Site Assessment & Delineation
Spill Investigation Program
After a spill has been reported and contained, the next step is understanding the full extent
of the impact. This is called delineation — determining how far the spill has spread, both
horizontally and vertically, in soil and water.
Delineation is the responsibility of the responsible party and their consultants. DEQ uses
the results to determine what cleanup is required. While field methods can guide delineation
work, laboratory analysis from an NDDEQ-certified laboratory is required to confirm
successful cleanup.
The full technical requirements are in the
Guidelines for the Assessment and Remediation of Oilfield Releases .
Example Scenarios
The following examples illustrate how delineation is approached for different spill types.
All scenarios are fictional. Maps are not to scale.
A pipeline breaks at a depth of 8 feet, and a rancher finds a produced water spill
due to visible standing water and salt crusting on flat rangeland. The spill has been
reported, the area fenced, and standing fluids removed by vacuum truck. Because
excavation will be used for remediation, delineation occurs during that process.
The following delineation steps are taken:
Two background surface soil samples are collected from unimpacted flat areas of
the same field. Field EC meter readings are taken at the same locations —
approximately 1 mS/cm.
An EC meter is used to determine the approximate horizontal extent of the spill.
Locations where readings approach background are flagged as potential sidewall
locations.
The spill is horizontally excavated to the flagged areas.
The spill is vertically excavated until EC readings near the pipeline break
approach background levels.
EC readings are collected from the surface, floor, and all sidewalls of the
excavation.
The final excavation is approximately 10 ft long, 10 ft wide, and 10 ft deep.
One confirmation sample is collected from each of the four sidewalls, and one
floor sample is collected near the pipeline break.
Soil samples are sent to the laboratory and tested for produced water analytes
including percent sodium, SAR, chloride, bromide, sulfate, EC, pH, and TPH.
Figure: Soil delineation example map — saltwater pipeline spill.
A truck crashes into a slow-flowing creek, and diesel leaks from two fuel tanks
directly into the water, creating a sheen. The spill has been reported and
containment is in progress. The creek flows to the south.
The following delineation steps are taken:
Two background water samples are collected from upstream of the crash site.
A likely spill endpoint is determined using the visual indicator of sheen.
Water samples are collected in order from least to most contaminated —
Downstream Water, Endpoint Water, Water 1, and Spill Entry.
Samples are sent to the laboratory and tested for diesel analytes including
TPH and BTEX.
Figure: Water delineation example map — diesel truck crash. Bkg is an abbreviation for background.
An exposed flowline breaks over a narrow drainage, causing an emulsion spill.
The emulsion runs down the drainage into a small creek — a sheen is visible and
dead fish are present. The responsible party has reported the spill, contained it,
removed livestock, and begun vacuum truck removal of impacted water. The creek
flows to the south.
The following delineation steps are taken:
For the soil delineation:
Two background surface soil samples are collected from unimpacted areas
further up the same drainage. Background EC readings are approximately
4 mS/cm due to the drainage location.
The drainage is excavated to EC readings similar to background, with a final
depth of approximately 2 ft.
Soil samples are collected from the base of the drainage at 20 ft intervals,
in order from least to most contaminated — Soil Entry, Soil 1, Soil 2, and
Soil Release Point.
Soil samples are tested for produced water and oil analytes including percent
sodium, SAR, chloride, bromide, sulfate, EC, TPH, and pH.
For the water delineation:
Two background water samples are collected upstream — one from the surface
and one from the bottom of the water column.
A likely spill endpoint is determined using sheen for oil and chloride strips
for produced water.
Because the spill has both saltwater and oil components, each sample point
requires two samples — one from the top and one from the bottom of the
water column. Samples are collected in order from least to most contaminated —
Downstream Water, Endpoint Water, Water 1, Water 2, Water 3, and Entry Water.
Water samples are tested for produced water and oil analytes including percent
sodium, chloride, sulfate, alkalinity, TDS, bromide, ammonium, EC, TPH, BTEX,
and pH.
Figure: Soil and water delineation example map — emulsion pipeline spill.
Site Assessment & Work Plan Checklist
A site assessment and work plan (SAWP) documents the current state of a spill site and outlines the responsible party's plan for cleanup. It must be submitted to and approved by DEQ before remediation begins. The SAWP gives DEQ the information needed to evaluate the extent of the spill, confirm that delineation is complete, and ensure the proposed remediation approach is appropriate for the site. The following checklist outlines what must be included.
Below is a list of information to be included in a complete site assessment and work plan.
