# Geologic, **Hy dr**  **aulic, and**  **Geochemic al Con**  **tr ols**  **on F ate**  **, T ra**  **nsport, and Re**  **media tion of V**  **OCs**

**USEP A**  **- USGS**  **Fr actur**  **ed Ro**  **ck W orkshop**  **EP A R**  **egion 2**  **14 January**  **2014** 

# Allen M. Shapir **o, USGS** 

### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 2**  

# Div **er sity of Fr**  **actur ed**  **Ro ck Aquif** **er s** 

Gr anite and schist Mirror Lake, NH

Madison Limestone, Rapid City

, SD Biscayne Limestone,

Ft. Lauderdale, FL Lockatong Mudstone, We st Tr enton, NJ To nalite , Wa shington, DC Silurian Dolomite Argonne, IL

Sykesville Gneiss, Wa shington, DC

##  

# Fr **actur ed**  **ro ck aquif** **er s ar**  **e highly div er**  **se**  

# . . .how **ever**

**. . .all fr actur**  **ed ro**  **ck aquif er**  **s shar e**  **similar ph ys**  **ical a tt**  **ribut es**   

# Similar a **tt ribut**  **es pr ovide f** **or . . .**   

# Generic **discussion of ph ysical and chemical**  **tr ansport pr**  **ocesses**  

# St **andar diz**  **ed appr**  **oaches t o char**  **act eriz**  **ation and**  **monit oring**   

# Design and **application of diagnostic and**  **modeling to**  **ols**  

# Expect sit **e specific comple xities**  

# Div **er sity of Fr**  **actur ed**  **Ro ck Aquif** **er s** 

**Controls on F**  **ate, T ra**  **nsport, and**  **Remediation of V OCs**  **3**Sand and gravel, glacial outwash

Cape Cod, Massachuset ts Schematic of intergranular void space in an unconsolidated sand Length - to - width ratio of void space ~1

Heterogeneous nature of geologic materials is limited. . .direction of groundwater flow can be readily identified fr om the hydraulic gradient. . . “ P ore” scale variability in fluid velocity (magnitude and direction) results in spreading of a chemical constituent. . . 

## Gr **oundw ate**  **r flow**  **Chemical tr**  **ansport**

**Controls on F**  **ate, T ra**  **nsport, and**  **Remediation of V OCs**  **4** 

# Expect **at ions**  **fo r unconsolida**  **te d**  **por ous**  **media**

**Similar interpretations of groundwater**  **flow and chemical tr**  **ansport cannot**  **be applied to fr**  **actured rock aquifers**  **because of unique**  **physical attributes of fr**  **actured rock. . .**  Dimensions of the void space are small relative to scale of the problem of interest (groundwater flow, chemical transport)

# Expectations **of fractured rock:**  **Hierarch y of void spac** **e**

**Controls on F**  **ate, T ra**  **nsport, and**  **Remediation of V OCs**  **5**

Iron - hydroxide precipitate staining the rock matrix ( **primary/intrinsic rock porosity**  )

Fractures exposed on a road cut ( **fracture porosity** ) **Fault zone** exposed on a road cut **Granite and schist, Mirror Lak**  **e W atershed**  **Grafton County**

**, New Hampshire** Residual wetting of rock core ( **primary/intrinsic rock**  **porosity** )

Fractures parallel and perpendicular to bedding (

**fracture porosity** )

Schematic cross section

perpendicular to bedding s howing **fault zone** location **Lock atong**  **Mudstone, Newark Basin We**  **st Trenton, New Jersey**

### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 6**  

# Expect **at ions**  **of fr actur**  **ed ro**  **ck: Large variability in**  **capacity to transmit groundwater** Borehole H1 Mirror Lake W

atershed, NH

Granite and Schist

Packer apparatus used for testing individual or closely spaced fractures Shapiro and Hsieh, 1998; Shapiro et al., 2007 **Expect both**  **vertical and horizontal**  **va riability** **. . .**



### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 7**  

# Expectations **of fractured rock:** 

**K of the intrinsic rock (matrix)**  **porosity is orders**  **of magnitude**  **less than that**  **of fr actures**  

# Abrupt spatial changes **in hydraulic properties**L ocal and regional stress distribution, lithology , and weathering lead to comple x connectivity of fr actures and their h ydraulic properties. . .

Boundary Iron staining No staining Schist: f ewer fractures; longer, undulating fracture surfacesGranite: h igher fracture density; shorter, more planar fractures



### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 8**  **Combination of large**  **va riation**  **in K coupled with**  **complex fr**  **acture connectivity**  **= convoluted groundwater**  **flow paths** 

# Expectations **of fractured rock:**  **Complex fracture connectivity** 

Bedding plane parting along black, carbon - rich section of mudstone Joints perpendicular to bedding (parallel and perpendicular to rock face)

Fracture density perpendicular to bedding varies with proximity to fault **Granite and schist, Mirror**  **Lak e**  **Wa tershed**  **Grafton County**  **, New Hampshire**  **Lock atong**  **Mudstone, Newark Basin We**  **st Trenton, New Jersey**Fr acture surfaces have complex topology . . .fracture aperture varies due to points of contact and

asperities between fr acture walls

. . .similar to the large variability in h ydraulic properties that is anticipated fr om one fracture to the next, there is large variability in h ydraulic properties within an individual fr acture. . . Neretnieks et al., 1982; T

sang and Neretnieks 1998



### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 9**  **C onvoluted**  **groundwater flow paths**  **within individual fr**  **actures** 

# Expectations **of fractured rock:**  **Fracture surfaces have complex topology** 

# What’s important **? How do we approach this level of complexity**  **for site -**  **and regional**  **- scale investigations?**  • **Identify lithologic**  **and geomechanical**  **controls** • **Identify most permeable features and barriers to**  **groundwater flow over relevant**  **dimensions** • **Spatial connectivity of permeable features** • **Mapping and characterization of**  **every fracture is not warranted**  • **Variability within an individual fracture is below our resolution capacity** *

**Controls on F**  **ate, T ra**  **nsport, and**  **Remediation of V OCs**  **10** 

# Expect **at ions:**  **Con vo**  **lut ed gr**  **oundw ate**  **r flow paths**  **over dimensions fr**  **om me te**  **rs to**  **kilome te**  **rs . . .** Characterizing fluid advection and the migration of aqueous phase contaminants. . .monitoring h ydraulic head in discrete intervals of boreholes



### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 11**  

# Consequences of Comple **xity in Fr actur**  **ed R ock:** 

Characterizing h ydraulic head is a 3 - D concept. The direction of groundwater flow must be inferred in concert with the characterization of permeable features and flow barriers. 

# Char **act erizing**  **the dir ection**  **of gr oundwat**  **er flow** Characterizing fluid advection and the migration of aqueous phase contaminants. . .monitoring h ydraulic head in discrete intervals of boreholes



### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 12**  

# Consequences of Comple **xity in Fr actur**  **ed R ock:** 

**Char act**  **erizing the dir**  **ection of gr**  **oundwat er**  **flow**

Maintaining the integrity of multilevel monitoring equipment. . . p ro per monitoring of h ydraulic head is critical to inferring directions of groundwater flow .Borehole H1, Granite and Schist, Mirror Lak e W atershed, NH Monitoring geochemical conditions in fractured rock. . .boreholes open to multiple fractures. . .

Pumping. . .mixing contributions fr om multiple fractures . . .
Pumping. . .gr oundwater dr awn preferentially fr om most tr ansmissive fr actures. . .


### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 13**  

# Consequences of Comple **xity in Fr actur**  **ed R ock:** 

**Char act**  **erizing the dis**  **tribution of contaminants** 

### Naval Air W arfar e Center , W est T re nton, NJ , Lock atong Mudstone, Newark Basin TCE concentration (36BR open interval): 102 – 125 ft below land surface = 89,000  g/ L TCE concentration (36BR interval A): 102 – 112 ft below land surface = 19,000  g/ L



### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 14**  

# Consequences of Comple **xity in Fr actur**  **ed R ock:** 

**Char act**  **erizing the dis**  **tribution of contaminants** 

Tr ansmissivity of 36BR – interval A (102 – 112 ft below land surface) – 1.0 x 10 - 5 m 2 /s Tr ansmissivity of 36BR – interval B (112 – 125 ft below land surface) – 1.0 x 10 - 7 m 2 /s Flux averaged concentration: C A x (1.00/1.01) + C B x (0.01/1.01) = C openhole C A = 19,000  g/ L C openhole = 89,000  g/ L 

### C B 

### > 1,000,000  g/ LDNAPLs in geologic media DNAPL pooling at a boundary between larger beads [0.85 – 1.23 mm] (upper region) and smaller beads [0.49 – 0.70 mm] (lower region) Schwille 1988 Complex DNAPL migration in unsaturated sands. DNAPL shown in red (Sudan IV dye). Bedding dips 30 o below horizontal 15 cm
Poulsen and Kueper , 1992 • Capillary forces define the distribution of DNAPLs • Complex spatial distribution of DNAPLs (both vertically and laterally) from minor variations in pore space geometry • DNAPLs at great depths - density > groundwater • DNAPL “pool” heights force DNAPL into small pore throats; hydraulic conditions may not be capable of removing DNAPL from small pore throats • Pumping and drilling may re - mobilize “pools” of DNAPL • DNAPLs dissolve into groundwater • Dissolved - phase DNAPLs diffuse into lower - permeability geologic materials • VOCs sorb to geologic materials with organic content



### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 15**  

# Consequences of Comple **xity in Fr actur**  **ed R ock:** 

**Comple x**  **spa tial**  **dis tribution**  **of contaminants**Comple x topology of fractures affects contaminant distribution. . .

Entry of DNAPLs into fractures depends on ph ysical properties of fractures and the DNAPL, a nd capillary forces. . . Kueper and McWhorter , 1992; Kueper et al., 2003



### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 16**  

# Consequences of Comple **xity in Fr actur**  **ed R ock:** 

**Comple x**  **spa tial**  **dis tribution**  **of contaminants**Fr acture aperture affects contaminant distribution. . .

• For a given “pool height ” of DNAPL, fractures to the right of these curves would allow entry of DNAPL
• 9 micron (9 x 10 - 6 meters) fracture apertur e needed to stop 1 meter “pool” height of TCE
• Diameter of human hair ~50 microns Kueper and McWhorter , 1992; Kueper et al., 2003



### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 17**  

# Consequences of Comple **xity in Fr actur**  **ed R ock:** 

**Comple x**  **spa tial**  **dis tribution**  **of contaminants**Retention and slow release of contaminants in “flow limited” regions of the aquifer. . .a significant impediment to achieving remedial objectives in a reasonable time frame. . . from Doner and Sale, Colorado State University

**Low -**  **permeability material**  **embedded in a permeable**  **sand. . .** 

**Dye injection. . .**



### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 18**  

# Consequences of Comple **xity in Fr actur**  **ed R ock:**  **Significance of “flow limit**  **ed” r egions**  **of the aquif er** 

**Flushing. . .** • Low permeability material may not be significant with respect to volumetric groundwater flow. . .

• During contaminant “loading”, dye diffuses from permeable pathways to low permeability materials due to concentration gradient

• During “flushing”, dye diffuses from low permeability materials to permeable pathways due to concentration gradientThe primary/intrinsic porosity of the rock (rock matrix) offers a fluid - filled void space available to chemical constituents . . .

Wo od et al., 1996

Fr equency histogram of porosity in rock types of the Mirror Lak e W atershed, New Hampshire

Iron hydroxide staining on fracture surfaces and in the rock matrix. . .oxygen diffusing into the rock matrix and reacting

with dissolved iron 

### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 19**  

# Consequences of Comple **xity in Fr actur**  **ed R ock:**  **Significance of “flow limit**  **ed” r egions**  **of the aquif er** Lock atong Mudstone Na val Air W arfare Center

, W est T renton, NJ Depth where DNAPL detected during coring Detection limit for TCE in groundwater samples is 1  g/L



### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 20**  

# Consequences of Comple **xity in Fr actur**  **ed R ock:**  **Significance of “flow limit**  **ed” r egions**  **of the aquif er** Depth(feetbelowlandsurface)

Sandstone Simi Hills, Ventura County , California Monitoring i nterval #6

Monitoring i nterval #3 Sterling et al., 2005 Multilevel m onitoring Jan 1998

# Matrix Dif

fusion in Fr actur ed R ock

100 meters25meters

Vertical exaggeration x 4 Log 10 (C/C o )

- 25 - 20 - 15 - 10 - 5 0 Fracture (v = 100 m/ yr ) Ro ck matrix C = Co (0 < t < 10 years) C = 0 (t > 10 years)

# Matrix Dif

fusion in Fr actur ed R ock

100 meters25meters

Vertical exaggeration x 4 Log 10 (C/C o )

- 25 - 20 - 15 - 10 - 5 0 Fracture (v = 100 m/ yr ) Ro ck matrix C = Co (0 < t < 10 years) C = 0 (t > 10 years)

- 1 - 3 - 10 - 15

- 5 - 20

elapsed time = 10 years

# Matrix Dif

fusion in Fr actur ed R ock

100 meters25meters

Vertical exaggeration x 4 Log 10 (C/C o )

- 25 - 20 - 15 - 10 - 5 0 Fracture (v = 100 m/ yr ) Ro ck matrix C = Co (0 < t < 10 years) C = 0 (t > 10 years)

- 3 - 1 - 1 - 3 - 10 - 15

- 5
elapsed time = 20 years

# Matrix Dif

fusion in Fr actur ed R ock

100 meters25meters

Vertical exaggeration x 4 Log 10 (C/C o )

- 25 - 20 - 15 - 10 - 5 0 Fracture (v = 100 m/ yr ) Ro ck matrix C = Co (0 < t < 10 years) C = 0 (t > 10 years)

- 5

- 3

- 3 - 10

- 1 - 1 elapsed time = 30 years

# Matrix Dif

fusion in Fr actur ed R ock

100 meters25meters

Vertical exaggeration x 4 Log 10 (C/C o )

- 25 - 20 - 15 - 10 - 5 0 C = Co (0 < t < 10 years) C = 0 (t > 10 years)

- 5

- 3

- 3 elapsed time = 50 years Concentration gradient driving contaminant mass toward the fracture. . . Concentration gradient driving contaminant mass away from the fracture. .

Over time, concentration gradient toward fracture decreases. . . reducing mass flux to the fracture.

### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 26**  

# Consequences of Comple **xity in Fr actur**  **ed R ock:** 

**Ma trix**  **diffusion. . .a cur**  **se or a blessing ?**

the curse . . .retention of contaminants in flow limited regions of the aquifer

. . .limiting access to remediation amendments. . .slow release of contaminants to permeable pathways yields a long - term contaminant source. . . An e xample: Pulse injection and monitoring 50 m downgradient

the blessing . . .retention of contaminants in flow limited regions of the aquifer . . .delaying downgradient migration of contaminants. . .attenuating the downgradient concentrations. . . . . .matrix diffusion is the rationale for the licensing of selected geologic en vironments as sites for waste isolation (e.g., WIPP site, New Mexico, USA)Lock atong Mudstone Na val Air W arfare Center

, W est T renton, NJ



### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 27**  

# Consequences of Comple **xity in Fr actur**  **ed R ock:**  **Other pr ocesses in “flow limit**  **ed” re**  **gions of the aquif** **er** Sharp concentration gradients in the rock matrix adjacent to fractures. . . Over time, diffusion tends to diminish sharp concentration gradients. . . Retention and release of contaminants also controlled by surface processes (sorption/desorption) on fracture surfaces and in the rock matrix. . . Organic contaminants (e.g., TCE) have a surface affinity for organic materials (e.g., organic carbon) Sorption/desorption changes dynamics for retention and release of contaminantsNa val Air W arfare Center , W est T renton, NJ Isocontours of TCE concentration at 100 ft below land surface Mudstone units of the Lock atong Fromation

on Cross Section G – G’ G G’

F F’ 100 ft below land surface Interpreting contaminant distribution based on water samples collected from short (~20 ft ) interv als open in a fr actured mudstone. . .



### Controls **on F ate, T** **ra nsport,**  **and Remediation of V**  **OCs 28**  

# Consequences of Comple **xity in Fr actur**  **ed R ock:**  **Interpreting the spa**  **tial dis**  **tribution of con taminants** 

Lacombe 2011 Interpretation of concentrations in mobile groundwater (fractures). . .does not necessarily reflect total in situ contaminant mass. . .

# How do we approach this level of complexity **for site -**  **and regional**  **- scale investigations?**  • **“Classical” (Gaussian -**  **shaped) plumes are unlikely**  • **Differentiate between contaminants in mobile and**  **immobile (flow**  **- limited) regions of the aquifer**  • **Quantify contaminant mass in flow -**  **limited regions of the aquifer. . . the rock**  **matrix may retain significant contaminant mass (aqueous chemical**  **diffusion and surface processes)**  • **Grasp the significance of residence times and mass exchange between fractures and the rock**  **matrix**

**Controls on F**  **ate, T ra**  **nsport, and**  **Remediation of V OCs**  **29** 

# What’s important **? Expect**  **at ions:**  **Comple x spatial**  **dis tribution of**  **con ta**  **minan ts**  **in fr actur**  **es and the r**  **ock matrix. . .** 

# Final Though **ts**

**Controls on F**  **ate, T ra**  **nsport, and**  **Remediation of V OCs**  **30** 

# Keep in mind. . .fractured rock **aquifers have similar physical attributes.**  **. .as well as site specific complexities. . . These (similar) attributes are the starting point for the**  **development of Conceptual Site Models**  **. . .a conceptual understanding of the hydrogeologic**  **and biogeochemical controls**  **on groundwater flow and contaminant fate and transport. . .site specific complexities are needed to fill in the details. . .**  **These (similar) attributes need to be recognized in**  **characterization, monitoring, and modeling at fractured rock sites. . .**