Att_02_140P8422Q0035_SOW_with_attachments.pdf

STATEMENT OF WORK

for

OREGON CAVE NATIONAL MONUMENT AND PRESERVE

CT ANALYSIS & TRACER STUDY

1.0 Background

Oregon Caves National Monument operates a small public water supply system (PWS ID: 41- 91998) that provides water for staff and park visitors. In November of 2020 Oregon Health Authority (OHA) conducted an inspection of the system and noted a deficiency regarding the way the park was calculating chlorine residual. OHA subsequently recommended that the park conduct a tracer study and prepare a CT analysis. The current layout of the system does not allow the park to readily calculate contact time within the system. The park is planning future modifications to the system, but the modifications will not be ready for several years due to funding. The NPS responded to the OHA by providing a theoretical CT analysis based on assumed conditions. The OHA accepted that analysis in the interim until such time that a proper tracer study could be completed. The park now intends to complete the tracer study and submit a revised CT analysis report as requested by OHA.

2.0 Scope

The scope of this project is to conduct a tracer study in accordance with Oregon standards and prepare a follow up CT analysis report for submittal to the OHA.

3.0 Work to be Performed

3.1 Task 1: Gather System Information

3.1.1 The park will provide existing system information including available record drawings, approximate system layout, valving, tank volumes, flow records, and operational parameters. The government will also provide previous correspondence with OHA.

3.1.2 Develop tracer study plan. In accordance with OHA/DWS standards, develop a tracer study plan and submit the plan to the state for approval.

3.2 Task 2: Complete Tracer Study

3.2.1 Contractor shall travel to the site and conduct a tracer study according to the plan.

3.2.2 Contractor shall provide all labor, equipment, tools, and chemicals as required to complete the study.

3.2.3 It is acknowledged by the government that the current system layout may preclude the effective implementation of the tracer study, and that without preliminary investigation it is impossible to know if a tracer study is feasible. There is currently no way for the park to monitor the storge volume in the water tanks (no level gages) and there are no flow meters on the downstream side. At a minimum the contractor should be prepared to address these issues, including taking manual measurements, and isolating flow with the support of an attached flow meter. Should other system parameters prohibit an effective tracer study the contractor shall identify those issues and make recommendations where to implement them.

3.3 Task 3: Prepare CT Analysis Report

3.3.1 Prepare a CT analysis Report and submit the report to OHA.

4.0 Location of Work

The tracer study will be completed at Oregon Caves National Monument. The Park Headquarters are located at 19000 Caves Highway, Cave Junction, OR 97523-9716.

Preparatory and follow-on analysis will be completed by the contractor.

5.0 Period of Performance

30-60 days after award, with consideration given to weather conditions.

6.0 Delivery Schedule

Provide the park with the results of the tracer study and copy of the completed CT analysis. Contractor shall submit the report to the state on behalf of the park. Contractor shall answer any follow-on questions from the state and provide edits if requested by

OHA.

7.0 Performance Standards

Conduct a tracer study and prepare a report that will be accepted by the OHA.

8.0 Special Requirements

8.1 Government-furnished Property

The government shall provide basic system information, including available record drawings showing the approximate system layout, valving, tank volumes, flow records, and operational parameters. The government will also provide previous correspondence with OHA.

Park Staff will be available during the study to assist the contractor (such as opening valves, accessing sample points, identifying system components, etc.)

8.2 Security

No special requirements.

8.3 Travel

The contractor will be required to travel to Oregon Caves National Monument in Josephine County, Oregon, to conduct the tracer study.

8.4 Non-disclosure/Conflict of Interest

N/A

8.5 Special requirements

The contractor will be required to comply with current federal and state protocols regarding Covid-19.

9.0 General Items

9.1 Index of Attachments

9.1.1 Attachment 1: 2010 Water Plant Schematic

9.1.2 Attachment 2: 2015 Water Storage Drawings

9.1.3 Attachment 3: 2016 Water Distribution Drawings

9.1.4 Attachment 4: Prior CT Analysis Letter Report

9.1.5 Attachment 2: OHA Tracer Study Plan Reference

AS BUILT DRAWINGS

New Tank System

Hilfiker Wall

New Fence

C4-B

4" DI Inlet

6" DI Outlet

6" DI Drain

4" SCH 80 PVC

Sample Tap

Retaining Wall

SWTP

Gate Valve

Rip Rap Drainage Area

SHEET C4-B

Flow Line of DI Outlet

ELEV 4193.15

Flow Line of 6" Drain

ELEV 4193.15

Flow Line of FInal Drain Outlet

ELEV 4193.15

Flow Line of 6" Outlet

ELEV 4192.27

Top of Valve Box

ELEV 4193.15

6' 36.5'

4' 9' 9' 11.5'

10'

4" Pipe Penetration Through Wall, 90 Down and 90 Across Floor

9'

12'

83'

16'

6" Supply Line From Tank to Valve Cluster = 49'

6" Drain Line From Tank To Drain Area = 28.5'

F.F Elev. 4195.73

6' Chain Link Fence

6' Chain Link Fence

Inlet Elev.

4218.30

Top of Footing Elev. 4195.73

Outlet Overflow Elev. 4217.24

3' Min

Top of Internal Overflow Baffle Elev. 4218.22

SHEET C4-C

New Tank Profile

6" Supply Line (Drain Line Not Shown)

Fence is 42" Above Finish Grade

"See C. Kull Engineered Drawings for Hilfiker Wall Construction Elevations"

12"

10'

5' 3.25'

See diagram A for layout of installed 8" Check Valve

Tie-In Points to Existing Line

8" Check Valve

8" Supply Line

Existing Valve Vault

Diagram A - Check Valve Installation

4" Sch 80 PVC

30"

42"

To Remain

Flow Line Elev at Pipe Penetration 4200.73

FF Elev. 4195.73

Supply Elev.

4206.98

Valve Elev.

4203.30

New Ground Profile

4" Sch 80 PVC Insulated

4" Sch 80 PVC

4218.30

22'

20'

21'

Mesh Screen is attached with Stainless Steel Hose Clamps

Inv. Elev of Float Valve 4202.54

All Pipe Material after Tank Penetration is 4" Sch 80 PVC

Stainless Steel Pipe Support

Installed Bedding Material: Sand

6'-0" Gate

April 5th, 2021 Oregon Public Health Division Drinking Water Services 444 A Street Springfield, OR 97477 Attn: Zach Golik, P.E.

Re: SS-2020-11-4191998, Water System Survey Action Plan

Dear Mr. Golik, This letter is regarding the Public Water System at Oregon Caves National Monument. On November 12th, 2020 you conducted an inspection of the Oregon Caves water system and subsequently sent a summary letter dated December 8th, 2020. In your letter you outlined a series of deficiencies that you observed during the visit and requested that the owner (Federal Government) provide you with a plan to address them. We prepared a letter for you dated January 5th, 2021 that addressed the deficiencies and described how the park intends to correct them. One of the deficiencies pertained to the need to conduct a tracer study to determine disinfection contact time (CT) parameters. To properly conduct the study the park will need to construct several improvements including a flow meter and storage tank level gage. Due to the time needed to implement these improvements you requested that the park perform an interim mathematical analysis to better understand how the existing system may be performing with regard to current state regulations. The following presents the results of the requested analysis.

CT Analysis

The first step in the analysis was to estimate the residence time of the water in the system after the disinfection process assuming worst-case conditions. Worse case conditions generally occur when the storage volume (i.e. water tank volume) is at its minimum and the system demand is at its maximum.

The current system utilizes two separate storage tanks for potable water storage. The primary potable water storage tank is a 50,000 gallon, 20-foot diameter steel tank. The secondary tank is an older 75,000-gallon rectangular concrete tank. The tanks are interconnected; however, the operational parameters are such that most of the potable water use passes through the primary tank.

Through a series of pressure regulating valves the water level fluctuation in the primary varies much more than the secondary tank. In general, the secondary tank only fluctuates by 12-18 inches, and is primarily used for fire storage. The secondary tank still has a potable connection and the park does maintain a chlorine residual in that tank. Eventually the intent may be to isolate

United States Department of the Interior

NATIONAL PARK SERVICE

Oregon Caves National Monument

19000 Caves Hwy Cave Junction, OR 97523 that tank entirely for fire flow. When the secondary tank does empty however, it does so in unison with the primary with a 50/50 ratio from each tank. For analysis purposes it was assumed that the secondary tank was excluded from the system. This produces a very conservative estimate of volume. Operational parameters are such that the lowest operating level of the primary is approximately 15 feet in depth. This equates to a volume of 35,250 gallons.

The inlet/outlet configuration of the primary tank is such that the baffling efficiency is estimated at 10%. The first service connection on the system is located at the historic Chalet building south of the tank. The main service line between the Chalet and tank is a 6-inch pipe that is approximately 415 feet long. Therefore, the minimum storage volume can be summarized as follows:

Volume Tank: 35,250 x 0.1 = 3,525 gal

Volume of the Pipe: 610 gal

Total Volume: 4,130 gal

Peak system demands were estimated using existing system records and prior studies. Peak day demand is estimated at 46,350 gal/day. This equates to an average peak day hourly demand of 1931 gal/hr. Water use throughout the day however is not consistent, and adjustments must be made to account for daily variation in use. The peak day hourly demand was estimated by assuming a peaking factor of 3.0, to return a peak hourly flow rate of 5793 gal/hr or 96 gal/min.

A peaking factor of 3.0 is consistent with 10-states-standards criteria for systems of this size. This flow represents the maximum flow rate that the system will theoretically experience during the peak use day of the year. Use of this flow rate for this calculation returns a very conservative estimate of CT value.

The shortest contact time (T) for the system was therefore calculated as follows:

4,130/96 = 43 minutes (T)

The previous estimate for this parameter was 300 minutes. This result is considerably smaller than the previous estimate by almost an order of magnitude.

Recorded chlorine residual values at the first user have typically ranged from .5 to 1.5 mg/l. The average residual is likely around 1 mg/l. Therefore, the estimated CT value is

CT(est) = 21.5 to 96, with an Average of 43

System Analysis

To understand how the calculated CT value relates to the existing system several parameters must be estimated to compare the calculated (actual) CT value to the required CT value. Required CT values can be looked up in tables published by the Oregon Health Authority. CT tables can be found at CT.pdf (oregon.gov)

Per OAR 333 061-0032 (1)A, the system must achieve:

(i) At least 99.9 percent (3-log) removal or inactivation of Giardia lamblia cysts between a point where the raw water is not subject to recontamination by surface water runoff and a point downstream before or at the first customer, Note: It is believed that this system is in Bin Classification 1 for Cryptosporidium, meaning that no additional treatment is required for Cryptosporidium.

Per OAR guidance, properly functioning conventional filtration plants are typically given credit for a 2.5-log Giardia removal. Therefore, a 0.5 log removal is assumed required from disinfection.

Typical system temperature is 5.0 C°. Water pH is typically around 7.5. From existing records, recorded chlorine residuals at the plant vary between 1 and 2 mg/l.

Therefore, from Appendix Table 4.2, the required CT value is typically between 30-33.

Using average CT values: CT(actual)/CT(required) = 43/31.5 = 1.36.

Therefore, it can be assumed that disinfection requirements are met. However, it is possible that given the correct conditions this ratio could drop below 1.0, which would result in disinfection requirements not being met. The conditions that could result in this are unlikely (especially given the conservative input values) however it is something to note.

Conclusion

The results of this analysis demonstrate that the previously calculated T value of 300 is likely over-estimated. An over-estimated T value could lead to a false belief that the system is operating well within defined parameters. However, based on typical system measurements, it does appear that under normal operating conditions the system should be able to achieve disinfection requirements.

Given that the ratio of actual CT to required CT may be approaching, or even dipping below 1.0 under extreme circumstances, it is important that staff closely monitor the system until a more appropriate tracer study can be completed. Should the calculated CT ratio show signs of dropping below 1.0, additional disinfection dosing will be required.

If you have any additional questions or comments please let us know. We will inform you when the corrective actions have been implemented as required.

Sincerely, Nathan Anderson, P.E.

Klamath Network Engineer cc:

David John – ORCA Maintenance Division.

Josh Haggett – ORCA Chief of Maintenance

Preparing a Tracer Study Plan

OHA Drinking Water Services

November 2019

A tracer study plan must be submitted for review and approval to Drinking Water Services prior to conducting a tracer study. Failure to receive prior approval may result in the tracer study results not being accepted and it having to be redone.

Be prepared to provide the following information in your tracer study plan:

• Who will be conducting the tracer study? When will the tracer study be conducted?

• What chemical will be used as the tracer? How will the tracer dosage be determined?

Note: Be sure to keep chlorine residual at levels to ensure disinfection CT (Chlorine residual x contact Time) requirements will be met at all times during the tracer study.

• What is the total volume of the reservoir or clearwell (i.e. contact chamber) being used for the tracer study?

• Is there additional transmission line volume between the contact chamber and the first user that will be included in the tracer study (not preferred)? If yes, explain why this additional volume needs to be included in the tracer study.

• Is there a flow meter at the contact chamber outlet that measures gpm? If no, how will peak hourly flow be determined for the tracer study?

• What is the peak hourly demand leaving the contact chamber?

• At what flow rate(s) will the tracer study be conducted? How will this flow be maintained during the tracer study?

• What is the lowest operating volume of the contact chamber?

• What is the planned contact chamber volume range from beginning to end of tracer study?

• A schematic must be provided that clearly shows:

o The contact chamber used for contact time o All chlorine injection points (including those used during normal operation as well as during the tracer study, if different).

o All chlorine measuring locations (including those used during normal operation as well as during the tracer study, if different).

o The first user.

Example schematic:

Surface

Water

Intake

Treatment

Plant

Contact

Chamber used for contact time

Chlorine injection point

(normal operation)

Chlorine measuring location

(normal operation)

First user