PUBLIC HEALTH ASSESSMENT
CRYSTAL CHEMICAL COMPANY SITE
HOUSTON, TEXAS
February 18, 1988
III. ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS
VI. PUBLIC HEALTH IMPLICATIONS
VII. CONCLUSIONS AND RECOMMENDATIONS
Based on the data submitted, surface and subsurface soils and the surface water and groundwater at the Crystal Chemical Company NPL site are contaminated with arsenic. The contamination is both on-site and off-site. Using the 1980 census figures, the population within a one-mile radius of the site is estimated to be 20,000. Known exposure pathways include direct dermal contact, ingestion of contaminated groundwater, surface water and/or surface soils and the inhalation of fugitive dusts. The media of most concern regarding acute and chronic adverse health effects are the surface soil and surface waters. The susceptible receptor populations are children playing in the area, maintenance workers around the site and contractors involved in remediation activities. The recommendations include: (1) issue a health advisory for the site; (2) inform area residents of the potential health threat of the site; (3) restrict access to the contaminated off-site areas; (4) post more warning signs around the site; (5) monitor surface soil post dredging of the flood control channel for additional contamination; (6) perform additional testing of flood channel waters and drainage ditches for contamination; and (7) periodic real-time air monitoring at the worksite periphery because of a possible increase in airborne arsenic during remediation activities.
A. Site Description
Crystal Chemical Company is a 5-acre site located on Westpark Drive in Houston, Texas. The company manufactured several different types of herbicides from 1968 to 1981. The major products were the arsenic based herbicides Mono- and Disodium methanearsenic acid (MSMA and DSMA) and Cacodylic acid (CACO). The area surrounding the site is zoned industrial or commercial. The land on which the site is located is owned by the Southern Pacific Transportation Company and was leased to Crystal Chemical Company.
The site is bordered to the west by Southern Pacific Railroad Easement and then by Houston Flood Control Channel #D124-00-0. The southern border has a railroad easement which separates the site from Security Lumber Company. The property to the east is owned by Southern Pacific and to the north (across Westpark Drive) is Guyon General Piping Inc., and Radnor Alloys. Guyon Alloys has been purchased by Radnor Alloys and shares the same location with Guyon General Piping. Within one-quarter mile to the northwest is the Walnut Bend Apartment Complex.
The main contaminants on-site and off-site are arsenic compounds with lesser amount of phenols. During the late 1970's there were several violations of the Texas Department of Water Resources standards primarily resulting from flooding of the site which the flood waters carrying the contaminants off-site. In addition, spray drift from the spray evaporators located in the process wastewater ponds #1 and #2 contributed to off-site contamination. In September 1981, the day before the U.S. Environmental Protection Agency (EPA) started its immediate removal action at the site, Crystal Chemical Company declared bankruptcy. The site was abandoned, leaving approximately 99,000 gallons of arsenic trioxide (a raw material) in a storage tank and approximately 600,000 gallons of process wastewater in the ponds. During EPA emergency cleanup, the liquid was removed from the ponds and disposed of in a commercial waste disposal facility. The top one-foot of soil was removed, mixed with lime and deposited in the wastewater ponds. A polyethylene cover was placed over the area and that was covered by approximately 6 to 12 inches of clay. The arsenic trioxide was sold, the buildings and equipment were decontaminated and sold, leaving the site vacant except for one small concrete block building, a utility pole, and an electrical service panel. A Remedial Investigation and Feasibility Study (RI/FS) were conducted between May and November 1983 and the report released in January 1984.
B. Site Visit
A site visit was conducted October 21-22, 1987. During the same time, a Southern Pacific Transportation Company contractor, AES was on-site collecting groundwater samples from the monitoring wells, and soil and sediment samples from areas adjacent to the site. In addition, the flood control channel was being dredged and the sediment was spread on the west bank of the channel. Samples were to be taken from the newly exposed sediment from the dredging operation and from the water in the flood control channel. The contractors actually performing the sampling were in level C personal protective equipment. Sampling was to end on October 23 and the results used to prepare a Supplemental Feasibility Study. This new study is expected in 4th quarter 1988.
A walk around the site revealed areas of severe erosion, areas devoid of vegetation, and low lying areas where surface water runoff collected. The site was surrounded by a six-foot high chain link fence topped with three strands of barb wire. There was only one sign posted on-site identifying the site as a hazardous area. However, there were other signs identifying the flood control channel as a hazardous area.
The easily accessible flood control channel bank adjacent to the site was devoid of vegetation and had severe erosion in several places. Earlier sampling results showed this area of the channel bank surficial soil and channel sediment to be contaminated with levels of arsenic exceeding 1000 mg/kg.
At the southwest corner of the site where the railroad tracks split and the spur onto Crystal Chemical property was located, was an area of approximately 750 square feet where surface water runoff collected and remained until it evaporated. This area was easily accessible by walking along the railroad tracks. Earlier sampling results indicated high levels of arsenic contamination (>1000 ppm) in this area. As a result, this area was to be sampled by the contractors. There were other areas within 100 feet that were devoid of vegetation and had experienced severe erosion into other drainage ditches.
The property east of the site was generally overgrown with weeds and scrub-type trees. However, there were areas adjacent to the property line which were bare. The largest such area was near the southeast side of the site, adjacent to the former location of pond #4.
North of the property was Westpark Drive, Radnor Alloys, and Guyon General Piping. There has been commercial development in the vicinity of the site which has led to the widening of Westpark Drive to the west of the site, along with the construction of a new bridge. The road directly in front of the site has not been widened and does not appear to be in use. Earlier sampling of the industrial water supply well at Guyon General Piping showed arsenic levels which exceeded the EPA-drinking water maximum contaminant level (MCL) of 0.05 mg/1 (5). The contractor was to take samples at this well also.
The area inside the fence was not entered because of the level C personal protective equipment requirement. Observations were made from the property line. The cap showed some deterioration near the northwest corner and the black polyethylene liner was clearly visible. This area had slight erosion with the surface water running to the north. The site was clear of structures except a small concrete block building, a utility pole, and a wood panel with several electrical circuit boxes attached.
III. ENVIRONMENTAL CONTAMINATION AND PHYSICAL HAZARDS
The major contamination both on-site and off-site is from arsenical compounds. These compounds consist of MSMA, DSMA, CACO, and trimethyl arsine oxide (TMAO) and may be collectively referred to in this health assessment as arsenic. There were minimal concentrations of phenolic compounds; however, the levels reported do not present a potential health problem.
A. On-site Contamination
Arsenic concentrations in the subsurface soils at the former pond #1 location were the highest on-site. The concentration ranged from 27, 000 mg/kg at a depth of 4 feet to 923 mg/kg at 24 feet. The concentration of arsenic in the other former pond areas ranged from approximately 8500 mg/kg to 2500 mg/kg near the surface and extended vertically to several hundred mg/kg at depths to 15 feet.
The 35-foot sands is a geological formation approximately 35 feet beneath the surface, composed of a silty sand layer 5 to 15 feet thick sandwiched between sandy clay layers. The lower clay layer extends down another 65 feet. Groundwater from the 35-foot sands is contaminated with arsenic up to 600 mg/1. The groundwater is also contaminated in the 100-foot sands at levels of 0.08 mg/1. The 100-foot sands, a silty sand layer, is beneath the 65-foot thick sandy clay layer and has an undetermined thickness.
Areas of highest contamination are located at the former ponds and at the storage areas for raw materials and final products.
B. Off-site Contamination
Arsenic contamination has been found in surficial soil in the immediate areas surrounding the site as well as in the sediment downstream in the flood control channel. Samples taken along the property line show arsenic levels ranging from 200 mg/kg to 8,000 mg/kg. The higher levels can be attributed to the higher on-site concentrations and previous plant operations. Concentrations along the railroad right-of-way adjacent to the arsenic trioxide storage area were the highest with levels between 5,000 and 8,000 mg/kg. There were high levels of arsenic in the flood control channel sediments adjacent to the site with concentrations 1,000 feet downstream exceeding 100 mg/kg. Soil and air monitoring samples taken at the apartment complex and the former Montessori School (currently a day- care center, approximately 1,200 feet south) did not exceed background concentrations.
Groundwater contamination has been found in three off-site industrial wells. Two wells at Houston Shell and Concrete are contaminated with arsenic at levels 0.10 mg/1 and 0.17 mg/1. Houston Shell and Concrete is no longer operating this facility and the wells are out of service. The other well is at Guyon General Piping, which uses the water for industrial washwater. The level in this well is 0.06 mg/1, which exceeds the National Primary Drinking Water Standards.
C. Food Chains
The area around the site is not used for agricultural enterprises and the flood control channel is not large enough to support appreciable quantities of edible aquatic life. However, samples were taken of crawfish and guppies and the results indicated some low arsenic levels. Whole organism analysis of the crawfish indicated concentrations of arsenic up to 3.3 mg/kg. Whole organism analysis of the fish samples also indicated arsenic concentration ranging from 0.75 mg/kg to 0.85 mg/kg. These levels are reported to be within the normal levels for animal tissues (1).
Numerous doves were observed during the site visit. Doves are migratory birds having short residence times in any given area. The hunting regulations strictly govern the length of the hunting season and the number of birds taken per day. If these birds were taken for food, they would not pose a health threat because arsenic intake levels from foraging on and around the site would be limited, arsenic does not biomagnify, the birds do not remain in an area for great lengths of time, and the hunting season is short. In any event, the site is located within the city limits and consequently, in a "no hunting" area.
No edible plants were noticed no-site or around the site. Plant uptake of arsenic depends upon several factors including plant species and the availability of the arsenic for uptake. Depending on plant species, arsenic which is available in the 3 to 30 ppm concentration range may be toxic to the plant. The arsenic level in living plants approaching phytotoxicity levels is usually less than 5 mg/kg on a dry weight basis. Even if there were some edible plants present and living, the levels of arsenic ingested would be of little concern.
D. Physical Hazards
The previously mentioned structures were the only ones present on-site and do not appear to present a hazard.
The site is located in a rapidly growing part of Houston. Within a one-mile radius there are shopping centers, restaurants, apartments, single family housing, commercial offices, and light industrial businesses. There are approximately 8,000 apartment units and 2,500 condominiums in the area, and 9 million square feet of commercial space employing some 65,000 workers (6). In the immediate vicinity there are several vacant lots, as well as some light industrial businesses and the family section of an apartment complex. One apartment complex, Walnut Bend Apartments, has their family section located adjacent to the flood control channel and approximately 1,000 feet northwest of the site. It houses an estimated 100 children ranging from infant to high school age. The complex does not have a designated playground area for the children.
A. Site Characterization
The data package received primarily contained information 4 years old. The latest data received was submitted in July 1986 and consisted of sample results from 4 monitoring wells and a blank sample. Monitoring well #5, just off-site to the north of the entrance to the site, was the only well sampled which showed the presence of contamination. Two samples were taken from well #5 and the concentrations were reported as 412 mg/1 and 434 mg/1. The other monitoring wells, (7, 8 and 13) and the blank were reported as none detected (i.e. <0.01 mg/1).
The number and type (soil, surface water, sediment, etc.) of samples taken during the initial investigation were adequate for characterizing the site at that time. However, more current data would help to determine the extent of migration of the contaminants off-site and any increase in groundwater contamination.
A Data Review Summary was received for the latest sample results (1986), indicating the data for those 6 samples had met the EPA acceptability criteria. There was little quality control data provided in the initial RI/FS. Neither the Case Narrative, prepared by the contractor, nor the Data Review Summary, prepared by the EPA reviewer, were included in the data package. The quality control tables presented in the remedial investigation were incomplete. The tables for phenol were more complete than the tables for arsenic; however, it is the arsenic concentrations that are of the highest public health concern. There was neither indication of the acceptability of the recovery data of the arsenic spikes nor the acceptability of the spiking concentrations. It was difficult to determine if the data quality objectives were met; therefore, it was assumed that the data was of sufficient quality. The conclusions presented in this health assessment are based on the information received. The accuracy of these conclusions accordingly depends on the availability and reliability of the data.
The remedial action alternatives were evaluated with respect to which alternatives would provide protection of public health. A brief summary of the alternatives is in the Appendix. To best protect public health, the removal of contamination from the site is required; however, other remedial alternatives may be acceptable. The level of arsenic remaining should be such that there is no further potential for increase in groundwater contamination and that the current groundwater level be reduced. There is concern for those currently using contaminated groundwater; therefore, consideration should be given to reducing groundwater contaminant levels to below the EPA MCL's, or alternatively, those industries presently using contaminated groundwater should be provided with alternative water supplies. Soil and sediment contamination levels should be reduced to levels that do not increase groundwater and/or surface water concentrations, or in themselves pose a health threat.
B. Environmental Pathways
One of the possible pathways leading to environmental contamination is through surficial soil, which has extremely high levels of arsenic along the property line. The surficial soil is of particular concern since it will not support vegetation in the higher contaminated areas. This allows for easier mobility of the contaminants by other environmental vehicles.
The surface cap along the edges of the site has deteriorated sufficiently to allow surface water from rain events to carry contaminants off-site. The deteriorated cap also allows for water to penetrate the surface and carry contaminants down the underlying aquifers. The runoff also carries contaminants further off-site, to the railroad tracks, flood control channel, and other drainage ditches. Surface water can easily move the contamination (dissolved or adsorbed to soil) further from site because the flow is unhindered by vegetation.
The sediment in the flood control channel was contaminated by surface water runoff from the site. This water brings highly contaminated surficial soil into the channel through the erosion process and also dissolved arsenic through direct contact with the soil. The sediment contributes to contamination downstream by being carried in the current, or allowing some dissolution into the water. During dredging operations, this sediment is spread along the side of the bank it is directly exposed and accessible.
The groundwater is heavily contaminated with arsenic in the shallower zones. This is evidenced by the concentration in monitoring well #5 exceeding 400 mg/1 at a depth of 35 feet. Other industrial wells in the area also have shown past contamination exceeding the EPA MCL for arsenic. These wells are screened at 200- to 250-foot depths.
Wind erosion re-entrainment of dusts is of concern since there are high levels of arsenic in the surficial soils. The re-entrainment can occur through various mechanisms e.g., by dust particles being picked up naturally by the wind, or air currents, vibrations, and mechanical movement created by trains or other machinery operating in the area. One of the more important mechanisms will be through site cleanup, where the equipment performing the excavation may introduce large quantities of particulates into the air.
C. Human Exposure Pathways
The human exposure pathways consistent with the environmental pathways include:
VI. PUBLIC HEALTH IMPLICATIONS
The public health implications resulting from human exposure to arsenical compounds from the Crystal Chemical site (on-site and off-site) will be discussed via exposure to specific environmental media. Phenolic compounds were also prevalent but were at concentrations which would not pose a risk to public health.
A. Soil
1. Surface Soil
Arsenic generally occurs in soil predominantly in an organic, insoluble adsorbed state, and consists primarily of a mixture of the trivalent and pentavalent chemical states (7). The relative toxicity of arsenite is generally greater than that of arsenate (8). Arsenate exists predominantly in aerobic soils and arsenite is primarily observed under an anaerobic state, a state which is not uncommon under temporarily flooded conditions. This chemical parameter is particularly applicable to this site, where soil along the banks of the Flood Control Channel is a primary health concern.
No regulatory standards have been determined for arsenic in soil to date. Background concentrations in soil average 5-6 mg/kg (9) and may reach as high as 40 mg/kg. Ingestion of soil by children (9 months to 5 years of age) is estimated to be approximately 100 mg/day (10) and, consequently, based on this estimate, direct exposure to arsenic via ingestion is estimated at 0.20-200 ug/day.
Of the 49 sampled locations, background concentrations of arsenic (20 mg/kg) were determined at areas further from the site. This level does not itself represent a public health threat. The area presenting a potential public health concern is located immediately adjacent to the site fence line radiating up to 50 feet in all directions. For instance, north, west and south of the site, levels as high and greater than 1000 mg/kg have been determined. Arsenic levels of approximately 200-600 mg/kg have been determined in the easterly direction. These levels represent 5-25 times the maximal background levels. Upon visitation of the site, ATSDR found evidence of mechanical dredging of the Flood Control Channel adjacent to the site, which may significantly increase arsenic exposure via surface soil along the banks.
Susceptible receptor populations of most concern are: (1) children playing in the area (an apartment complex northwest of the site houses approximately 100 children, and no playground or play area is readily available, (2) workers involved in remediation, and (3) trespassers. The primary human exposure pathways presenting a possible health risk are exposure via: (1) ingestion (2) dermal contact, and (3) inhalation. These human exposure routes may result in both acute and chronic adverse health effects.
Acute arsenic poisoning may result in nausea, vomiting, diarrhea, anemia, and cardiac dysfunction in high risk populations. Trivalent arsenic is rapidly absorbed across the stomach into the intestines and into the bloodstream, and subsequently can readily lead to systemic injury. Renal damage may result in hematuria, glycosuria and necrosis (11, 12).
Another clinical manifestation, resulting from chronic oral exposure to arsenic, is liver disease and liver cancer. The induction of portal hypertension and cirrhosis of the liver may result from chronic arsenic exposure (13, 14). Neurological dysfunction is also common after acute and chronic arsenic exposure and may lead to hearing loss and mental retardation in children (15). Systemic effects, as a result of oral exposure, can be observed in humans at levels of 30-300 ug/kg/day (Lowest Observed Adverse Effect Level (LOAEL)). Short-term exposure to maximal surface soil levels along the Flood Channel of this site of greater than 1000 mg/kg may lead to possible systemic effects in small children playing and, subsequently, ingesting soil in the area. Potential skin lesions may also arise (30-200 ug/kg/day) (LOAEL) with chronic oral exposure at the same concentrations. These skin abnormalities may include hyperpigmentation and hyperkeratosis on the palms and soles of the skin and epidemiological studies reveal a dose dependent relationship between arsenic concentrations and skin cancers (15). Another condition, which is observed with endemic arsenism in Taiwan and positively correlated with hyperpigmentation and keratosis, is Blackfoot disease. Blackfoot disease is a peripheral vascular condition which may eventually progress to ulceration and gangrene of the extremities (15, 16). Arsenic may act as a contact allergen leading to local inflammation. Dermal exposure to arsenic at this site would be of particular concern to maintenance workers involved in dredging of the channel. Children playing in the area may also be exposed dermally to newly exposed soil arsenic contaminants. No precise dose estimates are currently available; however, dermal contact may lead to mild to severe dermatitis of the skin. Additional sampling of this medium is presently in progress.
2. Soil Borings
Inorganic arsenic in the form of arsenate is the predominant arsenical species in the soil borings with maximal concentrations on-site as high as 27,300 mg/kg. Off-site contamination was generally low, except at 35-50 sand zones and at shallow depths east and west of the site in areas that receive storm water run-off from the site. The soil borings do not represent a significant health threat to the receptor populations off-site. However, remedial workers would be advised to wear derma1 protective gear and respirators to avoid possible skin dermatitis and mucous membrane irritations of the eye, nose, and throat resulting from remedial activities in handling soil boring particles on site. NIOSH precautions recommends permissible exposure limits in the workplace at a time weighted average (TWA) of 10 ug/m3 (17).
3. Sediment
The sediment may act as a reservoir for arsenic migrating from the surface waters. Fifty-two samples were initially taken of the sediment from the drainage ditches adjacent to the site. Arsenic concentrations up to 1340 mg/kg were determined and would contribute substantially to the surface soil arsenic concentration. Oral and dermal exposure to arsenic along the banks would be a health concern to children and maintenance workers and remedial workers.
B. Water
1. Surface Water
Exposure to arsenic via surface water, adjacent to the site, is another vehicle of concern to human health. Inorganic arsenic is very mobile in water and levels as high as 200 mg/l have been reported in surface water runoff and approximately 1000 mg/l in standing water. Surface water runoff from the site with contamination as high as 100-200 mg/l was collected adjacent to the southwest corner, where the soil arsenic concentrations were 5,000-8,000 mg/kg. The maximum contaminant level (MCL) for arsenic in the drinking water is 50 ug/l. Children playing and splashing in the runoff would facilitate dermal exposure and possible incidental ingestion of levels high enough to present a significant health risk.
2. Groundwater
Arsenic in the groundwater was predominantly organic in form and existed at high levels on the site (500-600 mg/l). This value is substantially higher than the 50 ug/l standard for drinking water. Remedial workers are currently gathering water samples on site and were equipped for Class C exposure. A site visit revealed no evidence of the residential use of domestic private wells immediately off-site. However, nearby industrial use of wells (Guyon General Piping) may indicate possible oral exposure and dermal exposure via safety showers and a washing of the hands. The levels in these wells (60 ug/l) exceed the drinking water standard of 50 ug/l. Groundwater, in general, does not appear to be a primary public health concern to nearby residential areas.
C. Air
The systemic effects, which may result from inhalation, are similar to those resulting from the chronic oral exposure pathway. For instance, EPA and OSHA permissible exposure limit (PEL) regulatory standard for arsenic in air is 10 ug/m3. Mild irritation to the skin, nose, and throat may occur at 100 ug/m3 and hyperkeratosis at approximately 300 ug/m3. Of much greater concern, is the potential for inhalation of arsenic to increase the risk of lung cancer. Non-occupational exposure to arsenic is thought to increase the risk of lung cancer in areas several kilometers away from arsenic emitting smelters (18). ACGIH recommends a TLV-TWA of 0.2 mg/m3 based on human health effects. Most inhaled arsenic is inorganic and is rapidly absorbed across the lungs and into the bloodstream. Initial air monitoring found inorganic arsenic levels at the site substantially below regulatory standards 0.005-0.04 ug/m3. From this study, air does not seem to be a present health concern in regard to arsenic exposure. However, 27,000 mg/kg arsenic concentrations in soil have been determined in the areas of the former shallow ponds. Possible inhalation of inorganic arsenic via particulates in the air would be the medium of concern to public health during future excavation of these contaminated areas. As a result of the reportedly high concentrations of inorganic arsenic detected in soil, fugitive dusts generated from remedial activities may exceed OSHA standards on-site and outside the site periphery. Thus, airborne arsenic should be monitored for potential exceedance of the OSHA (PEL) standard (10 ug/m3).
D. Food Chain
Exposure to arsenic via the food chain at this site does not appear to be a potential health risk.
VI. CONCLUSIONS AND RECOMMENDATIONS
A. Conclusions
The remedial action alternatives were evaluated with respect to which alternatives would provide the best protection of public health. Alternatives B and E-1, (see Appendix), offer the most protection since both alternatives provide for the removal of the contamination from the site. Some of the remaining alternatives (A, D, E-2, or F) may also adequately respond to public health concerns.
In conclusion, we find that the media of most concern, in regard to adverse health effects, are the surface soil and surface waters. The susceptible receptor populations are children playing in the area and workers involved in remediation on-site and off-site via oral, dermal, and inhalation exposure.
B. Recommendations
Environmental Reviewer:
Max M. Howie, Jr.
Environmental Health Specialist
Health Sciences Branch
Health Effects Reviewer:
Cynthia M. Harris, Ph.D.
Toxicologist
Health Sciences Branch
Remediation Alternatives
Alternative A: Construct an on-site landfill vault: excavate all hazardous wastes; place 78,000 cubic yards of waste inside the vault and use an additional 21,000 cubic yards as backfill (if not contaminated); dispose of 63,000 cubic yards of soil from initial excavation at a commercial disposal facility; install a groundwater withdrawal system on- and off-site.
Alternative B: Excavate all hazardous wastes both on-site and off-site, approximately 135,000 cubic yards; dispose of all wastes at a commercial disposal facility; a groundwater withdrawal system on- and off-site; dispose of pumped groundwater at a commercial disposal facility; backfill, grade and revegetate excavated areas.
Alternative C: No action; monitor groundwater; inspect and repair cap.
Alternative D: Excavate Pond #1 to a depth of 20 feet, Pond #2 to 15 feet, and Pond #3 to 10 feet; dispose of excavated wastes from on-site and off-site at a commercial disposal facility; install surface cap; install a slurry trench barrier around the site and the contaminated groundwater off-site; install a pressure relief system within the contained area to prevent the rise of groundwater levels.
Alternative E-1: Excavate all on-site and off-site hazardous wastes (135,000 cubic yards); dispose of at a commercial disposal facility; backfill, grade and revegetate excavated areas; install a slurry wall barrier around the groundwater contamination on-site and off-site; install a pressure relief system to prevent the rise of groundwater within the contained area.
Alternative E-2: Construct an on-site landfill vault; excavate all hazardous wastes; place 78,000 cubic yards in vault and use 21,000 cubic yards for backfill (if not contaminated); on-site and off-site slurry wall barrier around groundwater contamination; dispose of 63,000 cubic yards from initial excavation at a commercial disposal facility; install a pressure relief system to prevent the rise of groundwater within the contained areas (if necessary).
Alternative F: Excavate Pond #l to a depth of 20 feet, Pond #2 to 15 feet and Pond #3 to 10 feet; excavate the remainder of the site to a depth of 7 feet; dispose of excavated wastes at a commercial disposal facility (about 56,000 cubic yards from on-site and about 24,000 cubic yards from off-site); construct a surface cap; install a slurry wall barrier around the site and off-site groundwater contamination; install a pressure relief system to prevent the rise of groundwater into the contained area.
Alternative G: Construct a surface cap; construct a slurry wall barrier around the site and around the area of shallow off-site groundwater contamination; install a pressure relief system to prevent the rise of groundwater within the contained area.
