Reclamation report, Basalt Waste Isolation Project, boreholes 1990

Abstract

In 1968, a program was started to assess the feasibility of storing Hanford Sitedefense waste in deep caverns constructed in basalt. This progrmu was expanded in 1976 to include investigations of the Hanford Site as a potential location for a mined commercial nuclearwaste repository. Some 98 boreholes were drilled, deepened, or modified to study the geology and hydrologyof the Hanford basalts. These boreholes were sited,on 71 drill pads ranging in size.from 0.1 to over 2.6 ha. Reclamation of these sites was begun in 1988 as a consequenceof terminationof the Basalt Waste IsolationProjectsite characterizationprogram. The objectiveof the reclamation programwas to returnsites as nearlyas practicableto conditions existing before the disturbance.Vegetation established on the sites mustbe native andself-sustaining. Reclamation was begun in 1988 as a two-phase programin which siteswere clearedof added materialsand seeded and planted in 1%8 and 1989. This reportexamines the success of that effort. Sandberg'sbluegrass was the most common grass foundat ali sites where it was seeded. The greatest abundanceof bluegrasswas found on sites BensonRanch, DC-15, DC-32, DC-33, DH-27, DH-28, and DH-34. Sites without bluegrass where sucb was plantedwere DB-1, DB-2, DB-15, DC-12, RRL-4, RRL-5, RRL-7, and RRL-16. Bottlebrushsquirreltailappearedat low densities. Ricegrassdensity was significantly higher on DC-15 and DC-25 than on other sites. Needle-and-threadgrass density was sparsebutrelatively uniform across sites. Downy wheatgrass and ricegraasperformedexceptionally weil. Shrubmortalityrateswere higher than expected, averagingjust under45%. Hopsagestffferedthe greatestmortality(62%)as a consequenceof predation by jackrabbits. The lowest mortality was experiencedby grey rabbitbrush(41%). Differences in grassgrowth were primarilya resultof the failureof the winter rainsduring 1989-1990. Plants growingin differentsoil typesresponded differently to this stress. Furroworientationhadno effects on performance, anddifferingnutrientlevels had no noticeableeffects except in markedlypooror unstablesoils (sandsandpit-run material)where additionalnw ients enhancedbluegrass growth. Deep-rootedgra_s fared betterduringthe droughtthan did the moreshauow-rootedbluegrass. The main sourceof mortalityfor the shrubsother than hopsage was probablyrelated to exposure to dryingwinds. Plants at the edge of the revegetatedareaswere somewhat sheltered fromwinds by the neighboringadultshrubs. Overall,the extreme mortalitycan probablybe attributedto the droughtduringthe critical periodbefore the shrubsplantedin fall of 1989 were able to establisha strongroot system. A numberof sites currentlymeet revegetation goals for grass and shrubcover, though most do not. A numberof sites are without any cover at all. Althoughmany sites currentlymeet the reclamationstandardsin terms of grass cover, there is no evidence to suggestthat they will continue to do so. Bluegrass density in springof 1989averaged 15.6 plants/m of seeded row. By spring 1990, the averagedensity at thes...

Basalt Waste Isolation Project Reclamation Support Project:

“…Approximately 58% of all borehole reclamation sites were found to be well below their respective reclamation objectives, with 25% of sites devoid of grass or shrub growth. Analyses indicated that the primary causes of failure were the lack of winter rains during 1989-1990, exposure to drying winds, grazing by blacktailed jackrabbits (Lepus californicus) on shrubs, and residual herbicide activity on some sites (Brandt et al 1991a).…”

Plant reestablishment after soil disturbance: Effects of soils, treatment, and time

“…Reintroducing native species to disturbed areas of the Hanford Site has proven difficult (Brandt et al 1992). Competition from alien weeds such as cheatgrass and Russian thistle (Salsolakalt) may play a role in limiting revegetation with native species; however, other potentially significant factors affecting revegetation success at least over the short term include soil physical properties, moisture availability, and extreme winter temperatures (Brandt et al 1990(Brandt et al , 1991(Brandt et al , 1992.…”