02_24_20.00_28_Amend_0001.pdf

Mill Creek Dam Forebay Silt Removal & Debris Barrier Maintenance W912EF18B0016 Amendment 0001

SECTION TABLE OF CONTENTS

DIVISION 02 - EXISTING CONDITIONS

SECTION 02 24 20.00 28

WATER QUALITY MONITORING

PART 1 GENERAL

1.1 SUBMITTALS

1.2 WATER QUALITY MONITORING PLAN

1.3 QUALIFICATIONS

1.4 WATER QUALITY PARAMETERS

PART 2 PRODUCTS

2.1 WATER QUALITY MONITORING EQUIPMENT

2.1.1 Sondes

2.1.2 Turbidimeter

2.1.3 Computers

PART 3 EXECUTION

3.1 MONITORING AND REPORTING

3.1.1 Monitoring

3.1.2 Sampling Locations

3.1.3 Sampling Timing

3.1.4 Equipment Calibration

3.1.5 Pre-excavation Monitoring System Test

3.2 WATER QUALITY MONITORING REPORT

3.2.1 Electronic Files

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WATER QUALITY MONITORING

PART 1 GENERAL

This section specifies the requirements for water quality monitoring including preparation of a water quality monitoring plan, sampling and testing, and preparation of a final report. Water quality monitoring shall be performed before lowering the forebay, and for the duration of all sediment removal work.

1.1 SUBMITTALS

Government approval is required for submittals with a "G" designation;

submittals having an "I" designation are for information only. Designation following the "G" or "I" designation identifies the office that will review the submittal for the Government. Submit in accordance with SECTION

01 33 00 SUBMITTAL PROCEDURES:

SD-01 Preconstruction Submittals

Water Quality Monitoring Plan; G, PEC

SD-06 Test Reports

Equipment Calibration; I, PEC

Water Quality Monitoring Report; I, PEC

1.2 WATER QUALITY MONITORING PLAN

Prior to commencement of any sediment removal work, the Contractor shall submit and receive approval of a Water Quality Monitoring Plan. The Plan shall include, at a minimum, the following:

1. Name, address, and phone number of company performing the water quality monitoring.

2. Resume for each employee including a detailed description of their qualifications to perform water quality monitoring.

3. List of all equipment and materials to be used.

4. Manufacturer's specifications for each piece of equipment to be used.

5. Calibration history for each piece of equipment.

1.3 QUALIFICATIONS

Water quality monitoring shall be performed by an independent water quality monitoring service, hired by the Contractor. The monitoring service shall be regularly engaged in the business of water quality sampling and testing and shall have a minimum of 3 years of experience in water Water quality monitoring shall be performed for the parameters specified, using equipment

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Line and methods that meet the requirements of this specification.

1.4 WATER QUALITY PARAMETERS

Water quality monitoring shall be performed for the following parameters:

1. pH (units)

2. turbidity (nephelometric units, NTU)

3. dissolved oxygen (mg/L)

4. temperature (ºC)

PART 2 PRODUCTS

2.1 WATER QUALITY MONITORING EQUIPMENT

Water quality monitoring equipment, listed below, shall be furnished and maintained by the Contractor and shall be used for monitoring of all forebay cleanout activities. The Contractor shall replace any non-functioning equipment within 24 hours.

2.1.1 Sondes

The Contractor shall provide multiparameter probes (sondes), as required, with access to a minimum of 2 spares, meeting the following requirements:

a. A pH sensor accurate to ± 0.2 pH units with a resolution of 0.01 units.

b. A turbidity sensor with a light source wavelength ranging from 860 nm to 880 nm and accurate to ± 5% of the reading or ± 2 NTUs, whichever is greater.

c. A dissolved oxygen sensor accurate to ± 0.2 mg/L.

d. A temperature sensor accurate to ± 0.10 ºC.

e. Internal memory sufficient to store 10 days of sensor readings at 5-minute intervals.

f. Weighted sensor guard sufficient to hold the sonde and cable vertical and protect the sensors from direct contact with objects larger than 3/4-inch diameter.

2.1.2 Turbidimeter

A turbidimeter shall be resistant to shock and weather and shall be reliable and accurate under adverse field conditions. The instrument shall use a near-infrared light source with a wavelength between 860 nm and 880

nm. Meter accuracy shall be ±5% of the reading or ±2 NTU (whichever is greater), with a range from 0-1,000 NTU, and a repeatability of ±1% of the reading.

2.1.3 Computers

Laptop computers for instrument set-up, calibration, and manual downloading if necessary. The computers shall be suitable for use under adverse field

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conditions (i.e. weather and shock resistant, a display that is visible in full sunlight) with an appropriate electronic interface ability to connect to monitoring equipment (e.g. at least one RS-232 port).

PART 3 EXECUTION

3.1 MONITORING AND REPORTING

3.1.1 Monitoring

The Contractor shall perform water quality monitoring for the specified parameters during all excavation and disposal operations.

3.1.2 Sampling Locations

One monitor shall be placed 50 to 100 feet upstream from the work area to obtain background data. A second monitor shall be placed at the first channel spanning weir below the Diversion Dam. A third monitor shall be placed approximately ½ way between the Division Dam and the Diversion Dam (located approximately ½ mile downstream of the excavation area). A fourth monitor is to be placed near the Mill Creek Division Dam about a mile downstream from the debris removal work, close to the project office.

3.1.3 Sampling Timing

Timing of sampling shall be as follows:

During all forebay cleanout activities, all water quality parameters shall be monitored at 15-minute intervals. Monitoring shall be done during the entire work window (July 15 through August 31) and during elevated turbidity conditions (10 NTU above background) after the work window is passed. This may require continuous monitoring past the end of the normal work day into the evening or next day. Data sondes are to be downloaded daily after completion of the day's work.

3.1.4 Equipment Calibration

Sondes, the turbidimeter and the dissolved oxygen sensor shall be calibrated prior to use. The Contractor shall clean and recalibrate all equipment whenever there is any indication that the equipment is not performing properly. Calibration of the instruments shall be in accordance with the equipment manufacturer's recommendations. The Contractor shall submit calibration sheets as required by Paragraph: WATER QUALITY

MONITORING REPORT.

3.1.5 Pre-excavation Monitoring System Test

The Contractor shall have the monitoring equipment installed and tested 2 working days prior to the start of work. Testing shall include recording of data by the sondes and downloading of the data. The Contracting Officer may perform a field verification of the monitoring system with the Contractor.

3.2 WATER QUALITY MONITORING REPORT

No later than 5 days, following completion of all excavation and disposal activities, the Contractor shall submit a final water quality monitoring report. The report shall contain:

1. Field methods used for sonde calibration.

2. Calibration information to include:

a. performance curve verification and instrument detection limits (IDL) and method detection limits (MDL) for each sonde

b. calibration sheets indicating corrective actions taken if the equipment calibration was out of specification

c. suppliers and lot numbers of calibration and reference standards

d. spectrophotometer and turbidimeter calibration curves

3. GPS coordinates and total depth where field measurements were taken.

4. Results of the discrete in-vitro turbidity.

5. Statistical analyses (e.g. means, standard deviations, t-tests, and 95 percent confidence intervals) along with a discussion that correlates the quality of the data measured by the sondes to the calibration and in-vitro data.

6. Project event log documenting all non-routine events that occurred during the project, and what corrective measures were taken in each instance.

7. Location and date of sampling shall be included for all data in the report.

3.2.1 Electronic Files

The Contractor shall submit two (2) copies of all information (e.g.

electronic data, scanned material, analyses, graphs, and tables) to the Contracting Officer on compact disks (CD)in Microsoft Office format.

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