Background Information for Maps and Tables (Read First)

Many of the maps and tables on this website are from the Draft Remedial Investigation Report, OU-3, WR Grace Superfund Site, Acton, MA, by GeoTrans, Inc. August 30, 2002. The Remedial Investigation Report (“RI”) was produced by WR Grace’s consultant, GeoTrans, in order to comply with federal requirements as part of the EPA “Superfund” process. This “RI” Report is available in the Public Repository at the Acton Memorial Library.

A. MAPS

The WR Grace property, comprises approximately 260 acres, and is located in the southeastern corner of Acton, and part of Concord. It is accessed from Independence Road, off of Parker Street in Acton. (See Map 1- Area map.)

The WR Grace Superfund Site includes all locations on and off the WR Grace property that have been affected by the migration of contaminants from the Grace property. The site therefore extends to the Assabet River in the south, (near Route 62) and beyond Fort Pond Brook to the northeast (near Route 2, and School Street Extension). See plume maps.

Areas on the WR Grace Site that could have been sources of contamination are shown on Map 2 – Source Areas (Figure 1-3, from the RI.) The MBTA rail line, Sinking Pond, and Independence Road can be used as landmarks to help viewers orient themselves. The potential source areas include: the former Primary Lagoon, the former Emergency Lagoon, the capped Industrial Landfill, the former Secondary Lagoon, the former Boiler Lagoon, the former North Lagoon, the former Tank Car area, the former Battery Separator area, the former Blowdown Pit, and the former Neutralization Pit.

The locations of the five public drinking water wells affected by the site are marked on the contaminant plume maps: Assabet 1 and Assabet 2/2A are in the southwestern portion of the site. The three School Street Public Wells/Wellfields: Lawsbrook, Scribner, and Christofferson, are in the northeastern portion of the site. Additional contamination is being drawn to the School Street public drinking water wells due to their pumping.

Plume Maps
The dated plume maps, on this website, show the extent of contamination of groundwater as known at that particular time. VDC (vinylidene chloride, also known as 1,1-dichloroethene or DCE) is the most wide spread contaminant at the site. Additional maps showing cross sections of the VDC, benzene, and vinyl chloride plumes (so that one can see the relative depth of contaminants), can be found in the RI Report by GeoTrans, available in the public repository at the Acton Memorial Library. Figures showing the distribution of high levels of arsenic and other inorganic compounds are also included in the RI (See Figures 3-21 through 3-30).

1984 Map vs. Later Maps: The VDC contamination is depicted on the maps in color contours representing different contaminant concentrations, regardless of depth. Areas that are not colored may be “white” either because the area was never sampled (and there may or may not have been contamination there), or because the area was sampled and no contamination was found at concentrations above drinking water standards. A comparison of the 1984 map to the later maps illustrates this point. The lack of a delineated plume to the northeast in the 1984 map was due to a lack of data, not due to an absence of contamination. Contamination to the northeast was not delineated by WR Grace until after 2000.

Changes in the contaminant plume can be seen when comparing three VDC maps from 2001 and 2002 to each other. (Maps 4, 5, and 6). The apparent movement of the VDC groundwater plume across Fort Pond Brook in the northeast area, most likely reflects more extensive sampling information, rather than an actual migration of contaminants.

According to the 2002 RI Report, contaminant levels have decreased considerably on the southern part of the site since 1984 due to:

  • cessation of contaminant disposal in impoundments,/lagoons
  • the operation of the Aquifer Restoration System, and
  • source removal (soils)

To date there has not been any cleanup on the northeastern portion of the site.

Map Data:

VDC Contamination in Groundwater
Map 3, the 1984 map, depicts data collected by WR Grace before 1984 on the southern part of the site, as well as data collected between 1984 and 1987, by other investigators, on what is now known as the northeastern part of the Site.

Map 4 represents data collected between September 2000 and February 2001. This same plume is shown in the August 2001 EPA Community Update. (Street names and a dashed line depicting the limit of the Private Well Survey Area have been added to the figure.)

Map 5 represents data collected between July 2001 and June 2002. This is the same plume that is depicted in the Aug. 2002 RI Report (See Figure 3-3), and in the December 2002 EPA Community Update (See Figure 1). (Local street locations have been added to the figure.)

Map 6 shows a cross-section of the VDC contamination along a transect extending from the former Blowdown Pit to just past the Scribner Public Wellfield, from the same data set used to create Map 5. This same vertical distribution of the VDC groundwater plume is depicted in the Aug. 2002 RI Report (See Figure 3-5), and in the December 2002 EPA Community Update (See Figure 2). Map 6 allows one to see the relative and varying depths of groundwater contamination in the northeastern part of the site. Note that the contamination is at shallow depths at the blowdown pit which was a source area, and then is mostly deep and within the bedrock under residential areas, but then rises to shallower depths close to Fort Pond Brook, and Scribner, one of the School Street Public Water Supply Wells/Wellfields..

Map 7 represents data collected as part of the annual water quality sampling round between October 14, 2002 and November 12, 2002. A new round of sampling was completed in the Fall of 2003. The 2003 annual water quality data, along with corresponding plume maps should be made publicly available in early 2004.

Other Groundwater Contaminants
Map 8 represents the plume of vinyl chloride contaminated groundwater on the site, mapped using data collected between July 2001 and June 2002. This same plume is depicted in the Aug. 2002 RI Report (See Figure 3-9).

Map 9 represents the plume of benzene contaminated groundwater on the site, mapped using data collected between July 2001 and June 2002. This same plume is depicted in the Aug. 2002 RI Report (See Figure 3-15).

B. TABLES

Table 1. is the Summary of compounds detected in groundwater, August 2000-June 2002 that is found in the Aug. 2002 RI Report (See Table 3-3). This Table lists the VOCs, (volatile organic compounds), SVOCs (semi-volatile organic compounds), and Inorganic Compounds that groundwater was sampled for and the number of detections above a given “Screening Value” (water quality standard that was used as a benchmark).

Thirty VOCs were detected onsite, and 12 of these were detected above their screening value (See asterisks). Twelve SVOCs were detected onsite. Four of these were detected above their screening values. Twenty-three inorganic compounds were detected onsite, and 14 were detected above their screening values. Section 3 of the August 2002 RI Report provides further details and context to explain the significance of these results.

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