28a_NCS000250_SP01 G181 Procedures for Monitoring Borrow Pit Discharge

PROCEDURE FOR MONITORING BORROW PIT DISCHARGE:
(2-20-07) (Rev. 4-5-19) 105-16, 230,801 SPl G181
Water discharge from borrow pit sites shall not cause surface waters to exceed 50 NTUs
(nephelometric turbidity unit) in streams not designated as trout waters and 10 NTUs in streams,
lakes or reservoirs designated as trout waters. For lakes and reservoirs not designated as trout
waters, the turbidity shall not exceed 25 NTUs. If the turbidity exceeds these levels due to natural
background conditions, the existing turbidity level shall not be increased.
If during any operating day, the downstream water quality exceeds the standard, the Contractor
shall do all of the following:
(A) Either cease discharge or modify the discharge volume or turbidity levels to bring the
downstream turbidity levels into compliance, or
(B) Evaluate the upstream conditions to determine if the exceedance of the standard is due to
natural background conditions. If the background turbidity measurements exceed the
standard, operation of the pit and discharge can continue as long as the stream turbidity
levels are not increased due to the discharge.
(C) Measure and record the turbidity test results (time, date and sampler) at all defined
sampling locations 30 minutes after startup and at a minimum, one additional sampling of
all sampling locations during that 24-hour period in which the borrow pit is discharging.
(D) Notify DWQ within 24 hours of any stream turbidity standard exceedances that are not
brought into compliance.
During the Environmental Assessment required by Article 230-4 of the 2018 Standard
Specifications, the Contractor shall define the point at which the discharge enters into the State's
surface waters and the appropriate sampling locations. Sampling locations shall include points
upstream and downstream from the point at which the discharge enters these waters. Upstream
sampling location shall be located so that it is not influenced by backwater conditions and
represents natural background conditions. Downstream sampling location shall be located at the
point where complete mixing of the discharge and receiving water has occurred.
The discharge shall be closely monitored when water from the dewatering activities is introduced
into jurisdictional wetlands. Any time visible sedimentation (deposition of sediment) on the
wetland surface is observed, the dewatering activity will be suspended until turbidity levels in the
stilling basin can be reduced to a level where sediment deposition does not occur. Staining of
wetland surfaces from suspended clay particles, occurring after evaporation or infiltration, does
not constitute sedimentation. No activities shall occur in wetlands that adversely affect the
functioning of a wetland. Visible sedimentation will be considered an indication of possible
adverse impacts on wetland use.
The Engineer will perform independent turbidity tests on a random basis. These results will be
maintained in a log within the project records. Records will include, at a minimum, turbidity test
results, time, date and name of sampler. Should the Department's test results exceed those of the
NCDOT NPDES NCS000250

Contractor's test results, an immediate test shall be performed jointly with the results superseding
the previous test results of both the Department and the Contractor.
The Contractor shall use the NCDOT Turbidity Reduction Options for Borrow Pits Matrix,
available at https://connect.ncdot.gov/resources/roadside/FieldOperationsDocuments/
TurbidityReductionOptionSheet.pdf to plan, design, construct, and maintain BMPs to address
water quality standards. Tier I Methods include stilling basins which are standard compensatory
BMPs. Other Tier I methods are noncompensatory and shall be used when needed to meet the
stream turbidity standards. Tier II Methods are also noncompensatory and are options that may
be needed for protection of rare or unique resources or where special environmental conditions
exist at the site which have led to additional requirements being placed in the DWQ's 401
Certifications and approval letters, Isolated Wetland Permits, Riparian Buffer Authorization or a
DOT Reclamation Plan's Environmental Assessment for the specific site. Should the Contractor
exhaust all Tier I Methods on a site exclusive of rare or unique resources or special environmental
conditions, Tier II Methods may be required by regulators on a case by case basis per supplemental
agreement.
The Contractor may use cation exchange capacity (CEC) values from proposed site borings to plan
and develop the bid for the project. CEC values exceeding 15 milliequivalents per 100 grams of
soil may indicate a high potential for turbidity and should be avoided when dewatering into surface
water is proposed.
No additional compensation for monitoring borrow pit discharge will be paid.
NCDOT NPDES NCS000250