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Trends In Land Use, Sewage, and Stormwater and Their Relationship With Coastal Water Quality in St. Thomas, U.S. Virgin Islands

Dr. Maci Bortman
February 19, 1998

This research investigated the health of coastal embayments adjacent to urbanized watersheds of a subtropical, Caribbean island by analyzing land use changes, historical water quality monitoring data, and sewage treatment and disposal information, and modeling storm water runoff quantity and quality. The results of this research found both temporal and spatial trends in degraded water quality in coastal embayments where treated sewage is discharged directly to coastal waters. Water quality improved in embayments shortly after sewage discharges ceased; however, physical and environmental changes (i.e., removing mangroves, opening salt ponds, dredging, bottom scouring by vessels), boat sewage, and storm water runoff are currently threatening the health of these coastal waters.

One of the major sources of contaminants degrading water quality was sewage (treated, partially treated, and raw) discharges from municipal sewage treatment plants. All the municipal sewage treatment plants examined in this study were working poorly and records show they have been for years. Most of the sewage treatment plants did not meet secondary treatment levels as required by the federal Clean Water Act. Recent efforts to expand the supply of piped, potable water to new areas served by improperly working sewage treatments plants are further threatening the marine environment. Piped water will likely lead to increased water consumption rather than moderation, because residents will no longer need to rely on limited, stored water supplies in their cisterns. This will lead to further increases in sewage discharged to coastal waters.

Cisterns play an important role in controlling non-point source pollution from increasing urbanization. Modeling results suggest there is no increase in storm water runoff due to development because a significant portion of storm water is diverted to cisterns. However, pollutant concentrations in storm water are predicted to have increased with time due to urbanization resulting in pulses of storm water runoff to coastal waters that are higher in biological oxygen demand, nutrient, and sediment concentrations.

Resorts and condominium complexes, which own and operate unregulated private sewage treatment plants, reuse treated wastewater for irrigation. This may increase human health risks and runoff resulting in non-point pollution to coastal waters. This practice needs to be further examined.

Potable water supply and sewage sanitation should be considered together and developed as a single system. A single water supply - sewage system integrated into a comprehensive land and water use plan that balances growth management with water supply, and adequate treatment and disposal would be considerably more protective of the marine environment than practices in place today.

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Bacterial Indicator Organisms In Cistern Water In The U. S. Virgin Islands

Dr. Robert Ruskin
April 16, 1998

Because cisterns are exposed to the environment via their direct attachment to catchment surfaces, cistern water quality is often poor. In the U.S. Virgin Islands cisterns are involved in supplying the water needs not only for private homes, but hotels, businesses and public housing, making them subject to the mandates of the Federal Safe Drinking Water Act. This study compares the results of the occurrence of various water quality indicators in Private Residential, Public Housing, and Hotel and Guest House cisterns in the U.S. Virgin Islands in a side-by-side analysis. 

Forty-seven separate independent variables were created and tested for correlation, of which only the rate at which chlorination was applied was significant. A high degree of correlation was found to exist between total coliform and fecal coliforms. A moderate, but still significant correlation was found to exist between the coliform heterotrophic levels in the cistern was also noted. There was no correlation between any of the bacterial indicators studied and the opportunistic pathogen Pseudomonas aeruginosa. 

The results show, depending upon the type and amount of chlorination received, different bacterial indicators will predominate and that there is a logical succession from one to the next with chlorination. On the unchlorinated end of the scale, normally associated with private residential homes, there is a correlation between the heterotrophic bacteria and total coliform. On the other end where chlorination is constant, normally associated with public water supply systems, correlation is between total coliform and fecal coliform. The proportion at which these indicators occur is a function of the diligence at which chlorination takes place. Regression analysis showed that the heterophs and total coliform were the most resistant. Thus, what is seen is fecal coliform unmasking based upon chlorination pattern. 

Depending upon whether the cistern is a private or public water supply system which is mandated to be treated, an appropriate indicator system based upon the likelihood of treatment can be suggested. For unchlorinated private residential home cisterns the prime indicator should be the heterotrophic plate count, and for chlorinated systems the take-action organism should be fecal coliform. P.aeruginosa should be tested for in both domestic cistern water supplies and public cistern water supply systems.

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Minimizing The Impact Of El Nino Induced Drought In The Western Pacific

Dr. Leroy F. Heitz P.E.
July 20, 1998

The 1982-83 El Niño, by many measures, is still regarded as the strongest drought-causing event in this century. The 1997-98 El Niño has already exceeded it by measures, and may yet develop into a record-breaking event. The impacts on the Western Pacific included a shortened rainy season, drier than normal conditions in fall of 1997, and strongly suppressed rainfall in the spring of 1998. 

The University of Guam Water and Energy Research Institute (WERI) is involved in a regional effort called the Pacific ENSO Application Center. The roles of the Center include regional research on and predication of El Niño related climate variability, and interpretation of these predictions to provide usable information to regional decision-makers for management of their water resources. 

This presentation will provide a brief introduction to climatic processes that operate in the Pacific Ocean during El Niño. Dr. Heitz will also discuss how the ENSO Application Center helped to minimize the effects of this year's drought. Finally, Dr. Heitz will discuss WERI's Rain Water Catchment System (RWCS) research and outreach programs and their effect on minimizing the impact of drought in the islands in the Western Pacific.

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Alternative Onsite Sewage Disposal Systems In The United States Virgin Islands

Janice D. Hodge and Brian Emerich
October 6, 1998

Disposal of residential sanitary waste is a challenge in many areas of the U.S. Virgin Islands not served by the public sewer system. Conventional septic tank/seepage pit systems are proving to be inadequate due to the shallow soils, steep slopes and also the increasing numbers of these systems. Proper disposal of sewage is critical in the tourism based Virgin Islands economy not only because of public health concerns but also due to the adverse effects of untreated sewage on the pristine marine waters which are a source of both recreation and food. 

The Virgin Islands Department of Planning and Natural Resources and the Water Resources Research Institute at the University of the Virgin Islands have investigated alternative methods of treating sanitary waste for individual residences. Subsurface flow constructed wetlands were installed as pilot systems; these systems have proven to be effective and have the potential for widespread application in areas where environmental constraints are similar to those in the U.S. Virgin Islands.

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St. John Erosion Study - A Work In Progress

Carlos Ramos
December 10, 1998

The island of St. John, US Virgin Islands, is well known for its white sandy beaches and the richness of its marine environment. The high quality of these natural resources were responsible for the establishment of the Virgin Islands National Park in 1956 and its subsequent designation as an international biosphere reserve in 1976. Throughout the years these resources have attracted an ever-increasing number of tourists and new homeowners to the island. Improvements in the infrastructure needed to accommodate the needs of temporary or long-term visitors eventually resulted in environmental stresses that induced a degradation of those same resources that initially attracted them to the island. Of particular interest to residents and local authorities has been the apparent detrimental effects of high upland sediment yield rates into the near shore reef environment.  Previous studies suggest that the unpaved road network on the island is currently the main source of sediment and that the current erosion rates are much higher than those during the plantation era. This study responds to the need for the identification of specific sediment sources responsible for high input rates of terrigenous materials into the near shore zone. 

The field sampling design for this study uses a strategy known as sediment budgeting. Completion of a sediment budget requires measuring sediment production rates from different types of eroding surfaces, and a quantitative evaluation of sediment transport rates at different scales through the fluvial system. Sediment production measurements are being taken at the plot scale from both natural hill slopes and from the different components of the road prism (i.e. fill-slopes, cut-slopes, and road tread), while sediment transport rates through the fluvial system are being measured at both sub-catchment and watershed scales. 

Among the wide variety of techniques that are being used to complete this analysis, we should mention the following: use of bounded plots with catchment basins to measure sediment production rates from undisturbed hill slopes; placement of sediment traps to collect sediment from different road surfaces; installation of suspended-sediment sampling and runoff measuring stations to quantify runoff and sediment transport rates at both plot and watershed scales; volumetric analysis of erosional features on road surfaces; and detailed mapping of morphological features in the fluvial system. The erosion and sediment transport measurement effort is complimented by precipitation data collected by a network of recording rain gauges located throughout the island. 

Data collected during the 1998 and 1999 field seasons will be used to develop an empirical model that predicts sediment transport rates for several watersheds in St. John. This erosion and sediment yield model will be set up in a GIS environment that will allow analysts to identify both the most important sediment sources already existing in a watershed and the most sensitive areas where land disturbance should be minimized or avoided to prevent future high sediment yield rates.

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Tropical Microbiota And Its Influence On Water Quality

Dr. Gary Toranzos
March 19, 1999

For the last 100 years two groups of bacteria have been used as indicators of water quality all over the world. The Total Coliform and the Fecal Coliform groups are now part of the water quality guidelines used by the World Health Organization and virtually every single country in the world. However, as more data have become available, it has been shown that these two groups of bacteria are part of the indigenous environmental microbiota, especially in tropical countries. As a result, new indicators need to be developed. Nevertheless, under certain circumstances these indicators are still useful. 

The indigenous microbiota in tropical areas of the world present special problems, since the current indicator system was developed in temperate areas of the world. Little is known about the microbiota of tropical areas. Studies in Puerto Rico, Hawaii and other tropical areas of the world, as well as in sub-tropical areas, indicate that a new set of indicators needs to be developed. Bacterial viruses seem to be the most appropriate at the present time, but the system still needs to be evaluated thoroughly. More studies are needed to determine if members of the tropical microbiota, other than the coliform and "fecal" coliform group, interfere with the analysis of water quality.

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US Geological Survey Activities in the US Virgin Islands

October 5, 1999 

USGS Data Collection Program in Puerto Rico and the US Virgin Islands

 Pedro L. Diaz 

The USGS maintains and operates a data collection network throughout Puerto Rico and the US Virgin Islands in cooperation with local government agencies. The network consists of 125 hydrologic data collection sites that include streamflow, lake-stage, rainfall, and meteorological stations. Data collected at these stations are transmitted to a geostationary satellite, which in turn transmit the information to a receiving station in San Juan, Puerto Rico. The received data are interpreted by computer, and the data are made available to cooperating agencies. The stage and streamflow data are also made available to the general public on the World Wide Web at http://pr.water.usgs.gov and http://vi.water.usgs.gov. The transmitted data serves as a real-time hazard alert network and it has proven useful to government agencies during storms and floods. 

U.S. Virgin Islands Ground-Water Program

Sigfredo Torres-Gonzalez

The U.S. Geological Survey, (USGS) has more than 40 ground-water investigation publications available for the U.S. Virgin Islands. Information available from the USGS includes ground-water quality data (anions, cations, some metals), and piezometric levels form the aquifers. The presence of the USGS in these islands is essential in documenting the hydrologic and hydrogeologic conditions for different water-use schemes and for understanding ground-water flow and magnitude in the important aquifers, particularly the Kingshill Aquifer in St. Croix. Of particular concern are the issues of saline-water intrusion in coastal aquifers, the impact of land-use changes and practices on protected catchment areas of wells, and the impact of surface-water discharges on the coastal marine environment.

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Appropriate Recreational Water Quality Standards for Hawaii and Other Tropical Regions Based on Concentrations of Clostridium perfringens

Dr. Roger Fujioka
November 12, 1999

Historically, concentrations of fecal bacterial indicators such as total coliform (TC), fecal coliform (FC), E. coli (EC) and enterococci (EN) have been used to establish recreational water quality standards in the United States. In using these fecal indicators to assess the hygienic quality of environmental waters, it is assumed that the sources of these indicator bacteria is feces of humans or animals, that there are no major environmental sources of these bacteria, and that these fecal indicator bacteria do not multiply in the environment. 

We have documented that all of the U.S. Environmental Protection Agency recommended fecal indicators (TC, FC, EC, and EN) of water quality are naturally present in high concentrations in the environment of Hawaii (streams, soil) and that these bacteria are multiplying in the soil environment. We have thus concluded that these fecal indicators are unreliable indicators of fecal contamination and should not be used to determine the hygienic quality of water in Hawaii. 

In contrast, Clostridium perfringens is a reliable indicator of fecal contamination in Hawaii because (1) it is an anaerobic bacteria and therefore is not able to multiply in the aerobic environment; (2) it forms spores whose survival characteristics to disinfection and to environmental conditions (sunlight, marine waters) approximate that of pathogens (enteric viruses); (3) it is consistently present in humans and in sewage but not in bird feces, which have been acknowledged to be a primary source of fecal contamination of all environments ; (4) it does not have significant environment sources (streams, soil) in Hawaii; and (5) it can be reliably and easily enumerated using a membrane filtration method. Thus, C. perfringens should be used to establish recreational water quality standards in Hawaii and other tropical islands.

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The Effects of Land Development on a Coral Reef Community

December 20, 1999

Monitoring the Effects of Coastal Development on the Near-shore Reef Environment

Dr. Richard S. Nemeth

Clearing of land for development has been identified as one of the major contributors to reef decline. Disturbance of stable top soils greatly increases erosion during heavy rainfall and subsequent runoff to the sea is often heavily laden with fine sediments that are harmful to corals and other reef organisms. 

This study has documented rates of sedimentation, water quality and changes in the coral reef community at Caret Bay, St. Thomas USVI before, during and after construction of condominiums. Five permanent transects were established perpendicular to shore and represented a range of potential impact. Monthly surveys were conducted by divers using randomly placed 1 m² quadrats along transects. 

Sediment load and water were related to rainfall.  During the fall of 1997, an unusually heavy rainfall (6’’ in 48 hours) caused considerable sediment to enter the sea. Immediately following this event, we observed signs of stress on the corals, evident as loss of pigment. Most of the corals that lost pigment, however, recovered after several months. Results to date indicate a stable coral community with seasonal trends in encrusting gorgonians sponges, and macro algae. The strict sediment control measure and the relatively exposed coastline at Caret Bay probably contributed to minimizing the effects of sediment on the reef community. 

This study provides evidence that coral reef monitoring and assessment are essential in recording the relative impact of development on a site by site basis and that these data will assist in managing and mitigating future development.

Caret Bay Villas - Sediment Control

William F. McComb

Caret Bay Villas is a fourteen-unit condominium project on 4.74 acres of land located on the north central coast of St. Thomas, US Virgin Islands. The land is steep, 40 to 60%, and the soil is rocky, overlain with a layer of dark brown clay loam. The parcel of land is along the shore with a steep cliff extending inland up to 100' feet from the shoreline. The project was started in mid-August 1997 and substantially completed in March 1999, a period of 18 months. 

Caret Bay Villas was developed by Maier & Martschitsch, Inc. a Virgin Islands registered company whose principal is from Austria. The earth and site work contractor was S & S Services and the general contractor was Zenith Development Corp., both from St. Thomas. The project design engineer for all site work, erosion & sediment control and building engineering design was W. F. McComb Engineering, P.C. of St. Thomas. 

The Project had extensive erosion and sedimentation controls including final landscaping as the developer had to protect the cliff line and nearby marine environment. A key element was that there was a part-time on-site engineer who could oversee not only the earthwork, but also erosion and sediment control. An extensive monitoring program was developed and conducted by E.C.C. at U.V.I.

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