Dewatering and Treatment Case Studies
High Flow Dewatering and Excavation
Dewatering and Treatment
High Flow Dewatering and Excavation top
A regional petroleum distributor contracted with Aztech Technologies, Inc.
to oversee a facility reconstruction at one of their gasoline stations and convenient
stores in Westchester County, New York. The site is located in a deltaic sand deposit
near a major surface body of water, and the local groundwater table is tidally influenced.
To facilitate in the reconstruction activities, soil excavation and soil dewatering were
implemented at the site. In order to achieve the goals set forth by the client, Aztech
worked with the general contractor to develop a concise schedule, engineer and build a
portable treatment system to handle the influx and sustained groundwater flow at the site,
oversee the soil excavation and implement insitu chemical oxidation to stimulate the natural
biodegradation of residual petroleum impacts.
During the preliminary stages of the project, Aztech advanced two geotechnical soil
borings to provide information to the general contractor, so that a proper shoring and soil
dewatering system would be emplaced. Aztech used their own truck mounted hollow stem auger-drilling
rig, equipped with soil sampling equipment to drilling the geotechnical soil borings. An
Aztech geologist oversaw the drilling operations and logged the soil cores. Additional soil
borings were also advanced to define the extent of the petroleum impacts onsite. In total
seventeen soil borings were advanced to define the source material soil excavation limits.
Aztech obtained a Stipulation Agreement with the New York State Department of Environmental
Conservation for the treatment and discharge of petroleum impacted groundwater at the site on
behalf of the client. Additionally, Aztech obtained an air discharge permit with the Westchester
County Department of Health for point emissions air discharge.
For the dewatering treatment system, Aztech used the groundwater quality data provided
from routine quarterly monitoring and sampling events and pump-down test data to engineer and
build a trailer mounted portable treatment system. The system was designed to effectively treat
up to 250-gallons per minute using four sediment filters, two air-strippers, and computerized
controls. The treatment system was constructed in 17 days and mobilized to the site for
operations. Aztech provided technicians to operate and maintain the treatment system throughout
the reconstruction activities. Approximately 1.8 million gallons of groundwater were treated
over an eight-week period, with 1.2 million gallons during the first eight days as the site water
table was dropped.
For the soil excavation, handling, and disposal phase of the project, Aztech coordinated
with the general contractor the construction contractor, the client, and the disposal facilities
to progress the project and maintain the milestones and deadlines established by the client.
In total, approximately 3,600 tons of petroleum impacted soil was excavated and treated by thermal
desorption during an eight-week period.
Following the reconstruction activities, Aztech installed seven groundwater monitoring wells
throughout the site. These monitoring wells are currently being used to determine the effectiveness
of the source material excavation in remediating the site groundwater. Aztech has also performed
one insitu chemical oxidation injection event to further reduce localized groundwater impacts.
Preliminary groundwater data indicates that the source material excavation and insitu chemical
oxidation application have successfully provided remediation at the site. It is Aztech's goal to
achieve regulatory closure at the site within the calendar year.
Dewatering and Treatment top
Aztech Technologies, Inc. was retained to excavate petroleum-impacted soil present
beneath the the future site of a public building being constructed in Schoharie County, NY.
The building site was a vacant parcel of land that had once been occupied
by a gasoline retail facility and service garage. Petroleum-impacted soil and groundwater
were encountered during a geotechnical investigation at the property.
Groundwater was encountered at approximately 10 feet below grade. However
at 12 to 13 feet below grade, the geology coarsened from overlying sands and
silts to well-rounded gravel and cobbles. The latter produced a significant
amount of groundwater. As such, groundwater was frequently retrieved from
the
excavation with a vacuum truck. Additionally, groundwater was removed via trash
pumps set into the excavation. The water was subsequently treated by Aztech’s
portable dewatering treatment equipment. A total of 87,372 gallons of groundwater
was treated through this system and discharged.
As the excavation was dewatered, petroleum impacted material was excavated from
between 6 and 14 feet below grade. However, in some areas it was encountered at shallower depths (e.g.
three to four feet below grade). A total of 6,200 tons of petroleum-impacted
soil was removed for disposal.
Aztech’s observations indicated that apparently heavily impacted soil
did not have the expected negative influence on groundwater quality. Since
the vast majority of source material was removed natural attenuation was sufficient
to complete site remediation.
