open channel flow guide - solartron mobrey

8/14/2019 Open Channel Flow Guide - Solartron Mobrey

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1234process measurement solutions

The Guidefor implementing dependable & accurate open

channel flow measurement


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THE GUIDE

For implementing dependable and accurateopen channel flow measurement

1.0 The Importance of Dependable Flow Measurement

1.1 Environment Agency Requirements

1.2 The Benefits of Open Channel Devices

1.3 BS3680

2.0 A Turnkey Solution from Solartron Mobrey

2.1 Flow Audit Surveys

2.2 Installation

2.3 Certification

2.4 Health and Safety

3.0 Document Examples

3.1 Survey Forms

3.2 Survey Report

3.3 Certificate of Conformity

3.4 Calibration Data and Performance Curves

3.5 Survey Method Statement

4.0 Reference Documents

4.1 Selecting a Flow Specialist

4.2 Reference List Discharge Flow Compliance Works

5.0 Published Articles

5.1 A benchmark for flow measurement accuracy

5.2 Implementing effluent flow monitoring regulations and guidelines

5.3 Logistics of effluent flow measurement problem solved.


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1.0 The Importance of Dependable Flow Measurement

Unreliable flow data can result in inefficient plant operation and unnecessary investment inplant upgrades. This is particularly true in the case of measurement of industrial and sewage

effluents, yet it is frequently given the least priority and attention.

Flow data obtained from a dependable source, enable plants to be operated in an efficientmanner. By optimising treatment processes, operators can ensure that maximum treatmentcapacities are achieved, before additional investment is made. Where it is necessary toreplace or upgrade plant equipment, operating capacities can be specified with confidence.

1.1 Environment Agency Requirements

In addition to providing the plant operator with important information, it is now a legislativerequirement that dischargers maintain accurate flow measurement records. The Environment

Agency is currently implementing a programme, directed at Continuous Sewage and TradeDischargers, to ensure accurate flow monitoring is in place, by specific time scales.The following are extracts from the Environment Agency document, Procedure for FlowMeasurement of Discharges (version 4.2 Sept 2000)

The Aims and Objectives of Flow MeasurementThe limits in discharge consents are based on the maximum quantity, or load, of pollutantsthat can be allowed in the receiving water. To control load, consents specify limits for flow andpollutant concentration. Even where the discharge meets the quality limits, the river may bedowngraded by excessive load because the discharge exceeds the consented maximum flow.It is thus necessary to monitor both the quantity and quality of discharges. The Agencyrequires reliable discharge flow data in order to regulate effectively discharges and receiving

water quality. In addition, the Agency requires up to date flow information to plan for futuregrowth of discharges.

The Water Resources Act 1991 (as amended by the Environment Act 1995) Schedule 10,paragraphs 3(4) (e) to (g) specifically provides for conditions in consents requiring theinstallation, maintenance and testing of meters to measure and record the volume and rate ofdischarges. It also allows the Agency to require the discharger to keep records and makereturns. Many existing consents place requirements on the discharger to obtain and providesuch information, as do the standard national consent conditions.

The policy requires the Agency to undertake a programme to insert conditions in consents toenforce the requirement for self monitoring of flows and reporting results to the Agency inaccordance with a specified timetable. The Agency will also audit the installations and makeprovision for checking returns against consent limits and archiving returns for planning andother purposes. Where necessary the Agency will use Enforcement Notices to carry out thispolicy.

Continuous Trade DischargesOn all new and revised consents for trade discharges, the provision and maintenance ofinstallations to measure and record the rate of flow and cumulative daily volume is essential.When pollutant concentration limits are imposed by a consent and monitored then it is equallyimportant to measure effluent flows. Where the maximum daily volume of trade effluentexceeds 50m3/day and the consent is subject to numeric quality and flow limits, the discharger

will normally be required to install and maintain a permanent flow monitoring installation andmake regular returns to the Agency. If the volume limit is 5 to 50m3/day flumes, v-notch weirsor other agreed means should be provided to allow the use of flow measurement equipment


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when required. The Agency may, exceptionally, require flow measurement structures for tradeflows less than 5 m3/d. In this case the Agency will justify the need.

Continuous Sewage DischargesWhere pollutant concentration limits are imposed by a consent and monitored then it is equally

important to measure effluent flows in order to provide quantitative estimates of the amount ofpollutant materials discharged.

All new and revised consents for continuous sewage discharges exceeding 5m3 /day willrequire the provision and maintenance of a structure, such as a flume or v-notch weir, wherethe rate of flow and cumulative daily volume can be measured and recorded.

At sewage discharges above 5 m3/d, which either have descriptive consent conditions or havea consented DWF less than 50m3/day, the discharger will provide a flow measuring location.However, the flow will only need to be monitored by the discharger when requested by theAgency, or the Agency may install portable flow monitoring equipment when required. If theAgency's information needs for a discharge in this size range will be satisfied by a simplerarrangement, then the Agency may allow the use of a simple physical measuring device, suchas a level board and V notch. Here Agency staff on sampling visits will record the flow and thedischarger may be required to keep records. Where an existing STW in this flow range has noprovision for flow monitoring it will not be necessary to modify it solely for that purpose, unlessthe Agency specifically requires flow measurement at that site. Flow monitoring should beprovided when the STW is next modified.

At discharges above 250 population equivalent, or have a DWF equal to or greater than 50m3 /day the Agency will normally require the discharger to install and maintain equipment tomeasure and record instantaneous and cumulative daily flows. Flow measurement will be acontinuing requirement for all these sites. For those discharges below the population

equivalent thresholds for the Urban Wastewater Treatment Directive, where the controlledwater quality is not significantly affected by the discharge and previous flow measurement hasshown that the daily volume measurement is less than 80% of the consent limit then, at thediscretion of the Agency, a reduced frequency of flow monitoring may be allowed. The reducedfrequency will require flow measurement by the discharger only during one year in every twoor three. The minimum frequency for flow monitoring will be one year in five. This reducesmonitoring effort for satisfactory discharges, while allowing changes in flow to be monitored. Ifthe circumstances change then the Agency may require an increased frequency or continuousmonitoring.

Intermittent DischargesFor storm sewage overflows at STWs, the Agency needs to be able to confirm that the flow at

which the storm overflow begins to operate is as required by the consent. As a minimum,where the overflow is fixed and flows cannot be adjusted, spot checks for consent compliancemay be adequate, subject to Agency agreement. Once confirmed they should be recheckedfrom time to time, or when the flows to the works may have changed.

Where the overflow setting can be adjusted, for instance by an adjustable weir plate, apenstock or by varying pump operation, then ensuring that pass forward flows meet consentrequirements can only be achieved by continuous recording during operation of the overflow.

Flow Meter SpecificationThe flow measurement and recording systems should be installed to British Standards (e.g.BS3680) They must be calibrated within predetermined levels of accuracy and the consentshould require a programme of maintenance and checking by the discharger. Continuousrecording devices should have a digital display and a logging capability.


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Implementation TimetableThe Agency will monitor implementation of the flow monitoring programme. All sewage worksabove UWWTD population equivalent thresholds and all sewage works and other dischargesbelow those limits that have been identified by the Agency as a priority, should have flowmeasurement in place as soon as is practicable. All eligible discharges should have flowmeasurement in place by April 2005.

For trade effluents and non-utility STW discharges the Agency will establish a prioritisedprogramme to require the provision of flow measuring facilities at each discharge. TheAgencys requirements will be explained to each discharger and an appropriate target date willbe discussed. If the discharger does not agree a target date acceptable to the Agency then theAgency will set a date and modify the consent accordingly. If the discharger does notundertake the measures voluntarily then the Agency will require them to do so by anEnforcement Notice (in accordance with the Agencys Enforcement Policy).

Quality Assurance

Flow monitoring should be supported by evidence that the uncertainty of the flow meteringdevice(s) is no greater than 8% of total daily flow. However, it is recognised that in a fewsituations, the flow may fall below the minimum recommended for the device and anuncertainty of >8% (at 25% of maximum design flow) may be unavoidable.

Implementation RequirementsThe Discharger will be responsible for meeting the consent requirements according to thespecifications set by the Agency. The Agency will give advice to Dischargers at their request.Following completion of the installation, the Discharger will be required to have the site auditedand certified for accuracy by an independent expert. The reports will be returned to theAgency. The Discharger will prepare a Quality Control Manual for site maintenance, data

collection, validation and supply to the Agency. They will be required to operate in accordancewith the Manual. The Agency will carry out an ongoing programme of inspection and audit ofsites and audit of compliance with the Manual.

The Agency has produced an R&D report that provides requirements for flow measurementinstallations for dischargers and audit proposals (R&D Technical Report P150. FlowMonitoring of Discharges: An Audit Manual). This will initially provide the Agencys

specification for the construction and performance of flow monitoring installations.


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1.2 The Benefits of Open Channel Devices.

Historically, the preferred method of measuring gravity fed effluent flowrates is via an openchannel flow structure, installed in conjunction with a suitable gauged head measurementdevice. This still remains the case. Over the years the methods of obtaining gauged headmeasurements have changed as technology has advanced, but the primary structures areessentially unchanged. Consequently the characteristics of this type of device are welldocumented and readily verified by competent personnel.

The type of flow structure used is dependent upon many factors, including the fluid conditions,site hydraulics and the operating flowrates. In the case of a sewage treatment works, a flumeis normally to be found on the works inlet, whilst either a flume or weir is normally used tomonitor final effluent flows.

Reasons why this type of measurement is generally preferred over more sophisticated andsometimes less expensive methods are:

The overall simplicity of the devices The technology is established and well documented.

The operation and measurement value can easily be verified

The ease and hence low cost of maintenance.Because of these factors the overall cost of ownership becomes comparable with systems thatinitially appear less expensive.

1.3 BS3680

When an open channel structure conforms to the requirements of the relevant section BS3680 Part 4, then its performance can be predicted. If the geometry or operating parameters

fall outside of those laid down in the standard, its characteristics cannot be verified withoutconducting exhaustive tests.

Since it is imperative that both site operator and the regulative authorities are provided withvalid data, the only acceptable solution is to ensure that structures substantially comply withthe appropriate standard.

Despite its importance, recent studies undertaken by several water companies, haveconcluded that the majority of their open channel flow structures, used to monitor flow totreatment and effluent discharges, at waste water treatment works, fail to meet therequirements of BS3680.

There were a variety of reasons why the structures failed to comply with the standard. Theseincluded:

Structure sizing incompatible with actual f lowrates

Damaged or bowed flumes and weir plates

Uneven channel beds

Poor upstream / downstream conditions

Instruments calibrated incorrectly

Sensors located in incorrect positions


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2.0A Turnkey Solution from Solartron Mobrey

Solartron Mobrey are able to provide a complete turnkey service relating to flow measurementstructures.

This service can include:

Flow audit survey and report on the condition and suitability of existing installations

Survey and report to recommend the most suitable method of providing a new flowmeasurement installation.

Cost estimates for both new and remedial works.

All aspects of construction and installation associated with the provision of new structuresor remedial works on existing installations.

Instrument calibration and commissioning.

Certification of completed installations to verify compliance.

Solartron Mobrey ultrasonic instruments are widely used within the water industry, but werecognise that some companies may wish to utilise alternative suppliers; although

disappointing, this is not a problem to our engineers, who are well versed in the installationand calibration of instruments produced by all current major manufacturers.

2.1 Flow Audit Surveys

A survey consists of three main activities:1. A visual inspection which includes: obtaining an understanding of the process,

assessing the operating conditions and effects of any adjacent equipment or pipework,taking note of scum marks which could indicate problematic operating conditions andnoting the overall condition of the structure.

2. An inspection of all critical dimensions including, all dimensions associated with theprimary structure, structure levels and the position of the gauged head measurementsensor.

3. An inspection of the head measurement system including, verification of allprogrammed parameters, a calibration check and noting the overall condition of thesystem.

Survey findings are recorded on forms, which have been developed to suit the type ofstructure.

Following the survey, calculations are carried out to verify geometric compliance and producemeasurement uncertainty curves. The results are reviewed and are combined with the

physical findings of the survey to produce a summarised report.

The equipment use by Solartron Mobrey engineers, whilst carrying out flow audit surveys,includes the following:

Calibrated surveyors level, tripod and measuring staff

Spirit levels

Purpose made internal callipers

steel rules and measuring tapes

Digital camera

Certified multimeter

Portable computer

Personal protection equipment

Cleaning and sterilisation materials

Mobile telephone


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2.2 Installation

Solartron Mobrey are able to undertake every aspect associated with the construction of openchannel structures and the installation of associated instrumentation, cabling etc. Activitiesinclude: Supply of GRP / GRC / PVC flumes and stainless steel weir plates.

Supply of all instrumentation, calibration reference plates, enclosures, cabling etc.

All works associated with structure construction / repairs.

All works associated with instrument installation.

All works associated with over-pumping, in order to obtain access to thestructure.

2.3 Certification

Upon completion of construction / remedial works, the structure is re-surveyed and assumingall aspects of the installation provide substantial compliance with BS3680, a certificate ofcompliance is issued in conjunction with calibration records, performance curves and tables.

2.4 Health and Safety

All site personnel are experienced in the operation and hazards present on sewage andprocess plants, and are familiar with the health and hygiene requirements.

The where applicable the site operators Heath & Safety procedure will be adopted. Whereprocedures are not available for the activities, Solartron Mobrey procedures will be adopted.

All works are carried out in accordance with previously agreed Method Statements.

Although no entries will be made without prior arrangement, at least one site operative will beconfined space trained. This is considered necessary in order to recognise unidentifiedhazards.


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Flow Survey - General InformationFlow Survey - General Information

Customer :

Site Name: Site Code:

Survey by: Date:

Primary DeviceDuty: Type: Rectangular flume

Material of construction (PVC, GRP etc)

Visual condition of flume

Visual condition of approach channel

Comment on approach velocity

Details of obstructions < 30 X hmax upstream of flume

Details of any re-circulation flows being returned upstream of the flume and method of

measurement

Is there a standing wave present in the exit transition of the flume

Details of any obstructions downstream of the flume that could cause drowning

Bestobell Service

Survey Rect Flume (01_01_1).xls Page 1 of 1 pages


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Flow Survey - dimensionsFlow Survey - dimensionsFlow Survey - dimensionsFlow Survey - dimensions

Channel and Throat widths 'B' & 'b' (mm)

1 2 3 4 5 6

Normal

Maximum

Roughness

Channel and Flume survey staff readings (mm)

Exit

1 2 3 4 5 6 7

Comments

Flume Dimensions

Height

Uninterrupted Approach

A

Approach / flume offset

Hump height

Flume height

Overall Length

Channel levels

Sensor Location

A

B

C

D

Measurement

height

Staff

Channel width 'B'

Channel dimensions

Approach 'L1'

Prismatic 'L'

Exit 'L2'

Throat width 'b'

Scum Lines

Flume levels

Distance from flume

Height from datum

B

location

1 23

45 6

1A 2A 3A

4A 5A 6A

4B 5B 6B

7A

5x'B' 5x'hmax'

5x'B' 5x'hmax'

A

B

CD

Bestobell Service



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Flow Survey - Instrument detailsFlow Survey - Instrument detailsFlow Survey - Instrument detailsFlow Survey - Instrument details

Blanking distance mm

EPROM No

Location: Type:

Manufacturer

Level Sensor Model No

Temp Sensor Model No

Controller Model No

DescriptionCalibrated

Value

MSP Par No Others Par

No

Original

Value

Secondary Device

General Condition:

Bestobell Service



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Flow Survey - General InformationFlow Survey - General InformationFlow Survey - General InformationFlow Survey - General Information

Customer :

Site Name: Site Code:

Survey by: Date:

Primary Device

Duty: Type:

Material of construction (PVC, GRP etc)

Secondary Device

Location: Type:

Summary

Rectangular FlumeFlow to Treatment

For substantial compliance with BS3680, it is recommended

that the FTT flume throat be refurbished to reduce width

variance, and the bed levelled to acceptable limits.

The gauged head sensor requires re-positioning and lowering

for improved accuracy, and a calibration reference plate

installed. The control unit requires re-programming with the

correct parameters.

In order to record the total treated flow, we recommend that an

electromagnetic flowmeter be installed in the 150mm storm

return pipeline. The flowrates derived from both this and the

FTT structure should then be summated.

Work required:

* Refurbish flume cheeks / level bed

* Fit calibration reference plate and re-position sensor

* Re-programme control unit

* Install storm return magmeter and chamber

* Verify the storm event flowrate

* Certify the measurement system

Concrete flume and channel

In control room Warren Jones WJ460

General Condition: The approach velocity is smooth and tranquil, albeit the channel and flume are covered with slime. There is a 280mm

high step in the channel, approx 2100mm upstream of the flume. The variance in flume throat width, exceeds both BS3680 and practical

limits. This is largely due to the poor concrete finish at the entry to the throat, and could be rectified.

The level variance in approach channel bed marginally exceed practical limits, whilst the variance in the flume bed is excessive.

The flume discharges correctly with no signs of backing-up or drowning.

This point of measuremnt does not capture storm return flows, which are returned downstream of the flume, into a common wet well. A

separate flowmeter will need to be provided for this.

Consent Discharge Flow Monitoring can be achieved by summating the FTT and the storm return flow

measurements. The storm event setting requires proving, but does not require a logging.

General Condition: The control unit is in reasonable condition and uses both channels - CH1 = Inlet to works,

CH2 = FTT.

The calibrated range of 120l/s is acceptable for the operating conditions, although several programmed

parameters are incorrect.

The gauged head sensor is too close to the flume for BS3680 compliance, and could be lowered to improve

measurement accuracy.

A calibration reference plate is not fitted.

This structure does not comply with BS3680

A Water Company

22-Aug-00Paul Cherry / Shawn Mantle

ABC WWTW

Bestobell Service

Photo Here

FTT Flume

Storm Return pipeline

Example report (01_01_1).xls Page 2 of 6 pages


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1 2 3 4 5 6

603 602 605 311 310 302

604 604 605 311 310 302

606 604 606 309 309 302

606 606 608 309 309 302

400 1640 Normal 240

1200 6000 Maximum 350

1100 0 Roughness 0.6

2700 Blank Dist 300

1640 670

0 1570


Exit

1 2 3 4 5 6 7

3845 3842 3845 3846 3843 3833 3687

3846 3843 3834

Comments

Flume Dimensions

Height


A


Hump height

Flume height

Overall Length

Channel levels

Sensor Location

A

B

C

D

Measurement

height

Staff

Channel width 'B'

Channel dimensions

Approach 'L1'

Prismatic 'L'

Exit 'L2'

Throat width 'b'

Scum Lines

Flume levels

Distance from flume

Height from datum

B

location

1 23

45 6

1A 2A 3A

4A 5A 6A

4B 5B 6B

7A

5x'B' 5x'hmax'

5x'B' 5x'hmax'

Bestobell Service

A

B

C

D

Max Scum

Norm scum

Base



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Flow Survey - Instrument detailsFlow Survey - Instrument detailsFlow Survey - Instrument detailsFlow Survey - Instrument details

Blanking distance 300 mm

WJ460 EPROM No

Manufacturer

Level Sensor Model No

Temp Sensor Model No

Controller Model No

Warren Jones

DescriptionCalibrated

Value

L

'B'

Average

ks

Q max

h max

Pulse

Units

Interval

MSP Par No Others Par

No

Displayed value

'b'

Original

Value

300

1200

602

1

120

387

0

Lit/sec

5

180

Bestobell Service



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Flow Survey - Conformance / Uncertainty DataFlow Survey - Conformance / Uncertainty DataFlow Survey - Conformance / Uncertainty DataFlow Survey - Conformance / Uncertainty Data

BS3680 Conformance (Limits)

302

1.26

0.32

0.51

* Width < 3.07 4.50

* Transv < 1.00 0.50 * Longt < 1.20 6.50

1.94 2.00

670

6000

Calculation data

605 0.6

307 15

1200 0.50 0.3

1640 1.0

1183 4.33%

1570

387

Estimated uncertainties assuming substantial compliance with BS3680

Head Flow Flow Flow eh CD CV % of Error X

(mm) (Lit/sec) (M3/hr) (ML/D) (mm) Flow % +/-

0.0 0.00 0.00 0.00

19.4 1.07 3.86 0.09 7.75 0.7309 1.0404 0.9% 61.04%

38.7 3.55 12.78 0.31 7.66 0.8482 1.0503 2.8% 30.39%

58.1 6.68 24.06 0.58 7.56 0.8679 1.0519 5.3% 20.31%

77.4 10.49 37.75 0.91 7.46 0.8834 1.0532 8.4% 15.31%

96.8 14.88 53.55 1.29 7.37 0.8959 1.0542 11.8% 12.35%

116.1 19.76 71.15 1.71 7.27 0.9047 1.0550 15.7% 10.40%

135.5 25.11 90.40 2.17 7.17 0.9117 1.0556 20.0% 9.03%

154.8 30.89 111.20 2.67 7.08 0.9175 1.0561 24.6% 8.03%

174.2 37.05 133.39 3.20 6.98 0.9220 1.0565 29.5% 7.26%

193.5 43.58 156.88 3.77 6.88 0.9256 1.0568 34.7% 6.67%

212.9 50.44 181.60 4.36 6.79 0.9285 1.0571 40.2% 6.19%

232.2 57.64 207.49 4.98 6.69 0.9308 1.0573 45.9% 5.81%

251.6 65.14 234.50 5.63 6.59 0.9329 1.0575 51.9% 5.50%

270.9 72.94 262.59 6.30 6.50 0.9345 1.0576 58.1% 5.24%

290.3 81.03 291.70 7.00 6.40 0.9360 1.0577 64.5% 5.02%

309.6 89.40 321.83 7.72 6.30 0.9373 1.0578 71.2% 4.84%

329.0 98.05 353.00 8.47 6.21 0.9386 1.0579 78.1% 4.68%

348.3 106.97 385.10 9.24 6.11 0.9397 1.0581 85.2% 4.55%

367.7 116.15 418.12 10.03 6.01 0.9407 1.0581 92.5% 4.43%

387.0 125.57 452.04 10.85 5.92 0.9417 1.0582 100.0% 4.33%

Uncertainty @ 25 % of QmaxSensor height (mm)

Estimate of Normal Flowrate l/s

Mean fluid temp (oC)

r (measurement error ) %Error in Flow calculation %

Uncertainty in zero datum (mm)

Uncertainty @ Qmax

Maximum head "h" mm

Hump Height "p" (mm)

Approach level varn. 100mm

hmax/b shall be < 3

hmax

/L shall be < 0.67

bhmax/B(hmax+p) shall be < 0.7

Sensor location at 3 to 4 hmax (mm)

Uninterupted approach (mm)

Channel Width "B" (mm)

Bestobell Service

* The maximum acceptable dimensional

variance is indicative of practical limits, and

exceeds the variance limits stated within

paragraph 6.3.3 of BS3680 Part 4C



17/35


18/35

Customer name: A Water Company

Site name: ABC WWTW

Site asset code:

Duty: Flow to Treatment

Type of primary device: Concrete Rectangular Flume

Type of secondary device: Warren Jones 460 (Channel 2)

Calibrated range (hmax / flow rate / uncertainty): 380 mm/ 120 l/s /3.50 %

25% calibrated range (h / flowrate / uncertainty): 153.4 mm/ 30 l/s /5.17 %

We hereby certify that on the date of inspection, the above installation

substantially conformed to the appropriate section of BS3680 part 4, subjectto the exclusions / comments below.

Exclusions/comments:

BESTOBELL

SERVICE

Lake View

Cooper Street

Hazel Grove

StockportCheshire

SK7 4LT

0161 483 0931

CERTIFICAT E OF CONFORMITYCERTIFICAT E OF CONFORMITYCERTIFICAT E OF CONFORMITYCERTIFICAT E OF CONFORMITY

Date of Inspection : 19/12/00

Maintenance: In order to maintain compliance, the operation of head sensinginstrumentation must be checked at regular intervals. The structure must beregularly inspected and kept clear of silt, debris and biological growth.(Changes in operating conditions, unauthorised modifications to structures oradjustments to instrument calibration will invalidate this certificate).

By :

S Mantle


19/35

ABC WWTW

A Water Company

Flow Survey Report

Bestobell Service

Lake View, Cooper Street,

Hazel Grove, Stockport,

Cheshire SK7 4LT

Telephone 0161 483 0931

Example laminate (01_01_1).xls Page1 of 5


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1 2 3 4 5 6

603 602 605 305 304 302

604 604 605 304 303 302

606 604 606 304 302 302

606 606 608 303 302 302

400 1640 Normal

1200 6000 Maximum

1100 0 Roughness 0.6

2700 Blank Dist 250

1640 1380

0 816


Exit

1 2 3 4 5 6 7

3837 3835 3836 3836 3835 3837 3680

3836 3835 3836

Comments

Flume Dimensions

Height


A


Hump height

Flume height

Overall Length

Channel levels

Sensor Location

A

B

C

D

Measurement

height

Staff

Channel width 'B'

Channel dimensions

Approach 'L1'

Prismatic 'L'

Exit 'L2'

Throat width 'b'

Scum Lines

Flume levels

Distance from flume

Height from datum

B

location

1 23

45 6

1A 2A 3A

4A 5A 6A

4B 5B 6B

7A

5x'B' 5x'hmax'

5x'B' 5x'hmax'

Bestobell Service

A

B

C

D

Max Scum

Norm scum

Base

Example laminate (01_01_1).xls Page 2 of 5 pages


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Flow Survey - Conformance / Uncertainty DataFlow Survey - Conformance / Uncertainty DataFlow Survey - Conformance / Uncertainty DataFlow Survey - Conformance / Uncertainty Data

BS3680 Conformance (Limits)

302

1.25

0.32

0.50

* Width < 3.03 1.50

* Transv < 1.00 0.50 * Longt < 1.20 1.00

1.90 0.50

1380

6000

Calculation data

605 0.6

303 15

1200 0.520 0.3

1640 1.0

436 3.50%

816 5.17%

380

Calculated Uncertainties

Head Flow Flow Flow eh CD CV % of Error X

(mm) (Lit/sec) (M3/hr) (ML/D) (mm) Flow % +/-

0.0 0.00 0.00 0.00

19.0 1.02 3.66 0.09 4.14 0.7238 1.0387 0.8% 34.44%

38.0 3.40 12.24 0.29 4.05 0.8471 1.0488 2.8% 17.21%

57.0 6.40 23.04 0.55 3.95 0.8667 1.0503 5.3% 11.70%

76.0 10.04 36.13 0.87 3.85 0.8819 1.0515 8.3% 9.01%

95.0 14.24 51.27 1.23 3.75 0.8945 1.0525 11.8% 7.43%

114.0 18.92 68.11 1.63 3.65 0.9034 1.0533 15.7% 6.41%

133.0 24.04 86.56 2.08 3.55 0.9106 1.0539 20.0% 5.71%

152.0 29.58 106.47 2.56 3.45 0.9163 1.0544 24.6% 5.20%

171.0 35.48 127.73 3.07 3.35 0.9209 1.0547 29.5% 4.83%

190.0 41.73 150.23 3.61 3.26 0.9245 1.0551 34.7% 4.54%

209.0 48.31 173.92 4.17 3.16 0.9275 1.0553 40.2% 4.32%

228.0 55.20 198.73 4.77 3.06 0.9299 1.0555 45.9% 4.14%

247.0 62.39 224.61 5.39 2.96 0.9320 1.0557 51.9% 4.00%

266.0 69.86 251.51 6.04 2.86 0.9337 1.0558 58.1% 3.89%

285.0 77.61 279.41 6.71 2.76 0.9352 1.0559 64.5% 3.79%

304.0 85.63 308.26 7.40 2.66 0.9364 1.0560 71.2% 3.72%

323.0 93.92 338.11 8.11 2.56 0.9377 1.0562 78.1% 3.65%

342.0 102.46 368.87 8.85 2.46 0.9389 1.0563 85.2% 3.59%

361.0 111.25 400.51 9.61 2.37 0.9399 1.0563 92.5% 3.54%

380.0 120.28 433.00 10.39 2.27 0.9409 1.0564 100.0% 3.50%

Uncertainty @ 25 % of QmaxSensor height (mm)

Estimate of Normal Flowrate l/s

Mean fluid temp (oC)

r (measurement error ) %Error in Flow calculation %

Uncertainty in zero datum (mm)

Uncertainty @ Qmax

Maximum head "h" mm


Approach level varn. 100mm

hmax/b shall be < 3

hmax

/L shall be < 0.67

bhmax/B(hmax+p) shall be < 0.7

Sensor location at 3 to 4 hmax (mm)

Uninterupted approach (mm)


Bestobell Service

* The maximum acceptable dimensional

variance is indicative of practical limits, and

exceeds the variance limits stated within

paragraph 6.3.3 of BS3680 Part 4C



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Discharge / Uncertainty CurvesDischarge / Uncertainty CurvesDischarge / Uncertainty CurvesDischarge / Uncertainty Curves

Bestobell Service

Stage Discharge Curve

0

50

100

150

200

250

300

350

400

0 20 40 60 80 100 120 140

Flow (litres/sec)

Gau

gedHead(mm)

Uncertainty Curve

0%

10%

20%

30%

40%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Flow rate (%)

+/-%U

ncertainty



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Customer : A Water Company Date Certified 19/12/00

Site Name: ABC WWTW

Duty: Flow to Treatment

605 380

303 120

1200

0 h (mm) q (l/s)

0.6 n1 0 0.0

1640 n2 38 3.4

380 n3 76 10.0

250 n4 114 18.9

816 n5 152 29.6

n6 190 41.7

3.50% n7 228 55.2

3.68% n8 266 69.9

4.04% n9 304 85.6

5.17% n10 342 102.5

n11 380 120.3

Maximum Minimum 4 to 20

0.432 0.428 0

N/A N/A 120.3

l/sFLOW CALCULATION M

3

5

Head (mm) CD CV Flow (l/s) mA o/p 180

19.0 0.7238 1.0387 1.02 4.14

38.0 0.8471 1.0488 3.40 4.45

57.0 0.8667 1.0503 6.40 4.85

76.0 0.8819 1.0515 10.0 5.33

95.0 0.8945 1.0525 14.2 5.89

114.0 0.9034 1.0533 18.9 6.52

133.0 0.9106 1.0539 24.0 7.20

152.0 0.9163 1.0544 29.6 7.93

171.0 0.9209 1.0547 35.5 8.72

190.0 0.9245 1.0551 41.7 9.55

209.0 0.9275 1.0553 48.3 10.43

228.0 0.9299 1.0555 55.2 11.34

247.0 0.9320 1.0557 62.4 12.30

266.0 0.9337 1.0558 69.9 13.29

285.0 0.9352 1.0559 77.6 14.32

304.0 0.9364 1.0560 85.6 15.39

323.0 0.9377 1.0562 93.9 16.49

342.0 0.9389 1.0563 102 17.63

361.0 0.9399 1.0563 111 18.80

380.0 0.9409 1.0564 120 20.00

Flow Readin l/s

Sensor height (mm)

Uncertainty at Max Flow

Uncertainty at 75%

Uncertainty at 50%

Calibration DataCalibration DataCalibration DataCalibration Data

WJ460 CONFIGURATIONFLUME DETAILS

Uncertainty at 25%

Roughness "k" (mm)

Flume Depth "H" (mm)

CHANNEL 2 PARAMETERS

Maximum head "h" (mm)

Throat Width "b" (mm)

Throat Length "L" (mm)

Sensor Dead Band (mm)


Output range (mA)

4 mA output (l/s)

Ref. Target readings

Target height (m)


Average

q-max (l/s)

h-max (mm)

Definable Flow Device

Volume Units

20 mA out ut l/s

Flow units

Interval

Bestobell Service


24/35

Example Survey Method (01_01_1).doc Page 1 of 3

Bestobell Service

Client A Water Company

Method Statement for Open Channel Flow Structure Survey Page 1 of 3

1. Scope of Work

1.1.Assessment of open channel flow monitoring facilities, for conformance with BritishStandard 3680

2. Health and Safety

2.1. All works will be carried out in general accordance with the site owners Heath & Safetyprocedures.

2.2. Authorisation / permits shall be obtained from the site owner prior to site entry.

2.3. BSCL / Mobrey operatives SHALL NOT ENTER any category of CONFINED SPACEwithout specific written authorisation. If arrangements have not been made prior to thesurvey visit, with the appropriate safety procedures in place, structure details / dimensionsmust be obtained from existing documentation.

2.4. BSCL / Mobrey operatives SHALL NOT carry out detailed inspection / measurement ofstructures, where it is considered dangerous to do so. eg wide / deep / fast flowingchannels. If arrangements have not been made prior to the survey visit, with theappropriate safety procedures in place, structure details / dimensions must be obtainedfrom existing documentation.

2.5. BSCL / Mobrey operatives SHALL NOT carry out any changes to calibration parameters

without having obtained permission from the appropriate responsible person.

3. Method

3.1. Visually inspect the primary device, observing:a. Whether critical conditions exist, presence of a standing waveb. General condition of the structurec. Approach velocity, surface conditions, scum marksd. Location of penstocks, bends, recirculation pipework, grit deposition

3.2. Photograph and sketch the main features of the installation

3.3. Measure all critical dimensions and levels of the structure, recording the results on theappropriate survey record sheets. (See paragraphs 2.3 & 2..4)

3.4. Visually inspect the secondary device, noting location and condition

3.5. Interrogate the secondary device noting all calibration parameters.

3.6. Where the installation substantially conforms to the appropriate section of BS 3680prepare certification documentation noting any reservations and recommendations whichwould result in an improved measurement accuracy

3.7. Where the installation fails to comply with the appropriate section of BS 3680 prepare areport identifying the reasons for none compliance and provide an overview ofrecommended remedial works.


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Bestobell Service



4. Programme of Work

4.1. The work shall generally be carried out in accordance an agreed programme. All work willbe carried out on weekdays between the hours of 8.00 and 18.00

5. Personnel

5.1. The name(s) of the assigned engineer(s) and mobile telephone number will be notified atthe time of arranging the survey

5.2. All personnel employed on the surveys are experienced in the operation and hazardspresent on a sewage treatment plant, will be familiar with the health and hygiene

requirements and Water Company Heath & Safety procedures.

5.3. Although no entries will be made without prior arrangement, at least one of the engineerswill be confined space trained. This is considered necessary in order to recogniseunidentified hazards.

6. Equipment

6.1. The surveying engineer will be equipped with the following:

Calibrated surveyors level, tripod and measuring staff, spirit level, internal callipers, 1m

steel rule and measuring tapeDigital cameraCertified multimeterPortable computerPersonal protection equipmentCleaning and sterilisation materialsMobile telephone

7. Contacts

7.1. All activities will be administered from:

Bestobell Service Co. LimitedLake View,Cooper Street,Hazel Grove,StockportSK7 4LT

Telephone 0161 483 5051 / 0931Fax 0161 483 4145

7.2. The person responsible for this contract is:

Mr Les Hunter Contracts Manager (mobile telephone 07768 641558)


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Bestobell Service



7.3. Normal office hours are 0830 - 1700 Monday to Thursday and 0830 1630 Friday

7.4. For both safety and administrative purposes, the survey team shall notify the above officeupon entering and leaving each site


27/35

Selecting a Flow Specialist

Environment Agency Requirements

The Environment Agency is currently implementing a programme, to ensure that both Sewage andTrade Dischargers, provide meaningful and dependable discharge flow records to the Agency.The requirements of this programme are detailed within the Environment Agency document,Procedure for Flow Measurement of Discharges (version 4.2 Sept 2000)

This document states that:

As soon as practicable after completion of the flow recorder installation the ConsentHolder shall employ an independent expert to certify that the installation complies with theAgencys specification. The Consent Holder shall satisfy himself as to the professionalcompetence of the expert. A copy of the certifiers report shall be provided to the Agencywhen it is available.

How does a Consent Holder assess the competence of the expert ?Currently, there is no authoritative body, which assesses the competency and provide accreditationof procedures, for this type of flow specialist. Given the involved nature the work and the level ofexpenditure involved, this can mean that the selection and appointment of a flow specialist,becomes extremely difficult and onerous.

It is important to recognise that the certification of an open channel flow system, involvesverification of all aspects associated with the system. i.e.the suitability of application, the geometryof the installed structure, the correct installation of the sensor head and the correct calibration ofthe recording instrument. There are many companies that have experience in individual aspects ofthe system, but few having an established track record, in being able to offer a turnkey capability.

In selecting a Flow Specialist, the Consent Holder should ensure that the following criteria aresatisfied.

The Flow Specialist should be able to demonstrate:

A practical knowledge in the application of the Environment Agency document, Procedurefor Flow Measurement of Discharges (version 4.2 Sept 2000).

A broad knowledge of the wastewater treatment process, inlet / outlet configurations, re-

circulation practices etc, so as to ensure correct application, and operation of flowstructures.

Proven, documented procedures, in the practical application of BS3680 open channel flowstructures.

The ability to provide and substantiate measurement uncertainty data, in accordance withBS3680, and the requirements of the Environment Agency.

An in depth capability in the assessment of existing flow structures, providingrecommendations for remedial works / provision of new structures.

Sufficient practical knowledge to provide recommendations based on the least costoption, in order to fulfil budget, operational and EA requirements.


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Proven procedures, which ensure that all aspects of Quality and Health and Safety aremaintained in all stages of the surveying, design, supply and installation activitiesassociated with open channel flow structures.

The ability to undertake full responsibility for all activities associated with design, supply,installation, calibration and certification for both remedial works, and provision of newmeasurement structures.

A capability in supporting the variety of instrumentation utilised in both open channel andclosed pipe flow measurement.

A broad flow application knowledge, to enable alternatives to BS3680 measurementtechniques to be proposed and supported, when considered appropriate.

Sufficient financial and labour resource, to fulfil the project requirements.

An insight into many of the above requirements can be gained from an accurate assessment of acompanys past experience, in delivering similar f low related projects.

Solartron Mobrey have been involved with the measurement of f low discharges for over 6 years.During this period, we have been involved with several Water Companies in the implementation oftheir Flow Audit Schemes.To date we have carried out over 600 flow surveys, and completed remedial works atapproximately 300 sites, of various sizes.All works have been successfully completed to client satisfaction, and certified to substantiallycomply with BS3680, satisfying Environment Agency legislation.


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Reference list Discharge flow compliance works

Page 1 of 2

Bestobell Service

Date Customer Contact Value Description

1996-98AnglianWater

David Tyler01480323962

1,500k

Survey / report / remedial works / certification of

structures at over 200 STW sites. Remedial worksincluded: replacement and calibration of instruments(Mobrey, Milltronics & GLI), construction of flume / weirchambers, installation / replacement of flumes andweirs, overpumping etc.

1998SevernTrentWater

Ian Wright0116

234034037k

Survey / report / cost estimate of flow structures at 88STW sites.

1998 -ongoing

YorkshireWater

RobBainbridge

01756706857

95kSurvey / report / certify over 150 flow structures andmagmeter installations. Work included calibrationverification by drop testing where necessary.

1998 SouthernWater

Chris

Brooks01303264124

37k Survey / report / cost estimate of flow structures at 50WWTW sites.

1999SevernTrentWater

AlanBramley0128351255

47k

Clay Cross STW. Works included levelling the approachand flume, in the flow to works channel. Installation ofan MSPLOG system. Installation of a magmeter andpenstock to monitor and control flow to treatment,including chamber construction, pipework modificationsand associated controls.

1999AnglianWater

Tony Bland01842725730

15k

Replacement of GLI instruments with Mobrey MSP90units, to provide Year 2000 compliance at 11 STW sites.Works also included certification of the completedinstallation.

1999Yorkshire

Water

RobBainbridge

01756706857

64kRemedial works to flow structures at 5 STW sites. Theworks included : replacement and calibration ofinstruments, replacement of flumes and weirs,overpumping etc.

1999 -2000

SevernTrentWater

Ray Cox0121 722

449615k

Survey / report / cost estimate of flow structures at over20 STW sites.

1999 -2000

AnglianWater

Steve Riley01603247174

180k

Survey / report on structures at 45 STW sites.Undertake remedial works at 20 sites includingreplacement and calibration of instruments (Mobrey,Milltronics & GLI), construction of flume/ weir chambers,installation / replacement of flumes and weirs,overpumping etc.

1999 -2000

SouthernWater

Ian Derham01962716547

295k

Remedial works to flow structures at 15 WWTW sites,including replacement and calibration of instruments(GLI), construction of flume/ weir chambers, installation /replacement of flumes and weirs, overpumping etc.

2000

SevernTrentWater

(Carl Bro)

StephenMerchant

01179232221

65k

Remedial works to flow structures at 13 WWTW sites,including replacement and calibration of instruments(GLI & Milltronics), installation / replacement of flumesand weirs, overpumping etc.

2000ThamesWater

IanSimmonds

01322220727

19k

Longreach STW, supply, install and certify new PVCfume within elevated storm overflow channel. Channelwidth 1500mm, throat width 1000mm, flow range2600l/s

2000Yorkshire

Water

RobBainbridge

01756706857

25kHarrogate South STW, replacement of 400l/s FTTflume, including levelling of approach and flume beds,overpumping etc


30/35

Reference list Discharge flow compliance works

Page 2 of 2

Bestobell Service

2000 -ongoing

Southern

Water(Morrisons)

Dave Bone

01273663277

350k

Remedial works to flow structures at 16 WWTW sites,including replacement and calibration of instruments

(GLI), construction of magmeter chambers, installation /replacement of flumes, weirs and magmeters,overpumping etc.


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32/35

Four 12-inch and two 8-inch diesel pumps were used for the over-pumping operation in order

to satisfy the possible maximum flows of 1500 lit/sec. A temporary dam was craned into

positioned across the channel to provide a well for the pump suction hoses. The pumping

equipment was set-up during days preceding the works, and the final discharge hose sections

fitted when the road was closed at 8pm.

Paul Cherry of the Bestobell / Mobrey team remembers: In the event, there was no rain that

night, so we did not have to cope with maximum flows. The team worked under floodlights and

completed the installation of the weir plate in a matter of hours. By early hours of the morning

the weir was operational, and the road was open again.

Level measurement at the weir point is provided by an ultrasonic level meter, which is fitted

with a specially modified head verification device, for checking calibration of the meter without

having to go down into the channel.

In addition to the Peel Common project, Bestobell has now completed remedial work on Open

Channel Flow Structures at various other sites on behalf of Southern Water. On completion of

the work, each installation has been certified as being substantially compliant with the

requirements of BS3680.

Ends

For further information contact:

Peta Glenister: Tel: (01753) 534646. Fax: (01753) 823589. email: [email protected]

Editorial contact:

Rachel Owen, Black & White Technical Marketing Communications, 8 Sceptre House,57 The Hundred, Romsey SO51 8BZ. Tel: 01794 521156. Fax: 01794 521157.Email: [email protected]

Solartron Mobrey is one of the worlds largest suppliers of instrumentation for level measurement,serving markets in 66 countries, through a worldwide network of distributors and agents.

Web site: www.mobrey.com


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1

1

MM278Issue date: To Water & Waste Treatment only 1

stJuly 1999

Implementing effluent flow monitoring regulations and guidelinesBy Alasdair Ward of Solartron Mobrey

Nearly all the Consent to Discharge orders granted by the Environment Agencyto larger sewage treatment works include a requirement for continuous

monitoring of flow volumes. Although the Agency has not been in a position to

actively enforce this requirement until now, it will begin implementing a new

programme of checks later this year, designed to ensure compliance. In this

article, Alasdair Ward of Solartron Mobrey warns that there is a great deal of

work to be done if the industry is to meet the EA requirements. He calls forclarification from the Agency on some of the detail, and advocates a more

structured approach to the whole issue of flow auditing and site certification.

The UK enactment of European Directives under the Water Resources Act 1991 and the subsequent

Environment Act 1995 demand that the Environment Agency (EA) achieves certain Water Quality

Objectives. In carrying out this work, and as part of its wider duty to protect the environment, the

Agency requires dischargers to measure and record effluent flows. This requirement is included in

most Consents to Discharge granted by the EA for medium and larger discharges of trade and sewage

effluent.

Until now, Consent to Discharge conditions relating to flow measurement has not been widely

enforced. The Agency has the power for criminal prosecution of non-compliant companies, with the

possibility of significant fines for repeated offences. Under a new policy, the Agency will soon start

to implement a programme of enforcement, designed to ensure compliance among dischargers.

Where Consents already include flow measurement conditions, these will be enforced. Where they do

not, appropriate conditions will be added.

98% of the waste water treatment sites in UK have at least some open channel flow, and for many it is

the primary method of discharge. Hence much of the discussion on the subject of discharge centres

on issues of open channel flow measurement.

As one of the first steps in its programme to ensure compliance, the EA published its Technical Report

P150 Flow Monitoring of Discharges: An Audit Manual* in January 1999. It is based on, and distils the

essential relevant information from the European Directive, and from the British StandardBS3680 Methods

of Measurement of Liquid Flow in Open Channels, whichdetails correct design and use of primary flow

structures such as flumes and weirs. Based on the existing documentation and experimental data, the EA

report has identified a minimum accuracy of8% for discharge flow monitoring. Interestingly, early work


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2

2

by Mobreys flow audit team in this area indicated that about 90% of all open channel flow structures in

the UK do not meet this 8% accuracy standard. According to the Environment Agency, many sites are

inadvertently sub-standard, and may not even be aware that there is a problem. In other words, if the full

force of the law were to be applied across the UK right now, most operators would be seriously in breach

of the terms of their Consent to Discharge. Typical problems include design inaccuracies, build-up ofdeposits over time, inappropriate up- or down-stream flow conditions and incorrectly calibrated secondary

instrumentation.

Technical Report P150 sets out guidelines for the flow audit procedure, and is the document, which will be

used by Agency personnel involved in surveying sites. It is available for companies carrying out their own

flow audits. The Agency will require that dischargers install flow monitoring to the required specification

and have the installation certified by an external body. The Agency will audit a number of installations

each year.

Discrepancies

There is no doubt that Technical Report P150 is a useful, and much needed document, the widespread use

of which is to be encouraged throughout the industry. However, having studied it, the author believes that

there a few discrepancies between it and other standards, which need to be cleared up if confusion is to be

avoided. These discrepancies include:

In section 2.2.2.7 Construction of the Primary Device, P150 quotes the BS3680 tolerances for flumeconstruction. In fact these tolerances are almost universally unachievable in practice, and most flow

engineers tend to employ more practical guidelines to ensure accuracy of the flume. According to the

Agency, implementation is being discussed internally at the moment, but it seems likely that, as long

as the overall accuracy of the installation can be shown to be 8%, these tolerance details will

probably not be enforced.

In section 2.2.3Installation Effects, the technical report quotes BS3680 saying that the distance thatshould be allowed upstream of a weir is 10 times the maximum width of the nappe plus five time the

maximum head. The report omits to say that this distance is not required by the British Standard if

the approach velocity is negligible. If there is no disturbance to the water, then the upstream distances

are not necessary for accurate measurement.

Despite these discrepancies, the technical report provides the industry with a good starting point. It will

help to clarify thinking on the subject and provides a useful tool for use by discharges and Agency

surveyors. Interestingly, the Agency is apparently considering production of a shorter, less technical

version of the document, aimed at managers and non-technical staff.

Compliance and the case for accreditation

In order to comply with the legislation on effluent discharge, water companies must prove to the EA that

they are monitoring flows adequately. In other words, they must complete a full flow audit, correct any


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3

errors and implement a maintenance programme to ensure accuracy is maintained. Importantly, they must

document all of these procedures in a manner suitable for inspection by the EA, in order to prove

compliance.

There are already a few companies Mobrey being one of them - offering flow auditing and consultancyfor compliance with the new regulations. When work is completed to the required standard, a certificate of

compliance is issued, which can be used as documentation for inspection by the EA. However, since the

EA does not operate an accreditation scheme for bodies carrying out this work, there is no cast iron

guarantee of quality, or that the work will meet EA requirements.

Today the legislation is new and those with the necessary skills and experience to carry out this work are

few, and for the most part, are well known in the industry. However, without proper regulation, there is a

danger of cowboy and / or inexperienced operators in the future offering sub-standard compliance

audits. Flow is a complex subject, but one on which there are vast amounts of experimental data. With the

right knowledge and experience even the most complex flow systems can be fully audited to the required

accuracy.

The publication ofFlow Monitoring of Discharges: An Audit Manual is a great first step by the EA in

helping the industry to implement new legislation, but it does not go far enough. There is a strong case for

an accreditation scheme for companies offering consultancy and contract civil work (such as the

Competent Body scheme which authorises test labs to certify compliance with regulations on

electromagnetic compatibility for new products, for the electronics industry). Such a scheme would set

minimum levels of quality and give the industry a practical means of ensuring compliance.

Ends

For further information contact:

Peta Glenister: Tel: (01753) 756600. Fax: (01753) 823589. email: [email protected]

Editorial contact:

Rachel Owen, Black & White Technical Marketing Communications, 8 Sceptre House,57 The Hundred, Romsey SO51 8BZ. Tel: 01794 521156. Fax: 01794 521157.

Email: [email protected]

Solartron Mobrey is one of the worlds largest suppliers of instrumentation for level measurement,serving markets in 66 countries, through a worldwide network of distributors and agents.

Web site: www.mobrey.com