CONE PERMEAMETER IN-SITU PERMEABILITY MEASUREMENTS WITH DIRECT PUSH TECHNIQUES

CONE PERMEAMETER IN-SITU PERMEABILITY MEASUREMENTS WITH DIRECT PUSH TECHNIQUES Bill Lowy, Neva Mason, and Veaun Chipman Science and Engineeing Associates 3205 Richads Lane, Suite A, Santa Fe, NM 87505 Phone: (505) 424-6955 Fax: (505) 424-6956 email: blowy@seabase.com ABSTRACT Soil pemeability, which defines the magnitude of fluid flow (gas o liquid) unde imposed pessue gadients, is one of the most impotant hydologic paametes to measue when pedicting fluid o contaminant movement in the subsuface, designing envionmental emediation systems, o simply chaacteizing a geologic site. Science and Engineeing Associates, Inc. (SEA), has developed the Cone Pemeamete, a cone penetomete technology that measues the in-situ ai pemeability o hydaulic conductivity in unconsolidated media. The cone pemeamete od incopoates a well-defined injection zone and multiple pessue pots placed at discete locations fom the injection zone. A pemeability value is obtain by injecting a known flowate of ai o wate, measuing the pessue esponse along the pemeamete od, and then applying a one-dimensional, spheical, steady-state Dacy flow model to the measued injection ate and pessue pofile. Nea to the injection point the pessue field is distoted by a combination of the cylindical injection zone and the compacted soil nea the od suface. A fundamental pemise of the measuement is that, as the distance fom the injection point is inceased, the esulting pessue distibution will become spheical. This method measues the pessue gadient fa enough fom the injection point to avoid the distoted field. The Cone Pemeamete measuement system has the following benefits ove existing in-situ pemeability methods: All the advantages of diect push: minimal waste, isk eduction, fast emplacement, low unit measuement cost 3 to 10 minute measuement time pe elevation Rapid mobilization and minimal site distubance Complements standad CPT geophysical measuements Highe spatial esolution possible than boehole techniques (<10 vs. 50+ cm.) Potentially moe accuate and quantified pemeability measuements Compaed to the poe pessue dissipation technique, which can only measue in low pemeability wate satuated media, the Cone Pemeamete TM system can measue five odes of magnitude in both satuated and unsatuated envionments The initial eseach and feasibility assessment of this system was completed in ealy 1997 as the fist phase of a contact suppoted by the DOE Chaacteization,

Monitoing, and Senso Technology (CMST) pogam though the Fedeal Enegy Technology Cente. In the second phase of this same study the Cone Pemeamete system was successfully employed in the unsatuated zone and below the wate table at the Savannah Rive Site in two sepaate demonstations in Apil and June of 1998. A thid deployment took place in Novembe 1998 at the Hanfod site, and a fouth at Cape Canaveal in Decembe 1998 and Januay 1999. This pesentation will detail the measuement appoach and eview field measuement esults. THE NEED FOR PERMEABILITY DATA Soil pemeability defines the magnitude of fluid flow (gas o liquid) unde imposed pessue gadients. It is one of the most impotant paametes to measue when pedicting fluid o contaminant movement in the subsuface, designing envionmental emediation systems, o simply chaacteizing a site. In the case of satuated geologic media, natual pessue gadients exist due to changes in slope (hydaulic gadients). Fo unsatuated geologic media, changes in baometic pessue impose natual pessue gadients on soil gas. Unnatual pessue gadients ae imposed by soil vapo extaction, active venting, pump-and-teat, ai spaging, in-situ vitification, and othe emediation pocesses equiing the active movement of fluids though geologic media. The design of these pocesses equies knowledge of the flow chaacteistics of the soil. The most impotant is its pemeability. Soil pemeability can vay by seveal odes of magnitude in a given geologic o hydogeologic setting. The vaiability of pemeability is illustated by the ange of values shown in the table below fo diffeent media. Table 1. Typical pemeability values fo vaious media (1 Dacy equals 9.87x10-9 cm 2 ). Media Sat. Hydaulic Conductivity K (cm/s) Pemeability k (Dacy) Clay 4.6e-7 4.8e-4 Sand 4.7e-2 49 Gavel 4.7 4900 Gavel/Sand Mixtue 0.47 490 Sandstone 4.7 4900 Limestone/Shale 4.7e-5 4.9e-2 Ganite 4.6e-7 4.8e-4 CURRENT METHODS In-situ pemeability measuements ae typically conducted in open o sceened holes fomed by conventional dilling techniques. In satuated geologic media, the pemeability is obtained with boehole flowmetes, dawdown tests, o isolated packe

measuements. Soil gas pemeability measuements ae obtained eithe with total boehole flow o isolated packe measuements in uncased o sceened wells. Obtaining pemeability data in conventionally dilled boeholes can be expensive, pimaily due to the cost of boehole installation. If it is possible to measue pemeability with diect push techniques like cone penetometes, sonic emplacements, o smalle manual o tuck-mounted equipment (such as Geopobes), significant savings can be ealized though educed time, inceased safety, minimal seconday waste geneation, and integation with the othe measuements obtained duing the pocess (such as the geophysical data obtained duing instumented cone penetomete emplacements). THE CHALLENGE OF PERMEABILITY MEASUREMENTS WITH DIRECT PUSH TECHNIQUES Diect push emplacements pose difficult measuement poblems fo pemeability deteminations. Typically, the ods ae elatively small, esticting the size of instument hadwae that can be used fo the measuement. In cone penetomete applications (CPT), fo example, the od outside diamete may be 2 and the inside diamete only 0.75. The majo issue, howeve, is the eduction in pemeability adjacent to the od suface due to the compaction of the soil caused by the od emplacement. This alteation of the soil flow chaacteistics can be significant and would esult in atificially low pemeability data with conventional techniques. A method called the poe pessue dissipation technique has been used with cone penetometes to obtain hydaulic conductivity in satuated soils, and actually capitalizes on the compaction to obtain pemeability data. This method uses the poe pessue instumentation in the cone penetomete tip to sense the buildup and decay of poe pessue due to the emplacement of the od and the esulting compaction of the soil adjacent to the od. The appoach equies some undestanding of soil type to infe pemeability, but its majo limitation is that if the soil pemeability is too high the poe pessue will incease only slightly and decay too quickly to measue. Consequently, this technique is typically applied in soils with pemeability below 10-4 Dacies (10-7 cm/s hydaulic conductivity) in wate satuated conditions. THE THEORY Dacy s law is the classical epesentation fo low Reynolds numbe flow in poous media. It pedicts volumetic flow as being popotional to the fluid pessue gadient. Hydogeologists fequently use pemeability to specifically descibe wate flow though soil, incopoating the fluid viscosity in the tem. This tem is also fequently efeed to as the satuated hydaulic conductivity, K. Ai pemeability is the pemeability of the soil media to ai flow in its existing condition, wheein the moistue satuation of the soil is not necessaily known and is consideed pat of the soil matix. It is commonly used in the fom independent of fluid popeties, k. The ai pemeability of a soil sample will change as the degee of wate satuation changes, and is equal to the intinsic pemeability when the soil is at its lowest achievable wate satuation.

The basic pemise of the Cone Pemeamete TM appoach is that as fluid is injected (o extacted) fom a discete section of the penetomete sting, it will tend to esult in a spheical flow field as the fluid moves outwad fom the od. The flow field will become essentially spheical, even if the soil adjacent to the od is of a much lowe pemeability (due to compaction). Eventually, fo a given injection ate, the adial pessue pofile along the axis of the penetomete od is identical to that which would occu if the od (and compacted soil) did not exist. Measuement of the pessue gadient at a distance fom the injection point poduces adequate infomation to accuately infe the pemeability. The spheical flow model evolves fom the classic Dacy poous flow elation. The injection o extaction souce is epesented as a spheical volume with adius o. Fluid is added to (o emoved fom) the zone at a known ate. The medium has a pemeability, k, which is assumed homogeneous. At some distance inf the poe fluid pessue is at ambient conditions (P A ). m Soil with pemeability k Spheical souce volume o,p inf,p A Fig. 1. One-dimensional spheical flow geomety. Dacy s law defines the steady state volumetic flow ate pe unit aea (u, also known as the Dacy velocity) in a one-dimensional geomety as k dp u = (Eq.1) µ dx whee dp/dx is the applied pessue gadient causing the flow, k is the pemeability of the medium, and µ is the dynamic viscosity of the fluid. Fo one-dimensional flow, the volumetic flow ate Q ove the entie aea of inteest is k dp Q = u da = da (Eq.2) A Aµ dx The mass flow ate can then be detemined as k dp m& = ρ da µ dx (Eq.3)

To apply this in the measuement of effective soil gas pemeability, the deivation consides gas flow in the accessible poosity of the soil. Fo an ideal compessible gas the equation of state can be witten as P ρ = RT (Eq.4) whee R is the gas constant (the univesal gas constant divided by the gas molecula weight), and T is the absolute tempeatue. Substitution of the ideal compessible gas equation into the mass flow ate equation, eplacing dp/dx by dp/d, and integating ove the aea of a sphee gives m& 1 0 1 2πk = µ RT 2 2 ( P P ) 0 whee P 0 is the pessue at the souce location 0, and P is the pessue at some distance. Solving fo k yields the flow model used in the Cone Pemeamete TM ai pemeability method: µ RTm& k = 2π 1 ( ) 2 2 P0 P 0 1 (Eq.5) (Eq.6) A simila deivation is used fo satuated hydaulic conductivity measuements with the spheical geomety. The only diffeence in this case is that the fluid density ρ is constant, instead of pessue dependent. Solving fo k unde these conditions poduces an equivalent elationship fo incompessible flow: µ m& k = 4πρ 1 0 1 ( P P ) 0 (Eq.7) These models ae eadily incopoated in the field measuement system to poduce esults while the measuement is being conducted. THE CONE PERMEAMETER TM FIELD SYSTEM A penetomete od section is fabicated to allow ai o wate injection though a sceened egion. The adial pessue pofile is measued with multiple pessue measuement pots distibuted above o below the extaction zone. These points ae filteed penetations into the pobe that allow pessue communication to sensos embedded in the od. The pemeamete is fabicated in a standad 2 diamete od, with five pessue pots anging fom 0.02 m to 0.7 m fom the injection zone. At the suface a fluid pumping system contols the injection flowate. The data system collects the flow ate and esulting pessue pofiles, then calculates in eal time the infeed pemeability. The field system is shown in fig. 2. The Cone Pemeamete TM od, designed and fabicated by Applied Reseach Associates, Inc., incopoates a poven fluid injection design and highly accuate pessue sensing elements embedded in the od. The design allows the pemeability measuements to be conducted simultaneously with standad CPT

cone measuements (poe pessue, tip, and sleeve pessue), which esults in eal time, complementay data sets of soil type and hydogeologic popeties. The data system povides detailed analyses of pessue pofiles and pocess histoies fo eal-time display. Fig. 2. Pump box, data-acquisition system, and pemeamete od. Results of lab-scale tests in a cubic mete test cell ae depicted in the plot below. Using a mixtue of silica flou and sand to achieve a 1 Dacy medium, the Cone Pemeamete TM measued an ai pemeability of 0.68 Dacy. The pessue pofile was spheical fom less than 0.1 m to the oute measuement pot location at 0.7 m (fig. 3). Pessue (Pa) Pessue vs. Radial Distance 9.10E+04 9.00E+04 8.90E+04 8.80E+04 8.70E+04 Flow = 4.1 lpm k m = 0.68 Dacy 0.00 0.20 0.40 0.60 0.80 1.00 Radial Distance (m) Measued Pessues Spheical Model Fig 3. Laboatoy pessue pofile and infeed pemeability in 1 Dacy soil.

CASE STUDY: SATURATED HYDRAULIC CONDICTIVITY TESTING AT THE SAVANNAH RIVER SITE D AREA COAL PILE RUNOFF BASIN The fist demonstation of the Cone Pemeamete TM measuement system was conducted at the Savannah Rive Site D Aea Coal Pile Runoff Basin. This aea had been chaacteized pio to installation and testing of a baie system and intecepto well (1). The aea is undelain by a seies of intebedded sand, silt, and clay layes. The goundwate beneath the site is divided into two aquife systems. The shallow system contains a wate table aquife and a semi-confined aquife. The wate table and semiconfined aquifes ae sepaated by a dak silty clay semi-confining unit that is 10 to 15 feet thick. The top of the semi-confining unit is 50 to 60 ft. deep. These tests extended fom the wate table (at appoximately 4.8 ft. depth) into the top of the confining laye, with the deepest pemeamete measuements at appoximately 60 ft. The Cone Pemeamete TM was integated with a standad CPT cone tip and deployed by Applied Reseach Associates using a 30-ton tuck loaded to 26 tons. CPT data (poe pessue, sleeve stess, tip stess) was obtained simultaneously with the pemeamete measuements. The pemeamete measuements typically equied pushing the od to the desied depth, stating wate injection, and obseving flow and pessue histoies until a elatively steady condition was attained. This equied fom 3 to 10 minutes pe measuement station. On the second day of testing 35 measuements wee obtained in a five-hou peiod. The Cone Pemeamete TM data can be compaed with boehole flowmete and total flow satuated conductivity measuements taken in well DCB-25, appoximately 15-ft. distant. Dawdown measuements taken in 1996 esulted in satuated hydaulic conductivities (hoizontal) anging fom 5.9E-5 to 1.1E-3 cm/s, depending on the monito well used. The bulk conductivity data was combined with boehole flowmete data to develop a pofile of the conductivity vs. depth on 1-ft. intevals. The Cone Pemeamete TM data is plotted in fig. 4, compaed with the pevious boehole flowmete tests in DCB-25. Boehole flowmete data fo both the high (1.1E-3 cm/s) and low (5.9E-5 cm/s) bulk conductivity cases ae plotted, indicating the ange of uncetainty in the boehole flowmete data. The Cone Pemeamete TM data geneally falls between the high and low conductivity values.

Hydaulic Pemeability Conductivity (cm/s) (cm/s) 1.0E-08 1.0E-06 1.0E-04 1.0E-02 1.0E+00 10 15 20 25 30 35 Depth (ft) 40 45 50 55 60 Boehole Flowmete (Low End Results) Boehole Flowmete (High End Results) Cone Pemeamete Results Fig. 4. Cone Pemeamete TM satuated hydaulic conductivity data (nea DCB-25) fom the Savannah Rive Site.

STATUS OF THE CONE PERMEAMETER TM SYSTEM The initial eseach and feasibility assessment of this system was completed in ealy 1997 fo a contact suppoted by the DOE Chaacteization, Monitoing, and Senso Technology (CMST) pogam though the Fedeal Enegy Technology Cente. Numeical modeling and laboatoy tests demonstated that the basic pemise of the system s opeation was cedible. The pessue fields esulting fom injection of ai and wate into a mockup pobe wee spheical, and they could be measued in such a fashion that the nea field compaction esulting fom the pentomete emplacement could be avoided. Results fom this study ae documented in a topical poject epot (2). Given the positive esults of the initial feasibility assessment, an engineeing pototype of the measuement system was successfully employed both in the vadose zone and below the wate table in thee diffeent aeas at the Savannah Rive Site (SRS). Results fom this effot showed excellent ageement with pevious pemeability testing done at the site. The data also had a positive coelation with othe cone penetomete physical measuements taken concuently duing the testing sequence (i.e., the pemeability was highe in layes identified as sands and lowe in aeas composed of clay). A final field test of the Cone Pemeamete TM fo the CMST contact was completed in Decembe 1998 and Januay 1999 at Launch Complex 34, of the Cape Canaveal Ai Station, Floida. This data is unde eview. The technology was also successfully fielded in the vadose zone at two additional sites in 1998. With sponsoship fom Westinghouse Savannah Rive Rive Company in June 1998, the Cone Pemeamete TM was used to chaacteize the ai pemeability of the existing clay line at the Aea E Buial Gounds at SRS. Ove a two-day peiod, measuements wee conducted at 10 diffeent locations. Most ecently (Novembe, 1998), the Cone Pemeamete TM was employed at the 200 East Aea of the Hanfod Site, whee ai pemeability measuements wee pefomed in the Hanfod Fomation. Pemeability esults fom this test ae cuently unde eview and have not been eleased. Once the field demonstations ae completed, and mino modifications have been incopoated into the od design, the Cone Pemeamete TM system will be available fo sale to suppot cone penetomete opeations. Adaptation of the design to smalle emplacement systems, such as Geopobe units, is anticipated. REFERENCES 1. M.A. PHIFER ET AL., Inteim Repot, D-Aea Intecepto Well, DIW-1 Wate Table Aquife (U), Westinghouse Savannah Rive Company (Septembe 1996) 2. WILLIAM LOWRY, NEVA MASON, and DAN MEREWETHER, In-situ Pemeability Measuements with Diect Push Techniques: Phase I Topical Repot, SEASF-96-147, Science & Engineeing Associates (Novembe 1997)