Gravel, Stone and Soil Delivery in Kent, WA

Gravelly loam over dense till

At the center point of ZIP 98030, the USDA soil survey maps Alderwood gravelly sandy loam, 8 to 15 percent slopes. Alderwood makes up 85 percent of the map unit, so the description fits the spot well.^[1]

The top layer is gravelly sandy loam, a coarse soil with rounded stones mixed through it. The survey rates Alderwood moderately well drained and puts it in hydrologic group B, moderate infiltration. Water enters the upper soil easily, which is good for beds and lawns.^[1]

The rounded stones in Alderwood soil are glacial cobbles, smooth and hard. They slow down digging, and they make poor base material because they roll rather than lock. Sift them out of planting beds and use them as edging or as a dry creek liner instead.^[1]

Below, the survey records densic material at about 35 inches. In this region that dense layer is compacted glacial till, packed so hard that roots and water barely penetrate it. Rain soaks into the loam, hits the till and then moves sideways along it, which can leave the soil above saturated for long stretches of the wet season.^[1]

Shrink-swell in the top 100 cm is low, at 0.7 percent. The gravelly loam does not heave or crack with moisture changes, so the main concern is water, not soil movement.^[1]

Slopes in the map unit run from 8 to 15 percent, enough to move water and loose material downhill. The ground at the center point stands 380 feet above sea level.^[1],[2]

A long wet season

Weather normals for ZIP 98030 come from the NOAA station at Kent, WA, about 4 miles away. It averages 40.1 inches of precipitation a year, much of it as steady rain through the cooler months.^[3]

Lows at the Kent station reach 32 F or colder on 39 days in a normal year. Freezes are mostly light, but a cold snap on saturated ground can still heave a poorly drained base.^[3]

Summers are the dry exception. Soil that stays soggy all winter can harden and dry out by midsummer, so beds need drainage for the wet months and mulch for the dry ones.^[3]

The station's median last spring freeze is March 20, and its median first fall freeze is November 10. Planting can start after the March date, and outdoor building is easiest in the drier months before the November one.^[3]

Steady rain plus a hardpan means water perches. Yards can stay soggy well after a storm passes, and a gravel drive laid without drainage soon turns into mud and potholes.^[1],[3]

Mud control on a sloped lot

On slopes of 8 to 15 percent, gravel must lock or it migrates downhill. Strip the topsoil, grade the subgrade so it sheds water to one side, and lay woven fabric. Build the base with 1-1/2" Crushed Gravel or #4 Crushed Stone, then compact Road Base or Crushed Concrete on top in thin lifts.^[1]

Finish with Driveway Gravel or 3/4" Crushed Stone. Rounded Pea Gravel rolls on a slope and belongs on flat paths and play areas. Asphalt Millings make a firm, dark surface that holds up well under steady rain.^[3]

Add a ditch along the uphill side of the drive, lined with fabric and filled with #57 Crushed Stone or Drain Rock. It intercepts water moving downslope along the till before it reaches the drive. At the outlet, a pad of Riprap or River Rock keeps the flow from scouring the ground.^[1]

On longer drives, a crowned profile and water bars turn runoff off the surface before it can carve ruts down the slope. Regrade after the wettest months and top up with fresh Driveway Gravel where the surface has thinned.^[1]

Muddy areas around gates, sheds and parking spots firm up with a layer of Road Base over fabric, topped with 3/4" Crushed Stone. That combination drains well in a wet climate.^[1]

Water that perches on the hardpan

Basements and crawl spaces on this ground often take on water because the till holds it near the surface. A French drain along the uphill side of the house, set in Drain Rock around a perforated pipe, intercepts that perched water and carries it around the building.^[1]

Dry wells and soakage pits need care, since the dense layer at about 35 inches limits how deep water can go. Keep pits shallow and wide, filled with clean #4 Crushed Stone, or route water to a ditch or swale instead.^[1]

Moderately well drained soil over till can feel firm in summer and soft in winter. Plan heavy work, such as digging for a patio or an addition, for the drier months, when the ground carries equipment without rutting.^[1]

Downspouts need a plan in a wet climate. Splash beds of River Rock break up the stream, and buried lines in Drain Rock move water to a lower spot away from foundations.^[3]

Beds and lawns in the rain

Gravelly sandy loam drains well in the top layer, which suits most garden plants. Mixing Compost into beds adds organic matter and helps the soil hold water through the dry summer weeks.^[1]

Raised beds of Garden Soil lift roots above the wettest zone just over the till. Topsoil spread over thin or stony ground helps new lawns establish.^[1]

Gardens near the Kent station get a long growing year, with the median last freeze on March 20 and the median first freeze on November 10. Its midsummer weeks are the driest, so drip lines under mulch keep beds going then.^[3]

Mulch protects bare soil from heavy rain. Brown Shredded Mulch and Black Shredded Mulch interlock and stay put on slopes, and Wood Chips suit play areas and woodland paths. Playground Sand fills a covered sandbox.^[3]

Homes in ZIP 98030

King County contains ZIP 98030. The Census counts 13,736 housing units in the ZIP, and 50 percent are detached single-family houses.^[4]

The median home in ZIP 98030 was built in 1986, and owners live in 52 percent of the occupied ones.^[4]

Kent as a whole has 49,652 housing units, with 52 percent detached. The citywide median build year is 1985.^[4]

Houses from the mid-eighties may still have their original drives and walks, settled or cracked over the decades. Replacing a broken slab with a compacted gravel apron or a Walkway Gravel path is a common fix.^[4]

Half of the homes in ZIP 98030 are detached houses, close to the city's share, and their yards bring the widest range of projects, from drives to drainage to garden beds.^[4]

The Washington State Department of Transportation names Crushed Surfacing Base Course under Section 9-03.9(3) of its Standard Specifications for Road, Bridge, and Municipal Construction M 41-10 (2027).^[5]