lower aquifers to control lateral
  migration off site.
• Capture zone analysis with
  FLOWPATH indicates that 2 wells at
  49 and 65 m3/day are enough.
                                          34


    On-Site Water Treatment
• Two 454 Kg. granular activated carbon
  units in series.
• Reduce pesticide concentrations to
  below detection limits of 1 mg/L.
                                         35


             Conclusions
• Unplanned release of pesticides and
  other organic compounds.
• Pesticide levels in shallow aquifers
  exceed ODWO.
                                          36


            Conclusions...
• Lateral and vertical transport of
  pesticides a function of source area,
  physical/chemical properties, and
  groundwater flow conditions.
                                         37


             Conclusions
• Six pesticides have migrated 30 m
  downward through five layers and
  laterally approximately 200 m.
• Concentrations of five pesticides in
  bedrock aquifer are below ODWO.
                                            38
           Conclusions...
• Downward movement of pesticides
  largely influenced by nearby municipal
  wells.
• Variations in vertical gradients caused
  by irregularities in hydraulic
  connection between overburden and
  bedrock fracture system.
                                             39


            Conclusions...
• Groundwater pump and treat system to
  control further migration of pesticides.
• Activated carbon units efficiently
  remove contamination.
• System operates at 114 m3/day.

								
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