SWMU B-4 - Chronology

Year	Month	Action/Results	Action Performed By	Project Number
Unknown	Unknown	Classified documents and other trash burned on the site.	CSSA	NA
1992	October	Reviewed available records at CSSA during preliminary evaluation for groundwater contamination.	Parsons ES	Order 67
1995	February	Performed EM geophysical survey on February 2. Found three geophysical anomalies.	Parsons ES	Order 67
	February	Performed GPR survey on February 15 and 16. GPR profile inferred the location of three separate trenches.	Parsons ES	Order 67
	March	Drilled six soil borings (SB1-5) and (SB1A) between March 10 and 14 and collected soil/rock samples. No VOCs or SVOC were detected. The highest metals concentrations, including lead and copper levels exceeding RRS2 standards, were detected in SB1 which was drilled in a waste trench. Concentrations of cadmium, chromium, copper, lead, and nickel exceeded RRS1 standards in several of the borings. Results are summarized in Table B4-1.	Parsons ES Chemron JEDI	Order 67
	March	Collected groundwater sample from SB5 on March 15. No VOCs or SVOCs detected, and none of the metals concentrations exceeded RRS2 GW standards. Results are summarized in Table B4-2.	Parsons ES Chemron	Order 67
	July	Performed soil gas survey on July 13 and 14. Found PCE at highest concentrations in area which borders the oxidation pond.	Parsons ES	Order 67
	November	Performed second soil gas survey at southeast corner on November 15. Found PCE at concentrations less than 1 ug/L.	Parsons ES	Order 67
2000	April	Twelve soil borings drilled to characterize subsurface soils. Samples were analyzed for VOCs, metals, and explosives.	Parsons	RL83
2001	January – February	Twenty soil gas survey samples were collected and analyzed for chlorinated and aromatic volatile organics. No target compounds were detected.	Parsons	DO 5084
2002	June	Final RCRA Facility Investigation Report submitted recommending excavation of waste and confirmation sampling.	Parsons	RL83
2010	March	Surface soil samples collected at 21 locations. Mercury, barium, and lead were detected at concentrations exceeding residential assessment levels (RALs) and ecological benchmarks.	Weston	NA
	April	A total of 23 test pits were sampled in the four trenches identified by the 1995 geophysical survey. Sample analytes included VOCs, SVOCs, explosives, metal,s and total petroleum hydrocarbons (TPH). Barium, cadmium, copper, lead, mercury, nickel, and zinc were detected at concentrations exceeding RALs in various samples.	Weston	NA
	July	Additional assessment of mercury in surface soil north and northeast of SWMU B-4.	Weston	NA
2011 2012 2013	January - February	Disposal trenches were excavated and confirmation samples were collected from the sidewalls, ends, and floors of the trenches to insure complete removal of affected media. The confirmation results showed that all COCs were removed to residual concentrations less than Tier 1 or Tier 2 PCLs or ecological screening benchmarks. These results are summarized in the Affected Property Assessment Report.	Weston	NA
	May	Additional delineation of mercury identified during the July 2010 sampling event in surface soil north and northeast of SWMU B-4. This area was subsequently separated from SWMU B-4 and was designated as AOC-75.	Parsons	NA
	August	An additional disposal trench was discovered while re-dressing the site access road. Munitions debris and other non-soil debris removed during the January-February 2011 excavation were also separated and classified.	Parsons	NA
	February - March	Continued removal of affected soil and debris from the trench discovered in August 2011. Confirmation samples indicated all contaminant concentrations in excess of Tier 1 or Tier 2 PCLs or ecological screening benchmarks had been removed.	Parsons	NA
	October	Affected Property Assessment Report submitted to TCEQ.	Weston	NA
	February	Closure approved by TCEQ.	TCEQ	NA