July 15, 2019

Managing Concrete Truck Washout

We’ve been contacted several times in the last couple of years regarding the status and management of concrete truck washout water. Although EPA’s guidance notes that this material has “a pH near 12,” we have heard anecdotally that the pH of the washwater can be ≥12.5 under certain conditions. The only EPA guidance we have found that addresses this issue is a stormwater best management practice (BMP). Although that BMP provides guidance on the management of the washout from a stormwater perspective, it says nothing about the RCRA implications.

So what are the RCRA implications? Section 262.11(a) requires generators of a solid waste to make a hazardous waste determination at the point of waste generation (POG). In the absence of any EPA guidance, it would appear that the POG is where the washwater leaves the drums and chutes of concrete trucks and hoppers of concrete pump trucks. By testing or knowledge, the generator of this washout will have to determine if the pH is 1) <12.5, in which case the washout can be managed as nonhazardous; or 2) ≥12.5, in which case the washout must be managed as D002 from that point on.

Concrete truck washout is typically managed in low-walled roll-off bins, where the water is either 1) allowed to evaporate, or 2) accumulated before transportation to an industrial wastewater treatment facility. In either case, if the washout is hazardous, the roll-off bins will be hazardous waste containers subject to §262.16(b)(2) or 262.17(a)(1) standards, depending on generator category. These standards include labeling, inspections, and keeping the containers closed except when adding/removing the waste. (Very small quantity generators are subject to the reduced requirements of §262.14.) Also, evaporation of hazardous washwater would be considered treatment of hazardous waste and could trigger the need for a RCRA permit. (We are aware, however, that some states allow evaporation of hazardous wastewater in 90/180/270-day accumulation units without a RCRA permit.)

One way to minimize the RCRA implications of managing concrete truck washout with a pH that is ≥12.5 is to neutralize it under the elementary neutralization unit (ENU) exemption. This exemption from RCRA management/permitting is in the regulations at §§264.1(g)(6), 265.1(c)(10), and 270.1(c)(2)(v). The benefits of using the ENU exemption to neutralize the washout are 1) the roll-off bin becomes an ENU instead of a RCRA-regulated unit, and 2) once neutralized to pH<12.5, the washwater may be managed as nonhazardous from that point forward. Although fairly easy from a regulatory perspective, adding acid to the washout in a roll-off bin to lower the pH to <12.5 may not be practical, depending on the situation. Last, if the washout was D002 at the POG, any hardened solids that remain after the water is evaporated/removed may have to meet LDR treatment standards for D002 before disposal.

If the pH of the concrete washwater is <12.5 at the POG, evaporation of the water is allowed (provided no CAA requirements would prevent this practice), and the hardened solids can be either recycled (preferable) or disposed. Note, however, that safety data sheets for Portland cement (a primary component of concrete) show that small amounts of hexavalent chromium are contained in the product. Thus, baseline TCLP results for chromium in hardened washout solids sent for disposal could be a prudent practice.


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