HomeMy WebLinkAboutExh.01_PN_Project Narrative_210318_v2.pdf1
March 18, 2021
Matt Herrera, AICP, Senior Planner
City of Renton
1055 S. Grady Way
Renton, WA 98057
SUBJECT: Application for Critical Areas Exemption – South Renton Transit Center and Roadway
Improvements Borings Program
Dear Matt,
Sound Transit requests the City of Renton’s review of the enclosed application for a Critical Areas
Exemption for the South Renton Transit Center and Roadway Improvements Borings Program, consisting
of site investigative work (per Renton Municipal Code (RMC) 4‐3‐050.C.3).
The South Renton Transit Center and Roadway Improvements is a project component of Sound Transit’s
I‐405 Bus Rapid Transit (BRT) project, which will provide BRT service for 37 miles between Lynnwood
and Burien. The proposed South Renton Transit Center site is comprised of four parcels (192305 ‐ 9035,
9063, 9068, 9074) located northeast of the intersection of Rainier Avenue S (State Route (SR) 167) and S.
Grady Way. The four parcels that comprise the site are owned by Sound Transit. While there are existing
buildings on the site the prior businesses have been relocated and the site is currently unoccupied.
Roadway modifications to improve access to the site are proposed on Rainier Avenue S, S. Grady Way,
Hardie Avenue SW and Lake Avenue S. Prior to construction of the transit center, Sound Transit
proposes a borings program with drilling to collect geotechnical, geoarchaeological, and hazardous
materials data, along with utility potholing and excavation of an on‐site infiltration test pit. The purpose
of the borings program is to obtain additional information about existing conditions to inform that
facility’s design and help plan for its construction.
This letter describes the proposed investigative work and addresses Renton’s critical area exemption
criteria.
PROJECT DESCRIPTION
For all site investigative work, field activities would include: (1) marking the proposed explorations for
utility locating purposes; (2) completing soil sampling, drainage testing, utility potholing and installing
temporary groundwater monitoring wells that would be removed prior to the start of construction of
the transit center construction; (3) collecting soil and groundwater samples for laboratory analysis; and
(4) observing the investigation‐derived waste (IDW), and handling and transporting the IDW off‐site.
Appropriate best management practices for erosion and sediment control will be in place prior to the
start of work.
Critical Area Exemption: South Renton Transit Center and Roadway Improvements Borings Program
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Geotechnical Borings
Approximately eleven (11) machine‐drilled boreholes, 6 inches in diameter and reaching a target depth
of between 10 feet and 80 feet belowground surface (bgs), would be conducted for geotechnical and
seismic investigation. Approximately seven (7) of the geotechnical borings would be conducted on the
four parcels, owned by Sound Transit, that comprise the proposed South Renton Transit Center site. The
other four geotechnical borings are proposed as follows: one within the roadway of Hardie Avenue SW,
one within the center of Rainier Avenue S just south of S 7th Street, one along the eastern side of
Rainier Avenue S north of S Grady Way, and one alongside the Rainier Avenue S roadway just north of I‐
405. The proposed borehole locations are subject to minor location changes based on underground
utilities. Up to two (2) groundwater monitoring wells (approximately 2 inches in diameter) would also be
installed in the proposed geotechnical borings on the South Renton Transit Center site. The
groundwater monitoring wells would remain in place throughout design and would be decommissioned
during construction.
The drilling of the boreholes would require a truck‐mounted drill rig and support truck. The driller would
use best practices to contain suspected contaminants if encountered and the drill rig would be
decontaminated between borings. After the borings reach the target depth, the boreholes would be
abandoned in accordance with Washington State Department of Ecology (Ecology) requirements and
cuttings at the surface would be removed. Surface restoration for boreholes in paved areas would
consist of filling the borehole with bentonite chips (per Ecology requirements) to the base of the
pavement section and then matching the existing pavement thickness with cold patch.
Ground monitoring wells would be installed, in accordance with Ecology requirements, in two of the
borehole locations. A flush‐mounted monitoring well monument cover would be located directly over
these borehole locations. Upon completion of design, the monitoring wells would be decommissioned
by the contractor in accordance with Ecology requirements.
Geoarchaeological Borings
Within the proposed South Renton Transit Center site, 15 borings are planned for archaeological
investigation. All archaeological borings are planned to be conducted using a 2‐inch‐diameter, sleeved,
direct‐push geoprobe to a target depth of approximately 50 feet bgs. Proposed archaeological boring
locations would be marked; final locations may need to be adjusted based on underground utilities.
An archaeological monitor would be on‐site to label and catalog samples, and a geotechnical engineer
would attend the site intermittently to monitor progress and verify safety procedures are being
followed. Sleeved samples would not be opened for evaluation in the field, rather they would be
transported to a lab where an archaeological assessment and classification would be completed.
In accordance with Ecology requirements, all boring locations would be tremie grouted and cold patch
would be placed and compacted to match the existing pavement.
Infiltration Test Pit
One (1) infiltration test pit is proposed to be dug on the South Renton Transit Center site. The test pit
would meet Ecology’s 2019 Stormwater Management Manual for Western Washington requirements.
The test pit would be approximately 100 square feet at the bottom and approximately 5 to 10 feet deep.
Water would be added to the pit for a minimum of 6 hours and the test would continue until the pit is
Critical Area Exemption: South Renton Transit Center and Roadway Improvements Borings Program
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empty. Once the infiltration test is completed, the pit would be backfilled with clean soils (with
excavated materials if not contaminated, or clean fill from off‐site, if needed) and then patched, or
repaved, to match the existing pavement.
Utility Potholing
Up to 33 utility potholes are planned, approximately 8 within Rainier Avenue S and 25 on the South
Renton Transit Center site, to determine the exact location of some utility lines that may be critical for
design and construction of the South Renton Transit Center. Potholes would be typically 12 inches in
diameter and typically 3 to 6 feet deep; the depth would vary depending on the depth of the utility.
The potholing would be performed using truck‐mounted vacuum equipment that uses a high‐velocity air
stream to penetrate, expand, and break up soil. The loosened chunks of soil and rock would be removed
from the hole through the vacuum to reveal the buried utility. The information to be gathered from the
pothole process includes top of structure, bottom of structure, width or diameter of structure, general
condition of utility, pavement type and thickness, and general soil conditions. Each pothole would be
backfilled with the removed soil, compacted, and capped with asphalt or material consistent with the
surrounding area. Restoration would be as required by the City of Renton’s Standard Right‐of‐Way Use
Permit and the Washington State Department of Transportation (WSDOT) General Permit. After
patching, a small marker would be placed in the ground tagging the utility alignment.
Environmental Site Assessment Borings
Up to 24 environmental site assessment borings would be conducted to further identify hazardous
materials contamination on the South Renton Transit Center site. These hazardous materials
investigations would be conducted to augment the Phase II Environmental Site Assessment (ESA)
information and to further explore three areas that were identified as “hot spots” in the Phase II ESA.
Each of these hot spots is within an existing parking lot.
In each of the three areas, up to four borings would initially be conducted around areas previously
identified as “hot spots” in the Phase II ESA. If contamination is encountered, four additional borings
would be conducted at a step‐out of 10 feet from the initial boring to find the edge of the
contamination. Explorations would be advanced to approximately 10 feet bgs, or a few feet below first
observed and encountered groundwater, using direct‐push drilling methods. Four ground water
monitoring wells are proposed in the north and center portions of the South Renton Transit Center site.
Wells would be constructed using pre‐pack wells screens (installed approximately between 5 and 10 feet
bgs). Soil samples would also be collected near the monitoring wells. These wells would be properly
abandoned in place or removed prior to facility construction.
CRITICAL AREAS EXEMPTION REQUEST
The entire South Renton Transit Center site and the surrounding roadways is in a Wellhead Protection
Area Zone 2 and a Seismic Hazard Area critical area, as designated and mapped by the City of Renton.
Therefore, all of the proposed borings activities are located within these critical areas. Further, the area
south of SW Grady Way and east of Rainier Avenue S is mapped within a Special Flood Hazard Area (100
year flood) or Other Flood Areas (Zone X – 500 year flood) associated with Rolling Hills Creek. Three (3)
of the utility potholing locations along Rainier Avenue S, south of S. Grady Way, are located within or
near these mapped flood hazard areas. No other critical areas or associated buffers are located in this
area.
Critical Area Exemption: South Renton Transit Center and Roadway Improvements Borings Program
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Prior to any development or alteration of a property containing a critical area, RMC 4‐3‐050.C.1 notes
that the owner or designee must obtain a development permit, critical area permit, and/or letter of
exemption. RMC 4‐3‐050.C.2 notes that activities within critical areas that are considered exempt
activities may require obtaining a letter of exemption issued by the Administrator prior to initiation of
activities.
The table of exempt activities in RMC 4‐3‐050.C.3 identifies site investigative work, such as the proposed
geotechnical and archaeological borings, as an exempt activity that is permitted within critical areas and
associated buffers. Exempt site investigative work is described in footnote 4 of the table as follows:
4. Site investigative work necessary for land use application submittals such as surveys, soil logs,
percolation tests and other related activities. Investigative work shall not disturb any more than
five percent (5%) of the critical area and required buffer. In every case, impacts shall be
minimized and disturbed areas shall be immediately restored at a one‐to‐one (1:1) ratio. Within
shoreline jurisdiction, this includes the marking of property lines or corners on state‐owned lands,
when such marking does not significantly interfere with the normal public use of the surface
water. Limitations on site exploration and investigative activities are defined in WAC 173‐27‐
040(2)(m) for properties within shoreline jurisdiction.
The proposed site investigative work, in total, would impact less than 5 percent of the 361,000 square
foot SRTC site and would not disturb more than 5 percent of the overall Wellhead Protection Zone,
Seismic Hazard or Flood Hazard critical areas. All work would be performed in accordance with Ecology
requirements, which would include surface restoration and/or well covers. The proposed site
investigative work is not located within the shoreline jurisdiction.
Within Wellhead Protection Areas, footnote 1 in Section 4‐3‐050.C.3 applies to site investigative work,
which reads as follows:
1. If a hazardous material, activity, and/or facility that is exempt pursuant to this Section has a
significant or substantial potential to degrade groundwater quality, then the Administrator may
require compliance with the Wellhead Protection Area requirements of this Section otherwise
relevant to that hazardous material activity and/or facility.
While the target depths of the proposed geotechnical and geoarchaeological borings would reach
groundwater on the site, they would not result in a significant or substantial degradation of
groundwater quality. Prior to conducting the borings program activities, a temporary erosion and
sediment control plan (TESCP) will be developed and will include best management practices (BMPs),
such as catch basin protection, which will be used to minimize the risk of turbid water leaving the site.
As noted in the project description, the drill rig will be decontaminated between borings in accordance
with a decontamination plan to avoid potential cross‐contamination between bore holes. After borings
in paved areas reach target depth, the boreholes will be abandoned in accordance with Ecology
requirements and cuttings at the surface will be removed. IDW materials (soil and groundwater) will be
contained in 55‐gallon drums and properly disposed of at a permitted facility.
CONCLUSION
In conclusion, the proposed South Renton Transit Center and Roadway Improvements borings program
is consistent with RMC 4‐3‐050.C.3 as site investigative work that is an exempt activity within critical
areas and associated buffers.
Critical Area Exemption: South Renton Transit Center and Roadway Improvements Borings Program
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Please feel free to contact me at (206) 660‐3968 or Dangelei.fox@soundtransit.org if you have any
questions or need additional information. Thank you for your time in processing this request.
Sincerely,
Dangelei Fox, PWS
Senior Environmental Planner
Sound Transit