JP2004082056A

JP2004082056A - Soil cleaning method by trench engineering method

Info

Publication number: JP2004082056A
Application number: JP2002249609A
Authority: JP
Inventors: Akira Oshitani; 押谷　明; Koichi Hiraishi; 平石　浩一; Yuji Kawamura; 河村　裕二; Takeshi Sakurai; 櫻井　健; Tokio Kamoshita; 鴨下　時男
Original assignee: Mitsubishi Materials Corp
Current assignee: Mitsubishi Materials Corp
Priority date: 2002-08-28
Filing date: 2002-08-28
Publication date: 2004-03-18
Anticipated expiration: 2022-08-28
Also published as: JP3894073B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soil cleaning method excellent in the cleaning effect for a polluted area. <P>SOLUTION: The soil cleaning method is characterized by including the steps of forming a water injection trench and a water pumping trench in soil; supplying cleaning water along the wall face of the water injection trench while applying pulses to the water; passing the cleaning water through a polluted area between the water injection trench and the water pumping trench; pumping up the cleaning water passed through the polluted area by the water pumping trench; and removing polluting substances from the pumped cleaning water. Since water is supplied along the wall face of the water injection trench, the cleaning water can evenly be supplied to the polluted area and since cleaning water supply is carried out by applying pulses to the cleaning water, excellent cleaning effect of the polluted area can be achieved and thus the effect of pulse application is significant. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明はトレンチ工法による土壌浄化方法に関する。より詳しくは、浄化処理する土壌にトレンチを施工し、このトレンチの壁面を通じて脈動を与えながら洗浄水を土壌中に流すことによって汚染域を効果的にかつ未処理部分を残すことなく洗浄する土壌浄化方法に関する。
【０００２】
【従来の技術】
汚染土壌の浄化方法として従来から各種の処理方法が知られている。例えば、（イ）汚染土壌中に設けた削孔を通じて洗浄水を土中に噴射し、この噴射圧によって掘削した汚染土壌を水の還流によって地上に排出し、浄化処理する方法（特開２００１−１６２２６２）、（ロ）汚染域を囲むように複数の注水井と揚水井とを設け、注水井を通じて洗浄水を汚染土壌中に注水し、汚染域を経由した洗浄水を揚水井によって地上に汲み上げて浄化処理し、これを再び注水井を通じて土中に戻す浄化方法（特開平１０−２７７５３１号）、（ハ）揚水井戸を通じて汲上げた地下水を加熱し、注水井戸を通じて加熱地下水を汚染域に送り込み、土壌中の有害物質の気化を促進させる浄化方法（特開平９−１７４０３４号）、（ニ）汚染域の下流側に設けた揚水井戸を通じて汚染地下水を汲み上げ、地上で浄化処理した水を上流側の注水井戸を通じて土中に戻し、この浄化水が汚染域を流れることよって汚染域を洗浄し、再び揚水して浄化処理するサイクルを繰り返す浄化方法（特開平８−３２３３３８号）などが知られている。
【０００３】
さらに、（ホ）汚染域に複数本の散水井戸を掘削し、この井戸にウオータジェット装置を挿入し、乳化材を含む清浄水を散水井戸から土壌中に噴射して汚染土を粉砕しながら散水して土壌を浄化する方法（特許第２７５５０８３号）が知られており、また（ヘ）地下水面より深く止水壁を設け、止水壁で囲まれた領域に注水孔と揚水孔を掘削し、注水孔から水を導入して地下水位を上昇させて汚染域を洗浄すると共に注水孔から揚水孔に向かう地下水流を発生させ、汚染物質を含む地下水を揚水孔から汲み上げて汚染物質を除去した後に注水孔を通じて再び地下水を土中に戻す浄化方法（特許第３１９１１３２号）が知られている。
【０００４】
しかし、汚染域を水洗処理する従来の上記土壌浄化方法は、何れも汚染域に多数の注水井ないし揚水井を設け、これらの井戸を通じて浄化水を注揚水する処理方法であるため、汚染域全体に洗浄水が流れるようにするためには多数の注水井や揚水井を必要とする。しかも、汚染域に対して注水場所が点状であるため、井戸を多数設けても井戸から流出される洗浄水が汚染域に均一に拡散するのが難しく、汚染域を通過する洗浄水ないし地下水の流束密度が一定とならず、洗浄終了までに要する時間が、最低流束密度の汚染域に時間に律速されると云う問題がある。
【０００５】
さらに、上記（ホ）のように地表面から洗浄水を土中に浸透させる方法では、汚染部位にまで水が拡散して浸透する時間が処理時間の律速となり、処理効率を高めるために揚水井戸からの汲み上げ水量を多くすると、地下水位が揚水井に向かって勾配を有するようになるため、洗浄水の流束が揚水井に向かって偏り、揚水井から離れた地点では未洗浄部分が残るという問題を生じる。また、上記（ヘ）の方法では、洗浄水の流束は個々の注水井から個々の揚水井に向かって流れるが、その向きと流速は井戸の位置関係によって定まるので均一ではなく、そのため洗浄部位と洗浄速度が流束密度の低い部分の洗浄速度によって律速されるという問題がある。
【０００６】
【発明が解決しようとする課題】
本発明は土壌の汚染域に洗浄水を流して浄化する処理方法において、従来方法の上記問題を解決したものであり、浄化処理する土壌にトレンチを施工し、このトレンチの壁面を通じて脈動を与えながら洗浄水を土壌中に流すことによって汚染域を効果的にかつ未処理部分を残すことなく洗浄する土壌浄化方法を提供するものである。
【０００７】
【課題を解決する手段】
すなわち、本発明は、（１）土壌中に注水トレンチと揚水トレンチを設け、脈動を与えながら洗浄水を注水トレンチの壁面から土壌中に放水して、注水トレンチと揚水トレンチの間の汚染域に洗浄水を流し、汚染域を経由した洗浄水を揚水トレンチから汲み上げて洗浄水中の汚染物質を除去することを特徴とする土壌浄化方法に関する。
【０００８】
本発明の土壌浄化方法は、具体的には、例えば（２）汚染域を囲む遮水壁を設け、遮水壁で囲まれた領域の上流側に注水トレンチを設けると共に下流側に揚水トレンチを設け、各トレンチは地下の難透水層に達する深さに掘削し、各トレンチの外周壁を遮水壁によって形成する一方、トレンチ内壁の上側部分を遮水壁とし、また下側部分を透水性壁面によって形成し、脈動を与えられて注水トレンチの下部透水性内壁面から放水され、汚染域を流れた洗浄水を揚水トレンチから揚水して浄化処理する土壌浄化方法である。
【０００９】
本発明の土壌浄化方法は、（３）注水トレンチの透水性内壁面底部から上部遮水壁の任意の高さまで透水材料を充填すると共にその上側に還元材料を含む砂材を充填して注水トレンチに上部還元水生成層と下部透水層とを形成し、上部還元水生成層に供給された洗浄水が還元性を有して下部透水層に流下し、還元性の洗浄水が土壌中に放水される土壌浄化方法、（４）注水トレンチと揚水トレンチの間に水位測定孔を設け、測定した水位に基づいて注水量ないし揚水量を制御する土壌浄化方法、（５）注水トレンチの下側に、上向きに加圧水を放水する管路を横設し、汚染物質の下方への拡散を抑止する土壌浄化方法、（６）注水トレンチの側方に、注水トレンチと異なる向きに第２注水トレンチを設け、両トレンチから放水される洗浄水の脈動を干渉させて脈動を増幅させることによって洗浄効果を高める土壌浄化方法を含む。
【００１０】
本発明の土壌浄化方法は、注水トレンチの壁面から洗浄水が放水されるので、従来の注水井戸用いた場合と異なり、放水面が広く、汚染域に対して洗浄水を均一に流すことができる。さらに、単なる加圧放水とは異なり、洗浄水に脈動を与えて放水するので、汚染域の洗浄効果が優れる。また、放水面が広いので脈動を与える効果が大きい。さらに、注水トレンチの上部に還元水生成層を形成し、還元性の洗浄水を下部透水層から土壌中に放水することによって、土壌中の汚染物質である六価クロムなどが還元されて無害化される。この他に、水位測定孔を設け、測定水位に基づいて注水量ないし揚水量を制御することによって土壌中の汚染域を流れる洗浄水の水位を適正に保ち、洗浄効果を高めることができる。また、注水トレンチの下側に、上向きに加圧水を放水する管路を水平方向に設けることによって、汚染物質の下方への拡散を抑止し、注水トレンチの側方に、注水トレンチと異なる向きに第２注水トレンチを設け、両トレンチから放水される洗浄水の脈動を干渉させて脈動を増幅させることによって洗浄効果を高めることができる。
【００１１】
【発明の実施の形態】
以下、本発明の土壌浄化方法について図面を参照して具体的に説明する。図１は注水トレンチおよび揚水トレンチなどの配置を示す模式平面図、図２にはその模式縦断面図、図３は注水トレンチの下側に加圧水供給管路を設けた配置を示す模式縦断面図、図４は注水トレンチに対して第２注水トレンチを設けた構成例を示す模式平面図である。
【００１２】
図示する本発明の土壌浄化システムは、汚染域Ａを囲むように遮水壁１０を設け、遮水壁１０で囲まれた領域の上流側に注水トレンチ１１を設けると共に下流側に揚水トレンチ１２が設けられている。注水トレンチ１１と揚水トレンチ１２は両側の遮水壁１０に沿って細長く形成されており、汚染域Ａをはさんで相対向して設置されている。各トレンチ１１、１２は地下の難透水層２０に達する深さに掘削されており、トレンチ１１、１２の外周は遮水壁１０によって囲まれている。また、各トレンチ１１、１２の内壁の上側部分は遮水壁１０によって形成されており、その下側部分は透水性壁面によって形成されている。
【００１３】
具体的には、例えば、注水トレンチ１１の内壁の上側部分は遮水性のコンクリート壁などによって形成されており、注水トレンチ１１の下側部分には砕石や砂利などの透水材料が充填され、この透水材料が内壁下部の壁面を形成している。さらに、好ましくは、注水トレンチ１１の底部から上部遮水壁の任意の高さまで透水材料を充填して下部透水層１３が形成され、さらにその上側に還元材料を含む砂材を充填して上部還元水生成層１４が形成されている。なお、施工場所を遮水壁１０によって囲めば洗浄水が施工域外に拡散するのを防止できるので、汚染域の洗浄効果が向上するが、施工場所の条件によっては遮水壁１０を一部だけに設けても良く、あるいは設けなくても良い。
【００１４】
一方、揚水トレンチ１２の上側部分は遮水性のコンクリート壁などによって形成されており、内壁下部は多数の通孔を有する透水性のコンクリート壁によって形成されている。また、揚水トレンチ１２の底部には揚水ポンプ１５が設置されている。
【００１５】
注水トレンチ１１および揚水トレンチ１２は鋼矢板で挟んだ構造もしくは鋼管杭を連結した構造でも良い。トレンチ部分の洗浄水が容易に移動できる構造であって、外周部分が遮水性壁面によって形成されており、所定の深度に通水用の孔ないしストレーナーを施工できる構造であれば良い。この外周遮水壁によって洗浄を行う汚染域の地下水とその周囲の地下水との混合を抑止する。難透水層（粘土層等）まで、あるいは洗浄対象深度より十分深い深度まで外周遮水壁を打ち込むのが好ましい。また、内壁上部の遮水壁は洗浄を行う深度より上側への漏水を防止し、かつ洗浄水の注水側水頭圧を維持するために、地上部から土中の洗浄域に入り込む程度の深度まで打ち込むのが好ましい。この、内壁上部の遮水壁の高さを調整することによって、汚染域に対して集中的に洗浄水が流れるように制御することができる。
【００１６】
注水トレンチ１１には洗浄水の注水管路１６が接続しており、注水バルブ１７が装着されている。一方、揚水トレンチ１２には汲み上げた洗浄水を処理設備（図示せず）に導く揚水管路１８が接続している。注水トレンチ１１には水圧を変動して脈動を与えた洗浄水が管路１６を通じて導入される。洗浄水に与える脈動の水圧および周期は汚染域の状況によって設定される。一般的には、水圧は０．１〜０．８気圧、脈動周期は１回／日から数十回／日が適当である。このような脈動を３０〜３００日程度継続して注水することによって浄化効果を高めることができる。水圧が低いと洗浄水の注水量が低下して土壌の洗浄効率が著しく低下する。一方、水圧が高すぎると注水井の地面からの抜け上がりや地表面への浸水が場所によって生じる。また、脈動周期が１回／日より少なくと通常の地下水流による洗浄効果と変わらず、一方、周期が数十回／日より多くても注水量が増加する割には洗浄効果が上がらず、排水処理の負担のみが増すことになる。
なお、洗浄水の脈動が失われないように注水トレンチ１１には蓋を設けて密閉し、水面の上方に隙間が生じ無いように洗浄水を満たすのが好ましい。脈動を与えられた洗浄水は管路１６を通じて注水トレンチ１１に供給され、下部透水性内壁面から土中に放水され、注水トレンチ１１と揚水トレンチ１２の間に位置する汚染域を流れてポンプ１５によって揚水トレンチ１２から地上に揚水され、管路１８を通じて処理設備に送られ、洗浄水に含まれる汚染物質が処理設備で除去される。
【００１７】
下部透水層１３の上側に還元水生成層１４を形成した注水トレンチ１１においては、注水トレンチ１１に供給された洗浄水がこの層１４を通過することによって酸化還元電位の低い水に変えられる。この還元性を有する洗浄水が還元性を有して下部透水層に流下し、還元性の洗浄水が土壌中に放水される注水トレンチ１１の下部に浸透して透水層１３から土中に放水される。この還元性洗浄水によって、還元作用により安定化する物質、例えば六価クロムなどは３価クロムに変わり、安定化する。この３価クロムを含む洗浄水は揚水トレンチ１２を通じて地上の処理設備に導かれ、３価クロムが洗浄水から分離除去される。還元水生成層１４は砂や不織布等を充填した部分に還元剤（鉄粉、銅粉、黄鉄鉱粉等）を添加して形成することができる。鉄粉の添加量は５％程度で良い。
【００１８】
なお、従来、鉄粉や鉄化合物を硅砂等に混合した物、あるいはコロイド状還元材などを掘削土に加えて安定化する方法、これらの材料を土壌中に抗状に打設する方法、液体と一緒に土壌中に圧入する方法などが知られている。これらは鉄等の投入により、有機系化合物を還元分解し、また重金属系化合物を安定化することによって土壌を浄化する方法であるが、これらの方法において土壌への鉄の投入量は最低でも数％以上が必要であり、条件によっては、地下水中の鉄濃度が高くなって赤水等の問題を引き起こす原因となる。一般に鉄の使用量は水質基準では０．３ｍｇ／Ｌに定められており、過剰の鉄類の投入は好ましくない。
【００１９】
本発明の土壌浄化方法では、鉄粉や鉄化合物を直接に土中に投入するのではなく、注水トレンチ上部で洗浄水を鉄粉等の還元材に接触させて少量の鉄粉を洗浄水に溶解させ、この少量の鉄による還元力を利用する。因みに、カラム試験の結果では、洗浄水中の鉄濃度は０．３ｍｇ／Ｌ以下である。また、浄化処理した後は注水トレンチ上部の還元水生成層を容易に撤去できるので、地下水への過剰な鉄の流出はなく、施工後も長期的な環境保全を図ることができる。さらに、土壌中の六価クロムを還元して効果的に除去するため、注水量を低減することができる。具体的には、例えば約０．５ｍｇ／Ｌの六価クロム濃度の汚染域に還元水生成層（５％Ｆｅ粉＋硅砂混合層）を通過させた洗浄水を通水させることによって、六価クロム濃度を０．０２ｍｇ／Ｌまで低減させることができる。
【００２０】
図示する土壌浄化システムでは、注水トレンチ１１と揚水トレンチ１２の間に水位測定孔３１、３２が設けられている。なお、水位の勾配を測定できるように一方の水位測定孔３１は上流側の注水トレンチ１１の近傍に設けられており、他方の水位測定孔３２は下流側の揚水トレンチ１２の近傍に設けられている。この水位測定孔３１、３２および注水トレンチ１１と揚水トレンチ１２の内部に水位測定センターを設け、地下水位のモニタリングを行う。
【００２１】
さらに、水位測定センターと注水バルブ１７および揚水ポンプ１５を結ぶ水位制御ユニット３３が形成されている。この制御系３３は水位センサーの情報に基づいて注水バルブ１７および揚水ポンプ１５の運転を制御し、上流側と下流側の水位を目的の範囲に保ち、汚染域に洗浄水か適切に流れるように自動制御する。注水トレンチ１１の水位センサーや上流側水位測定孔の水位センサーの測定値が所定水位より低い場合には注水バルブ１７を開いて注水を行い、あるいは揚水ポンプ１５を停止する。一方、所定水位より高い場合には注水バルブ１７を閉じ、または揚水ポンプ１５を稼動させる。下流側の水位が所定範囲から外れる場合にも同様の操作によって水位が所定範囲内に保たれる。
【００２２】
図３は、注水トレンチ１１の下側に加圧水を放水する管路３４を横設し、汚染物質の下方への拡散を抑止した構成例である。管路３４は上向きに加圧水を放水するように水平方向に横設されており、上向きの放水孔が多数設けられている。この管路３４は水平方向に複数本並べて設置しても良い。図示する例では、管路３４は難透水層２０の下側の透水層に配設されており、難透水層２０を漏水してくる地下水が下方に拡散するのを抑止する。
【００２３】
図４は注水トレンチ１１の側方に、注水トレンチと異なる向きに第２注水トレンチ４０を設けた構成例である。第２注水トレンチ４０は外周の遮水壁１０に沿って設けられており、上記注水トレンチ１１と同様の構造を有している。この構造においては、両側のトレンチ１１、４０から放水される洗浄水の脈動が増幅するように脈動を干渉させることによって、全体の注水量を増加せずに洗浄効果を高めることができる。
【００２４】
【実施例】
〔実施例１〕
図１に示す土壌浄化システムにおいて、洗浄水に表１に示す圧力と周期の脈動を与えて土壌中の汚染域を洗浄した。この結果を表１に示した。また、洗浄水に脈動を与えずに洗浄した結果を比較例として示した。本実施例ではクロム濃度の低減率が、還元剤を用いないもの（Ｎｏ．１）は５０％、還元剤を用いたもの（Ｎｏ．２〜Ｎｏ．４）は８０％〜９０％であり、非常に高い。一方、洗浄水を脈動しない比較例のクロム濃度低減は１０％であり、本発明例に比べて著しく低い。
【００２５】
〔実施例２〕
図３に示す加圧放水管路３４を設けた土壌浄化システムにおいて、洗浄水に表１に示す圧力と周期の脈動を与えて土壌中の汚染域を洗浄した。この結果を表１に示した（Ｎｏ．−−−）。本実施例では汚染域の下側への拡散が防止されるのでクロム濃度の低減率が９３％に向上している。
【００２６】
【表１】

【００２７】
〔実施例３〕
図４に示す第２注水トレンチを設けた土壌浄化システムにおいて、洗浄水に表２に示す圧力と周期の脈動を与えて土壌中の汚染域を洗浄した。この結果を表２に示した。なお、比較のため第２注水トレンチを設けない例を対比して示した。本実施例は第２注水トレンチを設けない例よりも注水量は少ないがクロム濃度低減率はほぼ同等であり、注水量を増加せずに洗浄効果を向上できることが確認された。
【００２８】
【表２】

【００２９】
【発明の効果】
本発明の土壌浄化方法では、注水トレンチの壁面から洗浄水が放水されるので放水面が広く、汚染域に対して洗浄水を均一に流すことができる。さらに、洗浄水に脈動を与えて放水するので汚染域の洗浄効果が優れる。また、放水面が広いので脈動を与える効果が大きい。因みに、従来の処理方法における注水井戸では加圧水が放水されるが、これに脈動を与えても個々の通液孔から放水されるために脈動による効果が殆どない。注水井戸を多数設けても同様である。一方、本発明では洗浄水を壁面から放水するので洗浄水の脈動による効果が大きく、汚染域の洗浄効果を高めることができる。土壌粒子表面に付着している汚染物は洗浄水に接触して洗い流されるが、土壌を構成している粘土鉱物の内側に存在している汚染物は洗浄水の流速を高めるだけでは十分に除去することができない。洗浄水を加圧脈動して粘土鉱物の内側と外側の圧力差を大きくすることによって内側の汚染物が外側に引き出され、洗浄効果が大幅に向上する。
【００３０】
さらに、注水トレンチの上部に還元水生成層を形成し、還元性の洗浄水を下部透水層から土壌中に放水することによって、土壌中の汚染物質である六価クロムなどが還元されて安定化される。また、水位測定孔を設け、測定水位に基づいて注水量ないし揚水量を制御することによって土壌中の汚染域を流れる洗浄水の水位を適正に保ち、洗浄効果が向上する。さらに、注水トレンチの下側に、上向きに加圧水を放水する管路を水平方向に設けることによって、汚染物質の下方への拡散が抑止され、施工域について信頼性の高い浄化効果が達成される。また、注水トレンチの側方に注水トレンチと異なる向きに第２注水トレンチを設け、両トレンチから放水される洗浄水の脈動を干渉させて脈動を増幅させれば、全体の注水量を増加せずに洗浄効果が向上する。
【図面の簡単な説明】
【図１】注水トレンチおよび揚水トレンチなどの配置を示す模式平面図
【図２】図１に示す浄化構造の模式縦断面図
【図３】注水トレンチ下側に加圧水供給管路を設けた配置を示す模式縦断面図
【図４】注水トレンチに対して第２注水トレンチを設けた構成例を示す模式平面図。
【符号の説明】１０−遮水壁、１１−注水トレンチ、１２−揚水トレンチ、１３−透水層、１４−還元水生成層、１５−揚水ポンプ、１６−注水管路、１７−注水バルブ、１８−揚水管路、２０−難透水層、３１、３２−水位測定孔、
３３−水位コントロールユニット、３４−加圧水放水管路、４０−第２注水トレンチ。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a soil purification method using a trench method. More specifically, a soil purification method in which a trench is constructed in soil to be purified, and washing water is allowed to flow into the soil while pulsating through the walls of the trench to effectively clean the contaminated area without leaving untreated portions. About the method.
[0002]
[Prior art]
Conventionally, various treatment methods have been known as methods for purifying contaminated soil. For example, (a) a method of injecting cleaning water into the soil through a borehole provided in the contaminated soil, discharging the contaminated soil excavated by the injection pressure to the ground by returning water, and purifying (Japanese Patent Application Laid-Open No. 2001-2001) 162262), (b) A plurality of injection wells and pumping wells are provided to surround the contaminated area, washing water is injected into the contaminated soil through the injection well, and the washing water passing through the contaminated area is pumped to the ground by the pumping well. (JP-A-10-277331), (c) heating groundwater pumped through a pumping well and sending the heated groundwater to the contaminated area through a water injection well. A purification method that promotes the vaporization of harmful substances in soil (Japanese Patent Laid-Open No. 9-174034), and (d) water that has been purified on the ground by pumping up contaminated groundwater through a pumping well provided downstream of the contaminated area. A purification method (Japanese Patent Application Laid-Open No. 8-323338) is known in which the purified water is returned to the soil through a water injection well on the upstream side, and the purified water flows through the contaminated area to wash the contaminated area, and then repeats a cycle of pumping and purifying again. Have been.
[0003]
Furthermore, (e) drilling multiple watering wells in the contaminated area, inserting a water jet device into these wells, spraying clean water containing emulsifier from the watering wells into the soil, and pulverizing the contaminated soil while watering it. (Patent No. 2755083) is known, and (f) a water blocking wall is provided deeper than the groundwater surface, and a water injection hole and a water pumping hole are excavated in an area surrounded by the water blocking wall. Introducing water from the injection hole to raise the groundwater level to clean the contaminated area, generate a groundwater flow from the injection hole to the pumping hole, and remove the pollutant by pumping the groundwater containing the pollutant from the pumping hole. A purification method for returning groundwater to the soil again through a water injection hole later (Japanese Patent No. 3191132) is known.
[0004]
However, the above-mentioned conventional soil purification method of washing the contaminated area with water is a treatment method in which a large number of injection wells or pumping wells are provided in the contaminated area, and purified water is injected and pumped through these wells. A large number of injection wells and pumping wells are required to allow the flushing water to flow. In addition, since the water injection site is point-shaped with respect to the contaminated area, even if a large number of wells are provided, it is difficult for the washing water flowing out of the well to uniformly diffuse into the contaminated area, and the washing water or groundwater passing through the contaminated area is difficult. However, there is a problem that the flux density is not constant, and the time required to complete the cleaning is limited by the time to the contaminated region having the lowest flux density.
[0005]
Further, in the method of infiltrating the washing water from the ground surface into the soil as described in (e) above, the time required for the water to diffuse and permeate to the contaminated site is a rate-determining treatment time, and the pumping well is used to improve the treatment efficiency. If the amount of water pumped from the pump is increased, the groundwater level will have a gradient toward the pumping well, and the flux of washing water will be biased toward the pumping well, leaving unwashed parts at points away from the pumping well. Cause problems. In the above method (f), the flux of the washing water flows from each injection well toward each pumping well, but the direction and the flow velocity are not uniform because they are determined by the positional relationship of the wells. In addition, there is a problem that the cleaning speed is determined by the cleaning speed of the portion having a low flux density.
[0006]
[Problems to be solved by the invention]
The present invention solves the above-mentioned problems of the conventional method in a treatment method of flowing washing water to a contaminated area of soil, in which a trench is constructed in soil to be purified, and pulsation is applied through the wall surface of the trench. It is an object of the present invention to provide a soil purification method for washing a contaminated area effectively by flowing washing water into soil without leaving an untreated portion.
[0007]
[Means to solve the problem]
That is, the present invention provides (1) a water injection trench and a water pumping trench provided in soil, and washing water is discharged into the soil from the wall surface of the water injection trench while pulsating, and the water is supplied to a contaminated area between the water injection trench and the water pumping trench. The present invention relates to a soil purification method characterized by flowing washing water, pumping washing water passing through a contaminated area from a pumping trench, and removing contaminants in the washing water.
[0008]
Specifically, the soil purification method of the present invention includes, for example, (2) providing a water impermeable wall surrounding a contaminated area, providing a water injection trench upstream of a region surrounded by the water impermeable wall, and installing a water pumping trench downstream. Each trench is excavated to the depth reaching the underground impervious layer, and the outer peripheral wall of each trench is formed by a water impermeable wall, while the upper part of the trench inner wall is used as a water impermeable wall, and the lower part is permeable This is a soil purification method in which rinsing water formed by a wall surface, which is given a pulsation, is discharged from a lower permeable inner wall surface of a water injection trench, and flows through a contaminated area and is purified through a pumping trench.
[0009]
According to the soil purification method of the present invention, (3) the water injection trench is filled by filling a water permeable material from the bottom of the water permeable inner wall surface of the water injection trench to an arbitrary height of the upper impermeable wall and filling a sand material containing a reducing material above the water permeable material. An upper reduced water generation layer and a lower permeable layer are formed in the upper part, and the washing water supplied to the upper reduced water generation layer flows down to the lower permeable layer with reducing property, and the reducing washing water is discharged into the soil. (4) A soil purification method in which a water level measurement hole is provided between a water injection trench and a water pumping trench to control the amount of water injection or water pumping based on the measured water level, and (5) a soil purification method below the water injection trench. A soil purification method for arranging a pipe for discharging pressurized water upward to suppress the diffusion of contaminants downward, and (6) providing a second water injection trench beside the water injection trench in a direction different from that of the water injection trench. , Cleaning water discharged from both trenches The dynamic causing interference including soil purification method to enhance the cleaning effect by amplifying the pulsations.
[0010]
In the soil purification method of the present invention, the cleaning water is discharged from the wall surface of the water injection trench, so that unlike the case where the conventional water injection well is used, the water discharge surface is wide and the cleaning water can be uniformly flowed to the contaminated area. . Furthermore, unlike mere pressurized water discharge, the wash water is discharged with pulsation, so that the cleaning effect of the contaminated area is excellent. In addition, since the water discharge surface is wide, the effect of giving pulsation is large. Furthermore, a reduced water generation layer is formed at the top of the water injection trench, and the reducing cleaning water is discharged from the lower permeable layer into the soil, thereby reducing hexavalent chromium and other contaminants in the soil and rendering them harmless. Is done. In addition, by providing a water level measurement hole and controlling the water injection amount or the pumping amount based on the measured water level, the water level of the cleaning water flowing through the contaminated area in the soil can be appropriately maintained, and the cleaning effect can be enhanced. In addition, by providing a pipe for discharging pressurized water upward in the horizontal direction below the water injection trench, the diffusion of contaminants downward is suppressed, and the side of the water injection trench is oriented differently from the water injection trench. (2) The cleaning effect can be enhanced by providing two water injection trenches and amplifying the pulsation by interfering with the pulsation of the cleaning water discharged from both trenches.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the soil purification method of the present invention will be specifically described with reference to the drawings. FIG. 1 is a schematic plan view showing an arrangement of a water injection trench and a pumping trench, FIG. 2 is a schematic vertical sectional view thereof, and FIG. 3 is a schematic vertical sectional view showing an arrangement in which a pressurized water supply pipe is provided below a water injection trench. FIG. 4 is a schematic plan view showing a configuration example in which a second water injection trench is provided for the water injection trench.
[0012]
In the illustrated soil purification system of the present invention, a water impermeable wall 10 is provided so as to surround the contaminated area A, a water injection trench 11 is provided on the upstream side of the area surrounded by the water impermeable wall 10, and a water pumping trench 12 is provided on the downstream side. Is provided. The water injection trench 11 and the water pumping trench 12 are formed to be elongated along the water-impervious walls 10 on both sides, and are installed to face each other with the contamination area A interposed therebetween. Each of the trenches 11 and 12 is excavated to a depth reaching the underground impermeable layer 20, and the outer peripheries of the trenches 11 and 12 are surrounded by the impermeable wall 10. The upper part of the inner wall of each of the trenches 11 and 12 is formed by a water impermeable wall 10, and the lower part is formed by a water permeable wall.
[0013]
Specifically, for example, the upper part of the inner wall of the water injection trench 11 is formed by a water-blocking concrete wall or the like, and the lower part of the water injection trench 11 is filled with a water-permeable material such as crushed stone or gravel. The material forms the lower wall surface of the inner wall. Further, preferably, a lower permeable layer 13 is formed by filling a permeable material from the bottom of the water injection trench 11 to an arbitrary height of the upper impermeable wall, and a sand material containing a reducing material is further filled above the lower permeable layer 13. A water generation layer 14 is formed. In addition, if the construction location is surrounded by the impermeable wall 10, the washing water can be prevented from diffusing out of the construction area, so that the cleaning effect of the contaminated area is improved. May or may not be provided.
[0014]
On the other hand, the upper part of the pumping trench 12 is formed by a water-blocking concrete wall or the like, and the lower part of the inner wall is formed by a water-permeable concrete wall having a large number of through holes. A pump 15 is provided at the bottom of the pumping trench 12.
[0015]
The water injection trench 11 and the water pumping trench 12 may have a structure sandwiched by steel sheet piles or a structure in which steel pipe piles are connected. Any structure may be used as long as it is a structure in which the cleaning water in the trench portion can easily move, the outer peripheral portion is formed by a water-impervious wall surface, and a hole or strainer for water passage can be constructed at a predetermined depth. This outer impermeable wall prevents mixing of the groundwater in the contaminated area to be cleaned with the surrounding groundwater. It is preferable to drive the outer impermeable wall to a hardly permeable layer (clay layer or the like) or to a depth sufficiently deeper than the depth to be cleaned. In addition, the impermeable wall at the top of the inner wall prevents water leakage above the washing depth and maintains the head pressure on the water injection side from the ground to a depth enough to enter the washing area in the soil. It is preferable to drive. By adjusting the height of the impermeable wall above the inner wall, it is possible to control the washing water to flow intensively in the contaminated area.
[0016]
A water injection pipe line 16 is connected to the water injection trench 11, and a water injection valve 17 is mounted. On the other hand, the pumping trench 12 is connected to a pumping line 18 for guiding the pumped washing water to a treatment facility (not shown). Rinse water is introduced into the water injection trench 11 through the conduit 16 by pulsating the water pressure. The pressure and frequency of the pulsation applied to the washing water are set according to the condition of the contaminated area. In general, it is appropriate that the water pressure is 0.1 to 0.8 atm and the pulsation cycle is once to several tens of times / day. By purifying such pulsation continuously for about 30 to 300 days, the purification effect can be enhanced. When the water pressure is low, the injection amount of the washing water is reduced, and the washing efficiency of the soil is significantly reduced. On the other hand, if the water pressure is too high, the injection well rises from the ground or infiltrates the ground surface depending on the location. In addition, if the pulsation cycle is less than 1 time / day, the cleaning effect by the normal groundwater flow is not changed. On the other hand, even if the pulsation cycle is more than tens of times / day, the cleaning effect does not increase despite the increase in water injection amount. Only the burden of wastewater treatment will increase.
It is preferable that the water injection trench 11 be provided with a lid and hermetically sealed so that the pulsation of the cleaning water is not lost, and filled with the cleaning water so that no gap is formed above the water surface. The pulsated washing water is supplied to the water injection trench 11 through the pipe line 16, discharged into the soil from the lower water permeable inner wall surface, flows through the contaminated area located between the water injection trench 11 and the water pumping trench 12, and flows through the pump 15. As a result, the water is pumped to the ground from the water pumping trench 12 and sent to the treatment facility through a pipe 18 to remove contaminants contained in the cleaning water.
[0017]
In the water injection trench 11 in which the reduced water generation layer 14 is formed above the lower water permeable layer 13, the cleaning water supplied to the water injection trench 11 passes through this layer 14 and is converted into water having a low oxidation-reduction potential. The washing water having a reducing property flows down to the lower permeable layer with the reducing property, and the reducing washing water permeates into the lower part of the water injection trench 11 where water is discharged into the soil and is discharged from the permeable layer 13 into the soil. Is done. The substance which is stabilized by the reducing action, for example, hexavalent chromium, is changed to trivalent chromium by this reducing washing water and is stabilized. The cleaning water containing the trivalent chromium is led to a processing facility on the ground through the pumping trench 12, and the trivalent chromium is separated and removed from the cleaning water. The reduced water generation layer 14 can be formed by adding a reducing agent (iron powder, copper powder, pyrite powder, or the like) to a portion filled with sand, nonwoven fabric, or the like. The addition amount of iron powder may be about 5%.
[0018]
Conventionally, a method in which iron powder or an iron compound is mixed with silica sand, or a method in which a colloidal reducing agent is added to excavated soil to stabilize the material, a method in which these materials are cast into soil in a resistive manner, And the method of injecting it into the soil together with water. These are methods of purifying soil by reductively decomposing organic compounds by adding iron or the like and stabilizing heavy metal compounds.However, in these methods, the amount of iron input to soil is at least a few. % Or more is necessary, and depending on the conditions, the iron concentration in the groundwater becomes high, which causes problems such as red water. Generally, the amount of iron used is determined to be 0.3 mg / L on the basis of water quality, and it is not preferable to add excessive irons.
[0019]
In the soil purification method of the present invention, a small amount of iron powder is converted into cleaning water by contacting cleaning water with a reducing material such as iron powder at the upper part of the water injection trench, instead of directly charging iron powder or an iron compound into the soil. Dissolve and utilize the reducing power of this small amount of iron. Incidentally, according to the results of the column test, the iron concentration in the washing water is 0.3 mg / L or less. Further, after the purification treatment, the reduced water generation layer above the water injection trench can be easily removed, so that there is no excess iron outflow into the groundwater, and long-term environmental conservation can be achieved even after the construction. Furthermore, since hexavalent chromium in the soil is reduced and effectively removed, the amount of injected water can be reduced. Specifically, for example, by passing washing water that has passed through a reduced water generating layer (a mixed layer of 5% Fe powder and silica sand) into a contaminated area having a hexavalent chromium concentration of about 0.5 mg / L, The chromium concentration can be reduced to 0.02 mg / L.
[0020]
In the illustrated soil purification system, water level measurement holes 31 and 32 are provided between the water injection trench 11 and the water pumping trench 12. Note that one water level measurement hole 31 is provided near the upstream water injection trench 11 so that the water level gradient can be measured, and the other water level measurement hole 32 is provided near the downstream water pumping trench 12. I have. A water level measurement center is provided inside the water level measurement holes 31 and 32, the water injection trench 11 and the water pumping trench 12, and the groundwater level is monitored.
[0021]
Further, a water level control unit 33 that connects the water level measurement center with the water injection valve 17 and the water pump 15 is formed. The control system 33 controls the operation of the water injection valve 17 and the water pump 15 based on the information of the water level sensor, to maintain the upstream and downstream water levels within a target range, and to allow the washing water to appropriately flow into the contaminated area. Control automatically. When the measured value of the water level sensor of the water injection trench 11 or the water level sensor of the upstream water level measurement hole is lower than the predetermined water level, the water injection valve 17 is opened to perform water injection, or the water pump 15 is stopped. On the other hand, when the water level is higher than the predetermined water level, the water injection valve 17 is closed or the water pump 15 is operated. When the water level on the downstream side is out of the predetermined range, the water level is maintained in the predetermined range by the same operation.
[0022]
FIG. 3 shows a configuration example in which a pipeline 34 for discharging pressurized water is provided below the water injection trench 11 to suppress the diffusion of pollutants downward. The pipeline 34 is provided horizontally in the horizontal direction so as to discharge pressurized water upward, and is provided with a large number of upward discharge holes. A plurality of pipes 34 may be arranged in a horizontal direction. In the illustrated example, the pipeline 34 is provided in the lower permeable layer below the poorly permeable layer 20, and prevents the groundwater leaking from the poorly permeable layer 20 from diffusing downward.
[0023]
FIG. 4 shows a configuration example in which a second water injection trench 40 is provided on the side of the water injection trench 11 in a direction different from that of the water injection trench. The second water injection trench 40 is provided along the outer water impervious wall 10 and has the same structure as the water injection trench 11. In this structure, the pulsation is interfered so that the pulsation of the cleaning water discharged from the trenches 11 and 40 on both sides is amplified, so that the cleaning effect can be enhanced without increasing the total water injection amount.
[0024]
【Example】
[Example 1]
In the soil purification system shown in FIG. 1, the pulsation of the pressure and cycle shown in Table 1 was given to the washing water to wash the contaminated area in the soil. The results are shown in Table 1. The results of cleaning without pulsation of the cleaning water are shown as comparative examples. In this embodiment, the reduction rate of the chromium concentration is 50% for the case where the reducing agent is not used (No. 1), and 80% to 90% for the case where the reducing agent is used (No. 2 to No. 4). Very high. On the other hand, the chromium concentration reduction of the comparative example in which the washing water was not pulsated was 10%, which was significantly lower than that of the inventive example.
[0025]
[Example 2]
In the soil purification system provided with the pressurized water discharge pipe 34 shown in FIG. 3, the pulsation of the pressure and cycle shown in Table 1 was given to the washing water to wash the contaminated area in the soil. The results are shown in Table 1 (No. ---). In the present embodiment, since the diffusion to the lower side of the contaminated area is prevented, the reduction rate of the chromium concentration is improved to 93%.
[0026]
[Table 1]

[0027]
[Example 3]
In the soil purification system provided with the second water injection trench shown in FIG. 4, the pulsation of the pressure and cycle shown in Table 2 was applied to the cleaning water to clean the contaminated area in the soil. The results are shown in Table 2. For comparison, an example in which the second water injection trench is not provided is shown in comparison. In this example, although the amount of water injection was smaller than the example without the second water injection trench, the chromium concentration reduction rate was almost the same, and it was confirmed that the cleaning effect could be improved without increasing the amount of water injection.
[0028]
[Table 2]

[0029]
【The invention's effect】
According to the soil purification method of the present invention, the cleaning water is discharged from the wall surface of the water injection trench, so that the water discharge surface is wide, and the cleaning water can flow uniformly to the contaminated area. Furthermore, since the cleaning water is given a pulsation and discharged, the cleaning effect of the contaminated area is excellent. In addition, since the water discharge surface is wide, the effect of giving pulsation is large. Incidentally, the pressurized water is discharged in the water injection well in the conventional treatment method. However, even if pulsation is given to this, there is almost no effect due to pulsation since the water is discharged from each liquid passage hole. The same is true even if many water injection wells are provided. On the other hand, in the present invention, since the cleaning water is discharged from the wall surface, the effect of the pulsation of the cleaning water is large, and the cleaning effect of the contaminated area can be enhanced. Contaminants adhering to the surface of soil particles are washed away by contact with the wash water, but contaminants existing inside the clay minerals that make up the soil are sufficiently removed only by increasing the flow rate of the wash water Can not do it. The cleaning water is pressurized and pulsated to increase the pressure difference between the inside and the outside of the clay mineral, whereby contaminants on the inside are drawn out and the cleaning effect is greatly improved.
[0030]
In addition, a reduced water generation layer is formed at the top of the water injection trench, and reducing washing water is discharged from the lower permeable layer into the soil, thereby reducing and stabilizing hexavalent chromium and other contaminants in the soil. Is done. In addition, by providing a water level measurement hole and controlling the water injection amount or the pumping amount based on the measured water level, the water level of the wash water flowing through the contaminated area in the soil is properly maintained, and the cleaning effect is improved. Further, by providing a pipe for discharging pressurized water upward in the horizontal direction below the water injection trench, diffusion of pollutants downward is suppressed, and a highly reliable purification effect in the construction area is achieved. In addition, if the second water injection trench is provided in a direction different from the water injection trench on the side of the water injection trench, and the pulsation is amplified by interfering with the pulsation of the cleaning water discharged from both trenches, the total water injection amount does not increase. The cleaning effect is improved.
[Brief description of the drawings]
1 is a schematic plan view showing an arrangement of a water injection trench, a water pumping trench, etc. [FIG. 2] A schematic vertical sectional view of a purification structure shown in FIG. 1 [FIG. 3] An arrangement in which a pressurized water supply pipe is provided below a water injection trench. FIG. 4 is a schematic plan view showing a configuration example in which a second water injection trench is provided for the water injection trench.
[Description of Signs] 10-impermeable wall, 11-water injection trench, 12-water pumping trench, 13-water permeable layer, 14-reduced water generation layer, 15-water pump, 16-water injection line, 17-water injection valve, 18 -Pumping pipeline, 20-impervious layer, 31, 32-water level measurement hole,
33-water level control unit, 34-pressurized water discharge line, 40-second water injection trench.

Claims

A water injection trench and a water pumping trench are provided in the soil, and washing water is discharged into the soil from the wall of the water injection trench while pulsating, and the cleaning water flows into the contaminated area between the water injection trench and the water pumping trench, and passes through the contaminated area. A soil purification method comprising: removing contaminants in the washing water by pumping the washed water from a pumping trench.

A water impermeable wall surrounding the contaminated area is provided, a water injection trench is provided upstream of the area surrounded by the water impermeable wall and a water pumping trench is provided downstream, and each trench is excavated to a depth reaching the underground impermeable layer. The outer peripheral wall of each trench is formed by a water impervious wall, while the upper part of the inner wall of the trench is formed as a water impervious wall, and the lower part is formed by a water permeable wall. The soil purification method according to claim 1, wherein the cleaning water discharged from the wall surface and flowing through the contaminated area is purified through a pumping trench.

Fill the water-permeable material from the bottom of the water-permeable inner wall surface of the water-injection trench to an arbitrary height of the upper water-impervious wall, and fill a sand material containing a reducing material above the water-injection trench to fill the water-injection trench with the upper reduced water generation layer and the lower water-permeable layer. 3. The soil according to claim 1, wherein the washing water supplied to the upper reduced water generation layer flows down to the lower permeable layer with a reducing property, and the reducing washing water is discharged into the soil. 4. Purification method.

4. The soil purification method according to claim 1, wherein a water level measurement hole is provided between the water injection trench and the water pumping trench, and a water injection amount or a water pumping amount is controlled based on the measured water level.

The soil purification method according to any one of claims 1 to 4, wherein a pipe line for discharging pressurized water is provided horizontally below the water injection trench to suppress diffusion of pollutants downward.

The cleaning effect is enhanced by providing a second water injection trench in a side of the water injection trench in a direction different from that of the water injection trench and interfering with the pulsation of the cleaning water discharged from both trenches to amplify the pulsation, thereby enhancing the cleaning effect. The soil purification method according to any one of the above.