STORMWATER INFILTRATION TESTING AT DEPTH

Size: px

Start display at page:

Download "STORMWATER INFILTRATION TESTING AT DEPTH"

Roger Martin
5 years ago
Views:

1 STORMWATER INFILTRATION TESTING AT DEPTH Clay Emerson PhD PE CFM Princeton Hydro, LLC Pennsylvania Stormwater Symposium Stormwater from the Ground Up October 17, 2013

2 OUTLINE Purpose AWRA Sub-Committee Methods Field Demonstration Conclusions

3 PURPOSE NJ BMP Manual requires infiltration tests 8 ft below the proposed basin bottom elevation. (PA 4 ft) NJDEP Most commonly used infiltration testing techniques are neither safe nor practical at depths greater than ~6ft.

4 PURPOSE No one wants this to be the last thing they ever see.

5 PURPOSE Why are we interested in Infiltration Testing? To determine the soil s suitability for concentrated stormwater infiltration To predict the performance of the BMP for design purposes. Note: Infiltration testing must be part of a larger site characterization which includes soil classification, underlying geology, depth to groundwater, etc.

6 PURPOSE There is nothing good about a deep infiltration basin. Closer to water table. Decreases frequency of drying cycles. 7ft Favors anaerobic conditions. Surface layer compaction due to hydraulic loading.

7 AWRA SUB-COMMITTEE Based on input from NJ-AWRA members and NJDEP, the Groundwater Sub-Committee was convened to provide guidance. Dedicated core group of diverse volunteer professionals (scientists, engineers, and planners oh my)

8 METHODS Five infiltration test methods were identified: Slug Test Aquifer Pumping Test Cased Borehole Infiltrometer Core Sample with Laboratory Analysis Direct-Push Hydraulic Profiling (HPT)

9 SLUG TEST A volume slug of water is quickly added to or removed from a well. Commonly used and well established test. The aquifer response is used to estimate hydraulic conductivity. Saturated zone only. HydroSOLVE, Inc.

10 AQUIFER PUMPING TEST Groundwater is pumped and the aquifer response is measured and related to a horizontal hydraulic conductivity. Considered the gold standard. Large or small scale tests can be run. Saturated zone only.

11 CASED BOREHOLE Solid open bottom well casing (PVC pipe) installed to test depth. Annular space is sealed with bentonite and well is presoaked. Series of timed trials are run until test intake rate stabilizes.

12 CASED BOREHOLE No solid basis for commonly used analysis based on Hvorslev (1951) reference. This is not the MD/NY test!!! Often applied in the unsaturated zone, however original reference is for saturated conditions and low hydraulic conductivity. Small sample size.

CASED BOREHOLE 16 Intake Rate [in/hr] 12 8 4 TP-1 Field Measured Rate Field Best Fit Exponential Function Calibrated VS2D 0 0 0.4 0.8 1.2 1.6 Time [hr] Observed Intake = 0.77 in/hr K VS2D = 0.

13 CASED BOREHOLE 16 Intake Rate [in/hr] TP-1 Field Measured Rate Field Best Fit Exponential Function Calibrated VS2D Time [hr] Observed Intake = 0.77 in/hr K VS2D = 0.11 in/hr Finite difference numerical modeling Measured falling head used as a variable pressure head boundary condition Hydraulic conductivity is adjusted until the modeled intake rate matches the observed rate

14 CORE SAMPLE ANALYSIS Undisturbed sample is collected. Proper sampling is critical. Small sample size.

15 CORE SAMPLE ANALYSIS q [in/hr] K=1.8 in/hr Laboratory Measured Darcy Flux Best Fit Linear Direct physical measurement of hydraulic conductivity. Undisturbed rigid thin wall tube samples. Simplified and experimentally controlled hydraulic conditions. Unsaturated? No problem H/L

16 DIRECT-PUSH HYDRAULIC PROFILING Continuous measurement of electrical conductivity (clay vs. sand). Small port injects water, pressure and flow are measured. Calibration curves from field test sites used to relate Q and P to hydraulic conductivity (scatter ~one order of magnitude).

17 DIRECT-PUSH HYDRAULIC PROFILING Rapid and continuous subsurface profiling tool. Difficult to rely solely on K estimates.

18 FIELD DEMONSTRATION NJ-AWRA and USGS arranged a field demonstration of testing techniques. Test techniques were demonstrated by committee members and GeoProbe representatives.

19 FIELD DEMONSTRATION Two existing wells were used to run slugs tests and a small scale aquifer pump test.

20 FIELD DEMONSTRATION HPT demonstration by GeoProbe Cased borehole and singlering infiltration test were also run.

21 FIELD DEMONSTRATION Method* Depth (ft) Result (in/hr) Notes HPT (6.5 to 23.5) 0 to 170 ~50 in/hr near other test depths Pump Test Horizontal hydraulic conductivity, b=10ft Slug Test , 8.2 Falling head Cased Borehole Single-Ring Infiltrometer Diameter, <1 gallon used, presoak and four trials Four trials very consistent response *These are all measures of different samples.

22 CONCLUSIONS The NJ-AWRA provided an excellent opportunity for informal information exchange. Methods were compared and contrasted, none are ideal. All are provide useful information, but none are stand alone solutions.

23 Thanks and Recognition NJ-AWRA, NJDEP, USGS, GeoProbe Mark Anderson, Sandy Blick, Glen Carleton, Mark Denno, Mike Haberland, Titus Magnanao, Shane McAleer, Anthony McCracken Sr., Keithe Merl, Virginia Michelin, Tony Navoy, Laura Nicholson, Tim Reilly, John Robinson Jr., Melissa Stevens and others.

24 QUESTIONS Clay Emerson PhD PE CFM Princeton Hydro, LLC

American Society for Testing and Materials, 1979, Permeability and Groundwater Contaminant Transport ASTM Publication Code Number

American Society for Testing and Materials, 1979, Permeability and Groundwater Contaminant Transport ASTM Publication Code Number Infiltration Testing at Depth Recommendations provided by the Groundwater Committee of the New Jersey Section of the American Water Resources Association (AWRA) Abstract: The New Jersey Department of Environmental