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freefall only where the interval to be sealed is dry and no more than 30 feet in depth. Fill material shall be placed by methods that prevent bridging and voids. 2. Timing of Placement. Sealing material shall be placed in one continuous operation (or"pour") from the bottom to the top of the well or boring,unless conditions in the well or boring dictate that sealing operations be conducted in a staged manner, and prior approval is obtained from the enforcing agency. 3. Ground Water Flow. Special care shall be used to restrict the flow of ground water into a well or boring while placing sealing and fill material, if subsurface pressure producing the flow is significant. 4. Sealing Pressure. Pressure required for the placement of cement-based sealing materials shall be maintained long enough for cement-based sealing materials to properly set. 5. Verification. It shall be verified that the volume of sealing and fill material placed during destruction operations equals or exceeds the volume to be filled and sealed. This is to help determine whether the well or boring has been properly destroyed and that no jamming or bridging of the fill or scaling err?Penal has oeetarred. D. SeaIinyand R1I k1areriaIs. Materials used for sealing exploratory borings and mOni it)iing wells Shall have low permcabilitics so that [he volume of waver and passible pollutants and I cOT)tarn inarnis passing through lhcrn will be of minimal consequence. Sealing material shall be compatible with the chemical criviron men L info which ii is placed, and shall have rrmechanicai propk,r'[i" consistcnt with prc&cnt and future site uses. # Suital}lc sealing materials include neat cemelit, sand-cement, and bentunito. all of which are described in Section 9 of these standards.. Bentanite shall rLoi be uscd as a scaling; material 0ppif�iIL r.nn.tN of fra0LLred ruck, unless oIhcrwisc: approwv d by the enforcing agency. Drilling raud or drill cuuin&; ;ere nor acceptable as any part cif sealing material for well destruction. # C oncn:tC relay lac in;w as a scaling m.L[erial W [he approval of the enforcing agency. j Fill material, If any, shall meet the requirenients of Section 23 of the Wuicr 1' 01 Standards. Fill M[crial shall ba free of polls =,N and con[uminan[s and shall tiol be subject tea decomposilion or conm)]i daIion uf(cr placement, DriIIing mud or cuttings are no[ acccpt3blc: as any part of fill nimerial. i _ Add i(ion al Ruki uirements for Mori itorin g Wells and Fa€ lora toEy Morin Lis in 1)rhan Areas. The following 4ddiI ion al rgtiircrtients shut1 bc: met for d titroyiLig monitoring wells and exploratory i borings in urban arias, anle,ss otherwise approved by the enforcing agen : 1. The upper surface car the sc ling m�gierial shall end at a depth a 5 feet below ground surface; and, 2, If the well casing was not extracted during destruction and sealing operations, a hole .shall be c:x vatc d azx)und the w0l casing to a depth of 5 feet helow ground surface after sealing operations have been wmpleted and (lie sealing material hus acic-quately sei and cnzccl. Thc: cxposcd welt casing shall then he rcrnow d by cutting the casing at the Lo(toni of the eceavation. Ilie excavation shall be backfiIled with glean, native soil or other suilable material. -53- +