Superfund Explanation of Significant Difference for the Record of Decision Kellog-deering Well Field Norwalk CT


                                    EPA/ESD/RO1-97/164
                                    1997
EPA Superfund
     Explanation of Significant Differences:
     KELLOGG-DEERING WELL FIELD
     EPA ID: CTD980670814
     OU02
     NORWALK, CT
     03/31/1997

-------

                                                       

                  DECLARATION FOR THE EXPLANATION OF
                     SIGNIFICANT DIFFERENCES

SITE NAME AND LOCATION

The Kellogg-Deering Well Field Superfund Site/Second Operable Unit Norwalk, Connecticut.

STATEMENT OF PURPOSE

This decision document sets forth the basis for the determination to issue the attached Explanation of
Significant Differences  (BSD) for the Kellogg-Deering Well Field Superfund Site/Second Operable Unit in
Norwalk, Connecticut.

STATUTORY BASIS FOR ISSUANCE OF ESQ

Section 117(c) of the Comprehensive Environmental Response Compensation and Liability Act  (CERCLA)
reguires that, if any remedial or enforcement action is taken under Section 106 of CERCLA after adoption
of a final remedial action plan, and if such action differs in any significant respects from the final
plan (i.e., scope, performance or cost), the United States Environmental Protection Agency  (EPA) shall
publish an explanation of the significant differences and the reasons such changes were made. Current EPA
guidance (OSWER Directive 9355.3-02) further provides that issuance of an BSD is appropriate where the
Agency determines the need for changes to the Record of Decision (ROD) which are significant but which do
not fundamentally alter the overall remedy. In the present case, because the reguired adjustments to the
ROD do not fundamentally alter the selected remedy for the Site, this BSD is being issued properly.

In accordance with Section 117(d) of CERCLA, this BSD will become part of the Administrative Record which
is available for public review at both the EPA Region I Record Center in Boston, Massachusetts and the
Norwalk Public Library in Norwalk, Connecticut.

DECLARATION

-------
EXPLANATION OF SIGNIFICANT DIFFERENCES
KELLOGG-DEERING SUPERFUND SITE
NORWALK, CONNECTICUT

I. INTRODUCTION

A. Site Name and Location

Site Name: Kellogg-Deering Superfund Site
Site Location: Norwalk, Fairfield County, Connecticut

B. Lead and Support Agencies

Lead Agency United States Environmental Protection Agency (EPA)
Support, Agency: Connecticut Department of Environmental Protection (CT DEP)

C. Legal Authority

Under Section 117(c) of the Comprehensive Environmental Response, Compensation and Liability Act
(CERCLA), 42 U.S.C. ° 9617 (c), Section 300.435(c) of the National Contingency Plan (NCP), 40 C.F.R. °
300.435(c), and EPA guidance (office of Solid Waste and Emergency Response (OSWER) Directive 9355.3-02),
if EPA determines that differences in the remedial action significantly change but do not fundamentally
alter the remedy selected in the Record of Decision (ROD) with respect to scope, performance, or cost,
EPA shall publish an explanation of the significant differences between the remedial action being
undertaken and the remedial action set forth in the ROD and the reasons such changes are being made.

D. Summary of Circumstances Necessitating this Explanation of Significant Differences

The September 1989 ROD for the second operable unit of the Kellogg-Deering Superfund Site (Site) included
the implementation of institutional controls to restrict the use of contaminated soil and groundwater at
the Site. Institutional controls have been established to restrict the use of contaminated soils at the
site as described in Section III below. EPA has determined that existing state and local laws and
permitting reguirements related to the use of groundwater are adeguate and reasonable institutional
controls to restrict the use of Site groundwater for private consumption and to ensure the protection of
human health. Therefore, EPA has determined that implementing further institutional controls to restrict
the use of groundwater is unnecessary. This change does not fundamentally alter the remedy selected in
the ROD.

E. Availability of Documents

This BSD and supporting documentation shall become part of the Administrative Record for the Site. The
BSD, supporting documentation for the BSD, and the Administrative Record are available to the public at
the following locations and may be reviewed at the times listed:

U.S. Environmental Protection Agency
Records Center
90 Canal Street
Boston, MA 02114
Weekdays from 10:00 a.m. to 1:00 p.m.,
and from 2:00 p.m. to 5:00 p.m.

Norwalk Public Library
Norwalk, Connecticut
Monday through Thursday from 10:30 a.m. to 8:30 p.m., and
Friday through Saturday from 10:30 a.m. to 5:30 p.m.

-------
II. SUMMARY OF SITE HISTORY, CONTAMINATION PROBLEMS, AND SELECTED REMEDY

A. Site History and Contamination Problems

The Kellogg-Deering well Field Superfund Site is located in Norwalk, Connecticut. The "Site" consists of
an approximately 10-acre municipal well field (the Kellogg-Deering Well Field) and adjacent areas that
contribute to the well field contamination. The well field portion of the Site is located along the
western tank of the Norwalk River in southwestern Fairfield County which is bordered on the east by the
Norwalk River and Route 7, on the north by residences along Broad-Street, on the west by residences along
Lakeview Avenue, and on the south both by wooded acreage and residences in the vicinity of East Lakeview
Drive and Nutmeg Place.

The site also includes light industrial and residential areas on the east side of the Norwalk River and
Route 7 highway. The 100 year floodplain of the Norwalk River encompasses the Kellogg-Deering Well Field
and low-lying bands along the banks of both sides of the river, including portions of the site.

The Kellogg-Deering Well Field (the "Well Field"), which is owned and operated by the Norwalk First
Taxing District (NFTD) Water Department, consists of four municipal water supply wells that supply
approximately 10 percent of the water for the 80,000 residents in the city of Norwalk. The water supply
wells are located in an aguifer that is classified as GA under the State of Connecticut's Water Quality
Standards. The Connecticut GA classification encompasses the immediate vicinity of the Kellogg-Deering
Well Field and indicates that the Well Field is an existing or potential public drinking water supply. A
more complete description of the Site can be found in Section 1 of the 1989 Supplemental Remedial
Investigation Report (RI).

In 1975 trichloroethene (TCE) was discovered in the groundwater at the Kellogg-Deering Well Field. The
wells with unacceptable concentrations of TCE were shut down until treatment systems were installed by
the NFTD Water Department in 1981. In 1984, the Kellogg-Deering Well Field was placed on the National
Priorities List(NPL) . For the purposes of EPA's study and cleanup, the boundaries of the Kellogg-Deering
Well Field Superfund Site were defined as the well field and all areas of contamination that contribute
to the contamination of the municipal wells.

The initial Remedial Investigation and Feasibility Study (RI/FS) at the Site was conducted between 1984
and 1986. The initial RI/FS supported the first operable unit (OU1) Record of Decision (ROD)issued in
September 1986. This ROD reguired completion of construction and operation of a new air stripping
facility at the Kellogg-Deering Well Field. This well head treatment facility became operational in 1988
and presently removes TCE and other organic compounds (VOCs) from the contaminated groundwater prior to
discharge into a conventional water treatment plant and water distribution system. The treatment was
designed to supply safe, potable water to the public. In May 1988 EPA certified in a letter to the NFTD
that the District had satisfactorily implemented the selected remediation. The first five year review was
completed in December 1992, which documents that the treatment facility continues to operate effectively
and be protective of human health and the environment. Another five review will be conducted later this
year.

A supplemental RI/FS began at the Site in 1987 to provide further information regarding the source(s) and
extent of groundwater contamination at the Site. In addition to better defining the area of groundwater
contamination, found during the initial RI. the supplemental RI also identified a major source area of
groundwater and soil contamination at the Elinco/Pitney Bowes/Matheis Court Complex (the Complex) located
upgradient on Main Street. TCE, tetrachloroethylene (PCE), and 1,2-dichloroethene (1,2-DCE) are the most
pronounced contaminants at the site in terms of their freguency of occurrence and concentrations. The
Complex is considered to be the primary source of soil and groundwater contamination at the Site.

After evaluating the feasible alternatives presented in the FS, the second ROD for the Site was signed in
September 29, 1989. The remedy selected by EPA, included treatment of VOC contaminated soil, and
groundwater at the Complex, and VOC contaminated groundwater in adjacent areas between the Complex and
the railroad known as the Source Remediation Area (SRA). The area of groundwater contamination between
the SRA and the Kellogg-Deering well field is described as the Downgradient Area (see Figure 1).

-------
B. Summary of the Selected Remedy

The 1989 ROD for the second operable unit (OU2) included (1) soil vapor extraction (SVE) to reduce VOC
concentrations in soil at the Complex, (2) extraction, treatment and discharge of groundwater at the SRA,
and (3) institutional controls to restrict soil excavation in areas of soil contamination and to restrict
well installations in areas of groundwater contamination. An integrated treatment system was selected to
aggressively remove VOC's from the groundwater and soil vapor to meet the cleanup levels detailed in the
ROD.

Pre-design activities for the site were completed in June of 1994. The Remedial Design was approved by
EPA in December 1994. EPA approved the Remedial Action (RA) Work Plan on August 3, 1995, thereby
initiating the RA. A detailed accounting of the start-up and construction activities are documented in
the Remedial Construction Report prepared by the PRPs RA contractor, GZA GeoEnvironmental Inc., approved
by EPA with modifications on September 1996.

The final design for the treatment of soil reguired the construction of an SVE system to meet the
following ROD objectives, to minimize further migration of VOC contamination from the soil above the
water table to the groundwater at concentrations that would exceed federal and state drinking water
standards; to reduce the risks associated with potential direct contact with contaminated soils if the
buildings and parking lot were removed; and to prevent contaminants from migrating into the indoor air of
the Complex buildings from underlying soils.

The final design for the treatment of groundwater reguired the construction of a groundwater extraction
and treatment system to meet the following primary objectives described in the ROD: to prevent further
introduction of contaminated groundwater from the SRA to the Downgradient Area west of the railroad
including the Well Field; to reduce the mass of VOCs at the SRA; and, to the extent feasible, to restore
groundwater in the SRA to federal and state drinking water standards. The new recovery system includes
four existing extraction wells at the Complex which were initially installed to comply with a 1987
Consent order issued by the Connecticut Department of Environmental Protection (CT DEP).

The contaminated water and air streams extracted from the Source Remediation Area are transported to a
treatment system at the Complex which includes an air stripper and vapor phase carbon units to remove the
VOCs. The treated water is discharged to the Norwalk River, and the treated air stream is discharged to
the atmosphere. To meet the cleanup objectives, the groundwater extraction and treatment system will
operate for approximately ten to thirty years. It is anticipated that the soil cleanup goals will be
attained in approximately five years.

EPA conducted an inspection of the treatment facility on September 4, 1996 and determined that the system
was constructed in accordance with the remedial design and remedial action plans and specifications. The
treatment system became operational on September 30, 1996.

III. EXPLANATION OF SIGNIFICANT DIFFERENCES

The 1989 ROD reguired that institutional controls be implemented at the Site to reduce the risk of future
ingestion of contaminated groundwater and to prevent excavation of soil at the Complex. While deed
restrictions have been implemented at the Complex to restrict groundwater use and soil excavation, no
deed restrictions have been sought to address groundwater contamination for the remaining properties that
are located within the Site.

Upon re-examination of applicable Connecticut law and the relevant Site conditions, EPA has determined
that additional deed restrictions are not necessary at this time. Currently there are no private water
supplies at the Site and there are no current exposure risks posed by contaminated groundwater to the
public. Moreover, Connecticut law strictly regulates the drilling of water supply wells. Chapter 482 of
the Connecticut General Statutes Annotated (C.G.S.A.) mandates that a well drilling permit must be
obtained before commencing work on any well, and provides that a well permit may not be issued unless the
proposed well site conforms to the state Public Health Code. Any exemptions in the law are not applicable
to properties on this Site. Section 19-13-B-51m of the Connecticut Public Health Code reguires any person

-------
seeking a well permit to demonstrate to the satisfaction of the local Department of Health that the well
site, measured from the boundary of the property, is not within 200 feet of a public, water supply.
Because all Site properties are located within 200 feet of the public water supply system, the Public
Health Code effectively bars the drilling of wells on the Site. Any exceptions in the Public Health Code
that might allow the drilling of wells within 200 feet of the public water supply are not applicable to
conditions at the Site. In addition, the Norwalk Public Health Department has been contacted and is aware
of the diminished water guality at the Site, as well as the applicable state laws and regulations.

EPA believes that the Connecticut statutory and regulatory restrictions described above serve as adequate
constraints on the potential use of groundwater at the Site and that these restrictions will ensure that
the remedy remains protective of human health and the environment. In the event that these state and
local laws and regulations are repealed or significantly revised, EPA will pursue additional measures to
restrict the use of groundwater (i.e., deed restrictions) at the Site. It shall be the responsibility of
the settling parties to bring to EPAs attention any changes in these laws and regulations.

IV. STATUS OF DOWNGRADIENT AREA

The ROD for OU2 addressed soil and groundwater contamination of the SRA only. The Downgradient Area
aguifer was determined to be a separate operable unit which would be addressed at a later date. This
decision was believed to be reasonable for the following reasons: the highest levels of contamination at
the Site are associated with the primary source area; cleanup of the SRA is expected to prevent any
further migration of contaminants from this area into the Downgradient Area; and further evaluation of
the impact of the SRA remediation on the Downgradient Area would confirm whether the Downgradient Area
cleanup will be protective and effective.

The OU2 recovery system has been designed to reduce concentrations of VOCs at the SRA and to prevent
further migration of these contaminants to the Downgradient Area. Pre-Design studies predicted that the
groundwater extraction network should effectively capture the contaminated groundwater within the SRA,
thus preventing the continued migration of contamination to the Downgradient Area.

The treatment system at the OU1 Well Field continues to operate effectively, reducing contaminant
concentrations in the extracted water to federal and state drinking water standards. Since the 1989 OU2
ROD, quarterly groundwater monitoring at new and existing monitoring wells have provided data to track
the migration of the contaminated plume at the Site. Additionally, groundwater data is regularly
collected and analyzed by the NFTD at the OU1  Well Field. While data from the quarterly monitoring
program indicate that groundwater contaminant concentrations in the Downgradient Area have not changed
significantly since the ROD was signed, data collected at the Well Field indicate that concentrations of
VOCs have decreased by approximately one order of magnitude since the treatment system became
operational.

The long-term Operation and Maintenance Plan (O&M) approved for the new SRA treatment system includes a
groundwater monitoring program implemented 1) to evaluate migration of the contaminant plume, 2) to
evaluate the success of the remedy in attaining the cleanup objectives and 3)to confirm that human health
and the environment in the Downgradient Area are being protected. The long-term groundwater monitoring
program at the Site includes wells in the Downgradient Area which will be regularly monitored throughout
the remediation of the SRA. This sampling and analysis program will ensure that the groundwater
extraction and treatment system at the SRA is containing contaminated groundwater at the primary source
area and will allow EPA to monitor the reduction in VOC concentrations within the aquifer over time.
Additionally, five-year reviews for each of OU1 and OU2 will be conducted to ensure that both recovery
systems continue to operate effectively and that Site contaminants do not pose an unacceptable exposure
risk to human health and the environment.

EPA anticipates that operation of the SRA treatment system, combined with natural groundwater flushing
and attenuation processes that are reasonably expected to occur in the subsurface (i.e., dilution,
biodegradation, dispersion, adsorption),  will cause a decrease in groundwater contaminant concentrations
in the downgradient Area over time. While it is reasonable to believe that Downgradient groundwater
conditions will improve significantly over, time, EPA recognizes that it may be technically infeasible to

-------
reduce VOC concentrations in the Site aquifer to concentrations below federal and state drinking water
standards (e.g. MCLS). This is because, as discussed in the Supplemental RI/FS, EPA suspects that dense
non-agueous phase liguids (DNAPL) may exist within fractured bedrock at the source area. DNAPL can act as
a continuing underground source of contamination to the groundwater. EPA also recognizes that there are
documented limitations of the pump and treat technology to attain concentrations as low as MCLs at sites
with fractured bedrock.

Based on the above noted site conditions and the absence of a current human health exposure, EPA believes
that it is unlikely that additional major construction activities at the Site will be needed. However.
the final remedial decision regarding the Downgradient Area will not be made until an evaluation of the
success of the OU2 treatment system in reducing contaminant concentrations in the groundwater at the Site
is performed. If necessary, modifications to the SRA monitoring and remediation system can be made.

V. SUPPORT AGENCY COMMENTS

The State of Connecticut has reviewed the information provided above in Section III regarding
institutional controls at the Site and concurs with the change.

VI. STATUTORY DETERMINATIONS

EPA has determined that the selected remedy specified in the 1989 ROD, with the above-described change,
remains protective of human health and the environment, complies with Federal and State requirements that
are applicable or relevant and appropriate to this remedial action, and is cost-effective. In addition,
the revised remedy utilizes permanent solutions and alternative treatment technologies to the maximum
extent practicable for this Site.

VII. PUBLIC PARTICIPATION

In accordance with Section 117(d) of CERCLA, the BSD and all supporting documentation that is included in
the Administrative Record for the Site is available for public review at the locations and the times
listed above in Section I.E.

-------