Glen Young Subsurface Investigations and Waste Management Unit Environmental Geology Section, Geological Survey Program Missouri Geological Survey

Transcription

1 Missouri Risk-Based Corrective Action (MRBCA) Process for Petroleum Storage Tanks, Determination of Whether a Water Bearing Zone Should be considered a Suitable Water Supply Source Glen Young Subsurface Investigations and Waste Management Unit Environmental Geology Section, Geological Survey Program Missouri Geological Survey

2 Suitability for Use Determination MRBCA Section defines the suitability for use based on: Total Dissolved Solids (TDS) Yield

3 The MRBCA states, All groundwater zones beneath and/or in the vicinity of the site that could potentially be targeted in the future for the installation of domestic water wells must be identified. For the purpose of this analysis, the saturated zone can be divided into multiple layers, but all layers within the saturated zone must be considered.

4 Available online as a PDF at

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7 Geosciences Technical Resource Assessment Tool (GeoSTRAT) Available online at

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13 Potosi Dolomite Davis Formation Bonneterre Formation

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15 Unconsolidated Zone Potosi Dolomite Ozark Aquifer Davis Formation St. Francois Confining Unit Bonneterre Formation St. Francois Aquifer

16 Yield The MRBCA states, Groundwater zones capable of producing a minimum of ¼ gallon per minute or 360 gallons per day on a sustained basis shall be considered as having sufficient yield to serve as a potential source of domestic water.

17 Yield The MRBCA also states, The yield of a bedrock aquifer should be based on the measured or calculated production of a 6-inch drilled well that penetrates the lesser of either the full saturated thickness of the aquifer or the uppermost 200 feet of the saturated zone.

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19 Groundwater Quality Groundwater containing less than 10,000 mg/l total dissolved solids shall be considered as having sufficient natural quality to serve as a potential source of domestic water.

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23 9,000 mg/l 4,000 mg/l 10,000 mg/l 20,000 mg/l

24 Unconsolidated Zone Total Dissolved Solids (TDS) Yield

25 Unconsolidated Zone Is the unconsolidated zone, in and of itself, suitable for use as an aquifer? Is the unconsolidated zone part of another groundwater zone?

26 Unconsolidated Zone Potosi Dolomite Ozark Aquifer Davis Formation St. Francois Confining Unit Bonneterre Formation St. Francois Aquifer

27 MRBCA Appendix D / Appendix E Equations These equations are: K = b x 1447 b = K x Where: K = hydraulic conductivity (gpd/ft 2 ) b = aquifer saturated thickness (feet)

28 Conservative Hydraulic Conductivity Value b = K x Based on data from Fetter or Freeze and Cherry, a conservative value for a type 2 soil could be estimated to be about 1 x 10-4 cm/sec. This converts to gpd/ft 2

29 Required Saturated Thickness b = (2.119) x b = feet Where: K = hydraulic conductivity (gpd/ft 2 ) b = aquifer saturated thickness (feet)

30 Unconsolidated Zone Potosi Dolomite Ozark Aquifer Davis Formation St. Francois Confining Unit Bonneterre Formation St. Francois Aquifer

31 MRBCA All groundwater zones beneath and/or in the vicinity of the site that could potentially be targeted in the future for the installation of domestic water wells must be identified.

32 Site Specific Data Collection Identify Groundwater Zones Identify Existing Wells AUL That Eliminates Reasonable Probability of Future Use? Yes No Yes Suitable for Use? No Yes Only Source? No Reasonable Probability of Future Use? Yes No Reasonable Probability of Impact by Site COCs? Yes No No Further Evaluation of Groundwater Use Pathway Required Carry Groundwater Use Pathway Forward Figure 6-1. Site Conceptual Model for Domestic Consumption of Groundwater Exposure Pathway Analysis

33 Unconsolidated Zone Potosi Dolomite Ozark Aquifer Davis Formation St. Francois Confining Unit Bonneterre Formation St. Francois Aquifer

34 Unconsolidated zone Glacial Drift and Alluvium

35 Conclusions: Suitability for use is based on the yield and TDS of the groundwater zone. Whether or not the groundwater zone will be used or whether it can be impacted is not a consideration in this in this part of the groundwater pathway evaluation.

36 Questions?