Soil Boring Investigation Addendum

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Addendum to Technical Memorandum on Soil Boring Investigation, Well 16 Source Characterization

August 1995

Thirty-four soil borings were drilled and sampled at seven solid waste management units (SWMUs) as part of an ongoing investigation to determine the source of chlorinated hydrocarbon contamination in groundwater near well 16 at Camp Stanley Storage Activity (CSSA). Soil boring locations were based on geophysical surveys. Table 1 summarizes these field activities.

Table 1. Summary of Geophysical Surveys and Drilling Activities

Site ID	Number of Geophysical Anomalies	Initial Number of Soil Borings	Redrill Number of Soil Borings	Initial Number of Soil/Rock Samples	Redrill Number of Soil/Rock Samples	Initial Number of Groundwater Samples	Redrill Number of Groundwater Samples
B-1	0	3	1	10	3	1	0
B-2	5	5	1	17	0	2	0
B-3	3	7	0	22	0	1	0
B-4	6	6	0	17*	0	1	0
B-19	0	3	3	10	9	1	3
B-28	2	6	2	19	6	1	1
O-1	1	4	0	15	0	1	0
* An additional sample was collected and analyzed for asbestos, which was not detected.

Summary of Analytical Results

Soil and groundwater samples were analyzed for volatile organic compounds (VOCs), semivolatile organic compounds 9SVOCs), and metals. Two sets of comparison criteria were used. 30 TAC 335 Subchapter S medium-specific concentrations (MSCs) for soil-air ingestion/inhalation criteria. Groundwater analytical results were compared to the Safe Drinking Water Act maximum contaminant levels (MCLs). MSCs and MCLs are only for comparison and are not intended as recommendations for closure actions. Contaminants of concern included cis- and trans-1,2-dichloroethene (DCE), trichloroethene (TCE), tetrachloroethenen (PCE), cadmium, chromium, nickel, and lead.

Volatile Organic Compounds

Volatile organics were detected in the soil/rock at B-2, B-3, and O-1, but were not detected at B-1, B-4, B-19, or B-28. Table 2 summarizes all analytes detected above comparison levels. Concentrations not in bold font were detected below comparison criteria.

Table 2. Analytes Detected Above Comparison Criteria

SWMU	Sample ID	PCE	TCE	cis-1,2- DCE	Vinyl chloride	Cadmium	Chromium	Lead	Nickel
Soil		(mg/kg)
MSCs: < 2 ft		207	285	108	0.0241	1020	5110	1000	20400
MSCs: > 2 ft		0.5	0.5	70	0.2	0.55	10	67.8	29.4
B-3	B3-SB3 (4-5)	<0.005	<0.002	<0.004	<0.003	1.8 (U)	12	12	9.3
	B3-SB4 (2-4)	<0.005	0.726	0.51	<0.003	47 (U)	760	3600	43
	B3-SB5 (18-19)	0.119	1.5	0.48	<0.003	0.79 (U)	3.4	4.1	7.6
	B3-SB6 (11-16)	2.0	18	2.0	<1.0	<1.0	<1.0	<1.0	N/A
O-1	OX-SB2 (0-2)	46	<0.2	<0.4	<0.3	1.5	320	12	18
O-1	OX-SB2 (0-2) Dup	49	<0.2	<0.4	<0.3	4.8	730	28	73
Water		(ug/L)
MCLs:		0.005	0.005	0.07	0.002	0.005	0.1	0.015	0.1
B-3	B3-SB1 (GW)	0.22	0.38	1.4	0.003	<0.005	<0.01	<0.03	<0.01
B-19	B19-SB2R (GW)	0.007	<0.002	<0.004	<0.003	N/A	N/A	N/A	N/A
N/A = not analyzed

Toluene was detected below MSCs at equivalent depths in three borings located near the B-2 northern trench.

PCE, TCE, cis- and trans-1,2-DCE, and xylenes were detected in soil at B-3. All concentrations detected were below MSCs except for TCE, which was detected above MSCs in three borings.

PCE, toluene and xylenes were detected at the oxidation pond (O-1); only PCE was detected above MSCs in one sample and its duplicate.

Eleven groundwater samples were collected as part of the investigation. VOCs were detected in two samples. PCE, cis-1,2-DCE, TCE, and vinyl chloride were all detected above their respective MCLs in B3-SB1 (GW). PCE was detected above MCL in B19-SB2R (GW) (Table 2).

Metals

Cadmium, chromium, nickel, and/or lead were detected at concentrations above comparison criteria at the investigated sites except B-1 and B-19 (Table 2). Comparison values were based on whether the soil could be easily ingested (0-2 ft) or whether it presented a potential for groundwater contamination (greater than 2 ft). Cadmium and chromium were the only metals detected at depths less than 2 feet that exceeded MSCs. One sample collected from B-2 and the other from O-1.

At depths greater than 2 ft, the four metals were detected above MSCs. Nickel and lead were detected in three samples, two from B-4 and one from B-3. Chromium was detected in two borings at B-3 and cadmium was detected in samples from two borings at B-28 and one at B-4.

Conclusions

	SWMUS B-3 and O-1 have the highest potential as source areas for the well 16 contamination. Perched water at B-3 contained concentrations of those chlorinated hydrocarbons detected in well 16 as well as the biodegradation product vinyl chloride.
	The lateral and vertical extent of contamination at the sites were not determined by this investigation.
	No VOCs were detected in soil/rock samples from B-19. PCE was detected in one of four groundwater samples.
	Eleven of forty-one borings yielded sufficient volumes of perched water to collect analytical samples at six of the SWMUs.
	Lithological information indicated the sites contained numerous small vertical fractures and solution cavities for groundwater to migrate vertically as well as horizontally. Due to these fractures, the extent of perched groundwater may increase during rainfall events and potentially allow contaminants to migrate along the fracture pathways.