Section 02242

Turbidity Barriers

Tender No.: 7559/07Page 1

PART 1GENERAL

1.1GENERAL

.1The Contractors operations will be subject to the maximum allowable increase in total suspended solids (Max-TSS) within the watercourse.

1.2DEFINITIONS

.1“Instream” means those parts of the bed and banks of a water body that are both with and without terrestrial vegetation.

.2“Max-TSS” means the maximum allowable increase of total suspended solids in the watercourse from the levels at the compliance point downstream of the turbidity control structure from those immediately upstream of the worksite containment.

.3“Visually Conspicuous Plume” means a plume of suspended solids that can be visually observed in the watercourse.

.4“Normal Construction Activity” means any construction activity that will not cause elevated turbidity levels, and no visual indications of elevated turbidity levels.

.5“Scheduled Construction Activity” means any planned activity that can be expected to result in additional turbidity in the watercourse, including the installation and removal of cofferdams, silt curtains, placing of riprap in the water, grading, etc.

.6“Accidental Occurrence” means any situation, beyond the Contractor’s control, that results in elevated turbidity levels in excess of the specified compliance limits, including situations like the unexpected breaching of a cofferdam due to flood conditions exceeding the design levels.

1.3SAMPLING AND TESTING(QUALITY CONTROL AND QUALITY ASSURANCE)

.1Perform all sampling and testing of total suspended solids as specified herein.

.2Provide copies of the results of all sampling and testing in a daily summary format. Upon completion of Construction Activities, submit a final report containing all sampling and testing data.

.3The Minister will carry out random quality assurance inspection as a means to monitor the Contractor’s quality control program. Assist and cooperate with the Minister during the collection of water quality samples.

.4Prior to the start of construction, carry out sufficient testing to determine the normally occurring linear relationship between total suspended solids concentration and turbidity in the watercourse. Pay services of a qualified laboratory to determine the relationship.

.5Take at least 15 test samples and establish the linear relationship. Follow the procedures outlined in www. Infratrans.gov.abtransportation.alberta.ca, Environmental Management.

.6During construction, perform the following:

.1Measure the suspended solids in Nephelometric Turbidity Units (NTU) accurate to within 2%.

.2Convert NTU into mg/l using the industry standard method.

.3Measure upstream and downstream NTU levels within 30 minutes of each other, unless there is a sediment release (see monitoring frequency below).

.4Take one measurement at one-half the depth of the watercourse for watercourses less than one metre in depth. For watercourses greater than one metre in depth, take two measurements, one at 20% depth and one at 80% depth of the watercourse.

1.4SAMPLING FREQUENCY

.1Perform total suspended solid sampling at the following frequency:

Site Condition / Monitoring Frequency
Normal Construction Activities / During instream work, sample twice a day, at intervals more than eight hours apart, both at the upstream background site and all specified downstream compliance sites(1).
Scheduled Construction Activities and Accidental Occurrences / During daylight hours, sample as frequently as possible, and as directed by the Minister, at the upstream background site and the specified downstream compliance sites until total suspended solids(TSS) levels have returned to acceptable background limits.

Note(1):With prior approval of the Minister, testing frequency may be reduced if the Contractor’s environmental controls are determined to be effective at controlling turbidity to less than 5 mg/l in excess of normal background levels for a period of five consecutive days.

1.5COMPLIANCE POINT LOCATIONS

.1Monitor the total suspended solids at the following compliance point locations:

Type of Watercourse / Downstream Compliance Point Distance 1(1) / Downstream Compliance Point Distance 2 / Downstream Compliance Point Distance 3
Ponded systems such as lakes, pools, wetlands and similar other waterbodies where velocities are less than 0.5 m/s / The lesser of 30 m, or the maximum surface dimension of the waterbody. Samples must be taken 30 m apart around the circumference of the turbidity barrier. / 20m (dependent on the size of the waterbody). Samples must be taken 30 m apart around the circumference of the turbidity barrier. / 20 m (dependent on the size of the waterbody). Samples must be taken 30 m apart around the circumference of the turbidity barrier.
Wetted streams less than 10 m wide / 1 stream width downstream (1) / 2 stream widths downstream (1) / 3 stream widths downstream (1)
Wetted streams between 10 m and 30m wide / 30 m downstream (1) / 60 m downstream (1) / 90 m downstream (1)
Wetted streams greater than 30 m but less than 60 m wide / 60 m downstream (1) / 120 m downstream (1) / 180 m downstream (1)
Wetted streams greater than 60 m wide / 90 m downstream (1) / 180 m downstream (1) / 270 m downstream (1)

Note (1):If there is a plume then measure total suspended solids at various locations across the watercourse, in accordance with the following:

  1. Take samples from the middle of the plume.
  2. Take samples as close to the source of the plume as possible (within safety limits).
  3. If the watercourse is less than 5 m wide then only one measurement is required across the stream width. Take measurement within the plume.
  4. If the watercourse is greater than 5 m wide, measurement must be taken at a minimum of three locations across the watercourse; within the plume, half-way across the channel, and 2/3 of the channel width measured from the bank closest to the point where the discharge originated.

1.6MAXIMUM ALLOWABLE INCREASE OF TOTAL SUSPENDED SOLIDS

.1Visual Limits

.1In the event that a Visually Conspicuous Plume does exist, cease all activities which will have the potential to generate sediment in the watercourse.

.2Compliance Criteria

.1Criteria are set by the Canadian Council of Ministers of the Environment Guidelines.

.2Utilize equipment, labour and procedures in a manner that ensures the maximum allowable levels of suspended solids are maintained at or below the following levels:

Site Conditions / Compliance Criteria – (MAXTSS in Excess of Normal Background Levels) / Contractor Action if TSS exceeds the Compliance Criteria
Normal Construction Activity / 5 mg/lin excess of normal background levels is continuously allowed(2) / Notify the Minister immediately.
Cease all instream work and immediately initiate remedial works.
If compliance criteria is exceeded for 2 or more hours, follow the Contractor Actions for Accidental Occurrences and/or Scheduled Construction activities.
Accidental Occurrences / 150 mg/l not exceeding 2 hours in duration and at no time exceeding 250 mg/l(3) / Notify the Minister immediately.
Cease all in-stream work and immediately initiate remedial works.
If compliance criteria is exceeded for 2 or more hours, notify authorities for Regulatory Requirements in accordance with the Environmental Management System Manual.
Scheduled Construction Activities / When background levels are less than or below 250 mg/l(2)
  1. A maximum increase of 25mg/l
  2. 5 mg/l for a 30 day period
  3. 25 mg/l for a 24 hour period
  4. At no time are 250 mg/lto be exceeded
When background levels are above 250 mg/l
  1. TSS may be increased by 10% above background levels for a 24 hour period
  2. TSS may be increased by 2% above background levels for a 30 day period
/ Notify the Minister immediately.
Cease all in-stream work and immediately initiate remedial works.
Complete the Scheduled Construction activities in an 8 hour day or cease all instream works until TSS levels return to acceptable limits.
If compliance criteria is exceeded for 2 or more hours, notify authorities for Regulatory Requirements in accordance with the Environmental Management System Manual.

Note (2):The Canadian Council of Ministers of the Environment

Note (3):Suggested guideline for Accidental Occurrences

.3Notify the Minister at least 48 hours prior to the start of any Scheduled Construction Activity.

.4In the event of an Accidental Occurrence that results in a Visually Conspicuous Plume of sediment, immediately notify the Minister and undertake any mitigative actions necessary to comply with the specified compliance criteria.

1.7SUBMITTALS

.1Provide the following submittals:

.2Shop Drawings of the turbidity barriers detailing the components and the material specifications of the components, 15 days prior to commencement of the Work. Provide a turbidity barriers system that has been designed and stamped by a professional Engineer registered with the Association of Professional Engineers, Geologists and Geophysicists of Alberta or a specialist in such Work authorized by the Minister.

.3Turbidity Control Execution Plan outlining the location of the turbidity barriers, the method of installation, anchorage details, maintenance and inspection procedures, the removal and storage procedures and contingency plans in case of a breach in the turbidity curtain, 15 days prior to commencement of the Work.

.4Final report referred to in 1.3.2.

PART 2PRODUCTS – NOT USED

PART 3EXECUTION

3.1INSTALLATION

.1Install provisions for turbidity control at the Travers Inlet site during all periods of construction that may impact the quality of water in Travers Reservoir including at least the following:

.1 Initial construction of the cofferdam.

.2Placement of riprap and bedding material.

.2Install the temporary turbidity barrier system in accordance with the turbidity control execution plan.

.3Remove the turbidity barriers during the periods they are not required.

END OF SECTION