Case Studies of 1,4-Dioxane Releases, Treatment, and Drinking Water Contamination - Environmental Investigation and Remediation - page 383

below ground surface (bgs). The carbonate unit is predominantly dolostone with thin beds of sand
and clay and phosphate deposits (Cilek et al., 2004).
The percentage of silt in the shallow Holocene sediments increases with depth, and the sand
grain size decreases from i ne to very i ne. The transition to the undifferentiated Arcadia Formation
occurs at approximately 15-18 ft bgs, where phosphatic sands and pebble-size quartz grains appear.
With increasing depth, there is a gradual increase of phosphatic sand and percentage of clay (nearly
20%). At about 30 ft bgs is a thick clay unit, the Venice Clay, described as a mix of gray to olive-
green clayey sand, tan lime mud, and limestone or dolostone fragments with quartz and phosphatic
sands (Cilek et al., 2004). At approximately 300 ft bgs, the 3000-ft-thick carbonate Floridan aquifer
begins (Campbell and Scott, 1993; Cilek et al., 2004).
The production well nearest the site is an agricultural well located one-quarter mile to the east.
The agricultural water supply well is 805 ft deep and cased to 368 ft bgs (TetraTech, 1997). Most of
the irrigation and potable wells in the Tallevast community are less than 100 ft deep; they are cased
from land surface to between 20 and 30 ft bgs with an open-hole interval to total depth. The majority
of irrigation and potable wells at the site produce from the regional intermediate aquifer system.
Karst conditions are suggested by topographic features in the area, including low-lying marshy
areas and closed depressions; however, no sinkholes are reportedly present within 2 miles of the
site. Groundwater is located approximately 2 ft bgs (TetraTech, 1997). The groundwater hydraulic
high within the suri cial aquifer is near the south-central part of the ABC site, which also represents
the area's topographic high point. Proceeding away from this topographic high, the suri cial aqui-
fer's hydraulic head parallels the slope of decreasing ground surface elevation. Consequently,
groundwater l ows outward from the site, predominantly toward the northwest, north, northeast,
east, and southeast (Cilek et al., 2004).
In a stunning example of an unfortunate coincidence, the hydraulic mounding was later discov-
ered to be caused by a municipal waterline leak at the facility under a concrete slab adjacent to the
former sump location; the sump was the probable source of the contamination described here. The
broken pipe was discharging as much as 70,000 gallons/day, possibly for several years, and was
probably the principal cause of groundwater and contaminants l owing radially outward and away
from the former ABC facility (Arcadis-BBL, 2007a).
8.4.2 S ITE H ISTORY
ABC operated on a 5-acre parcel located near the northeast corner of the Sarasota-Bradenton air-
port. In 1957, a small machine shop called Visioneering opened its factory in Tallevast. In May
1961, Visioneering became the ABC, a subsidiary of Loral Metals Technology, which operated as a
machining and metalworking plant until 1996. ABC was one of the largest precision machiners of
beryllium, a lightweight, toxic metal that can withstand harsh environments. ABC became a con-
tract manufacturer of components for aerospace guidance systems and nuclear reactors. Because
beryllium has a low density and is stronger than steel, it is used by aerospace industry companies.
At ABC, beryllium machine parts were milled, lathed, and drilled into various components.
Components were i nished by electroplating, anodizing, and vapor degreasing and ultrasonic sol-
vent cleaning (Cilek et al., 2004; FDOH, 2007).
Solvent use and wastewater handling are inferred from aerial photographs and from company
records. A 1000-gallon solvent tank was used from 1960 until it was removed in 1986, when it
was replaced with drum storage for solvents. Air permit records show that three portable vapor
degreasers with 10- to 15-gallon methyl chloroform solvent tanks were used at the site. The i rst
degreaser was acquired in the 1960s; the other two in the 1970s. The methyl chloroform was sup-
plied by Ashland Chemical Company and contained 90-95% methyl chloroform and a proprietary
inhibitor package that included 1,4-dioxane (TetraTech, 1997; Ashland Chemical, 1986). All three
methyl chloroform degreasers were replaced in 1988 with ultrasonic cleaners that used Freon
(TetraTech, 1997).