Attachment 3 - Draft CLM045 Hurricane Ridge Predesign Report.pdf

DEPARTMENT OF THE INTERIOR

NATIONAL PARK SERVICE

COLUMBIA – PACIFIC NORTHWEST INTERIOR REGION 9

OLYMPIC NATIONAL PARK

PREDESIGN REPORT

for

LOSS ID: CLM045

HURRICANE RIDGE VISITOR CENTER

Prepared by Kerri Lynn Cook, PE

Olympic National Park 600 E. Park Ave.

Port Angeles, WA 98362

January 2020

Note for solicitation #140P8320R0003: Draft version is provided for informational purposes only. Approved version will be provided as soon as it is available from Washington Department of Health.

140P8320R0003, Attachment 3 ii

Approved by:

Washington State Department of Health

PENDING

iii

TABLE OF CONTENTS

1. CONTACT INFORMATION

OWNER

PRELIMINARY/SCHEMATIC DESIGN ENGINEER

PREDESIGN REPORT ENGINEER

FINAL DESIGN ENGINEER

2. SITE ADDRESS

3. VICINITY MAP

4. SITE MAP

5. ARCHAEOLOGICAL RESOURCES

6. UNDERGROUND UTILITES

7. SOIL MAPPING

8. LOSS PROJECT

FACILITIES

DRINKING WATER

LAND AREA

DEVELOPMENT REGULATIONS

LOSS PROJECT COMPLIANCE

PUBLIC SEWER

DESIGN FLOW & WASTE STRENGTH

TREATMENT & DISPERSAL METHOD

OWNERSHIP & MANAGEMENT REQUIREMENTS

9. SOIL LOGS

10. SOIL TYPE & HYDRAULIC LOADING RATE

11. PHYISICAL CHARACTERISTICS

TOPOGRAPHY & SLOPE

VEGETATION

PREDOMINANT SOIL TYPE

VERTICAL SEPARATION

SITE DRAINAGE PATTERNS

WATER TABLE & RESTRICTIVE LAYERS

12. MINIMUM LAND AREA REQURIEMENTS

13. NEPA CHECKLIST

REFERENCES

FIGURES

Figure 1. Vicinity map showing Hurricane Ridge Visitor Center LOSS project site with Olympic National Park boundary in dark green. .................................................................... 2.

Figure 2. Site map showing Hurricane Ridge Visitor Center existing and proposed LOSS with topography and other site features. ................................................................................. 3.

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Figure 3. Hurricane Ridge groundwater well, water storage reservoir, and water distribution line map. .................................................................................................................................. 4.

Figure 4. Olympic National Park 2008 General Management Plan (GMP) Zones for Hurricane Ridge. ..................................................................................................................... 6.

Figure 5. Hurricane Ridge Visitor Center average daily flow by month, 2012 – 2019. ......... 7.

Figure 6. Example cross-section of proposed drainfield 10’ sand bed construction at Hurricane Ridge. ..................................................................................................................... 9.

Figure 7. Carex sedge-dominated subalpine meadow vegetation at proposed drainfield sites. ....................................................................................................................................... 12.

TABLES

Table 1. Hurricane Ridge Visitor Center 7/6/19 septic tank effluent sample compared to TLE. ......................................................................................................................................... 7.

Table 2. Mass loading rate of Hurricane Ridge septic effluent parameters based on drainfield size compared to DOH-recommended maximum values ...................................... 10.

Table 3. Hurricane Ridge Visitor Center (HRVC) soil test pits and soil type by layer depth ............................................................................................................................................... 11.

Table 4. Slope measurements along north-south axis for each Hurricane Ridge Visitor Center soil test pit ................................................................................................................. 11.

APPENDIX A – SAMPLE RESULTS

APPENDIX B – SOIL LOGS & SITE MAP

APPENDIX C – NEPA DOCUMENTATION

January 2020 CLM045 Hurricane Ridge Visitor Center Predesign Report

1. CONTACT INFORMATION

OWNER

Sarah Creachbaum – Superintendent Olympic National Park 600 E. Park Ave.

Port Angeles, WA 98362

(360) 565-3002 Sarah_Creachbaum@nps.gov

PRELIMINARY/SCHEMATIC DESIGN ENGINEER

Quin Clements, PE – Vice-President and Principal of Civil Engineering Davido Consulting Group, Inc. (DCG) 1796 E. Main St., Suite 105 Freeland, WA 98249

(360) 331-4131 quin@dcgengr.com

PREDESIGN REPORT ENGINEER

Kerri Cook, PE – Park Engineer Olympic National Park 600 E. Park Ave.

Port Angeles, WA 98362

(360) 565-3161 Kerri_Cook@nps.gov

FINAL DESIGN ENGINEER

To Be Determined

2. SITE ADDRESS

The Hurricane Ridge Visitor Center is located approximately 18 miles from Port Angeles, WA near the end of Hurricane Ridge Road in Clallam County. The facility mailing address is tied to the Olympic National Park Visitor Center located at 3002 Mount Angeles Road, near the turnoff to Hurricane Ridge Road. A legal land description including section, township, and range data for the site are as follows: Twn 29 Rng 6W Sec 54.

3. VICINITY MAP

Figure 1 shows the project site location with the property boundaries of Olympic National Park shown in dark green. Adjacent parcels for Olympic National Forest are shown in light green, while Washington State Department of Natural Resources is shown in pink.

4. SITE MAP

Figure 2 shows the project property area with five-foot topographic contours, a Washington State Department of Ecology well, proposed primary and reserve drainfield boundaries, and five soil test pit locations. No items listed in WAC 246-272B-06050 are within the minimum horizontal setback distance noted in Table 3. No areas of soil or slope instability are prevalent within the project area. Data sources for the topographic map are Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community.

mailto:Sarah_Creachbaum@nps.gov mailto:quin@dcgengr.com mailto:Kerri_Cook@nps.gov

Figure 1. Vicinity map showing Hurricane Ridge Visitor Center LOSS project site with Olympic National Park boundary in dark green.

Hurricane Ridge Visitor Center

Figure 2. Site map showing Hurricane Ridge Visitor Center existing and proposed LOSS with topography and other site features.

Proposed Reserve

Drainfield

Proposed Primary

Drainfield

Soil Test Pits

DOE Well

#ALJ113

Existing Drainfield

5. ARCHAEOLOGICAL RESOURCES

Archaeologists at Olympic National Park conducted an archaeological inventory and evaluation of the Hurricane Ridge area in preparation for a utilities project during the summers of 2008 and 2009. A prehistoric archaeological site eligible for listing on the National Register of Historic Places is located within 1000 feet of the existing drainfield. However, no known significant archaeological resource sites are known to exist within 1000 feet of the proposed primary or reserve drainfield perimeters, and the project is expected to have no effect on archaeological resources or other historic properties. Tribal consultation for this proposed project was conducted in accordance with Section 106 of the National Historic Preservation Act (NHPA).

6. UNDERGROUND UTILITES

Electrical power for the Hurricane Ridge Visitor Center runs up Hurricane Ridge Road to a transformer located at the northwest corner of the building and is provided by Clallam County Public Utility District (PUD). Potable water is provided by Olympic National Park from a groundwater well. Chlorinated water is stored in a 100,000 gallon underground reservoir prior to distribution to the Visitor Center and two seasonal comfort stations located along Hurricane Hill Road, as shown in Figure 3.

Figure 3. Hurricane Ridge groundwater well, water storage reservoir, and water distribution line map.

7. SOIL MAPPING

USDA NRCS soil mapping is scheduled to occur in the summer of 2020 for the Hurricane Ridge area.

The bedrock formations underlying the entire area in the vicinity of the Hurricane Ridge Visitor Center are part of the “Needles-Gray Wolf Lithic Assemblage” as defined and mapped by Tabor et.al. (1972). In the Hurricane Ridge area this formation is characterized by thin, laminated beds of sandstone, siltstone, slate, and shale.

8. LOSS PROJECT

The Hurricane Ridge Visitor Center sewage treatment system consists of a 24,000 gallon dual chamber septic tank and 1600 square foot filter drainfield constructed in 1951. In October 2019, effluent ponding was observed in the drainfield and distribution box, indicating that the infiltrative surface is likely blocked with biological growth and solids from the wastewater. The purpose of this project is to significantly modify the existing large onsite sewage system (LOSS) to meet current peak flow conditions and comply with current regulations by installing new septic and dosing tanks, a new multi-zone sand-lined bed drainfield, pressurized gravelless chamber distribution, and electrical controls for duplex submersible pumps. A portion of the gravity collection system will be re-routed to direct wastewater to the new treatment infrastructure, and a new access road will be constructed for ongoing septic tank pumping and maintenance. Obsolete collection and treatment infrastructure will be decommissioned and abandoned in place, in accordance with WAC 246-272B-07500. Revegetation of disturbed areas will be completed by NPS personnel using subalpine meadow sod salvaged from construction, combined with collected seed and greenhouse-produced plugs.

FACILITIES

No residential facilities exist at Hurricane Ridge. Nonresidential facilities served by the existing and proposed LOSS consist of the Hurricane Ridge Visitor Center, which provides basic interpretive visitor services and restrooms. A concession-operated deli (250 sq ft) providing quick service with ordering and counter pickup and nearby seating for 28 is located on the lower floor of the building along with a concession-operated gift store (3,132 sq ft). During winter months the concessioner also offers weekend snowshoe and ski rentals at the gift shop.

DRINKING WATER

Drinking water is provided by Olympic National Park via the Hurricane Ridge Group A public water system ID# NP3904. The source for this water system is a groundwater well with Washington State Department of Ecology (DOE) well tag #ALJ113, which is chlorinated and stored in a 100,000 gallon underground reservoir prior to gravity distribution.

LAND AREA

The total land area available for the development of all LOSS components south and west of the Hurricane Ridge Visitor Center is approximately 8 acres.

DEVELOPMENT REGULATIONS

The Olympic National Park 2008 Final General Management Plan / Environmental Impact Statement (GMP) defines various management zones and the types of acceptable uses that can occur within those zones. Three GMP Zones are defined for the Hurricane Ridge area, as shown in Figure 4. The Development Zone contains concentrated visitor service facilities as well as park operational facilities.

This zone is targeted as the preferred location for constructing a maintenance access road and siting pump electrical controls, which are expected to be wall-mounted on the Visitor Center. The Day-Use Zone accommodates high to moderate levels of day use with some related park operational facilities allowed.

This zone is targeted as the preferred location for rerouting gravity sewage collection lines to the new septic and dosing tanks as well as the proposed primary and reserve drainfields. The Wilderness Zone is not considered appropriate for LOSS components.

Figure 4. Olympic National Park 2008 General Management Plan (GMP) Zones for Hurricane Ridge.

LOSS PROJECT COMPLIANCE

The proposed LOSS project complies with the 2008 GMP development guidelines, as described above.

No sensitive or critical areas have been designated within one thousand feet of the proposed primary and reserve drainfield perimeters, and no additional extraordinary circumstances apply.

PUBLIC SEWER

No public sewer exists within a nine-mile radius of the Hurricane Ridge Visitor Center.

DESIGN FLOW & WASTE STRENGTH

The expected project design flow is 10,000 gpd. Figure 5 shows average daily flow for the Hurricane Ridge Visitor Center, monitored and recorded monthly via building water meters for the years 2012 – 2019. While average daily flow has exceeded 10,000 gpd on two occasions within the past eight years, the park is planning to replace all toilets and lavatory faucets with low-flow fixtures in 2021 as part of a scheduled building rehabilitation. These water efficiency improvements are expected to reduce the volume of wastewater generated at the Hurricane Ridge Visitor Center and ensure that the peak design flow of 10,000 gpd is not exceeded. The one-way Hurricane Ridge Road and park entrance station located at milepost 5, where visitors are held on peak visitation days until the Hurricane Ridge Visitor Center parking lot has capacity to accommodate additional vehicles, further limits peak flows. Visitation at this facility fluctuates seasonally, with peak usage occurring in July and August. Annual average daily flow calculated over the past five years is approximately 3200 gpd, or less than one third of peak design flow.

Figure 5. Hurricane Ridge Visitor Center average daily flow by month, 2012 – 2019.

Waste strength was characterized using a single septic tank effluent sample collected from the drainfield distribution box on July 6, 2019; a copy of the original laboratory certificate of analysis from Spectra Laboratories is included in Appendix A. Case narrative stated that QC parameter G/GA results were below the method defined range for Carbonaceous Biochemical Oxygen Demand (CBOD), indicating results may be biased low. CBOD5 results were therefore increased by approximately 15% to adjust for low bias. Given this adjustment, waste strength is more concentrated than Treatment Level E (TLE) residential strength sewage in terms of CBOD, as summarized in Table 1. In addition to higher CBOD, high nitrogen concentrations are also typical of visitor service facilities with public restrooms. Under-the-sink grease traps used in the concession-operated commercial kitchen appear to be keeping oil and grease concentrations at an acceptable level.

Table 1. Hurricane Ridge Visitor Center 7/6/19 septic tank effluent sample compared to TLE.

Effluent Parameter 7/6/19 Effluent Sample Treatment Level E Carbonaceous Biochemical Oxygen Demand, CBOD5 130 mg/L* 125 mg/L Nitrate + Nitrite – N 0.03 mg/L --- Total Kjeldahl Nitrogen, TKN 81.9 mg/L --- Total Suspended Solids, TSS 34.0 mg/L 80 mg/L Fecal Coliform, FC >20,000 CFU/100ml --- Oil & Grease, O&G 7.9 mg/L 20 mg/L *CBOD5 result of 113 mg/L was increased 15% to adjust for low bias indicated by laboratory QC results.

TREATMENT & DISPERSAL METHOD

The proposed wastewater treatment consists of 30,000 gallons of septic tank capacity to provide primary settling. Septic tank capacity was determined as three times the daily design flow of 10,000 gpd, in accordance with WAC 246-272B-06450, and will include an effluent pre-filter screen with a maximum mesh size of one eighth inch. A subsequent pump chamber sized for approximately 14,000 gallons to provide routine dosing as well as twenty-four hours of peak design flow reserve capacity (emergency storage) will house duplex alternating pumps. No grease interceptor will be installed as part of this project because kitchen drain lines combine with sanitary sewage lines inside the building, and re-plumbing building sewer lines is outside the scope of this project. However, best management practices for commercial kitchens will be enforced to limit impacts of oil and grease from the concession-operated commercial kitchen.

Sand lined beds consisting of ASTM C-33 specification sand media to meet Treatment Level B prior to disposal in Type 1 soils are proposed as a combined treatment and soil dispersal design. Beds will be designed and constructed in 10-foot-wide (maximum) zones. Each zone bed will be constructed level, along the topographic contour, and will be excavated to a depth ranging from 42” to 78” below ground surface, or until the bed excavation passes through the site’s restrictive layer and penetrates the original, undisturbed Type 1 soil (see Section 9. Soil Logs below). Excavation will extend 36” below final infiltration surface and be backfilled with sand filter media if needed to ensure 36” vertical separation.

Spacing between beds constructed on contour is recommended to be 15 feet instead of the allowable 10 feet due to the relatively steep (~25%) site slope conditions.

Gravelless chambers with pressure distribution has been selected as the park’s preferred effluent dispersal method due to the lower initial and lifecycle cost as well as greater simplicity of operations and maintenance when compared to a subsurface drip system. All pressure distribution laterals will include cleanouts and monitoring ports at the distal ends to provide access at finished grade. Pressure distribution with timed dosing will be accomplished with duplex alternating pumps. The pump control panel and alarm notification will be wall-mounted in a lockable enclosure and located along the western side of the Visitor Center. Minimum dosing frequency will be established as six equally spaced timed doses per day with a maximum hydraulic loading rate of one gallon per square foot per day. Dosing will bet set to automatically alternate between distribution zones.

The Recommended Standards and Guidance for Performance, Application, Design, and Operation & Maintenance (RS&Gs) for gravelless distribution products such as chambers notes that the infiltrative surface may not be deeper than three feet (36”) below the finished grade, except under special conditions approved by the local health officer (DOH 2013). Due to the slope of the site combined with the minimum depth of cover over gravelless chambers and need for adequate freeze protection, the infiltrative surface on the upslope side of each sand bed is expected to be located deeper than 36” below finished grade. The On-site Wastewater Treatment Systems Manual (USEPA 2002) notes that maximum depth of the infiltration surface should be limited to no more than 3 to 4 feet below final grade to adequately reaerate the soil and satisfy the daily oxygen demand of the applied wastewater. The park is submitting a written waiver request from the requirement of WAC 246-272-06350(11) in conjunction with this Predesign Report to accommodate burial of the infiltrative surface up to 48”. See Figure 6 for an example cross-section of the proposed drainfield sand bed construction with gravelless chambers and pressure distribution.

Figure 6. Example cross-section of proposed drainfield 10’ sand bed construction at Hurricane Ridge.

In consideration of wastewater strength exceeding residential strength effluent due to higher levels of organic material, as measured by biochemical oxygen demand (BOD) and carbonaceous biochemical oxygen demand (CBOD), enlarging the drainfield area to reduce BOD mass loading was selected as the park’s preferred alternative for treatment in lieu of providing septic tank aeration or aerobic pretreatment.

The CBOD mass loading rate for peak flow conditions, assuming a minimum drainfield size of 10,000 square feet and an adjusted CBOD5 effluent sample result of 130 mg/L, can be calculated as follows:

𝑚𝑚𝑚𝑚

𝐿𝐿

𝑥𝑥

3.78 𝐿𝐿

1 𝑚𝑚𝑔𝑔𝑔𝑔 𝑥𝑥 1 𝑚𝑚

1,000 𝑚𝑚𝑚𝑚 𝑥𝑥

1 𝑔𝑔𝑙𝑙 454 𝑚𝑚 𝑥𝑥 10,000 𝑚𝑚𝑔𝑔𝑔𝑔 10,000 𝑠𝑠𝑠𝑠

= 1.1 𝑥𝑥 10−3𝑔𝑔𝑙𝑙𝑠𝑠/𝑠𝑠𝑡𝑡2/𝑔𝑔𝑔𝑔𝑑𝑑

The BOD5 test was not included in waste characterization of the July 6th sample. However, a comparison of BOD5 to CBOD5 values for water pollution studies conducted by the Environmental Protection Agency (EPA) found that this ratio should be consistent for a given waste stream (Brake 1998). While the ratio varies from waste stream to waste stream, the average BOD5/CBOD5 Ratio for 17 studies considered was 1.16, with actual ratios ranging from 1.10 to 1.21. Using an estimated ratio of 1.2 to convert CBOD to BOD, mass loading rates can be calculated for Hurricane Ridge effluent parameters and compared to Washington State Department of Health (DOH) maximum recommended values (Eliasson 2004), as shown in Table 2.

Gravelless Chambers & Pressure Pipe

Range of Depth to

Type 1 Soil

Native Soil Backfill

15’ Min Spacing to

Adjacent Bed

Weathered Bedrock

Min Cover

~25% Slope

10’

36” Min Vertical Separation

ASTM C-

33 Sand

Table 2. Mass loading rate of Hurricane Ridge septic effluent parameters based on drainfield size compared to DOH-recommended maximum values.

Wastewater 7/6/19 Mass Loading Rate (lbs/ft2/day) Effluent Parameter

Sample (mg/L)

10,000 sf drainfield

15,000 sf drainfield

20,000 sf drainfield

DOH Max.

Value

Carbonaceous BOD, CBOD5 130* 1.1 x 10-3 7.2 x 10-4 5.4 x 10-4 1.2 x 10-3 CBOD5 adjusted to BOD5** 156 1.3 x 10-3 8.7 x 10-4 6.5 x 10-4 1.0 x 10-3 Total Suspended Solids, TSS 34.0 2.8 x 10-4 1.9 x 10-4 1.4 x 10-4 8.0 x 10-4 Oil & Grease, O&G 7.9 6.6 x 10-5 4.4 x 10-5 3.3 x 10-5 2.5 x 10-4 *CBOD5 result of 113 mg/L was increased 15% to adjust for low bias indicated by laboratory QC results.

** A BOD5/CBOD5 ratio of 1.2 was used to convert data for comparison to DOH maximum values.

Underlined values exceed DOH-recommended maximum values in bold.

WAC 246-272B-06350(17)(c) notes that, with documentation and justification from the design engineer, the department may authorize reducing the constructed drainfield capacity from 150% to 100% if the reserve area has the capacity to receive 100% of the design flow, and the LOSS meets Treatment Level C or better with a design flow of 14,500 gpd or less. The calculations in Table 2 indicate that constructing the minimum required drainfield size of 10,000 square feet may lead to biological clogging due to organic overloading. Therefore, constructing and using 150% of the required drainfield capacity, in accordance with WAC 246-272B-06350(6)(c), will help ensure organic loading rates don’t exceed the maximum recommended design rate during peak flow conditions. Furthermore, it effectively reduces the hydraulic loading rate to 0.7 gal/ft2/day. Sizing the infiltration surface based on organic mass loading rather than daily hydraulic loading is expected to prevent soil or media clogging, which was likely the cause for failure of the current drainfield. Doubling the size of the infiltrative surface from 10,000 square feet to 20,000 square feet was considered unnecessary in terms of construction cost and environmental impact since annual average daily flow is less than one third of peak design flow, providing an additional factor of safety.

OWNERSHIP & MANAGEMENT REQUIREMENTS

The Management Plan previously prepared for LOSS facilities owned and operated by Olympic National Park and submitted to DOH on November 26, 2018 will be updated to include CLM045 Hurricane Ridge Visitor Center LOSS. This updated Management Plan will be prepared in accordance with WAC 246- 272B-04100.

9. SOIL LOGS

Four soil test pits were excavated on October 24, 2019 to characterize the soil type and conditions across both the proposed primary and reserve drainfield areas. A fifth soil test pit was excavated on October 30th to confirm soil profiles. The four initial test pits were reviewed by DOH Hydrogeologist Frank Baird on October 25th and confirmed via letter on November 15th. Field notes including initial soil logs and a soil test pit site map are included in Appendix B. During consultation with DOH at the October 25th site visit, initial interpretations of the dense B horizons were discussed and later revised from Soil Type 1 or 5 to Soil Type 7 based on the fact that this extremely gravelly silt or clay loam is functioning as a restrictive layer. The interface between this dense restrictive layer and weathered bedrock varied in depth and thickness but consisted of a notably less dense, extremely gravelly coarse sand (Soil Type 1). For the purpose of this project, the key soil features for design purposes are the depth to penetrate through dense restrictive Soil Type 7, and ensuring 36” of vertical separation between the infiltrative surface and weathered bedrock (>90% rock). Revised soil characterization for each of the five soil test pits is summarized by layer depth and soil type in Table 3.

Table 3. Hurricane Ridge Visitor Center (HRVC) soil test pits and soil type by layer depth.

Texture / Soil Type HRVC #1 HRVC #2 HRVC #3 HRVC #4 HRVC #5 Sandy Loam / Soil Type 4 0” – 22” 0” – 30” 0” – 26” 0” – 29” 0” – 22” Extremely Gravelly Silt Loam / Soil Type 7 22” – 60” 30” – 62” 26” – 44” 29” – 52” 22” – 62” Extremely Gravelly Sand / Soil Type 1 60” – 72” 62” – 78” 44” – 49” 52” – 57” 62” – 72” Weathered Bedrock / Soil Type 7 72”+ 78”+ 78”+ 78”+ 72”+

10. SOIL TYPE & HYDRAULIC LOADING RATE

For the purposes of this LOSS project, Soil Type 1 (extremely gravelly soils) with a maximum hydraulic loading rate of 1.0 gpd/sf of is being used to size the primary and reserve drainfields. As noted above, the park intends to construct and use 150% of the required infiltration size to effectively reduce the hydraulic loading rate to 0.7 gpd/sf due to higher than residential strength effluent.

11. PHYISICAL CHARACTERISTICS

The proposed primary and reserve drainfield sites for the Hurricane Ridge Visitor Center are adjacent to each other and nearly identical in terms of physical characteristics.

TOPOGRAPHY & SLOPE

Both sites are located on a south-facing aspect between approximately 5170 and 5220 feet elevation.

Slope was measured with a clinometer at each soil test pit during soil characterization and ranged from 19-26%, as shown in Table 4.

Table 4. Slope measurements along north-south axis for each Hurricane Ridge Visitor Center soil test pit.

Soil Test Pit Slope (%)

HRVC #1 20

HRVC #2 19

HRVC #3 26

HRVC #4 26

HRVC #5 21

VEGETATION

Vegetation within the proposed primary and reserve drainfield areas consists of subalpine meadow of primarily Carex specatabilis communities. A photo of this perennial grass meadow in late October is shown in Figure 7.

Reserve

Primary

Figure 7. Carex sedge-dominated subalpine meadow vegetation at proposed drainfield sites.

PREDOMINANT SOIL TYPE

The predominant soil type is a sandy loam (Soil Type 4) in the upper horizon atop a dense restrictive layer (Soil Type 7), which will be cut and filled with a minimum 24 inches of sand filter media. The predominant soil type for the interface between sand filter media and native, undisturbed soil will be an extremely gravelly sand (Soil Type 1) atop weathered bedrock characterized by thin, laminated beds of sandstone, siltstone, slate, and shale.

VERTICAL SEPARATION

A vertical separation of at least three feet is required between the infiltrative surface of the drainfield bed or trench and the highest seasonal water table or restrictive layer. The infiltrative surface will be constructed on 24” – 42” of ASTM C-33 sand, depending on the depth required to penetrate the dense restrictive layer found throughout the site. A combination of ASTM C-33 sand underlain by extremely gravelly Type 1 soil will provide a minimum 36” vertical separation to weathered bedrock once the dense restrictive layer is penetrated.

SITE DRAINAGE PATTERNS

No surface drainage is directed toward the proposed primary or reserve drainfield sites. Natural site drainage patterns are not expected to adversely affect the soil or performance of the LOSS and will be re-established as part of construction completion and site revegetation.

WATER TABLE & RESTRICTIVE LAYERS

Soil test pits were excavated to a depth of 72-78 inches. No sign of mottling or any other indication of a seasonally high water table was observed in any of the soil test pits. However, a restrictive layer of dense extremely gravelly silt or clay loam was observed in all five soil test pits ranging from 22 inches to as deep as 62 inches below ground surface. This restrictive layer was consistently underlain by a layer of extremely gravelly Type 1 soil atop weathered bedrock.

12. MINIMUM LAND AREA REQURIEMENTS

WAC 246-272B-03500 requires a dedicated minimum land area of 6.35 acres for a design flow of 10,000 gpd based on a maximum daily volume of effluent of 1,575 gpd per acre when the finest textured soil type within the vertical separation includes Soil Type 3, 4, or 5. This minimum land area requirement assumes residential strength effluent. This dedicated minimum land area requirement is easily met for the Hurricane Ridge Visitor Center LOSS and drainfield.

13. NEPA CHECKLIST

Under the NPS Director’s Order 12, and the 2015 NPS National Environmental Policy Act (NEPA) Handbook, categorical exclusion C.19 (Construction or rehabilitation in previously disturbed or developed areas, required to meet health or safety regulations, or to meet requirements for making facilities accessible for the handicapped) was selected as the appropriate NEPA pathway for this project.

A copy of the NEPA checklist and categorical exclusion (CE) determination is included in Appendix C.

REFERENCES

Brake, Perry F. 1998. Supplemental Guidance for the Determination of Biochemical Oxygen Demand (BOD5) and Carbonaceous BOD (CBOD5) in Water and Wastewater. Washington State Department of Ecology Environmental Assessments Program, Lab Accreditation Section. Publication No. 98-307.

March 1998. 3rd Printing, March 2003.

Eliasson, John. 2004. Rule Development Committee Issue Research Report Draft – Septic Tank Effluent

Values. Washington State Department of Health, Wastewater Management Program.

Tabor, R. W., Yeats, R. S. and Sorensen, M. L. 1972. Geologic map of the Mount Angeles Quadrangle, Clallam and Jefferson Counties, Washington: United States Geological Survey Map GQ-958. 1 sheet, scale 1:62500.

U.S. Environmental Protection Agency (USEPA). 2002. On-site Wastewater Treatment Systems Manual.

EPA-625/R-00/008. U.S. Environmental Protection Agency, Office of Research and Development, Office of Water.

Washington State Department of Health (DOH). 2013. Recommended Standards and Guidance for

Performance, Application, Design, and Operation & Maintenance (RS&Gs) – Gravelless Distribution Products. December 2013. Washington State Department of Health, Division of Environmental Health, Office of Shellfish and Water Protection.

Appendix A – Sample Results

Appendix B – Soil Logs & Site Map

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#0 #0

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Test pit 1 Test pit 2

Test pit 3 Test pit 4

Test pit 5

Olympic National Park Resource Management

Produced by OLYM Archeology October 2019

National Park Service U.S. Department of the Interior

0 150 30075 Feet

Hurricane Ridge Septic System Geo Tech Investigations

Legend #0 GeoTechPits

Appendix C – NEPA Documentation