# Presentation: 095810

## Pre-mobilization Error Checks of Multiparameter Field Instruments: 

**Presented by Pete Penoyer, **
**National Park Service**
**Water Resources Division, **
** **5th National Monitoring Conference
- San Jose, California
- May 7-11, 2006

**Pre-mobilization Error Checks of Multiparameter** **Field Instruments**:
**One Way of Promoting Servicewide Consistency in a Water Quality Monitoring Program**

**Notes:**
Shoreline photo from one of the islands of Channel Islands NP in Background Photo

## INTRODUCTION

**Background**
**Inventory and Monitoring Program resulted from National Parks Omnibus Act – (1998) Congressional Appropriation**
**Natural Resource Challenge**
**Established **_**Vital Signs Long Term  Monitoring Program**_** (base funded)**
**Ecological Monitoring Framework comprised of 6 Broad Categories or Monitoring Components**
**       **_**(Level 1**_**)                **_**(Level 2**_**)         **_**(Level 3**_**)           **_**Vital Sign**_**     **_**Potential Measure**_**	**
**	****Air & Climate**
**	****Geology & Soils**
**	**_**Water**_**..............****Water Quality...Water Chem....Water Chem....T,SC, pH, DO, -  ****	****	****	****	****	****	****Cat/An, Trc.M**
**	****Biological Integrity**
**	****Human Use**
**	****Landscapes****  **
**Establish baseline resource condition and determine status and trends of  NPS resources  related to water (includes –quality, quantity, chemistry, hydrology, aquatic flora and fauna etc.)**
**Regulatory – recognized impairments under CWA, (e.g. 303d listed) or elevated protection (e.g. ONRW status)**
**Non-regulatory – resource condition status and trend, threats, stressors, best indicators to measure at various scales**
*** DISCLAIMER** - Use of firm, trade, and brand names in this presentation is for identification purposes only and does not constitute endorsement by the National Park Service

**Notes:**
As an introduction - I’d like to begin with a little background and context for the type of monitoring program NPS has initiated and why establishing Servicewide consistency can be a challenge in such a program.
Congress passed the National Parks Omnibus Act in 1998 which funded the Natural Resource Challenge. 
A major component of the Natural Resource Challenge was the continued funding of Park Service resource inventory with the addition of base funding for a “Vital Signs Long Term Monitoring Program” 
The purpose of Vital Signs was to develop comprehensive , long-term monitoring of ecological resources within the U.S. National Parks.
Vital Signs are indicators, and are defined as a subset of physical, chemical and biological elements and processes of park ecosystems that are selected to represent the overall health or condition of park resources, known or hypothesized effedts of stressors, or elements that have important human values.”

Natural Resource Monitoring Components Include:	Air & Climate								(AGWBHL)							Geology & Soils
										Water
										Biological Integrity
										Human Use 
										Landscapes

## Vital Sign(?)

- Vital Sign –
**“****a subset of **_**physical**_**, **_**chemical**_** and **_**biological**_** **_**elements and processes**_** of park **_**ecosystems**_** that are selected to represent the overall **_**health or condition of park resources**_**, known or hypothesized **_**effects of stressors**_**, or elements that have **_**important human values**_**.”**

**Notes:**
But first - what is a Vital Sign or how do you define it?

## CONTEXT

**Vital Signs Ecological Monitoring Program**
- Decentralized or bottoms up approach but of national scope (no “nationally consistent study design” in the same sense as the NAWQA program)
- 270+ resource parks organized into 32 monitoring networks (some shared or common ecological and geographical basis)
- 32 separate monitoring plans with a local focus to meet resource management needs of Network parks
- A national component in compilation, management, storage and reporting of data [EPA STORET, WRD managed version (WRD STORET) with additional metadata requirements]

**Notes:**
In what contest is NPS conducting this program?
Unlike the NAWQA/EMAP program, the Vital Signs program takes a very decentralized bottoms up approach. 
Networks respond to local resource management needs and priorities, e.g. follow state protocols when in conducting monitoring in a regulatory context or other protocol customized for their region, indicator being monitored, or to meet need for integration with other vital signs.

## Vital Signs Monitoring Networks

**Vital Signs Monitoring Networks**

**Notes:**
This slide shows the general geographical areas covered by the 32 NPS Ecological Monitoring Networks.
Parks are small green outlines/spots are the resource parks and range as far south as Virgin Islands, across the continental US to Alaska and east from Acadia NP Maine to the Hawaiian Islands and American Samoa and Guam in the Pacific (both marine and terrestrial  Parks are included as are National Seashores, Lakeshores, National Monuments, Historic Sites, and National Battlegrounds with natural resources)

## Water Quality

**Water Quality is one of a subset of Monitoring Components related to aquatic resources**
**Required “core” set of water quality parameters to be collected in situ servicewide**
**Temperature (****oC)**
**Specific Conductance (****μS/cm)**
**pH  (std. units)**
**Dissolved Oxygen (mg/L)**
**Flow / Level**** (should be quantified but may be qualitative/estimated at a minimum – STORET Severity Index)**
-   *** Local networks build on or add to these core parameters (both field and lab parameters) based on Park’s specific needs and specific goals and objectives (management needs, other resource assessment or WQ monitoring issues are integrated with the other ecological monitoring to be conducted over the long term)**
**Example: **_**Integration**_** of Air Deposition monitoring (precip. acidity) with ANC WQ parameter data**

**Notes:**
An overall agency goal is to better understand the current condition or status and trends in our resources to meet the NPS mission of “preservation for the enjoyment of future generations” to better know and understand our resources
How we get there is like the devil “in the details” and largely driven by local resource management needs, concerns and priorities.
Beyond this set of 4 water column measurement parameters plus flow or level and meta data requirements, it is up to the networks to decide what indicator parameters to monitor for long term resource protection.
While we recognize that the variability in these core parameters do not necessarily lend themselves to long term trend analysis, they do provide very basic information about a waterbody and therefore will be collected at all sites to foster some servicewide consistency and comparability of data.

## Fostering Data Comparability and Consistency in a Decentralized Program

- Recognize that there are many** **_**strengths**_ as well as _**weaknesses**_ in a program of such decentralized control characterized by:
**Creativity, empowerment, responsibility for decisions shifted to those at the local level and those actually doing the plan development and implementation of monitoring**
**Better address local resource management issues and concerns**
**Program buy-in by park superintendents and staff**
**Flexibility to meet various State regulatory protocols under CWA**
**One size rarely fits all in NPS (particularly in resource monitoring with the diversity of NPS resources and monitoring situations)**
- Network/park staff with science advisors/cooperators select
- Additional parameters to monitor (beyond core set)
- Water bodies to monitor & Sampling design (e.g. judgmental, probabilistic, hybrid)
- Protocols & SOPs to follow (States, other Federal Agencies, customized)
- Instruments to procure*
- Major concern is fostering consistency in data collection and maximizing the comparability of resulting data where possible (seems to be a common problem or shared objective among the many agencies conducting water quality monitoring – can be more problematic when driven by local resource management needs or goals and objectives)

**Notes:**
This is a first step and results from the recognition that:
	- other federal agencies monitoring are also driven by local monitoring needs to address local issues (e.g. FS – Forest Supervisor may have particular issues or or questions to be answered by monitoring, not so different from other agency district offices of BLM, COE, Bureau of Rec. etc.) 
	- many vendor water quality instruments are reaching a common level or performance capability
For both synoptic and continuous monitoring – technology has leveled the playing field
	-Calibration methods and standards are becoming fairly uniform
	-Calibrated instruments have the potential to measure the basic set of water quality parameters quite 
           accurately and consistently
	Offers an opportunity to develop a protocol that can be widely accepted among many if not most monitoring agencies since fostering good quality data should be a commonly shared goal.

## HOW??  (one small way/step)

- Propose/initiate discussion of a “**straw man”** streamlined _protocol_ for error checking of water quality instruments/sensors to be applied servicewide in NPS and one that could be widely accepted and employed across multiple agencies (if feasible) – _focus of this presentation is:_
- to facilitate the shared goal of obtaining the best quality data at the least cost and burden to monitoring staff,
- using a multiparameter water quality instrument/sonde sensor _error check protocol_ as a possible example,
- performed post-calibration but pre-field mobilization (i.e. under controlled office or lab conditions before heading into field)

**Notes:**
We are hearing a lot these days about using common or shared protocols to facilitate data comparability.
This may be one small way or small step to achieve a greater level of data consistency and comparability and both higher confidence and documentation in the field measurements made.  It is nearly always a shared goal to obtain the best quality data possible at the least cost and burden to monitoring staff.

The fact that many vendor field instruments are achieving a common level of capability in obtaining representative values for water quality parameters offers an opportunity to take advantage of this in developing a common set of protocols which may be largely independent of local DQOs, or goals and objectives of a specific monitoring program.

What I am proposing here is a “straw man “ approach to develop a streamlined error check protocol for field instruments that can be widely adopted.  Because monitoring goals and objectives will often vary both within and between monitoring agencies and this will dictate actual field sampling methods followed and the type of analysis performed, establishing an error check protocol for field instruments prior to field mobilization should be a first test of reaching a common/shared protocol across different organizations conducting monitoring.

## WQ  FIELD INSTRUMENTS/MONITORS(2006)

- Sondes/Multiparameter Probes & Displays
**YSI 6 Series Datasondes & Minisondes**
- MDS 650 Display System
-  Software: Ecowatch for Windows*
**Hydrolab Series 5a Datasondes & Minisondes**
- Surveyor 4 display
- Software: Hydras3 LT*
**In-Situ Troll MP9000/9500**
- Rugged Reader
- Software: Win-Situ / Pocket-Situ*
- Also PDA based HydroPlus software  integrates Windows CE computer, GPS receiver, with any 3 of the above WQ Monitoring instruments
- 		* Others e.g. Eureka Environmental (NOT EVALUATED by NPS)
- 			Manta Multiprobe                  							- Amphibian Display
-                                         		 - Software: Easy Data
- 		(Horiba, Global Water, Stevens, etc.)
- * May combine with various telemetry systems for automated monitoring

**Notes:**
These are the field instruments/displays and operating software recently purchased by several Networks that intend to conduct synoptic and continuous monitoring under the VS program.  We at WRD have first hand experience with the top 3 in operation of these instruments and in performing relatively simple sensor error check protocols being proposed.  There is little reason to believe these sensor error check procedures would not largely apply to other instruments or a wide cross section of what is available on the market with little or no modification.

WRD Evaluated Vendor Instruments:
WQ Sondes – are bundled sensors – Provide significant flexibility and seem to be the direction most monitoring agencies are moving toward in their collection of common field parameters (NPS Core param. of T, SC, pH, DO, Level/Stage/Depth) and in particular when performing continuous monitoring.
Instruments WRD has looked at/tested that seem to have greatest flexibility, measurement capability/sensor expandability options, good vendor track records  
WQ Measurement System Components are:  the Sonde (with its bundle sensors – core parameters+); handheld display; software for communication from sonde to the handheld display or a laptop (all different and do not communicate with each other, but all can transfer to excel files for analysis and further processing

## WQ SENSORS

**Core Parameters** (_freshwater)_
**Temperature** (Co*)
**Specific Conductance** (uS/cm*) **(raw cond., salinity, TDS)**
**pH** su*
**Dissolved Oxygen** (DO) (mg/l*) (w/ barometric Pressure)
**Level/Depth** (vented or un-vented depends on use as depth or stage/level measurement)*
- Others
- Turbidity (NTU*)
- ORP (mv*)
- Chlorophyll a
- Ion selective: Nitrate, Ammonia, Chloride, (not recommended)
- TDG, Rhodamine WT, PAR; can fill other niche/specialty monitoring needs
- * required reporting units of measurement

**Notes:**
1. As hardware, software and ease of use of multiprobes has improved, they have begun to largely replace single parameter instruments instruments for field measurements (e.g. Temperature comp. for all – even turbidity, temperature and salinity for DO), use better hardware and software w/ built in algorithms for derived values – SC, TDS, and Salinity - from conductivity)
Order of listing is least to most problematic in continuous deployments (i.e. ease of fouling ,degree of drift etc.)
 However there is a new DO sensor, variously referred to as optical/digital/luminescent/ DO (sensor) that may become less of a fouling and drift issue than the pH sensor so pH will likely become the limiting sensor in continuous deployment driving the recalibration/maintenance frequency needed.

Temperature Sensor – fairly bullet proof (thermistor) but must come from the factory calibrated properly because all other sensors are automatically temperature compensated
Specific Conductance also fairly bullet proof measure as long as sensor is maintained (electrodes corrode/build up deposits)
pH can give you some problems particularly in low ionic strength waters and requires following storage and maintenance specified by contractor to be closely followed – may not be as long-lived
Turbidity is often a good optional sensor to add
 ORP is used primarily in groundwater moritoring
 Remaining sensors are normally not recommended as they can have several issues related to measurement sensitivity, MQL (relativel to lab analysis), and representativeness in what is actually being measured (e.g. chlorophyll).  These are used more in a research mode.

## Hydrolab H20

- YSI 600XL

- In-Situ Troll
- MP9000

**YSI 650      MDS**

**In-Situ Rugged Reader**

**Notes:**
This is just an illustration of some of the types of multiprobes out there – although that is an older version of Hydrolab equipment, the more modern version of the YSI 600XL (center) and In-Situ MP9000 Sondes (center) and their hand-held display systems

1. Hydrolab H20 (old Datasonde with stirrer for DO measurement) Surveyor Hand Held Display (not shown)
2. YSI 600 XL (minisonde – no internal storage memory unlike 600 XLM or datasondes, so used primarily for synoptic sampling) w/ 650 MDS hand held display
3. In-Situ TROLL MP9000 with Rugged Reader Display
Note: Stands and holding clamps are a must and greatly facilitate proper calibration
Other shared components
Sonde Itself – Handheld display – Connection cable – Sensors - Calibration cups, Sensor guards, Sonde/Vendor specific tools, battery/power cables and laptop/desktop computer interface cables
Also shown (far right) are DO flow cell and bubble box & calibration chamber for DO calibration in 100% DO saturated water vs more common DO calibration method (100% saturated air).
Point here is that the latest models of these systems for our core parameters and some others are getting comparable.  They all do the basics quite well.

## Why Don’t all Vendors Instruments Provide the Same Measurements for the Same Sample?

- Often use different _built-in algorithms_ to obtain a derived or computed value from an  _indirect_ measure
- e.g. Temp-meas. is based on expansion of a metal composite converted to a temp., pH based on meas. of mv potential across a glass membrane & automatically fit to different slopes for different temperatures (i.e. temperature compensated), DO-meas. potential (mv) across a membrane & relate that to a DO concentration w/ automated correction for salinity and temperature
- Vendors Sometimes Use Different Conventions
- e.g. **%DO** - YSI bases all measures on value for 100% DO _at sea level (Their std. “DOsat %” convention)__1__ _
-                 - In-Situ and Hydrolab base on actual 100% DO saturation for the site elevation your at
-                    [Thus: YSI instrument will always report a lower %DO value when above sea level _unless_ set up in
-                     **DOsat% Local** mode – Software version 2.13  (2001 & later)]
- 	 **ORP** – YSI & In-Situ based ORP measure on the Ag/AgCl Half-cell reaction  or 3M KCl **AgAgCl scale** (Ag/AgCl
-                     ref. electrode)
- 	         -   Hydrolab based ORP determination on Hydrogen Half-cell reaction or **NHE scale** (Ag/AgCl ref. sensor)
-         *results in ~ 200 mv difference in measured values due to the scale **“offset”** when calibrated with the same
-          standard (e.g. Zobell solution) using +428 mv **(NHE Hydrogen scale)**  vs +229 mv **(Ag/AgCl scale)** @ 25o C
- Always some measurement error differences (inaccuracy – due to **sensor differences** in _linearity_, _response time_, _sensitivity to pressure_, _temperature_, _flow_ and _drift_ that may cause bias/systematic error and lack of precision/random error plus _**operator controlled variables**__ _(e.g. quality of Calibration Stds., meas. residence time, sensor maintenance and calibration technique and frequency).
- 1 YSI Version 2.13 of 6 - Series code available since late 2001 now _allows_ setup in “DOsat %” Local, but _must do this_
-   _setup__ __ yourself_ as new sondes are still provided in the conventional DOsat % mode.  WRD recommends use of the
-     **“****DOsat **%**” Local** mode for purposes of standardization and Servicewide comparison of data (see ops manual for setup instructions).

**Notes:**
I won’t go into the details but there are reasons why properly calibrated instruments of different vendors (for a couple of parameters) will not and should not provide the same measurement value or result in some instances.  For example, in some cases ORP and DO %sat are two parameters that should not be expected to provide the same measurement value for the same environmental sample.

## Servicewide Consistency 

- How do we foster similar levels of data quality Servicewide and some consistency in instrument use _without_ placing undo burden on networks?
**In Recognition that:**
**Much of the reported data in future will be **_**synoptic**_** or **_**continuous**_** field measurements performed with these types of instruments/sondes under monitoring programs with **_**different goals and objectives**_
**Goals and objectives drive the monitoring protocols selected but everyone wants the highest quality data they can afford with minimum burden to monitoring staff**
**QA/QC of field measurements may not have been the best in the past (nor comparable to that of labs) – QAPP often lacking**
**There is elegance in simplicity (KISS - underlying MO) **
**Is interagency acceptance and wide application of a single protocol too much to hope for?**
**Are post-calibration error check protocols to be followed for at least the core field measurement parameters, a feasible way to go?**

**Notes:**

Could this title just as easily be “Interagency Consistency”  - but for now I am focusing on the NPS
Given our decentralized program structure:
WE do not mandate use of certain equipment for this program (nor do we want to) because the private sector vendors are very competitive and tend to leapfrog each other in capability, instrument quality and individual sensor performance over time.  There are also a lot of established user preferences out there.
The Issue of cooperating with other agencies and using their protocols (EPA EMAP, USGS NAWQA, States, particularly in any regulatory monitoring situation)

So how do we still foster some servicewide consistency

## Pre-mobilization Post-calibration Error Check Determinations

- Standardize across NPS and possibly adopt by other cooperators/agencies (NPS – to apply to core parameters at first – other sensor checks may be added later)
- Perform calibration and establish sensor error/accuracy under controlled office/lab setting before heading to field
-      (do sensors meet some acceptable error measurement criteria when measured against some standard or reference solution in a QC check*)
- Keep the protocol simple and general enough so that:
**can be performed easily at office or minimal (park) lab **
**does not require highly specialized equipment, overly expensive calibration standards/equipment, or significant training**
**would apply equally well to most/all vendor’s instruments**
- If sensor fails QC/error check, troubleshoot according to manufacturer’s O&M instructions or replace sensor if can not be brought into error specs.
- *variously referred to as “Maximum Acceptable Differences” (EMAP QAPP, 2001),  “Calibration Criteria” (USGS 2006) or “Range of Acceptable Differences” (USGS, 2000)

**Notes:**
One way is to take a standardized approach to error checking individual multiprobe/sonde sensors and determine if they fall within an acceptable range just before heading to the field.
Secondary benefit in that it would provide high level of confidence to operator that instrument is performing as it should and in measurement capability, providing that good field protocols are followed as well (may only have one MP instrument), catch faulty sensors, know just how linear they are behaving and their measurement accuracy before you get to the field.  Then calibrate in field at first site each day and only DO and possibly pH thereafter is really a must to recalibrate at each site (although should follow protocols specified under monitoring plan).

## Temperature Sensor (Thermistor) (oC)

**Calibration – None**
**Thermistors are **_**not calibrated locally **_**(only done by manufacturer; generally a one-time need)****, sensors can only be “**_**calibration**_** **_**checked”**_** by user against some NIST–certified or NIST-traceable* thermometer** (generally -5o to 45o C w/ 0.1o div. or similar)
**several other sensors provide temperature **_**compensated**_** values!!**
**thermistors are usually very linear and relatively bullet proof under today’s manufacturing specifications ****(least likely of all sensors to fail – report in units of ****oC****)**
**Error Check Protocol**
**single point error checks most easily done in sink water bath or bucket at/ very near **_**stabilized**_** room temperature ****(let water sit overnight in sink or use insulated container for error check of tap water bath at/near room temperature to minimize temp. gradient affects) **
**                                                                             ****      ****OR**
**Optional error check in temperature range of anticipated environmental water but will require stabilized water bath and minimizing temperature gradients (perform within insolated container) ****(read /est. Temp.  values to two decimal places – i.e. hundredths ****oC from 1 or 2  NIST-traceable thermometers****)**
- *_NIST-traceable_ thermometers are recommended (< $30 vs. > $600 for Certified)
- * see USGS protocols for more comprehensive calibration checks of thermistors to be performed quarterly or annually across a full range of temperatures (typically at 5 points from an ice water bath to 40 oC)
- USGS sensor (thermistor) Calibration Criteria for performing claibration checks in Continuous Monitoring applications (0.2 o C)

**Notes:**
This is how we propose it the “straw man” addressing each sensor error check post calibration but pre-mobilization.
Accurate Temperature measurement is very important (even turbidity measurements in some instruments is now temperature compensated)
First recognize that for most instruments Temperature calibration is largely only done by the manufacturer, so you really do not recalibrate the sensor, you only do a sensor check of the error and this is best done against a NIST–certified or NIST-traceable liquid in glass (usually mercury thermometer).  We are recommending the less expensive NIST-traceable Mercury-In-Glass (MIG) thermometer as being adequate and because they are relatively inexpensive (~$30) use two.
This is not substitute for but relies on full calibration/error check to be performed quarterly or annually under a program QAPP across full range (0 to 45o C) of possible environmental conditions.

## Specific Conductance (μS/cm)

- Is the Temperature Compensated (25oC) value of raw conductivity* (conductivity meas. can differ from SC by up to 3% per oC) **(also report raw conductivity value which is actually measured, specific conductance is a derived value)**
- Calibration
**Single Point calibration ****(follow triple rinse procedures & dry sensor)**
**Recommend use either a 1000 or **_**1413**_** μS/cm standard to calibrate ****(why – less likely to have solution carry-over issue)**
- Error Check Procedure
**Perform sensor error measurement check with both 100 μS/cm and 10,000 μS/cm calibration standards ****(use for monitoring waters in 1 to 10,000 μS/cm or more range)**
**Perform Sensor Measurement Error Calc. for each standard measured at end of range (100 μS/cm and 10,000 μS/cm)**
**Dry Sensor and confirm specific conductance in air (0 μS/cm)**
- * Can modify for use in salinity (salt water) measurements when marine monitoring.

**Notes:**
Measuring and reporting specific conductance removes the effects of temperature on the reported value and thus allows better determination of status and trends over time
 Using 1000 or 1413 uS/cm calibration standards in this range are less likely to result in error from solution carry over and with the sensors being so linear should result in more accurate calibrations that if you are trying to calibrate in the low SC range you may actually be measuring in.  Difficult to avoid some solution carry over.
Provides opportunity to check your DI water quality (SC should be less than 2 uS/cm) and after pH calibration to check the stability of your pH sensor measurement in low ionic strength waters.

## pH (su)

- Calibration
**Perform a 2-pt.calibration that brackets most likely environmental waters to be monitored (i.e. pH 7 buffer with either a pH 4 or pH 10 second buffer);**   Note: Multi-parameter field pH meters are  generally automatically temperature compensated by the instrument software/built-in algorithm to reflect changes in _sensor_ _slope_ (mv vs pH plot at different temperature), but not _calibration temperature compensated_ for buffer temperature variance (temperature induced _offsets in buffer [H+]_ due to buffers departure from standard temperature), so use the pH value provided for standard adjusted for the actual lab/office temperature (or other location) at which calibration is performed [small due to room temperature normally close to std. temp. (25 oC)]
- Error Check Procedure
**Use third remaining pH standard buffer as **_**error check**_** (e.g. pH 4 or pH 10)**
**If sensor** **fails error criteria, before rejecting, perform 3 point calibration (e.g. pH 4, 7 & 10) and then error check against pH 4 and 10 to determine if error criteria are met.**
***Check stability of pH measure in DI water if low ionic strength (<50 uS/cm) environmental water is likely to be encountered in field.  (Some vendors require a low ionic strength pH sensor for use in low ionic strength waters)**

**Notes:**
Defines the Nernst slope between the two calibration points so the third measured buffer outside that measured range could differ somewhat or be off significantly if the pH sensor is degraded  (old & worn out) or less linear.  Normally, in a 3 pt. pH calibration, two different slopes are generated (one slope for the pH 4 to 7 range and one slope for the pH 7 to 10 range) so the best fit to 3 pts. is not applied across the entire range.  When only one slope is determined and a 3rd pH standard is tested, this is the most conservative approach and will usually generate the largest sensor error.  If this fails, a 3pt. Calibration may be warranted before refurbishing or discarding the pH sensor.
2. Can now check stability of pH measure in low ionic strength water (<50 uS/cm) if that is likely to be encountered in field

## Dissolved Oxygen (DO mg/L)

**Calibration**
**Single point calibration in 100% water saturated air** for the local _station_ barometric pressure of site (i.e. barometric pressure that factors in current weather and elevation condition your at in mm-Hg uncorrected to sea level) – for new _luminescent DO sensors_ see manufacturer’s recommendations for calibration
**Error Check Procedure - ****Three or more **_**error check**_** methods available**:
**Prepare zero DO solution [sodium sulfite (~1g) & cobaltous chloride **
**     ****crystals (3 to 5) in 1 liter poly bottle of DI water prepares a check solution of         ****≤ 0.2 mg/L DO]**
**(2) Using a bubbler system generate a 100% O****2**** saturated water bath (at existing/current BP and altitude conditions) and compare probe measured value to DO tables (USGS) corrected for BP mm-Hg ****(uncorrected to sea level) **
**  **
**Perform Winkler Titration (idometric titration) on stabilized, saturated DO  water sample (e.g. from sink water bath) using Hach 8215/8332 Azide Modification methods for a sample in the range of either :**
**a. 1 mg/L  to 10 mg/L or**
**b. > 10 mg/L range**

**Notes:**
Theory – you have calibrated at one end of the DO range (i.e. 100% DO) so how do you confirm the sensor is linear when measuring the other extreme or near zero DO.  May only ensure that if DO probe reads too high you can catch that because DO sensors do not read/measure values less than zero.  Thus if DO sensor is nonlinear in a low sense will not be able to note that.
Luminescent DO (optical/digital DO terminology also used) is a very new technology that has been used in waste water treatment monitoring for several years and is now being applied to environmental waters.  It may largely replace in the future the current amperometric method (Clark Cell based) technology more prone to following and having several limitations associated with the use of a membrane.  At moment it is fairly costly (In-Situ and Hach-Hydrolab have released and YSI in process of release; technologies likely to improve and come down in price over time and with competition in this area.
This has made DO sensor deployments much less problematic and the pH sensor will likely beocme the most problematic in long term deployments.

## Additional QC Checks

- Vendor or Instrument Specific Checks – ( range per manufacturer’s spec.)
- pH buffer values - millivolt response & span/slope,
- DO charge, DO gain (unattended sampling mode)
- Conductivity Cell Constant (confirm appropriate for your use)
- General Reminders
- Battery/Power Level of Sonde/Display
- Barometer (of display or separate barometer)
- Internal Clock Time (datalogger)

**Notes:**

 Some other areas that could be addressed or serve as a reminder
These are Specific instrument checks that some vendors may offer with a recommended acceptable range

Additional general instrument checks that can/should be made before field mobilization
 In general, vendors should be encouraged to provide software that is transparent and offers a means to provide sensor QC checks to confirm operation within some acceptable range.

## SummaryPre-mobilization, Post-calibration Sensor Error Check Criteria Compared to other Field QC Criteria

|      CORE PARAMETER
      (NPS) | EPA EMAP et. al.   
          (2001)
  (Max. Accept. Diff.) |    NPS Proposed
   (2006 Guidance)
 (Error Check Criteria) |         USGS
         (2006)1
 (Calibration Criteria) |
| --- | --- | --- | --- |
| Temperature | ± 1 oC    | ± 0.4 oC | ± 0.2 oC |
| Specific Conductance | ± 5% | ± 5 μS/cm(2)
or 3% | ± 5 μS/cm(2)
or 3% |
| pH | ± 0.5 su | ± 0.3 su(3) | ± 0.2 pH units |
| DO conc.
DO %sat | ± 0.5 mg/L 
± 6% | ± 0.3 mg/L
± 4% | ± 0.3 mg/L |

- (1) Based on stabilization Criteria of Wilde and Radke (2005)
- (2) Whichever is greater
- (3)  After 3-pt. calibration, if necessary

**Notes:**
Some of the sensor check criteria that currently exist (EMAP – National Coastal Assessment QAPP, some states/other organizations)
* USGS “Calibration Criteria”  used in revised continuous monitoring document (Wagner et. al. 2006) and based on “Stabilization Criteria” of Wilde and Radke (2005) (unchanged in 2006 revision personal communication Rick Wagner, USGS)
 Failure to meet current rejection criteria would either preclude reporting field measurements (w/o a red flag tied to that parameter (i.e. failed QA/QC measurement error check) or would not go to the field until sensor was repaired or replaced.
For DO, use of ) 0.3 mg/l error criteria is preferred over % saturation.  DO % error is for STP of 0.3 mg/l error divided by 8.2 mg/l at STP = 3.7%

## Supplies Needed(minimum)

**NIST-traceable (inexpensive) thermometer (rec. two)**
**Conductivity calibration stds. (100, 1413, 10,000 ****μS/cm)**
**pH buffer std. solns. (pH of 4, 7, 10 su)**
**Sodium Sulfite (Anhydrous) & Cobalt Chloride Crystals**
**Bubble box or aquarium air pump w/stone bubbler, tubing and flow cell**
**DO Single Parameter Test Kit (e.g. Hach OX-DT) for Winkler titration**
**	*****any reference to a vendor product in this presentation is for example only and does not reflect an endorsement by NPS of their product**

**Notes:**
Needed supplies to perform these error checks are relatively minimal and inexpensive.
The NIST-traceable thermometers are approximately $30
The conductivity standards are commonly available but should be considered the minimum necessary for freshwater work
pH buffers are common standard buffer solutions
The anhydrous sodium sulfite and Cobalt Chloride crystals are readily available through a chemical supplier
In-situ makes the bubble box or equivalent bubbler set up can be acquired through local pet store
I used the DO test Kit of Hach (a relatively simple titration with digital titrator) but others are available or follow Standard Methods.

## Other Areas of Standardization

- Reporting units*
- Reporting conventions (significant figures)*
- Corrections for sensor fouling and instrument drift*
- Generally accepted minimum sensor stabilization times and criteria*
- Methods of sonde transportation to/from field and deployment under more extreme field conditions (cold, hot, geothermal, pressure change assoc. w/aircraft transport)
- Reduce shock, minimize exposure to temperature extremes, keep sensors moist & shielded from certain frequency ranges of EM radiation – clearinghouse of information on what works best in the field
- * Generally addressed well in USGS Continuous Monitoring documents (2000, 2006)

**Notes:**
There are other areas in which to make recommendations for standardization but they go beyond this simple protocol.  However, many of these are covered quite well in recent publications on the subject of continuous monitors by the USGS (Wagner et. al., 2006)

## Final Caveat

- Welcome any other input or suggestions to improve development of a standardized, WQ sensor error check protocol that would be widely accepted and could be expanded to additional parameters as appropriate:
-  that balances the desire for keeping this error check procedure as streamlined as possible so it will be widely used,
- while maintaining or improving its QA/QC aspects,
- encourages vendors to design hardware and software systems that provide for multiple QC check options
- 						pete_penoyer@nps.gov

**Notes:**
For those that view this as a worthwhile effort, I would welcome

## Acknowledgements

- NPS Staff who have reviewed and provided input and feedback to this straw man protocol
- USGS staff (Rick Wagner) who have provided many fruitful and informative discussions concerning water quality instrumentation
- Key Reference:  Wagner, R.J., Boulger, R.W., Jr., Oblinger, C.J., and Smith, B.A., 2006, Guidelines and standard procedures for continuous water-quality monitors-station operation, record computation, and data reporting: U.S. Geological Survey Tech-niques and Methods 1-D3, 51 p.+ 8 attachments; accessed April 20, 2006, at http://pubs.water.usgs.gov/tm1d3

**Notes:**
For those involved in sonde use whether in synoptic or continuous monitoring mode, I strongly recommend reading the recent USGS publication “Revised Guidelines and Standard Procedures for Continuous Water-Quality Monitors: Station Operation, Record Computation , and Data Reporting.  This is a very comprehensive piece of work and fills in many of the details I can only touch lightly on here.