Yelm Proposed Project NarrativeNarrative Description of Project – Yelm, WA Ready Mix – NPDES Permit No. WAG501184
Yelm Ready Mix located at 705 NW Rhoton Rd. proposes to relocate the site’s existing
infiltration pond from the northeastern to the northwestern area of the site. The relocation is
being proposed to increase maneuvering area for the site’s loader operator. The site infiltration
pond was sized according to the Drainage and Erosion Control Report in 2004 and has since
function as designed. The required storage volumes and proposed changes are summarized in the
tables below.
All process water is detained, treated, and infiltrated or re-used onsite and there will be no
changes to this as part of the proposed project. Infiltration is authorized under Sand and Gravel
General Permit No. WAG501184 issued on February 17th, 2021, by the Washington Department
of Ecology.
Concrete process water is routed via curbs, grading, and pumps to the site’s four settling sumps
(referenced as concrete re-use tanks/ponds in the attached drainage study). Water from the final
settling sump is pumped to the onsite treatment tank before discharging to an L-shaped swale
that bisects the property before turning east along the site’s northern boundary. Two catch basins
in the aggregate storage area receive and route water to the onsite infiltration pond. Water from
the front entrance/exit is captured by a drain and water along the internal access road is picked
up by a catch basin routed to an oil/water separator. Berms and/or grading along the site
boundaries direct stormwater inward, where it either infiltrates in situ or flows to the site’s
various water infrastructure. As part of the proposed project, the northeastern area of the site will
be regraded to direct water west and water from the aggregate storage area will be pumped to the
swale. Please see the attached figures.
Existing Storage Volumes Proposed Storage Volumes
Pond 7,360 cf Pond 12,880 cf
Concrete Re-Use
Tanks/Ponds
6,012 cf Concrete Re-Use
Tanks/Ponds
6,012 cf
Holding Basin 1,152 cf Holding Basin 1,152 cf
Setting Basin 4,257 cf Remove Settling
Basin
0 cf
Total 18,781 cf Total 20,044 cf
Required Volume per HYDRA model 14,410 cf
Existing Pond Dimensions Proposed Pond Dimensions
80’ x 46’ x 2’ = 7,360 cf and 3,680 sf
bond bottom infiltration area
80’ x 46’ x 3.5’ = 12,880 cf and 3,680
sf pond bottom infiltration area