Rosenberg Nathan CE 70 Site Assessment Tutu Well field The 108 acre Tutu Well field site, in a mountainous area of eastern central St. Thomas, U.S. Virgin Islands, consists of groundwater contamination from both known and unknown sources. In July 1987, residents began noticing a strong petroleum odor in the Tillet well, one of several commercially owned supply wells in the area. At that time, the well was used as a public drinking water source throughout the island. The Virgin Islands Department of Planning and Natural Resources (VIDPNR) requested that the U.S. Environmental Protection Agency (EPA) test the Tillet well and a few other wells in the area. Beginning in July and continuing through September of 1987 the EPA sampled approximately 24 wells and 123 cisterns [1]. Volatile and chlorinated hydrocarbons including benzene, toluene, 1,2-trans-dichloroethene (DCE), trichloroethene (TCE), and tetrachloroethene (PCE) were found in several of the wells [1]. The different types of wells included institutional wells, public supply wells, commercial wells, and private domestic wells. VIDPNR immediately issued an Administrative Order of Consent to the Tutu Texaco Service Station in order to investigate petroleum release from their underground storage tanks. Texaco was also ordered to stop all work which could further disturb the potentially contaminated area. In 1987, Esso Tutu Car Care Center was also issued a similar Administrative Order. On February 19, 1992, the Tutu Environmental Investigation Committee (comprised of Texaco Caribbean Inc. and Esso Virgin Island, Inc.) signed an agreement with EPA to perform a Remedial Investigation/Feasibility Study (RI/FS) at the Tutu Well field site [1]. The Tutu Well field site was proposed to
EPA's National Priorities List (NPL) in February 1992. The NPL is the federal list of hazardous waste sites that are able to receive Superfund cleanup dollars. In June 1993, EPA identified 9 Potentially Responsible Parties: 1. Tutu Texaco Service Station
The Tutu Texaco service station has been in operation since 1964 selling gasoline and diesel fuel and servicing automobiles. It is located north of the Tillett well on Highway 38. This facility contributed to groundwater contamination through both unleaded and leaded gasoline underground storage tanks (UST's). Three 4,000 gallon gasoline UST's were taken out of service in 1980 due to suspected leaks and integrity test failure. Those three tanks were removed in September 1988. Large and small holes were discovered in the tanks during the investigation. Strong odors of petroleum hydrocarbons and air readings above background were detected during the excavation [1].
2. Esso Tutu Service Station
The Esso Tutu car care center has been in operation since 1970 selling gasoline and servicing automobiles. It is located southwest of the Tillett well on Highway 438. This facility has contributed to the groundwater contamination through both leaded and unleaded gasoline UST's. In 1987, a leak test indicated that the integrity of the unleaded gasoline UST was questionable. In June 1989, multiple UST's were removed from the property. Slight odors of petroleum, oily sheens in the excavation pit, and readings above background levels were detected during the tank removals [1].
3. Ramsay Motor Company
This facility contributed to the Tutu well field contamination through a leaking UST and multiple leaking 55-gallon drums. During a 1989 site visit, it was observed that the drums were not properly contained and small amounts of oil appeared to be leaking. Oil stains and pools were seen on the property. In addition to waste oil, antifreeze, and a large variety of solvent-based auto flushes, degreasers, cleaners, and lubricants were also used at the facility. The hazardous materials found in those products included xylene, naphtha, ethoxylated nonyl phenol, propane, butyl cellosolve, 1,1,1-trichloroethane, PCE, petroleum distillates, and ethylene glycol. Samples collected in August 1987, September 1988, June 1989, and July 1989 indicated contamination by volatile organic compounds (VOC's) and semi-volatile organic compounds (SVOC's) [1].
4. Antilles Auto Parts This facility contributed to soil and groundwater contamination via 55-gallon drums and messy house keeping. Vehicle maintenance and repairs have been going on at this facility since 1992 [1].
5. Virgin Island Housing Authority (VIHA) Formerly Tropical Motors (an automobile dealership), the facility contributed to the groundwater contamination through a leaking UST. Records indicate that Hydraulic fluid was stored in the tank. VIHA has used this facility since 1978. In August 1987, waste oil samples collected from a UST were submitted for analysis, and were found to contain Benzene, toluene, ethyl benzene, and xylene [1].
6. Curriculum Center (former LAGA Building) This property was formerly a clothing manufacturing plant (LAGA Textile Company, 1969-1979, and Panex Co., 1979-1982). The facility contributed to the groundwater contamination via abandoned 55-gallon drums and other irresponsible waste disposal practices. During a site visit, it was observed that the abandoned drums were not contained and were scattered in a haphazard manner on the property. These drums were badly corroded or perforated and some were empty. In addition, past operations at the facility include the extensive use of PCE. Upon speaking with the General Manager of TSG Water Inc., Bob Petersen [2], I was told that this company had also "simply poured large amounts of PCE into trenches dug behind the building". Mr. Petersen also told me that he and the EPA had concluded that this company was the largest contributor to the spill of VOC's by a large margin. Since 1982, the VI Department of Education has used the facility for a library, warehouse for school supplies, and offices [1].
7. O'Henry Cleaners O'Henry Dry Cleaners has been operation since 1962. This facility contributed to the Tutu contamination through a leaching pit, a sump holding tank, a raw material (PCE) storage area, above-ground fuel tanks, drains, discharges for steam condensate from the presses and the clothes dryer, and 5-gallon containers of spent PCE residue or filters. Not much is known about the containment of these waste units, but PCE spills have reportedly occurred. Other products used on-site include dry cleaning fluids such as 2butoxyethanol, hexylene glycol, hydrofluoric acid, degreasers, unspecified volatile solvents, and dye strippers. In September 1988, PCE was detected in a soil sample
collected and submitted for analysis. In June 1989, three surface soil samples collected and submitted for analysis indicated the presence of TCE and PCE.
8. Tillet Gardens This facility contributed to groundwater contamination through leaking paint containers, a raw material storage area, floor drains, and evaporation pit. In November 1987, a soil gas survey (used to determine the amount of VOC's present in soil) detected hydrocarbons, including PCE, trichloroethane, and TCE in the Tillet Garden area. In September 1988, one soil sample was collected and submitted for analysis and xylene was detected at a low estimated concentration.
9. Western Auto
The Western Auto store operated in the Four Wind Plaza from the late 1970's until 1995. This facility to contributed the groundwater contamination through a leaking UST containing gasoline.
Demographics There are approximately 11,400 residents within a 1 mile radius of the Tutu well field, giving the contaminants plenty of opportunity to be present in drinking and bathing water. The water in the Tutu well field is pumped for both private and commercial use. Many homeowners have wells which are used for drinking water, and some companies also bottle the water for hotels, supermarkets, and restaurants [1].
The Phase II Remedial Investigation report for this site concluded that there are several distinct plumes of groundwater contamination and several properties which have
contributed to the groundwater contamination within the Tutu Well field NPL site. The Curriculum Center (former Laga Building) and O'Henry Dry Cleaners were identified in the Phase II report as major sources of chlorinated volatile organic compound (VOC's) groundwater contamination. The report also concluded that there is a moderate to high probability that dense nonaqueous phase liquids (DNAPL) are present in the fractured bedrock (the bedrock from which the local wells withdraw water). The presence of DNAPL in the fractured bedrock has since been confirmed.
As a result of this report, the Agency for Toxic Substances and Disease Registry has concluded that the Tutu wellfield poses public health hazard for past and present ingestion of contaminated groundwater [1]. ATDSR has estimated that the threat may have existed for up to 20 years [1]. In addition to risk of ingestion, there is also risk for possible inhalation and dermal exposure to VOC's when using contaminated groundwater inside homes for showering and flushing [1]. In addition to these risks, the presence of DNAPL in the bedrock underlying the well may have resulted in higher concentrations of contaminants.
This is obviously a complex site, with many different contaminants. However, the large percentage of contaminants on this site can be classified as either semi-volatile organic compounds (SVOC's) or as volatile organic compounds (VOC's). SVOC's and VOC's can often be treated in tandem because of their similar properties and chemical makeup. Often treatments for these contaminants take advantage of the fact that these chemicals volatilize (become airborne) rather easily when exposed to air or heated. Two
such treatments are air stripping and soil vapor extraction, both of which expose contaminants to air and then capture the contaminated air.
Air Stripping
This schematic of an air stripper shows how these machines utilize the volatility of VOC's by forcing high pressure air through the contaminated water, causing the contaminant to volatilize, bond to the air, and then rise to the surface of the water. Once there, the air is sucked out of the air stripper and is then either released to the atmosphere (if the concentrations are very low), or is forced through carbon filter, which removes contaminants most contaminants. After this, if the water is clean, it can be re-injected into the water table. If it is not clean, the water can be run through the machine again.
Air Stripping is relatively inexpensive, and works particularly well when used in tandem with other technologies such as carbon absorption (a carbon filter). For the Tutu site, it is attractive because it can remove 95-98% of VOC's. When used with carbon absorption, the percentage of VOC's removed approaches 99%. However, this site has very high concentrations of manganese, which, when exposed to air, can oxidize on parts of the air stripper and carbon filters, clogging the machinery and decreasing efficiency. Manganese is non-toxic, but will cause fouling, which is essentially buildup of mineral or
biological matter in the air stripper or carbon filter. Mineral fouling often results in biological fouling by promoting growths of bacteria. This fouling forces constant cleaning of the air stripper and frequent replacement of the carbon in the filter. These problems can, however, be solved by pre-treating the water upstream with an anti scalant. This allows the manganese to be removed from the water before it goes through the air stripper and carbon absorption machine. Another large problem on this site is the DNAPL "sinker" that has sunk into the fractured bedrock [2]. DNAPL in fractured bedrock is a very complex problem, with very few good solutions. Over time, by sucking contaminated water from within the plume in the bedrock, the plume's size could be reduced. Again, on speaking with Bob Petersen of TSG Water Inc. [2] , I found out that this was the case, and that the plume had been slowly shrinking over time using a pump and treat system. The water table in the fractured bedrock is not flowing very quickly, however, which meant that the pump and treat system with the air stripper had to be run intermittently [2]. This decreases efficiency and increases costs and time needed. In addition, I found out that drilling the wells into bedrock had been very time consuming and expensive because the bedrock had been extremely dense. So dense in fact, that the drilling company reportedly broke 5 drilling bits in the process of drilling the well [2]. Apparently this bedrock was the most dense that the company had ever dealt with. This poses a very expensive problem, but drilling into the bedrock is the only solution to getting any of a DNAPL plume to come out of fractured bedrock.
This technology is well suited to this site largely because it is so versatile. The cost is relatively low, which allows the PRP's, which are not very large corporations, to pay the cost in full. The cost of drilling the wells, which was very high, may have offset the low cost of the air stripper, but the wells were necessary. The machinery involved is efficient, and does not need very much space to be installed. Air stripping is also one of the best treatments for VOC's, which are the biggest problem in the Tutu well field.
Soil Vapor Extraction
The drawing at right illustrates a typical vapor extraction setup. Tubes with very small perforations are inserted into the ground and connected at the top to a vacuum, which pulls air through the tubes creating a pressure gradient in the soil. This causes VOC's to volatilize and be sucked into the air pump, where they are then treated and the clean air released into the atmosphere. This system needs soil that has low levels of fines and organics, because high levels of these components make airflow through soil more difficult. If air does not flow easily through the soil, the air pump will have to work harder and costs and efficiency levels will decrease.
Due to the fact that the contaminants have leaked into the fractured bedrock in this site, no one treatment will be sufficient to completely treat the Tutu well field. No
technology can, in one sweep, treat both shallow soil contamination and contamination of the water table in deep fractured bedrock. Although Soil vapor extraction is a bit expensive, it is the most efficient way of treating this type of soil with VOC's contamination. Air stripping used in tandem with carbon absorption is very efficient and very cost effective. By using the two treatments described above in tandem, this site is in the process of being efficiently remediated.