New Mexico
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KAFB Bulk Fuels Facility – Jet Fuel Plume Remediation

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About the Project  – Site & Regional Geology / Hydrology

geology in the field

 

Understanding the characteristics of the landscape affected by the jet fuel leak is a very critical component of developing efficient and effective strategies for removing the contamination and threat to Albuquerque’s drinking water supply.

As explained in the project’s Strategic Plan, this complex contamination site requires multiple strategies to address the multiple phases of fuel trapped in dry sediment and in the groundwater.

Technical experts working on this remediation project have been studying the sediment cores extracted from wells to be able to create a picture of what’s going on underground. Knowing the potential pathways the contamination took as it leaked down through the dry sediment and into the groundwater will help pinpoint areas to target for cleanup.

Some of the same sediment layers that exist underground in the area of the plume appear above ground in other places near KAFB.  So, studying these visible, above ground layers can help understand the nature of the underground sediment at the fuel site.   Studying above ground layers similar to those found underground can also be useful in characterizing the site.

 

cross section of rio grande sediment

This figure shows a cross section of the Rio Grande valley.

The orange, yellow, and pink sections represent the various underground sediment layers that would be exposed if you were to cut down through the ground like a slice of cake, across the area of the plume.

 

Click image for larger version.

Geology Introduction:

Stratigraphy of Basin-fill Deposits in the Rio Grande Valley

The Kirtland AFB BFF spill site is located on unconsolidated sediment deposits of the Middle Rio Grande Basin. These basin-fill deposits (colored units on the figure above), contain groundwater, and comprise the Santa Fe Group aquifer system.

  • The Santa Fe Group is primarily alluvium composed chiefly of sand and silt with lesser amounts of clay and gravel.
  • The majority of these alluvial deposits are fluvial – sediment transported into the Albuquerque basin by ancient streams and rivers that drained surrounding regions.
  • Other alluvium was washed down from the Sandias, deposited along the mountain front.
  • These depositional processes have been active for millions of years and consequently the Santa Fe Group locally is thousands of feet thick.
  • The varied transport processes and the available sediment combine to form a complex, three-dimensional system of truncated and overlapping units with contrasting properties.

 

Fluvial deposits are highly variable because the grain size and mixture of the material deposited depends on the nature of streamflow and on the amount of erosion that occurred.

  • Main channel deposits tend to be coarser grained and overbank flood deposits tend to contain a higher percentage of clay and silt.

Alluvial-colluvial deposits are composed of sediment ranging from boulder sized to sand and silt, depending on proximity to the mountain front.

Subsurface information on the site-specific geology and groundwater is obtained primarily from wells such as the groundwater monitoring wells that have been installed as part of the site characterization efforts.

Subsurface data is collected during the drilling and construction of wells and include:

  1. characteristics of soil cuttings removed by the drill bit;
  2. notes taken by the rig geologist and/or drillers on drilling conditions, including drilling rate;
  3. measurements of the physical properties of the soil and groundwater using borehole geophysical logging tools;
  4. aquifer properties as estimated from hydraulic tests (e.g., aquifer tests); and
  5. groundwater chemistry (Bartolino and Cole, 2002).

See Regional Stratigraphy poster for how data taken from project wells have created a model of the geologic deposits underground in the area of the KAFB plume.

Also see Progress in Plume Definition and Contamination Extraction poster for stratigraphy related to water table and EDB plume.

 

alluvial gravel deposit
1) Alluvial gravel deposit (fluvial) – example of river deposited gravel.
alluvial channel deposit

2) Alluvial fan deposit showing channel outline.

overbank deposit

3) Overbank deposit (fluvial) – example of sediment deposited by the ancestral Rio Grande as it flooded over it’s banks.

 

(click images for larger)

Photos taken in lower Tijeras Arroyo in south Albuquerque (2015)

Hydrology Introduction

Understanding the hydrology of the site is critical to the successful cleanup of the jet fuel leak.

Groundwater moves through the pore spaces between the grains and through fractures in the subsurface deposit.

  • Unconsolidated deposits consisting primarily of medium– to coarse-grained sand or gravel have interconnected pore spaces that allow water to move freely in the deposit; this kind of aquifer material makes for a highly productive aquifer.
  • Deposits consisting of a higher percentage of finer grained deposits (e.g., silt and clay) have large proportions of pore spaces but the pore spaces are smaller and interconnection is poor.As a result, water does not move freely in the finer grained materials which form confining layers in an aquifer system.
  • Main channel deposits tend to make more productive aquifers because of their coarse-grained size (see picure 1, above, right), whereas the overbank flood deposits (see picture 3 above, right) are more likely to form confining layers because of their fine-grained size.
  • Alluvial-colluvial deposits are variable and poorly sorted, with a rage of grain sizes, making them moderate to poor aquifers.

The groundwater in a well completed in an unconfined aquifer is equal to the water table. Differences in the groundwater measured at multiple wells completed at different depths in a single location (well nest) indicate the general direction of vertical flow with in the aquifer.

ABQ Aquifer Characteristics Near KAFB:

  • The aquifer at the Kirtland AFB BFF spill site contains naturally occurring upward vertical hydraulic gradients, as determined from measurements taken at groundwater monitoring wells. These upward gradients mean that deep groundwater, such as in the zones tapped by drinking water wells, has the potential to migrate upwards into shallower aquifer zones.
  • The depth to groundwater in the vicinity of the Kirtland AFB BFF spill site is presently approximately 480 feet below ground surface (bgs).
  • Prior to the development of the regional aquifer as a source of drinking water for the Albuquerque and surrounding areas, the regional direction of groundwater flow was to the southwest, flowing from the Sandia and Manzano Mountains towards the Rio Grande (Plummer et al., 2004).
  • Development and pumping of the regional aquifer as the primary source of water supply for the Albuquerque metropolitan area, however, created more than 120 feet of water level decline and altered the direction of groundwater flow in many areas of the aquifer.
  • The present direction of groundwater flow at the Kirtland AFB BFF spill site is to the northeast.
  • Beginning in 2008-2009, the water table at the site has risen by approximately 10 feet in response to reduced pumping from the municipal well fields; the reduction of pumping is part of the Albuquerque Bernalillo County Water Utility Authority water conservation efforts and integration of treated surface water into distribution.

 

The figure below illustrates how the stratigraphy (layers of sediment) of the area influences movement of the leaked fuel down to the water table.  (click image for larger)

sediments and fuel pathways