Attachment 14 - DOH Proceed to Engineering and Design (CLM045)_0004.pdf

STATE OF WASHINGTON

DEPARTMENT OF HEALTH

OFFICE of ENVIRONMENTAL HEALTH and SAFETY

243 Israel Road SE PO Box 47824, Tumwater, WA 98504

(360) 236-3330 711 Washington Relay Service

February 13, 2020

Ms. Sarah Creachbaum

Superintendent, Olympic National Park

600 East Park Avenue

Port Angeles, WA 98362-6798

Re: Notice to proceed to engineering design, Hurricane Ridge Visitor Center Large On-site Sewage System (LOSS), System ID CLM045; Project 2019-057

Dear Ms. Creachbaum:

On January 24, 2020 the Washington State Department of Health (Department) received the

Predesign Report from the National Park Service (NPS) for LOSS CLM045, Project 2019-057

(Hurricane Ridge Visitor Center Large On-Site Sewage System). After review of the Predesign

Report, I found that the treatment strategy proposed in the report is feasible.

The Department accepts the proposed drainfield sizing described in the Predesign Report (use average daily flow but construction of 150% of the primary drainfield as part of the project).

This strategy will accommodate the high flows in July and August, and the substantially lower flows in the ‘off season’ will provide time for the drainfields to reestablish appropriate biomass within the sand-lined trenches. The Department also accepts the sand-based system to provide

Treatment Level B prior to releasing the wastewater to the environment. Based on the information provided in the Site Risk Survey and Nitrate Balance, no further treatment is required, and no additional studies are required at this time.

This letter serves to notify you to proceed to final design, incorporating the items described below. The department will accept the NPS submitting the Engineering Report, design, and specifications in a single submittal. However, there are some changes to the proposed LOSS design that must be incorporated into the final design. These are described below.

1. Sand-lined filter trenches should be used in lieu of sand-lined beds. Ten-foot wide beds are infeasible with the steep slope in the drainfield area. The final design should include trenches with a maximum width of 36 inches.

2. A minimum depth of 36 inches of ASTM-33 sand below the dispersal piping is required in the trenches to provide adequate vertical separation.

3. The configuration of the drainfield should be modified to include the following:

a. The layout of the drainfield trenches should minimalize longitudinal loading. That is, to the extent practicable, the length of trench along a common contour should be maximized, and the number of parallel trenches at successively lower elevations should be minimized.

b. The primary drainfield area should be installed at elevations lower than the reserve drainfield area. This will protect the reserve drainfield area in the event of a failure in the primary drainfield.

c. The trench detail on drawing sheet CO3 shows the sand media penetrating into the Type 1 soils a minimum of six inches. The design should show that the Type 1 soil layer should be left in place, with the sand media sitting atop the Type 1 soil.

If the Type 1 soils are inadvertently removed during excavation, the layer should be reestablished with a suitable material to the original depth of the Type 1 soil layer.

4. The Sand-lined Bed Profile, shown on sheet CO3 of the drawings, indicates the drainfield laterals will have orifices in the 12-o’clock position. The final design should provide details and the Engineering Report describe the strategy used to ensure residual water in the laterals does not freeze and cause the pipe to crack in freezing weather.

5. A 5-way automatic distribution valve is noted on drawing sheet CO3. For the final design, the engineer should ensure a mechanical distribution valve is located to ensure proper function. Furthermore, the Engineering Report should describe how the design provides protection from freezing in the winter, before snowpack insulates the equipment. I recommend the NPS consider alternate strategies to distribute wastewater to each drainfield lobe, if proposed by the engineer and supported with technical data.

6. The volume of the septic tank and the volume of the pump/surge tank must comply with requirements of 246-272B-06450 WAC. The final design should ensure the tanks are sized based on the design flow (the peak flow expected in a day) and should ensure that the pump tank provides adequate capacity for 24 hours of emergency storage as well as surge capacity to equalize flows from high-use periods. I note that the regulations require the design flow be based on average flows with a peaking factor applied; though the

Predesign Report noted that the average wastewater flow is expected to be 10,000 gpd.

The Engineering Report must provide a peaking factor to convert average daily flow to design flow, and the design flow used to size the septic tank and pump tanks.

In addition to information required by 246-272B-04000, the project engineering report should include the items described below.

1. The soil logs should be corrected to align more closely with what the department and

NPS agreed to during the Site Visit. Specifically, that the soil identified as Type 7 is

Type 5, and that fractured bedrock, not type 7 soils, underlays the Type 1 soils.

2. TA peaking factor to convert average flow to design flow (peak daily flow) should be provided.

3. Technical data indicating the gravelless trenches used will be structurally sound under expected snow loads and overburden should be provided.

Should you have questions about the information provided in this letter, please do not hesitate to contact me at 360-236-3318 or Doritha.ramey@doh.wa.gov.

Sincerely, Dotti F. Ramey, P.E.

Supervisor, LOSS and Reclaimed Water Program cc: Kerri Cook, National Park Service

Frank Baird, DOH

Jennifer Garcelon, Clallam County Environmental Health Department mailto:Doritha.ramey@doh.wa.gov