Drainage units wrapped in sunlight-impeding wrapping

1. In a method of manufacturing, shipping, storing, and installing drainage units, wherein each drainage unit has a generally tubular shape, a length, a nominally circular cross section and an associated nominal diameter, wherein each drainage unit is comprised of polystyrene bead aggregate contained within a plastic netting sleeve, and wherein for shipment and storage a plurality of drainage units is assembled as a set of three side-by-side units, the set having a lengthwise axis and a width nominally equal to three of said drainage unit nominal diameters, the improvement which comprises:

(a) forming pellets comprised of recycled polystyrene that is a mix of white polystyrene and colored polystyrene, with a colorant having about 0.25 weight percent carbon black, and about 4 weight percent titanium dioxide filler;

(b) converting the pellets into beads of expanded polystyrene, the beads having a gray color and a property of absorbing solar radiation energy in the infra-red portion of solar radiation spectrum substantially more than all-white polystyrene beads having said about 4 weight percent titanium dioxide filler, which beads lack said about 0.25 weight percent carbon black;

(c) making a plurality of said drainage units having said beads as aggregate;

(d) arranging three of said drainage units in side-by-side fashion as a set of drainage units having a width and a lengthwise axis corresponding to said drainage unit lengths, and wrapping the set of drainage units with film made of plastic by winding the film around the set in a direction transverse to the lengthwise axis of the set, wherein the film has the property of inhibiting the transmission of solar radiation with respect to both the UV radiation portion thereof and the infra-red radiation portion thereof; and,

(e) transporting said set of drainage units in said wrapped condition to a point of use of said drainage units, exposing said set of drainage units to sunlight, then removing said film from said set of drainage units, and burying the drainage units of said set within soil.

2. The method of claim 1 further comprising, during step (d), applying tension to the film sufficient to change the cross section shape of each drainage unit, sufficient to make the width of the set of three drainage units at least about 5 percent less than the sum of three said nominal diameters, wherein the wrapping of film leaves portions of each lengthwise end of the set uncovered.

3. The method of claim 1 wherein when said set of drainage units is exposed to direct sunlight when in said wrapped condition during step (e), said aggregate has an infra-red light absorptivity which causes the beads contained as aggregate in each drainage unit to become heated to a temperature in excess of 150 degrees Fahrenheit.

4. The method of claim 1 wherein said plastic film of step (d) is opaque, optionally white.