WORK PLANS_FILE 2 - Laserfiche WebLink

Home Browse Search

S characterized as predominantly medium to dark -ray shale which readily weathers to a thick, clayey soil horizon. 'fwo'I'NRCC-designated aquifers exist beneath the Eagleford Croup at the site;file Woodbine and Trinity Aquifers (Texas Water Development Board, 1994). 'lhe hydrogeologic setting is not considered sensitive based on the depth and distance to the recharge zones for these beneficial use aquifers. Shallow, perched groudwatcr in the site vicinity is definitely hydrologically separated from these deeper aquifers by aquicludcs formed by unweathered shales of the Eagleford Group. 'There is no known beneficial use of shallow, perched groundwater within a 0.5 mile (0.8 Km) radius of the site, and the total dissolved solids concentration is 3,170 milligrams/liter(mg/1)in the shallow aquifer. Site specific geology consists of a very low permeability light to dark brown, soft, moist clay (CL) from surface to approximately 22 ti. (6.7 m) where a hard, gray shale is encountered; commonly causing auger refusal at or near the top. Cores taken h-om this shale aquiclude had a vertical Intrinsic permeability of approximately 7.72 X 10-1 r' centimeters (CM). This layer effectively limits the vertical migration of contaminants. Water levels in the aquifer perched in the weathered clays above this aquiclude occur at approximately 4 to 7 fl (1.2 to 2.1 in) bgs at the site. Local groundwater gradient iii this perched aquifer has consistently been toward the southeast in the vicinity of the on site source area (Figure 1). Shag tests have demonstrated conclusively that this shallow aquifer has a very low permeability and is not capable of producing 150 gallons/day [567.8 liters (1)/day] (TNRCC benchmark for consideration as a potentially beneficial use aquifer). This fact has allowed the application of the site specific target contaminant concentrations. HRC APPIACATiON As an alternative to natural attenuation alone as a response, action, injeetion of IIRC material into the saturated zone was chosen as the means of enhancing and expediting the biodegradation process, thus reducing dissolved-phase COC concentrations more rapidly. Utilizing site specific geological, hydrogeological, and geochemical data in conjunction with software provided by Regenesis, it was estimated that approximately 7,000 pounds (3,171 kg) of HRC should he sufficient for achieving target. concentrations at the site, and the time required to achieve target concentrations was estimated at two years or less. The NRC was injected into the shallow aquifer near the source area at the site from May 1 through May 12, 2000,and a total of approximately 7,000 pounds(3,171 kg)of HRC was injected. The injection area [approximately 3,000 it'` (283 m2)] encompassed the majority of the area with dissolved-phase COC concentrations greater than established target concentrations, which was estimated to be approximately 3,500 ft' (330.5 m2) located beneath and southeast of the former dry cleaners suite. The 1-IRC was injected into 45 injection borings within this area, and each boring was injected with HRC from approxifnately 7 ft to 22 ft in (2.1 to 6.7 m) depth. Twenty nine injection borings were advanced perpendicular to the ground surface, and 16 additional borings were advanced A angles of 15 and 30 degrees from vertical to extend beneath the building's foundation. Each of lire 45 in borings Were advanced using a Stratoprobc boring unit. A"top- down" injection system was utilized by advancing two ft (0.6 m) into the target interval and pumping the HRC material into the formation through a 2-ft (0.6 in) by 1.5-inch