Carlsbad Caverns

VULNERABILITY OF CARLSBAD CAVERN, NEW MEXICO TO POLLUTION FROM HUMAN ACTIVITIES AT THE SURFACE

Carlsbad Caverns National Park (CCNP), located in the southeastern corner of New Mexico, contains numerous caves that have formed in the fractured limestones of the Guadalupe Ridge (figure 1). The Park includes a visitors accessible cave system, called Carlsbad Cavern (photo 1). To support and manage the increasing number of visitors, the National Park Service has created over the years an extensive infrastructure with visitors, office, maintenance, and housing facilities, many of which are near or above the cavern (figure 2). The impact on the caves of the resulting human activity in and around these facilities has become a concern to Park management (photo 2). The focus of our project was to determine the potential impact of the man-made structures and human activities at the land surface on Carlsbad Cavern. Specifically, the study aimed at: 1) determining the cave areas most vulnerable to contamination from the land surface through infiltration of contaminants-carrying water into the soil and the subsequent movement of these contaminants towards the caves with the downwards flow of water, and 2) if impacts from human-related contaminant sources on the water quality in the caves are already noticeable.

The approach taken in this study focused on developing a thorough understanding of the hydrologic system, that is, the pathways and flow rates of water in the underground, and the processes that control them. Such understanding is reflected in a conceptual model formulated on basis of field investigations and analysis, the so-called "conceptualization and characterization approach." This work was augmented by a series of sampling tours to determine the relevant chemical characteristics of surface and underground water.

A number of factors present at the study site contribute to a relative high vulnerability of the caves for contamination from the surface, including: 1) in many places in the Park, especially on the ridge top and slopes, soil is absent and the bedrock is exposed (photos 3 and 4); 2) the presence in critical areas of highly permeable fracture zones providing a rather direct connection between the surface and certain cavern areas (near Chocolate High, New Mexico Room, Scenic Rooms, and Big Room, and underneath Bat Cave Draw); 3) the existence of extensive, well developed karst (that is, water-induced dissolution of carbonate rock) as illustrated by the extent of the caves; and 4) the presence of a gap in the Yates Siltstone layer where the Cavern's Main Corridor breaks through this layer. Factors that have a moderating influence on cave vulnerability include: 1) the arid climate (there is not much precipitation available to move contaminants downwards); 2) the presence in part of the study area of the rather continuous Yates Siltstone forcing infiltrating water (and contaminants) to move laterally, often away from the caves; and 3) the rock in which the Cavern is located, is unsaturated (that is, pores in rock are filled with both water and air), slowing down the movement of water and contaminants.

The study concluded that the most threatened areas in Carlsbad Cavern are: 1) Quintessential Right, 2) Left Hand Tunnel, 3) New Section, 4) the Main Corridor between Devil's Spring and Iceberg Rock, and 5) locations in Chocolate High, the New Mexico Room, the Scenic Rooms, and the Big Room area. Travel times from the surface to these cave areas vary from between 4 to 10 years in the Main Corridor to between 14 and 35 years in the Big Room.

Although Carlsbad Cavern is highly vulnerable to contamination from the surface, currently, there are few indications that massive contamination is occurring. Some smaller incidences have been detected, primarily related to chronic, low-level releases from sewer lines and parking lot runoff. However, it is conceivable that in the future a major contamination incident may take place if no preventive measures are taken. Furthermore, due to the long travel times it is expected that already an increased amount of contaminants is moving downwards as a result of the constantly growing number of visitors. To protect the caves from further contamination from the surface, the chance of a significant release at the surface needs to be reduced through removal of existing and potential sources, adaptation of management policies, implementation of accident mitigation procedures, and re-engineering of critical infrastructural components.

After a contaminant has entered the subsurface, little can be done to remove it until it arrives in an exposed cave. There, some measures can be taken to capture and remove the contaminant and to reduce its potential effect on humans and cave ecosystems. However, even then, most contamination incidents will be rather localized or will occur in areas not accessible for visitors, allowing most of the caves to be kept open for the public.

REFERENCES:

  • Van der Heijde, P.K.M., K.E. Kolm, H.E. Dawson, and M. Brooke. 1997. Determining Water Infiltration Routes from Structures Located above Carlsbad Cavern, Carlsbad Caverns National Park, Carlsbad, New Mexico. IGWMC/GWMI 97-01, Colorado School of Mines, Colorado.
     
  • Kolm, K.E., P.K.M. van der Heijde, J.S. Downey, and E.D. Gutentag. 1996. Conceptualization and Characterization of Ground-Water Flow Systems: Subsurface Fluid-flow (Ground-water and Vadose Zone) Modeling. ASTM STP 1288, J.D. Ritchey and J.O. Rumbaugh, Eds., Am. Society for Testing and Materials, Philadelphia, Pennsylvania.

This project was funded by the National Park Service and carried out by faculty and students of the Colorado School of Mines.

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Copyright 1997, 2011 Heath Hydrology, Inc. All rights reserved.

Figure 1. Project location.

Photo 1. Cave Entrance.

Photo 3. Park Road.

Photo 2. Maintenance Yard.

Figure 2. Site Map with major caverns and park facilities.