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Effect of hydrogeological and anthropogenic factors on the spatial and temporal distribution of CVOCs in the karst system of northern Puerto Rico

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This study evaluates factors affecting the spatial and temporal distribution of chlorinated volatile organic contaminants (CVOCs) in the highly productive aquifers of the karst region in northern Puerto Rico (KR-NPR). Historical records from 1982 to 2016 are analyzed using spatial and statistical methods to evaluate hydrogeological and anthropogenic factors affecting the presence and concentrations of multiple CVOCs in the KR-NPR. Results show extensive spatial and temporal distributions of CVOCs, as single entities and as mixtures. It is found that at least one type of CVOC is present above detection limits in 64% of the samples and 77% of the sampling sites during the study period. CVOC distribution in the KR-NPR is contaminant-dependent, with some species being strongly influenced by the source of contamination and hydrogeological characteristics of the system. Persistent presence of CVOCs in the KR-NPR system, even after contaminated sites have been subjected to active remediation, reflect the high capacity of the system to store and slowly release contaminants over long periods of time. This study shows that karst aquifers are highly vulnerable to contamination and can serve as a long-term route of contaminants to potential points of exposure.
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Environmental Earth Sciences (2019) 78:594
Eect ofhydrogeological andanthropogenic factors onthespatial
andtemporal distribution ofCVOCs inthekarst system ofnorthern
Puerto Rico
NormaI.Torres1 · VildaL.Rivera1· IngridY.Padilla1 · RaulE.Macchiavelli2· DavidKaeli3·
Received: 31 August 2018 / Accepted: 23 September 2019 / Published online: 4 October 2019
© Springer-Verlag GmbH Germany, part of Springer Nature 2019
This study evaluates factors affecting the spatial and temporal distribution of chlorinated volatile organic contaminants
(CVOCs) in the highly productive aquifers of the karst region in northern Puerto Rico (KR-NPR). Historical records from
1982 to 2016 are analyzed using spatial and statistical methods to evaluate hydrogeological and anthropogenic factors
affecting the presence and concentrations of multiple CVOCs in the KR-NPR. Results show extensive spatial and temporal
distributions of CVOCs, as single entities and as mixtures. It is found that at least one type of CVOC is present above detec-
tion limits in 64% of the samples and 77% of the sampling sites during the study period. CVOC distribution in the KR-NPR
is contaminant-dependent, with some species being strongly influenced by the source of contamination and hydrogeological
characteristics of the system. Persistent presence of CVOCs in the KR-NPR system, even after contaminated sites have been
subjected to active remediation, reflect the high capacity of the system to store and slowly release contaminants over long
periods of time. This study shows that karst aquifers are highly vulnerable to contamination and can serve as a long-term
route of contaminants to potential points of exposure.
Keywords Groundwater contamination· CVOCs· Karst aquifers· Statistical methods· Hydrogeological properties·
Anthropogenic factors
Karst aquifers serve as an important source of freshwater for
human consumption, industrial, and agricultural use. They
promote industrial, urban, and agricultural development, and
contribute to ecological integrity of the region (Padilla etal.
2011). Karst groundwater systems provide roughly 20–25%
of the global population water needs (Ford and Williams
2007; Butscher and Huggenberger 2009). Second only to
unconsolidated and semi-consolidated sand and gravel
aquifers, which supply nearly 80% of groundwater, karst
groundwater systems are among the most important sources
of groundwater in United States. They provide about 8% of
all groundwater needs in the country, of which 17% is used
for public supply (Maupin and Barber 2005). Other sources
of groundwater come from igneous and metamorphic rocks
(6%), sandstone rock (2%), sandstone, and carbonate rock
(2%) (Maupin and Barber 2005).
Karst systems have unique characteristics that make them
very different from other types of aquifers (Bakalowicz
This article is a part of Topical Collection in Environmental Earth
Sciences on Characterization, Modeling, and Remediation of Karst
in a Changing Environment, guest edited by Zexuan Xu, Nicolas
Massei, Ingrid Padilla, Andrew Hartmann, and Bill Hu.
Electronic supplementary material The online version of this
article (https :// 5-019-8611-7) contains
supplementary material, which is available to authorized users.
* Ingrid Y. Padilla
1 Department ofCivil Engineering andSurveying, University
ofPuerto Rico, PO Box9000, Mayagüez, PR00681, USA
2 Department ofAgroenvironmental Sciences, University
ofPuerto Rico, Mayagüez, PR00681, USA
3 Department ofElectrical andComputer Engineering,
Northeastern University, Boston, MA02115, USA
4 Department ofCivil andEnvironmental Engineering,
Northeastern University, Boston, MA02115, USA
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... tion water needs (Ford and Williams, 2007;Butscher and Huggenberger, 2009;Torres et al., 2019). In the United States, karst aquifers underlie 20% of the continent and provide over 40% of the groundwater used for drinking water purposes (Veni et al., 2001;Green et al., 2006). ...
... The karst aquifer system of northern Puerto Rico (KA-NPR) comprises 19% of the island and contains the most extensive and productive aquifers of the island (Padilla et al., 2011;Maihemuti et al., 2015;Torres et al., 2019). The area of study (Figure 1(a)) is located in the KA-NPR between the municipalities from Arecibo to Toa Baja. ...
... It outcrops to the south of the upper aquifer, where it is recharged. There is a direct connection between the upper and lower aquifers along the outcrop of the confining unit, allowing groundwater flow from the unconfined part of the lower aquifer into the upper aquifer (Torres-González et al., 1996;Torres et al., 2019). ...
... The weighted overlay tool in ArcGIS was employed for this purpose. The percent of influence for each thematic layer was, as in the case of the parameter weights, based on those found in the literature Da Costa et al., 2019;Andualem and Demeke, 2019) and were modified to consider local hydrogeological factors and field conditions of the study area (Torres-Gonzalez, 1985;Torres et al., 2018;Torres et al., 2019). The percent influence for each thematic layer is provided in Table 2. ...
Full-text available
The clastic sediments that accumulate in cave settings can be an important storage reservoir for organic carbon, affect contaminant fate and transport, and contribute to ecosystem processes. This study reports on grain size, total organic carbon (TOC) concentrations, and total organic carbon:total organic nitrogen (TOC:TON) ratios measured in sediments from two caves in Puerto Rico. El Tallonal Cave (TAL) is a small cave with a flowing stream; the sediments from TAL were collected from a deposit that is being actively eroded. Cueva Cave (CAM) is an upper level of the Río Camuy Cave System; the sediments from CAM were newly deposited by an internal river that rose in response to Hurricane Maria. Sediments collected from both caves were poorly sorted and contained no apparent stratigraphic correlation. CAM sediments contained a larger range in TOC concentrations but were overall lower than TOC in the TAL sediments. In TAL, the TOC concentrations were higher in sediments collected from below the usual water level. TOC:TON ratios from sediments at both caves were highly variable, highlighting the heterogeneous deposition and storage of organic matter. Despite the observed variation, TOC concentrations in both cave systems cause retardation of organic contaminants by up to two orders-of-magnitude, implying that deposited sediments influence the fate of organic contaminants in the groundwater; therefore, cave sediments could facilitate long term storage of organic carbon and associated contaminants.
Full-text available
It is well known that the same characteristics that make karst groundwater systems highly productive make them very vulnerable to contamination. Once in the subsurface, many contaminants move along and spread across flow lines, interact with media and environmental compartments, and react with chemical and biological entities. All of these processes occur within a highly dynamic and heterogeneous framework that affects the mobility, persistence, and potential exposure of humans and wildlife. Fundamental knowledge exists on many of these processes, and several predictive and characterization models have been developed and applied to karst systems. Yet tremendous challenges and uncertainty are faced when trying to predict exposure, implement remedial actions, and manage contaminated systems, particularly in a changing world. This paper discusses the state of knowledge, modeling capabilities, and sources of uncertainty when assessing the fate, transport, and exposure of legacy and emerging contaminants in karst systems. Although applicable to many sites, the discussion is framed around particular examples of extensive contamination in the karst region of northern Puerto Rico, and how these compare to more densely lithified karst systems associated with continental karst. It focuses on contaminants related to industrial, agricultural, and personal care activities. Despite the advancements made on understanding and modeling fate and transport processes, large uncertainty remains on source and system characteristics, scale-dependent model applicability, spatiotemporal data resolution, and the effect of hydrologic conditions and anthropogenic intervention.
Full-text available
Subsurface investigations of contaminated karst aquifers are generally regarded as extremely difficult. The difficulty not only is partly a result of the significant heterogeneity and anisotropy created by the existence of open and plugged ramiform conduit systems, but is also a result of the existence of an overlying epikarst. Even more intractable is the effective remediation of contaminated karst aquifers for basically the same reasons. The difficulties associated with investigating and remediating karst aquifers are further exacerbated when situated in areas with complex folding and faulting of strata. Couple the specifics of various contaminant types of varying degrees of reactivities, densities, and miscibilities (e.g., VOCs, LNAPLs, DNAPLs) with the complexities typical of karst terranes and the limitations of comprehensive karst investigations and effective remediation techniques quickly become evident. Typical remediation techniques, such as pump-and-treat operations, in situ thermal treatments, in situ chemical oxidation, bioremediation, and monitored natural attenuation all exhibit significantly reduced performances relative to other types of aquifers. Partially in recognition of the challenges associated with specific contaminant types and groundwater investigations and remediation techniques when applied to contaminated karst terranes the U.S. EPA developed the concept of a TI (Technical Impracticability) waiver in which remediation below MCLs (maximum contaminant levels) may not be required. Very few TI waivers have ever been issued, however, and obtaining a TI waiver is quite formidable. Remediation down to MCLs is a desirable goal, but the vagaries of karst terranes fully justify the concept of a TI waiver at some complex sites.
Conference Paper
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The northern karst region of Puerto Rico has a long and extensive history of toxic spills, chemical waste, and industrial solvent release into the subsurface. High potential for exposure in the region has prompted aggressive remediation measures, which have extended for over 40 years. Of particular concern is contamination with chlorinated volatile organic compounds (CVOCs) because of their ubiquitous presence and potential health impacts. This work evaluates historical groundwater quality data to assess the spatiotemporal distribution of CVOC contamination in the karst aquifer system of northern Puerto Rico, and its response to remedial action in two superfund sites contaminated with CVOCs. Historical data collected from different information sources with different monitoring objectives is evaluated spatially and temporally using Geographic Information System (GIS) and statistical analysis. The analysis shows a significant extent of contamination that comes from multiple sources and spreads beyond the demarked sources of pollution. CVOCs are detected in 65% of all samples and 78% of all sampled wells. Groundwater shows continued level of contamination over long periods of time, demonstrating a strong capacity of the karst groundwater system to store and slowly release contamination. Trichloroethene and Tetrachloroethene are the most frequently found, although other CVOCs (e.g., Trichloromethane, Dichloromethane, Carbon Tetrachloride) are detected as well. The spatial and temporal distributions of CVOCs seem to be highly dependent upon the monitoring scheme and objectives, indicating that the data does not adequately capture the contamination plumes. Targeted remedial action using pump and treat (air stripping) and soil vapor extraction in two superfund sites has reduced concentrations over time, but the spatial and temporal extent of the contamination reflect inability to completely capture the heterogeneous plumes.
Full-text available
Bioremediation strategies, including bioaugmentation with chlorinated ethene-degrading enrichment cultures, have been successfully applied in the cleanup of subsurface environments contaminated with tetrachloroethene (PCE) and/or trichloroethene (TCE). However, these compounds are frequently found in the environment as components of mixtures that may also contain chlorinated ethanes and methanes. Under these conditions, the implementation of bioremediation may be complicated by inhibition effects, particularly when multiple dehalorespirers are present. We investigated the ability of the 1,1,2,2-tetrachloroethane (TeCA)-dechlorinating culture WBC-2 to biotransform TeCA alone, or a mixture of TeCA plus PCE and carbon tetrachloride (CT), in microcosms. The microcosms contained electron donors provided to biostimulate the added culture and sediment collected from a wetland where numerous "hotspots" of contamination with chlorinated solvent mixtures exist. The dominant TeCA biodegradation mechanism mediated by the WBC-2 culture in the microcosms was different in the presence of these wetland sediments than in the sediment-free enrichment culture or in previous WBC-2 bioaugmented microcosms and column tests conducted with wetland sediment collected at nearby sites. The co-contaminants and their daughter products also inhibited TeCA biodegradation by WBC-2. These results highlight the need to conduct biodegradability assays at new sites, particularly when multiple contaminants and dehalorespiring populations are present.
In this paper, we present the use of Principal Component Analysis and customized software, to accelerate the spectral analysis of biological samples. The work is part of the mission of the National Institute of Environmental Health Sciences sponsored Puerto Rico Testsite for Exploring Contamination Threats Center, establishing linkages between environmental pollutants and preterm birth. This paper provides an overview of the data repository developed for the Center, and presents a use case analysis of biological sample data maintained in the database system.
The Great Lakes Basin (GLB) holds vast reserves of groundwater, the great majority of which eventually drains to the lakes. Urban growth significantly affects both the quality and quantity of this groundwater and thereby represents a potential threat to the long-term viability of the Great Lakes hydrologic system. Urban areas import, manufacture, store, transport, and utilise large volumes of chemicals, a proportion of which inevitably finds its way to the shallow sub-surface. In many cases, potentially polluting chemicals are applied directly to urban surfaces (e.g. as road salts, fertilizers and pesticides), are stored in the subsurface (e.g. gasoline tanks) or are released to the subsurface (e.g. septic systems). Because most of the basin's larger urban areas rely almost exclusively on lake-based supplies, very little attention is given to the accumulation of contaminants in shallow urban groundwaters and the serious risks they pose. Assessment of the problem is complicated by the widespread use of urban fill and a complex network of drains, pipes and tunnels that create "urban karst", a shallow artificial aquifer, unique to urban settings, that exerts a major, yet often unpredictable influence on groundwater flow and contaminant transport. Management of ground water pollution, and its impact on the receiving Great Lakes, will require rigorous audits of all urban sources of contamination together with the development and calibration of groundwater flow and transport models that will enable the fate of urban pollutants to be reliably predicted even when groundwater is not used for supply.
Karst aquifers differ from aquifers in porous media by the highly diverse pathways by which water and any associated contaminants travel from recharge to discharge. The effective hydraulic conductivities may vary by 10–12 orders of magnitude between alternate pathways through the same aquifer. There are three distinct contributions to the permeability: a system of pipe-like conduits with varying degrees of development and integration, a system of disolutionally modified fractures, and the primary permeability of the rock matrix. For any given aquifer, hydraulics and response to contamination inputs depend on the sources of recharge, the specific mix of permeability components, and the physical properties of the contaminants—in effect a matrix of interactions. Categories of contaminants include water-soluble compounds, both organic and inorganic, low-solubility liquids, both heavier and lighter than water, and particulates, organic and inorganic, ranging in size from nanometers to meters. Inputs are through sinking streams, storm flow into closed depressions, and infiltration through soils that may be thin and discontinuous. Natural discharge is typically through large springs that are frequently used as water supplies. Features that separate karst aquifers from porous media aquifers are large aperture pathways that permit particulate contaminants to enter the aquifer with little filtration, localization of flow paths into conduit systems which constrict contaminant concentrations to narrow pathways instead of spreading into a plume, and high-velocity flows which can move particulates and also transmit contaminants rapidly from point of injection to point of discharge. Storm flows are exceptionally important in the transmission of contaminants. Storm inputs raise the hydraulic head in the conduit system, increase both flow volume and velocity, and can flush both clastic sediments and contaminants that have remained in storage in the conduit system. During base flow, the conduit systems act as drains with hydraulic gradients in the surrounding fracture and matrix pointing to the conduit. During storm flow, increased head in the conduit reverses gradients, forcing contaminated storm water back into the fractures where it may intercept wells. Rising water levels can force the fumes of volatile organics upward to reach sinkholes and basements. Flooded surface streams may reverse the gradients in the master conduit systems and force contaminated surface water deep into the aquifer.
Poorly lithified to unconsolidated carbonate and clastic sedimentary rocks of Tertiary (Oligocene to Pliocene) and Quaternary (Pleistocene to Holocene) age compose the South Coast aquifer and the North Coast limestone aquifer system of Puerto Rico; poorly lithified to unlithified carbonate rocks of late Tertiary (early Miocene to Pliocene) age make up the Kingshill aquifer of St. Croix, U.S. Virgin Islands. The South Coast aquifer, North Coast limestone aquifer system, and Kingshill aquifer are the most areally extensive and function as the major sources of ground water in the U.S. Caribbean Islands Regional Aquifer-System Analysis (CI-RASA) study area. In Puerto Rico's South Coast ground-water province, more than 1,000 meters of clastic and carbonate rocks of Oligocene to Pliocene age infill the South Coast Tertiary Basin. The pattern of lithofacies within this basin appears to have been controlled by changes in base level that were, at times, dominated by tectonic movement (uplift and subsidence), but were also influenced by eustasy. Deposition of the 70-kilometer long and 3- to 8-kilometer wide fan-delta plain that covers much of the South Coast ground-water province occurred largely in response to glacially-induced changes in sea level and climate during the Quaternary period. Tectonic movement played a much less important role during the Quaternary. The North Coast ground-water province of Puerto Rico is underlain by a homoclinal coastal plain wedge of carbonate and siliciclastic rocks that infill the North Coast Tertiary Basin and thicken to more than 1,700 meters. A thin basal siliciclastic sequence of late Oligocene age is overlain by a thick section of mostly carbonate rocks of Oligocene to middle Miocene age. Globigerinid limestone of late Miocene to Pliocene age crops out and lies in the shallow subsurface areas of northwestern Puerto Rico. Oligocene to middle Miocene age rocks tentatively can be divided into five depositional sequences and associated systems tracts; these rocks record carbonate and minor siliciclastic deposition that occurred in response to changes in relative sea level. The Cibao Formation represents the most complex of these sequences and contains a varied facies of carbonate, mixed carbonate-siliciclastic, and siliciclastic rocks that reflect differential uplift, subsidence, and transgression of the sea. Uplift, graben formation, and gradual shallowing of the sea are reflected within the bathyal-dominated sedimentary facies of the Kingshill Limestone in St. Croix, U.S. Virgin Islands. Reef-tract limestone beds of Pliocene age were subject to exposure, resubmergence, and meteoric leaching of aragonitic skeletal debris; these beds contain patchy lenses of dolomite that are restricted to a small, structurally-controlled embayment. The South Coast aquifer, the principal water-bearing unit Puerto unit of Puerto Rico's South Coast ground-water province, consists of boulder- to silt-size detritus formed by large and small coalescing fan deltas of Pleistocene to Holocene age. Deep well data indicates that it is possible to vertically separate and group a highly complex and irregular-bedded detrital sequence that underlies distal parts of the fan-delta plain into discrete water-bearing units if correlated with 30- to 40-meter thick, eustatically-controlled depositional cycles. Lithofacies maps show that greatest hydraulic conductivity within the fan-delta plain is generally associated with proximal fan and midfan areas. Distal and interfan areas are least permeable. Alluvial valley aquifers located in the western part of the South Coast ground-water province are important local sources of water supply and appear to contain some of the same physical and hydraulic characteristics as the South Coast aquifer. Older sedimentary rocks within the basin are poor aquifers; conglomeratic beds are well-cemented, and carbonate beds do not contain well-developed solution features, except locally where the beds are overlain by alluvium. Ground-water occurs under unconfined conditions in proximal and midfan area, Confined conditions within deeper parts of the system and in interfan and some midfan areas are created largely by the intercalated nature of discontinuous fine-grained beds that retard vertical ground-water movement. The development of water resources in southern Puerto Rico has modified the hydrologic system of the South Coast aquifer considerably. Under predevelopment conditions, the South Coast aquifer was recharged in the unconfined, proximal fan and some midfan areas by infrequent rainfall and seepage from streams near the fan apex. Discharge occured as seabed seepage, baseflow wetlands, or evapotranspiration in areas underlain by a shallow water table. Under development condition, seepage from irrigation canals and areal recharge from furrow irrigation represented a principal mechanism for recharge to the aquifer. Increased ground-water withdrawals in the 1960's and 1970's resulted in declines in the water table to below sea level in some places and intrusion of salt water into the aquifer. By the middle 1980's, a reduction in ground-water withdrawals and a shift from furrow irrigation to drip-irrigation techniques resulted in the recovery of water levels. Under present-day (1986) conditions, regional ground-water flow is coastward but with local movement to some well fields. In addition to the discharge mechanisms described above, ground-water discharges also to coastal canals. The North Coast limestone aquifer system consists of limestone, lesser amounts of dolomite, and minor clastic detritus of Oligocene to Pliocene age that form an unconfined upper aquifer and a confined lower aquifer: these aquifers are separated by a clay, mudstone, and marl confining unit. Topographic relief and incision of carbonate coastal plain rocks by streams are the principal factors controlling the direction of ground-water flow. The North Coast limestone aquifer system is recharged principally by precipitation that enters the upper and lower aquifers where they crop out. Regional ground-water movement from the upper aquifer is to the major rivers, wells, coastal wetlands, coastal, nearshore, and offshore springs, or as seabed seepage. Regional discharge from the lower aquifer is to the major rivers along its unconfined parts or where the confining unit has been breached by streams. Discharge from the lower aquifer also occurs in the San Juan area where the Mucarabones Sand provides an avenue for diffuse upward ground-water flow. Transmissivity within the upper limestone aquifer appears to be largely regulated by the thickness of the freshwater lens. The lens is thickest and transmissivity is greatest in interstream areas that lie in a zone that closely corresponds to the landwardmost extent of the underlying saltwater wedge. Hydraulic conductivity of the upper aquifer generally increases in a coastward direction and reflects lithologic control, karstification in the upper 30 to 100 meters of the section, and enhanced permeability in a zone of freshwater and saltwater mixing. Transmissivity of the lower aquifer is an order of magnitude smaller than that of the upper aquifer: highest transmissivities in the lower aquifer largely correspond to a coarse grainstone-packstone and coral-patch-reef depositional facies contained within the outcropping parts of the Montebello Limestone Member and its subsurface equivalents. Porosity within the North Coast limestone aquifer system is high in grainstone-packstones and low in wackestone and marl. Dolomitized zones and moldic grainstone-packstone strata are the most porous carbonate rocks, but occur in thin beds that usually are only a few meters thick. Processes of karstification that include the development of caverous zones and large vugs, and dissolution along possible regional fracture sets has enhanced permeability within the upper part of the aquifer system. Stratigraphic and lithologic control play an important role controlling permeability within the lower part of the system. The Kingshill aquifer of St. Croix, in large part, is composed of deepwater limestone that contains only microscopic pores and is poorly permeable; however, the upper part of the aquifer, a shallow-water skeletal and reef limestone, is fairly permeable, but restricted in areal extent. Permeability within these uppermost beds of the aquifer has been enhanced by meteoric leaching, dissolution within a mixing zone of saltwater and fresh water, and dolomitization. However, most large-yield wells completed in the Kingshill aquifer are also screened in alluvium that overlies or infills incised channels. The alluvial deposits serve as a temporary storage zone for rainfall, runoff, and ground water slowly entering the Kingshill aquifer.