Demonstrating Stormwater Infiltration to UICs is Protective of Groundwater Quality GWPC Presentation September 28, 2010 Heidi Blischke, GSI Water Solutions, Inc. Barb Adkins, City of Portland, Oregon Rod Struck, City of Portland, Oregon
Presentation Outline Oregon DEQ s UIC Program City of Portland UICs What is and why use a Groundwater Protectiveness Demonstration? When can it be used? Fate and Transport Approach Results
DEQ Program - Requirements Inventory and registration with Oregon DEQ of all UICs Rule authorize UICs Permit application for UICs that cannot meet Rule Authorization DEQ UIC website: http://www.deq.state.or.us/wq/uic/uic.htm
City of Portland UICs WPCF 10-Year Permit Issued in 2005 Over 9,000 UICs only option in some areas Numeric stormwater standards City pro-active with street-cleaning, UIC sump clean-outs, curb bump-outs with rain gardens, etc. Corrective Action Plan (CAP) Corrective action alternatives Prioritization of non-compliant UICs and further actions
What is a Groundwater Protection Demonstration Analysis Fate and Transport Evaluation evaluate and document whether stormwater pollutant concentrations entering the UIC are reduced to levels protective of drinking water at the point the infiltrated stormwater reaches groundwater. Why not just decommission? Environmental Benefit manage stormwater by infiltrating precipitation maintains aquifer recharge, cools and treats the stormwater prior to reaching streams with endangered fish Cost Benefit Expensive to physically alter UICs and connect to storm sewers
When Would You Use Fate and Transport Analysis? Provide technical data to demonstrate groundwater is protected and support site-specific decisions or permit modifications Decrease separation distance Increase maximum allowable discharge limits (MADL) Develop MADLs for new pollutants Evaluate whether a pollutant entering a UIC is impacting groundwater Evaluate whether a groundwater user is exposed to pollutants entering UICs Demonstrate groundwater is protected/get a no further action determination from DEQ (NFA)
Selection of Approach Simple dilution, 1-D, 2-D, 3-D models?? Increasing complexity, increasing uncertainty in variables Model a typical UIC Site specific evaluation would be cost prohibitive Emphasis on typical data values no site-specific data collection Variables (need to keep it simple while realistic) Flow volume into UIC Geology and geochemistry Pollutants
Agreements with DEQ Complex: system is complex due to pulsed stormwater inputs, soil wetting and drying cycles, variability in soil type and texture with depth, etc. Model: use of a one-dimensional, constant source advection dispersion equation that incorporates sorption and degradation (biotic and abiotic) is appropriate to assess pollutant fate and transport. Because of the complexities in the hydrogeologic system and variability in stormwater concentrations, it is appropriate to evaluate average conditions for representing soil characteristics, degradation rates, etc. and determining potential groundwater impacts. The reasonable maximum scenario, as defined by DEQ and EPA guidance, would be used to provide an evaluation of uncertainties in the fate and transport calculations.
Conceptual Model PCP PAHs
PCP PAHs
Flow cascading from outlet to sump Sampling Point Point of Injection End of Pipe Point of Compliance = EDL
Conceptual Site Model
Pollutant Attenuation Vadose Zone Adsorption. Attenuation due to partitioning of substances in the liquid phase onto the surface of a solid substrate. Adsorption is a function of foc and Koc. Degradation. Degradation is pollutant attenuation due to biotic and abiotic processes. Degradation is described by a first-order decay constant. Dispersion. Dispersion describes pollutant attenuation due to pore water mixing. Dispersion is described by the dispersion coefficient, which is a function of pore water velocity and distance traveled by the contaminant.
Physical/Chemical Properties Pore Water Velocity, v. Pore water velocity is the rate that water moves downward through the unsaturated zone, and is directly proportional to soil moisture content. Porosity, h. Porosity is the percent of pore space in soil. Soil moisture content, Q. Soil moisture content is the percent of water in soil. Soil moisture content is equal to or less than porosity. Soil Bulk density, ρb. Soil bulk density is the density of soil, including soil particles and pore space. Fraction Organic Carbon, foc. Fraction organic carbon is a dimensionless measure of the quantity of organic carbon in soil (i.e., gcarbon /gsoil), and is used to estimate the capacity of a soil to adsorb contaminants. Organic Carbon Partitioning Coefficient, Koc. The organic carbon partitioning coefficient is defined for the contaminant, and specifies the degree to which it will partition between the organic carbon and water phases. In the case of PCP, this parameter is also ph-specific. Degradation Rate Constant, k. Degradation rate is a chemical specific, firstorder rate constant, and depends on whether the unsaturated zone is aerobic or anaerobic.
Geology/ Hydrogeology
Model Example - PCP Parameter Symbol Units Average Parameter Value Conservative Parameter Value UIC Properties Separation Distance y m 3.0 3.0 Infiltration Time t days 36.3 36.3 PCP Properties Physical and Chemical Soil Properties First-Order Rate Constant k d -1 2.21E-02 1.39E-02 Concentration C 0 mg/l 0.00145 0.002 Soil Porosity h - 0.325 0.325 Soil Moisture Content q - 0.28 0.28 Soil Bulk density r b g/cm 3 1.79 1.79 Fraction Organic Carbon f oc - 0.00393 0.00187 Organic Carbon Partition Coefficient K oc L/kg 877 703 Pore Water Velocity v m/d 0.0076 0.19 Calculations Retardation Factor R - 23.0 9.4 Dispersion Coefficient D m 2 /d 2.32E-03 5.79E-02 Normalized Dispersion D' m 2 /d 1.01E-04 6.16E-03 Normalized Velocity v' m/d 3.30E-04 2.02E-02 Normalized Degradation k' d -1 9.59E-04 1.48E-03 A 1 - - -5.66E+00-2.18E-01 A 2 - - 25.0112 2.4138 e A1 - - 3.48E-03 8.04E-01 erfc(a 2 ) - - 0.00E+00 6.41E-04 Concentration C ug/l 0.00E+00 5.15E-04 10 FEET SEPARATION DISTANCE AVERAGE PCP CONCENTRATIONS SITE SPECIFIC INPUT PARAMETERS OUTPUT: PCP CONCENTRATION AT WATER TABLE
Applications Generic Look-Up Table Individual Non-compliant UICs based on concentration UICs near water wells or insufficient vertical separation distance Establish MADLs for new pollutants Demonstrate groundwater protectiveness
Millions in Savings to City of Portland from the Groundwater Protectiveness Demonstration DEQ issued an NFA for 339 non-compliant due to vertical separation distance UICs savings from decommissioning, reconstruction, and/or connection to MS4 activities for these UICs DEQ issued an NFA for UICs within the 2-year TOT or 500 feet of potable wells DEQ issued NFA s for 6 pollutant specific non-compliant UICs DEQ issued approval for the Groundwater Protectiveness Demonstration for Ubiquitous Pollutants DEQ issued approval for the Framework for Groundwater Protectiveness Demonstration (acceptance of approach)
Questions?